1 MOVEMENT AND HABITAT SELECTION OF IMMATURE ALLIGATORS IN A RESTORED WETLAND IN FLORIDA By RIO THROM A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR T HE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013
2 2013 Rio Throm
3 To my grandmothers; Mary Emma Throm and Virginia Morris Knoefler
4 ACKNOWLEDGEMENTS First, I must thank the One who made all igators. I give the sincerest thanks to Franklin Percival for taking me under his wing when I was an undergraduate, and not only giving me the chance to have a career in wildlife management but one that also involves airboats. I am also greatly indebted t o everyone in the alligator research program, particularly Allan Woodward who encouraged me to ask ; and to Cameron Carter and Patrick Delaney both of whom went out of their way to give me technical support and confidence. I am so thankful to Erin Leone and Ken Rice, for speaking slowly and using multi colored markers when they discussed stati sti cs and study design with me and for serving on my committee. Arnold Brunell, William Gi uliano, and Robert McCleery offered constant encouragement and have added to my professional development in countless ways. I am grateful for Courtney Tye, who besides all her support though school, stayed up late with me before my defense and helped me remember how I computed my mo dels. I am thankful for Ryan Butryn for all his assistance with patch analysis and to Claire Williams and Caprice McRae who rescued me several times during my years at UF. I am thankful for the entire staff at the SJRWMD Apopka Field office for all their a ssistance during my field work. I am grateful for Andrew F anning and Joe Benedict for their support during the final months of writing this paper. I am thankful for the funding from FWC and the SJRWMD. And certainly, I would not even be close to where I am today if it was not for my f amily
5 TABLE OF CONTENTS page ACKNOWLEDGEMENTS ................................ ................................ ............................... 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 ABSTRACT ................................ ................................ ................................ ................... 10 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 13 On Crocodilian Movement ................................ ................................ ...................... 13 On Alligator Move ment ................................ ................................ ........................... 16 2 MOVEMENT AND MICRO HABITAT SELECTION OF IMMATURE ALLIGATORS IN A RESTORED CENTRAL FLORIDA MARSH ............................ 28 History of the Study Area ................................ ................................ ........................ 28 Immature Alligator Study on the NSRA ................................ ................................ ... 31 Objectives and Hypotheses ................................ ................................ .................... 32 3 METHODS ................................ ................................ ................................ .............. 38 Study Area ................................ ................................ ................................ .............. 38 Field Techniques ................................ ................................ ................................ .... 41 Data Protocols ................................ ................................ ................................ ........ 44 Data Analyses ................................ ................................ ................................ ......... 46 4 RESULTS ................................ ................................ ................................ ............... 49 5 DISCUSSION ................................ ................................ ................................ ......... 62 Environmental Effects ................................ ................................ ............................. 62 Biological Effects ................................ ................................ ................................ .... 64 Ecological Effects ................................ ................................ ................................ ... 65 Management Implications ................................ ................................ ....................... 69 6 THE MECHANISMS BEHIND IMMATURE ALLIGATOR MOVEMENT .................. 71 Background ................................ ................................ ................................ ............. 71 Dispersal ................................ ................................ ................................ ................. 72 Modeling Methods ................................ ................................ ................................ .. 73 Movement Probabilities ................................ ................................ ........................... 75 Home Range and Habitat Selection ................................ ................................ ........ 76
6 Modeling Methods ................................ ................................ ................................ .. 77 Movement Probabilities ................................ ................................ ........................... 78 Directional Movement ................................ ................................ ............................. 79 Modeling Methods/Movement Probabilities ................................ ............................ 80 Conclusions ................................ ................................ ................................ ............ 82 APPENDIX A MODELS ................................ ................................ ................................ ................. 85 B BEST MODEL OUTPUT ................................ ................................ ......................... 89 B HYPOTHESES EQUATIONS ................................ ................................ ................. 92 LIST OF REFERENCES ................................ ................................ ............................... 96 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 111
7 LIST OF TABLES Table page 4 1 AIC and relative weights of top two models in the model set examining factors affecting movement of immature alligators on the Apopka NSRA. ......... 50 4 2 The fixed eff ects from the top model of alligator movements in the NSRA of Lake Apopka during the 2008, 2009 field season. ................................ .............. 61 6 1 Parameters settings for H ypotheses 1, 2, and 3 and the probability of immatur e alligator movemen t for each scenario ................................ ................ 76 6 2 Parameters settings for H ypotheses 4, 5, and 6 and the probability of immature alligator movement for each scenario. ................................ ................ 79 6 3 Parameters settings for H ypotheses 7, 8, and 9 and the probability of immature alligator movement for each scenario.. ................................ ............... 81
8 LIST OF FIGURES Figure page 3 1 Location of the north shore restoration area (NSRA) in relation to Lake Apopka in central Florida. ................................ ................................ ................... 38 3 2 Locations of the study units, West Marsh, Du da, Phase 1 and Phase 2, on the Apopka North Shore Restoration Area in central Florida. ............................. 41 3 3 Radio transmitter mounted on an immature alligator in the NSRA on Lake Apopka, Florida during the 2 008 field season. ................................ .................... 43 3 4 The relation between the water level on the lake with water levels in the north shore restoration impoundments from June 2008 through June 2009.. .............. 45 3 5 The 2008 GIS vegetation overlay of the Lake Apopka NSRA that was used to qualify habitats. ................................ ................................ ................................ ... 48 4 1 Aerial image of the Apopka north shore restorati on area in central Florida with initial capture locations of the 53 alligators analyzed in the study. .............. 49 4 2 Cumulative rainfall related to time of year during the 2008 09 field season. ...... 51 4 3 Significant moves made by immature alligators on the Lake Apopka NSRA as they relate to the 2008 09 field season. ................................ ......................... 51 4 4 The proba bility of male and female immature alligators in the NSRA of Lake Apopka making a significant move based on the second moon phase .............. 53 4 5 The probability of male and female immature alligators mak ing a significant move based on air temperature in the Lake Apopka NSRA. .............................. 54 4 6 The probability of male and female immature alligators making a significant move based on rainfall in the Lak e Apopka NSRA ................................ ............. 55 4 7 The probability of male and female immature alligator s making a significant move based on water level in the Lake Apopka NSRA. ................................ ..... 56 4 8 The probability of immature alligator s making a significant move based on number of shallow marsh patches in the Lake Apopka NSRA. .......................... 57 4 9 The probability of male and f emale immature alligator s making a significant move based on number of floating marsh patches in the Lake Apopka NSRA .. 58 4 10 The probability of male and female immature alligator s making a sig nificant move based on body condition in the Lake Apopka NSRA ................................ 59
9 4 11 The probability of male and female immature alligator s making a significant move, based on length in the Lake Apopka NSRA. ................................ ............ 60
10 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science MOVEMENT AND HABITAT SELECTION OF IMMATURE ALLIGATORS IN A RESTORED WETLAND IN FLORIDA By Rio Whitney Diana Throm August 2013 Chair: H. Franklin Percival Cochair: Ken neth G. Rice Major: Interdisciplinary Ecology The purpose of this study was to identify factors that correlate with or influence American alligators ( A lligator mississippiensis ) tendency to reside in one habitat over another. Knowledge of the nature and impetus for movement of wildlife is important to understanding their spatial requirements, population processes, and life history c haracteristics for conservation Alligators use multiple habitats throughout life and it is also important to understand the matrix of habitats that support each life stage to effectively conserve populations. In this study I examined environmental, ecolo gical, and biologic al factors that influence habitat selection. The study was conducted on the northern shore of Lake Apopka where ca 15000 acres of marsh previously impounded for agriculture is being restored Approximately 90 immature alligators (43 75 cm snout vent length ) were outfitted with radio transmitters and located weekly for one year. I used a generalized linear mixed model with a binomial distribution using the GLMER function in the R statistical program to conduct the analysis I used Akaike Information Criterion (AIC) to rank the models based on the most parsimonious fit. For modeling purposes, I made the probability of an alligator
11 making a significant mov e to an area a function of one or more of the following variables; moon phase, precipi tation, air temp water level, class area, median patch snout vent length, sex, and body condition. The highest ranking model indicated that the probability of movement w as positively associated with moon pha se, average air temperature, cumulative precipi tation, number of shallow and floating marsh patches, and body condition. The probability of movement was negatively associated with water leve l and snout vent length. I used the model to further investigate the impetus behind alligator movement and the possibility of random movement I investigated these ideas by testing 9 scenarios (hypotheses) based on information obtained from my data set and using my model with best fit. My hy potheses specifically addressed innate dispersal habitat selection, and non random movement Based on th e results I found, it is likely that immature alligators move because of instinct ( P = 0.35 for males, P = 0.4 for females), but only during conditions that allow for easy travel ( P = 0.74 for males, P = 0.78 for females) It also seems that the moon influences their propensity for exploring ( P = 0.89 for males, P = 0.91 for females) It appears unlikely that that the main impetus for immature alligator movement is predator avoidance ( P = 0.06 for males, P = 0.08 for females) and there is a high probability that immature alligators are moving in a non random direction ( P = 0.79 for males, P = 0.82 for females) The results of this study can be used by the St. Johns River Water Management District ( SJRWMD ) to assess the usefulness of immature alligators as an indicator of contaminant concentrations in restored wetland s It will also help wildlife management
12 agencies better understand mechanisms b ehind immature dispersal so that survey results c an be better assessed This information is useful for alligator translocation or reintroductions, as the release of immature alligators into more suitable habitat may increase their chances of survival
13 CHAPTER 1 INTRODUCTION On Animal Movement Wild animal movements are usually related to improving their chances of survival and reproductive success ( Howard 1960 Manly 2002 ) Kn owledge of the nature and impetus for movement of wildlife is important to un derstanding their spatial requirements, population processes, and life history characteri stics for conservation, management and harvest ( Sanderson 1966 Kernohan et al. 2001 ). Understanding these functions is also important for developing habitat restorat ion plans (George and Zack 2001). A nimal movements vary in relation to time and space, so w ildlife movement may be analyzed over the course of a life span, seasonally, or daily T he focus of movements analysis can range from migration patterns to resource selection depending on the questions posed On Crocodilian Movement Crocodilians are ec totherms and thus, their daily and seasonal activity patterns are stron gly influenced by temperatures ( Lang 1987 Howarter 1999, Southwood and Avens 2010). Because cr ocodilians grow an order of magnitude in their life time (Wilkinson and Rhodes 1997) their resource requirements change markedly as they grow (Cott 1961, Chabreck 1972 Magnusson et al. 1987) which makes their life cycle s complex (Wilbur 1980). When a spe cies uses multiple habitats throughout its life, it is important to understand the matrix of habitats that support it to effectiv ely conserv e populations (Subalusky et al. 2009). In regions with seasonal rain patterns, crocodilians are often confined to d eep parts of rivers or waterholes in the dry season then they disperse throughout the floodplain during the rainy season. This has been observed for spectacled caiman
14 ( Crocodilus crocodilus ) (Ouboter and Nanhoe 1988, Campos et al. 2006) freshwater crocod ile s ( C. johnstoni ) (Webb et al. 1983a, Tucker et al. 1996), saltwater crocodile s ( C. porosus ) ( Kay et al. 2004, Brien et al. 2008) Orinoco crocodile s ( C. intermedius ) (Munoz and Thorbjarnarson 2000) and American alligator s ( Alligator mississippiensis ) (Ku shlan 1974 Morea 1999 ). Movement studies have been conducted in three types of crocodilian habitat; linear riverine /canal systems ( Webb et al. 1983b, Magnusson and Lima 1991, Tucker et al. 1997 Morea 1999 Munoz and Thorbjarnarson 2000 ) b road expanses o f wetlands such as marshes swamps, and large lakes (Chabreck 1965, Garrick and Lang 1977 Rodda 1984 b Hutton 1989, Hocutt et al. 1992 Brien et al. 2008 ) and isolated bodies of water such as ponds and billabongs ( Gorzula 1978, Tucker et al. 1996, Campos et al. 2006, Subalusky et al. 2009). Although crocodilians share many similarities in terms of ecology and biology ( Campbell 2003, Brazaitis and Watanabe 2011), movement studies conducted in these different systems are often not comparable (Ouboter and Na nhoe 1988, Tucker et al. 1997 Morea 1999 ). Crocodilians that inhabit riverine systems typically have linear ranges and movement in the form of Messel 1978 Rosenblatt a nd Heithaus 2011 ). Resources in these systems may be more delineated i.e. shallow water and emergent vegetation is close to shore whereas deep open water is in the middle of the stream (Hutton 1989). Studies of the freshwater crocodile in Australia have revealed that movement is more easily facilitated in riverine habitats with continuous flow than in restricted isolated bodies of water ( Webb et al. 1983 a Cooper Preston 1992 Tucker et al 1997 ). Webb and Messel (1978) reported that yearling saltwater cr ocodiles dispersed up to 38.9 km
15 downstream of their natal site, which may have been partly due to river and tidal currents assisting their movements. Webb and Messel (1978) also reported upstream dispersal of 6.8 km suggesting that young crocodiles may be active dispersers. A study conducted in south Florida by Morea (1999), found that alligators in open marsh habitat had significantly larger home ranges than alligators in nearby canals. In Queensland, Australia, Brien et al. (2008) found that home ranges of sal twater crocodiles in a water hole were smaller than that of the same species monitored in a tidal system (Kay 2004). Brien et al. (2008) noted that this finding seemed intuitive because animals in confined habitats often have smaller home ranges than the same species in unconfined habitat. A study of three Chinese alligators ( A. sienensis ) revealed that the ir movements may be limited to the reservoir in which they were released (Youzhong et al. 2004). Munoz and Thorbjarnarson (2000) studied the moveme nts of 8 captive reared Orinoco crocodiles that were released into the Capanaparo River and found that they dispersed both up and downstream from the release site. Although these crocodiles did not leave the system, the maximum dispersal was almost 12 km. The dwarf caiman ( Paleosuchus trigonatus ) uses shallow streams throughout the Amazon River basin, and moves into the forest for terrestrial retreats (Magnusson and Lima 1991). Hutton (1989) reported that immature Nile crocodile s ( C. niloticus ) in the Nge zi River, Zimbabwe, occupy a single home range where suitable nesting habitat i s found until they reach about 50 c m s nout vent length (SVL ) when they disperse downstream into the lake and occupy transient home ranges until they settle upon a suitable per manent home range. Crocodilians in marsh systems tend to have home ranges that are less linear ( Morea 1999, Campos et al. 2006 ) than home ranges of crocodilians in linear systems.
16 Resources in marshes and lakes may be more interspersed compared with riveri ne system s (Hutton1989). Movement in marsh systems may require that crocodilians travel over a diverse matrix of ma crohabitats (Campos et al. 2006, Subalusky et al. 2009). Immature American crocodiles ( C. acutus ) tracked in a lake in Panama (Rodda 1984 b ) e xhibited affiliation with shallow marsh habitat similar to home range characteristics of other crocodilians in lake or marsh settings such as American alligators (Rodda 1984 a ). On Alligator Movement Of the 23 crocodilian species, the most comprehensive re search has been done on the American alligator. It was over harvested during the early 20th century (King 1972), but rebounded after subsequent protection in the 1970s (Hines 1979 Joanen and McNease 1987 ). It has continued to be an important source of inc ome to consumptive users throughout the s outheastern United States as a popular game species and a source of commercially valuable hides and meat (Hines and Percival 1987 Hines 1990, Joanen et al. 1997 ). A s a tourist attraction, alligators also provide in come to local areas ( Barrow 2010 ). D ue to its economic and ecological value (Mazzotti and Brandt 1994) and its threat as a potential human predator (Woodward and David 1994), a better understanding of behavior and ecology of American alligator s has often been a priority for state management programs Animals usually move due to the need to acquire some resource or for an instinctive need to improve survival so alligator movement is unlikely to be random. Alligator movements have been studied in Louisiana (Chabreck 1965 ; Joanen and McNease 1970, 1972 ; McNease and Joanen 1974 ; Taylor 1976 ; Rootes 1989 ; Rootes and Chabreck 1993 a ; Addison 1993; Lance et al. 2011), Florida (Hines e t al. 1968 ; Deitz 1979 ; Goodwin and Marion 1979 ; Murphy 1981 ; Rodda 1984 a 1985 ; Morea 1999 ;
17 Rosenblatt and Heithaus 2011 ), Georgia (Subalusky et al. 2009), and South Carolina (Murphy 1977). Some factors that influence movement occur annually such as temperature cycles or breeding season O ther factors that might cause alligators to m ove are cyclic over longer periods such as droughts ( Hines 1968, Kushlan 1974 Howarter 1999 ) and flooding (Mazzot ti and Brandt 1994, Fujisaki et al 2009, Lance et al. 2011) Anecdotal commen ts regarding alligator movement have been reported from nearly e very state within their range, however for the purpose of this paper, I will only refer to studies purposefully conducted to investigate alligator movements. Alligator dispersal : Dispersal can be defined as the movement of an individual out of an area lar ger than its home range, with no predictable returns (Bunnell and Harestad 1983 ). Upon approaching or attaining puberty, most vertebrates make some sort of dispersal venture (Howard 1960 Sutherland et al. 2000 ). Animals that disperse based on innate funct ions are predisposed at birth to move beyond the parental home range and may even disperse into unfavorable habitat ignorin g nearby suitable habitat (Benard and McCauley 2008) E xample s of rapidly expanding range of exotic species, such as European starli ngs in North America or rabbits in Australia support the idea that some individuals are more inclined to disperse long distances even before the currently occupied habitat is at carrying capacity. Innate dispersal benefits the population by genetic mixing (Neigel and Avise 1993, Neslon 1993 Ibrahim et al. 1996) extending the range (Hengeveld 1994) re colonizing areas from catastrophic events (Shaw 1995) and reducing intraspecific conflict (Howard 1960 Kesler and Walters 2011 ). It is difficult to explain the directional movement of innate dispersers because the
18 instinctive behavior is often more advantageous to the species than the individual (Tinbergen 1951 Holyoak et al. 2008 ). Another reason animals disperse is for factors related to their environmen t. Environmental dispersers move specifically to acquire some lacking resource (Arcese 1989) and this type of dispersal is frequently density dependent (Howard 1960 Arditi et al. 2001, Guyer et al. 2012 ). When an animal population is a t equilibrium the distribution of individuals among habitats is stable, and no individual can improve its fitness by moving to another habitat. But as individuals, habitats, and populations change, the balance is disrupted and individuals will adjust the imbalance by disper sing to another habitat, resulting in increased fitness for the average animal. Dominant animals tend to exclude less dominant animals from optimal habitat, forcing them into suboptimal habitat (States 1976, Winker et al. 1995). Thus, w hen animals are in l ess optimal habitat they may constantly be moving, looking for better habitat. Hatchling alligators may s tart dispersing as soon as three months after hatching (Chopp 2003) or may stay near the nest site for consecutive years with new p ods of hatchlings ( Deitz 1979). However, they usually stay within 300 m of their natal site in a pod (sibling group) up to the ir first year of life (Foga rty 1974, Deitz 1979 Woodward et al. 1987 ). Alligator nests tend to be built in clusters (Woodward et al. 1984). A study done by Rice (19 92) found that spatial distribution of alligator nests on Lake Okeechobee was non random with the average nearest neighbor being 145 m. Thus, it seems probable that hatchlings found near a nest site may contain emigrants from other nearby n ests (Chopp 2003). A mark recapture study done by Chabreck (1965) was one of the first investigations on immature alligator movements. He found that they began to
19 disperse as immature s ( 25 50 cm SVL ) When immature alligators approach ed 45 cm SV L moveme nt fre quency started to decrease, however alligators 45 90 cm SV L moved at equal rates. Additionally, i mmature alligators tracked for 8 weeks in a Louisiana impoundment dispersed a mean distance of 1288 m (Addison 1993). Observations of immature alligator s in the E verglades by Hines et al. (1968) and Kushlan (1974) also suppor t these findings. W e found i n our study on Lake Apopka, that alligators around 45 cm SV L move d more than alligators near er to 75 cm SV L (Rauschenberger et al. 2010). Movement of y oung away from the nest site may be an innate function, uninfluenced by the environment, or it may be density related or a combination of the two Dispersal of young crocodilians may be prompted by the ir mothers driving them away (Hunt and Wa n tanabe 1982, Messel and Vorlicek 1987, Hutton 1989). Dodson (1975) indicated that the mechanical properties of the femoral retractor muscles and the longer limb lengths in immature alligators indicate a higher propensity for terrestrial locomotion of immature s relativ e to adults. T his suggests that alligators may be physically predisposed to disperse at a younger age Alligators 92 cm SV L are considered adults and they reportedly move less than immature alligators (McNease and Joanen 1974, Kushlan 1974 Subalusky et al. 2009 ). Chabreck (1965) speculated that adult females establish a home range in the marsh and seldom leave it e xcept for mating season. During the spring breeding season he observed that adult females tend to migrate from marshes to open water where the y are more likely to encounter males He also observed that a dult males move more frequently and over greater dist ances than females. T emperature changes, breeding
20 season, water levels, food supply, and water salinity were listed as factors that might affect natural movement (Chabreck 1965) Later studies done by Joanen and McNeas e (1970, 1972), Deitz (1979), Goodwin and Marion ( 1979 ) and Morea (1999) supported his findings. Joanen and McNease (1970) followed the movements of 5 adult female alligators in a Louisiana marsh during a 177 day period, which included both the breeding and nesting seasons. They found that th e greatest movement was during the breeding season when the females moved into open water from the marsh to mate and the great est distance travelled was 457 m. Augmented movements during breeding season were also noted in a north Florida lake (Goodwin and Marion 1979) and in the Everglades ( Foga rty 1974, Morea 1999). Chabreck (1965) observed that flooding facilitated dispersal of alligators, perhaps because new habitat becomes available. Conversely Foga rty (1974) noted that young alligators may delay disp ersal during drought years. Lance et al. (2011) reported that alligators travelled greater distances after hurricanes. Although adult alligators have travelled distances >50 km in 15 days (Tamarack 1989), 53 km (Joanen and McNease 1972), and 63 km (Elsey 2005), long range movements are typically less than 20 km for individuals in most studies (Joanen and McNease 1970,1972 ; Morea 1999, Lance et al. 2011 Rosenblatt and Heithaus 2011 ). Some notable dispersal movements of immature alligators as far as 40 9 0 km from the original capture site were reported in Louisiana (Lance et al. 2011). Alligator home range : Home range is a description of the space use pattern of an animal. Basic requirements such as food, water, cover, space, and mates are found within t he home range, and are usually readily available and ideally dispersed ( Leopold 1933 Fuller et al. 2004). Advantages to residing in an area with familiar geography
21 include; the ability to effectively exploit food resources and suitable microhabitats, loca te mates, travel efficiently and escape predators. H ome range is tied to growth and survival of the individual (Jewell 1966 Powell 2000, Mitchell and Powell 2012 ) Joanen and McNease (1970) commented that there was relatively little daily movement of ad ult female alligators in Rockefeller Refuge, Louisiana outside of the breeding season and the minimum home range sizes ranged from 2.6 16.6 ha. Rootes and Chabreck (1993 b ) did a subsequent study on 15 adult female alligators in Laccasine National Wildlif e Refuge in Louisiana and found home range size comparable to those found by Joanena and McNease (1970) Conversely, adult male alligators had greater home ranges than adult females ranging from 183 5,083 ha (Joanen and McNease 1972). Joanen and McNease ( 1972) noted that adult male alligators were more active in the summer, and that alligator movements were restricted to the den site during the winter. A dult alligators may seek warmer ambient temperatures during winter and thus, occupy different home ran ges in winter than in summer ( Joanen and McNease 1972, Murphy 1977 Goodwin and Marion 1979). M ovements between winter and summer sites were more related to temperatures than food, shelter, or breeding resources (Howarter 1999) Murphy (1977) noted that si gnificant movements by adults in the summer were preceded by concentrated activity in the area from which the alligator departed, followed by concentrated activity in the area to where the alligator moved. However, these results may be unique, as they occu rred in a thermally altered reservoir in South Carolina.
22 McNease and Joanen (1974) found that immature alligators were much more active over a wider range of environmental conditions than had been reported for movements of adult alligators They found that immature alligators had average home ranges of 178 ha for females and 229 ha for males. Likewise, Taylor (1976) reported greater activity of immature alligators on lakes in northern Louisiana. However the home ranges of those alligators were somewhat smal ler, with an average of 96 h a Addison (1993) found that an average seasonal movement for immature alligators in a freshwater marsh in Louisiana during the winter ( 398 m) was almost half of th e average summer movements (684 m). Addison also reported a larg e range in home ranges of immatures from 1 806 ha. Rauschenberger et al. ( 201 0) e stimated mean home range size for immature alligators in a central Florida marsh to be somewhat smaller at 5 7 ha, with a range from 38 70 ha. Alligator habitat selection : An imals tend to uphold their fi tness through habitat selection and will disperse among surrounding areas until fitness cannot be further increased ( Griffiths and Christian 1996, Morris 2006). Habitat preference is based on innate requirements whereas habitat utilization is a function of how the innate requirements can be met by availability of local resources (Johnson 1980 Mitchell and Powell 2012 ). Four general hierarchical levels of habitat selection are commonly referenced in literature: regional, landsca pe, macrohabitat, and microhabitat ( Turner and Gardner 1991, Aebischer et al. 1993, Urban et al. 1987) The regional level is based on geography (i.e. Southeastern Un ited States, Florida) Alligator habitat at a landscape level would be freshwat er bodies in Florida (i.e. the E verglades) Habitat selection at macro and micro levels varies with size and sex of the alligator as well as
23 season. An example of macro habitat selection for an adult male alligator would be an open water canal in the E verglades. M ic rohabitat is based on particular sites used for foraging, basking, predator avoidance and other resource needs. An example of micro habitat selection for an adult alligator would be a culvert opening in a canal where fish are likely to congregate (Morea 19 99). The density of animals in a habitat might not indicate habitat preference for a few reasons; the possibility of low population density resulting in unused habitat, ignorance of optimal existing habitat by individuals, or discontinuity of habitat type s (Brown 1984) Also, habitat selection may be density dependent. For example, if optimal habitat is at ca rrying capacity, less dominant animals may be forced to occupy neighboring suboptimal habitat regardless of whether the neighboring habitat is of sli ght or great difference in quality. This may result in greater than expected densities in poor habitat ( Winker et al. 1995, Kokko and Lundberg 2001, Railsback et al. 2003). Immature (<90cm SVL*) alligators under natural conditions apparently do not tend to exhibit territoriality (Dietz 1979). So in theory, utilization of habitats by immature alligator s would increase proportiona lly to alligator population density However this theory is complicated by the possibility of cannibalism by larger alligators (De lany and Abercrombie 1986, Rootes and Chabreck 1993 b Chopp 2003 ) which typically inhabit open water (Joanen and McNease 1972 Goodwin and Marion 1979 Morea 1999 ). Kushlan (1974) observed that as adult alligators were removed from a pond in south Florid a, the population of immatures increased. Whereas ponds that contained large alligators did not contain as many immatures. Therefore open water may be preferable
24 habitat for immature alligators, but proportionate use by immature alligators might be limite d by the potential predation by larger animals Immature alligators tend to occupy shallow marsh and lake perimeters (McNeas e and Joanen 1974, Taylor 1976 Webb et al. 2009 ). H abitat use, food preference s predators and competitors change with ontogeneti c changes in alligators as they grow ( Delany and Abercrombie 1986 Subalusky et al. 2009 ). Our studies on the Apopka North Shore Restoration Area ( NSRA ) suggest ed that alligators do not randomly wander about in search of optimum habitat (Rauschenberger et al. 2010). When an alligator moves from one habitat to another or moves a great distance it apparently is seeking improved conditions for growth and survival (Subalusky et al. 20 09). McNease and Joanen (1974 ) observed that interspersion of various water l evels, food options, and water areas influenced habitat preference s of immature alligators. I mmature alligators in a northern Louisiana lake and reservoir tended to prefer habitat containing cattail ( Typha spp.) in the fall and habitat containing logs and duck weed ( Lemna spp.) in the s pring and summer (Taylor 1976). Cannibalism and intraspecific competition is thought to increase as density increase s This can be especially evident during droughts when water is low, reducing available habitat ( Kushlan 19 74, Woodward et al. 1987 Elsey et al 2000 ), which is thought to instigate movement to new habitat. T he majority of previous studies on alligator movement were conducted in typical marsh habitat. However, one recent study in Georgia by Subalusky et al. (2 009) highlight ed the population dynamics of alligators living in disjunct wetlands in sand hill. Their study site was characterized by sand hill pinelands bordered by a river and scattered with seasonal wetlands. Reportedly, female alligators would traverse the sand
25 hills to the river to breed, and then return to small seasonal wetlands to nest and rear young. These seasonal wetlands were apparently good nurseries during most years because predator densities were low and food was plentiful for successful nes ting and hatchling survival The sub adult alligators dispersed into the river. Subalusky et al. (2009) reported that h abitat in seasonal wetlands resemble d marsh habitat that females from other studies preferred, and that adult males preferred open deep h abitat of the river to isolated wetlands. What is particularly interesting is the difficult matrix the females and immature s had to traverse when moving between the two aquatic systems. Alligator Navigation : Homing is thought to be comprised of 2 separate an animal to determine its geographic position relative to home and the compass step is responsible for maintaining an animal on course during the homeward movement (K ramer 1953). Griffin (1952) described 3 types of movements of displaced animals: 1) Type 1 the animal only uses landmarks to orient homeward. In this case, if an animal was using only this method of orientation, it would move randomly if released in an area of unfamiliarity; 2) Type 2 an animal uses some compass bearing to move in one direction, such as towards water, but not necessarily home; 3) Type 3 the animal can actually offset its displacement and return directly home. Type 3 is considered tru e navigation (Able 2001) Some common theories on the mechanism behind actual navigation are that animals may use an olfactory map (Hasler and Wisby 1951, Koch et al. 1969 kesson 2003 ), a route based information navigation system to sense dista nces (Land reth and Ferguson 1967 Wiltschko et al. 1978 Wiltschko and Wilschko 2003 ), and directions or multi c oordinate navigation (Rodda 1983 Lohmann and
26 Lohmann 1998 Bostrom et al 2012 ). Using olfactory maps to navigate, an animal could orient itself towards desirable or familiar smells. An animal using route based navigation would have to keep track of length and direction of each leg of its displacement for use on the homeward trip. Multi coordinate navigation is independent of displacement conditions, unlik e route based navigation. Multi coordinate navigation requires that the animal have an acute sensitivity to large scale gradients in at least two directions, such as geomagnetic dip angles (north and south poles) or horizontal (eastern or western) intensit ies (Rodda 1984 a Phillips 1996, Bostrom et al. 2012 ). H oming ability has been documented in adult (Woolard et al. 2004) and immature alligators ( Chabreck 1965, Hines et al. 1968, Rodda 1985). Immature alligators may use celestial cues, such as solar, stel lar, and lunar compass mechanisms to navigate, as well as proximity to the shoreline (M urphy 1981). Rodda (1984a) attempted to explain the mechanisms behind the ability of alligators to home and h e found evidence that they did not use olfactory cues to na vigate homeward, but more likely used some route based or water seeking form of true navigation (type 3) I mmature alligators are typically found in littoral zones of lakes or shallow marsh. However, it is unclear why they occupy these types of habitats. I t is possible that these habitats have more abundant prey than other habitats or perhaps they are forced to these areas by competition or predator avoidance. It is also unclear how they end up in these habitats. They may have some sense of these habitats in relation to alternative habitats and actively navigate there. Or, they may happen upon these areas in the course of instinctive natal dispersal. Understanding why and how immature alligators use these habitats will be useful for conservation and managem ent. *Snout vent lengths
27 (SVL) in the introduction were converted from total lengths (TL) by dividing TL by 2 (Woodward et al. 1995). This was done to keep the introductory discussion consistent with this study.
28 CHAPTER 2 MOVEMENT AND MICR O HABITAT SELEC TION OF IMMATURE ALLIGATORS IN A RESTORED CENTRAL FLORIDA MARSH History of the Study Area Lake Apopka was once world renowned by sportsmen for its clean water and superior bass fish ery (S hofner 1982). At that time, it was a clear lake, fed by springs, rain fall, and storm water runoff, with abundant macrophyte growth and healthy fish populations B y the early 196 0s, it had become one of the most degraded aquatic ecosystems in Florida (U.S environmental protection agency 1979). Located about 24 km northwest of Orlando lake Apopka lies between the Mount Dora ridge to the east, and the Lake W ales ridge to the wes t, and is the headwater of the O cklawaha chain of lakes. Historically, Lake A popka was F exceeded in size only by Lake Ok eechobee. In the 1940s, the Z ellwood drainage district, a consortium of vegetable farms, diked and drained an extensive marsh on the north side of the lake to make the rich peat soil availa ble to vegetable farming (S hofner 1982). Over the next decade, appr oximately 8,000 ha of marsh were drained, relegating Lake Apopka to hafer et al. 1986). Historically, vegetable farms along the north shore were shallowly flooded after every growing season to reduce soil erosion and combat nematodes. Fallow fields were usually flooded during the summer months, and the water was pumped back into the lake prior to the fall planting season. This influx of agricultural effluent was a major source of nutrient (nitrogen and phosphorus) pollution i nto the lake (SJRWMD 2004). Other sources of pollution to the lake include d discharge from citrus processing plants, nutrient and pesticide runoff from citrus groves, and sewage from the city of Winter Garden in to the southern part of the lake. This additi on of nutrients to the lake
29 led to chronic algal blooms, which are thought to have contributed to the decline of aquatic macrophytes in Lake Apopka (Canfield et al. 2005 Schelske et al. 2005) The shift from macrophytes to algae is believed to have subseq uently disturbed the nutrient cycling process of the system (Conrow et al. 1989 Canfield et al. 2000 ). Organochlorine pesticides (OCPs) were widely used from the 1940s to 1980s for crop pest control in the drained peat lands (known as muck farms) Aldrin, chlordane, DDT, dieldrin, endrin, and heptachlor were used as insecticides for pre emergence soil treatment (Natural Resource Council 1977). In addition to the chemical input from nearby agriculture there was a reported chemical spill in 1980 at the Tower Chemical Company located near the Gourd Neck area of the lake (U.S. EPA unpub. report). Subsequently, t he Lake Apopka Restoration Act of 1985 (Chapter 85 147, Laws of Florida) and the Lake Apopka Surface Water Improvement and Management Act of 1987 (Chap ter 85 97, Laws of Florida) initiated efforts to improve water quality in the lake. A portion of the farmland was acquired on the west side of the Apopka Beauclair Canal to develop a marsh flow way system that filters lake water to remove phosphorus (SJRW MD 2006). In 1996, the Florida legislature determined that it was in the public intere st to pursue a buy of the farms and restore agricultural lands along the north shore to wetlands The Lake Apopka Improvement and Management Act was passed to fund those actions (Section 373.461, Florida Statutes 1996). The St. Johns River Water Wetland Reserve Program, implemented a buy out plan to purchase the remaining farms. These two agenci es focused on restoring the north shore to marsh and modifying the levee arrangement that disconnected the original marsh system (SJRWMD 2004).
30 Currently, the main management objectives of SJRWMD on Lake Apopka are to reduce phosphorus in the lake, restore wetland habitat, and establish a scientific framework for restoring the eastern units of the North Shore Restoration Area (NSRA) (SJRWMD 2006). In 1998, when the land purchase from farmers was completed, fields were left flooded with 46 cm of water after the final summer harvest in an effort to deter growth of terrestrial vegetation and prevent contaminated water from returning to the lake. In the fall of 1998, migrating birds began to forage on these flooded agricultural fields. Subsequently, there was a major bird mortality event during the winter of 1998 1999, which was attributed to OCP poisoning from residual pesticides (SJRWMD 2004, Seplveda et al. 2005). A wide range of piscivorous birds were affected, presumably by eating contaminated fish. Howeve r, American white pelicans ( Pelecanus erythrorhynchos ), wood storks ( Mycteria americana ), great blue herons ( Ardea herodias ), and great egrets ( Ardea alba ) comprised most of the documented fatalities (SJRWMD 2004). Soon after the first bird mortalities occ urred, the SJRWMD began draining the fields, which remained de watered until 2008 (SJRWMD 2004). The SJRWMD worked closely with the U.S. Fish and Wildlife Service to establish protocols for restoring the agricultural fields to wetlands. In 2002, the first 276 ha were successfully flooded, and by 2009, over 3,000 ha of the former fields were undergoing wetland s restoration. Following the mortality event, a series of studies w as undertaken to investigate the effects of bioaccumulation of OCPs by piscivorous b irds inhabiting the NSRA. Bird eggs in nearby areas were assessed for OCP burdens, hatch rates, and eggshell
31 thickness. This provided SJRWMD with an indication of the health of a colony located in the NSRA. Although 27 species of piscivorous birds were kno wn to be affected by the avian mortality event in 1999, wood storks were of primary interest because of their federal listing as endangered (Coulter et al. 1999, SJRWMD 2004). Due to the uncertainty of foraging locations of wood storks and other wading bir ds, they were not considered a suitable tax on for making inferences about the OCP availability in the NSRA. Immature Alligator Study on the NSRA In 2007, a study was initiated by the Florida Cooperative Fish and Wildlife Research Unit Florida Fish and Wi ldlife Conservation Commission, U.S. Geological Survey, and the U.S. Fish and Wildlife Service to examine alternative monitoring strategies for OCP accumulation using alligators and anurans within selected impoundments of the NSRA (Rauschenberger et al. 20 10). Alligators can bioaccumulate contaminants found in aquatic habitats due to their long lives and high trophic level ( Delany et al. 1988, Khan and Tansel 2000, Campbell 2003). Because of this, and their relatively small home range (McNease and Joanen 19 74, Goodwin and Marion 1979), they were considered to be a potentially useful environmental indicator of OCPs (Campbell 2003, Rauschenberger et al 2004, Milnes and Guillette 2008). Immature a lligators in the 40 80 cm SVL size range were selected as potent ial surrogates for monitoring OCP levels on the NSRA because the size of their prey selection is similar to that of wading birds and they are more sedentary. Fish are the most common food consumed by wood storks, followed by arthropods, plant material, amp hibians, reptiles, mammals, and birds (Kahl 1964, Kushlan 1979, Coulter et al.
32 1999). Similar to wood storks, immature alligators are opportunistic feeders, and their diet typically includes many of the same prey groups (Chabreck 1972, Delany 1990). One of the main objectives of the Rauschenberger et al. (2010) study was to determine whether home ranges of immature alligators remained within specific impoundments that are being monitored for OCPs or if they move among the impoundments Previous studies have shown that average home range sizes of immature alligators were 1 78 ha for females and 229 ha for males (McNease and Joanen 1974), which are smaller than the size of typical management units (290 1203 ha) on the NSRA (SJRWMD 2006). The potential stimul i o f alligator movement among impoundments seemed to be apportioned to three general categories: environmental, ecological, and biological. Initial observations revealed that movements of some alligators would be static for consecutive weeks, and then they would move a considerable distance until they settled in some other area. Conversely, other alligators never moved far from the original capture location (Rauschenberger et al. 2010). Original capture location seemed to be an important factor affecting wh ether an animal was likely to move. However from a subjective standpoint the habitat appeared to be essentially the same across the study area. This study was designed to identify some of those stimuli driving alligator movement Objectives and Hypothese s The purpose of this study was to extend knowledge of why immature alligators move I examined environmental, ecological, and biological factors that influence their habitat selection. I hypothesized that alligators in relatively desirable habitat will mo ve undesirable characteristics
33 near the location from which an alligator moved, and comparing these characteristics to those of the location to which the alligator moved, could provide useful inf ormation on habitat and resource selection The Apopka NSRA marsh provide d an ideal site for this study because it allow ed comparison between lake and various marsh habitats. It also allo wed for documentation of the recolonization of newly flooded impoundm ents. Environmental factors : The environmental factors I used to assess association with movement were; air temperature, rainfall, and quarterly moon phase. I hypothesized that air temperature was an important factor related to movement due to the ectother mic nature of alligators (Lang 1987, Southwood and Avens 2010). I also hypothesized that rainfall, or water availability, was an important factor for alligator movement, both cumulative over a season, and after significant rain events. I surmised that all igators were more mobile after significant rain events because water availability facilitates movement in their habitat matrix. With higher water levels, the matrix that alligators travel through would have more open areas with less and shorter emergent ve getation (Carter 2010). Moon cycles have long been correlated with animal movements and have been known to play a role on activity times for many animals (Alsheimer 1999, Zimecki 2006; Penteriani et al. 2011). Gyuris (1994) found that p redation rates of ha tchling sea turtles by fish in creased during full moon phases. However, the predation was not nece ssarily due to the amount of illumination because the moon was not visible on all full moon nights. Woodward and Marion (1978) found that alligator activity i ncreased with amount of moonlight. Whereas, caimans have been shown to move mostly on nights when there is the lowest light (Gorzula 1978) Most studies conducted to analyze lunar cycles on
34 humans and animals show increased activity during full moon, speci fically waxing gibbous stages (Zimecki 2006 Grant et al. 2012 ), and Weaver (1974) hypothesized that this increased activity during full moon phases had some relation to gravitational and geomagnetic forces. Based on these findings, I hypothesized that moo n phase would affect alligator movement The environmental stimuli that alligators experience may influence when an alligator decides to move or explore, but not the direction of movement. Given these environmental variables, I hypothesized that immature a lligators would be more likely to move during warmer weather, after significant rainfall events, and during waxing gibbous moon phases. Ecological factors : The ecological factors I use d were ; water level, length of time flooded, adult density and habitat parameters such as class area, median patch characteristics of the habitat and may provide insight as to why an alligator would leave, stay, or move to a certain area. Water fl uctuations affect immature alligator habitat because as water levels increase, prey may disperse ( Kushlan and Jacobsen 1990, Fujisaki et al. 2009), vegetation may change (SJRWMD 2008) or larger alligators may move in to immature alligator habitat (Rauschen berger et al. 2010). During droughts crocodilians may be forced to move into deep permanent bodies of water until enough rainfall has accumulated and inundated habitat becomes available in more ephemeral portions of their home range (Chabreck 1965, Gorzula 1978). Water fluctuations also relate to habitat The length of time an area is flooded is an important factor because newly flooded areas ( 6 years) have a surge of primary productivity (Novak et al. 2004,
35 Aldous et al. 2007, Montgomery and Eames 2008) which may be ideal for immature alligators. Also newly flooded areas are less likely to have larger predator y alligators (Rauschenberger et al. 2010). Large males prefer deep open water (Chabreck 1965, Goodwin and Marion 1979) where as adult females tend to occupy marshes and swamps where immature s are more likely to reside (Goodwin and Marion 1979, Rootes and Chabreck 1993 b ). Although adult females are potential predators, large males tend to be the main threat (Addison 1993), probably due to their greate r size (Rootes and Chabreck 1993 b Delany et al. 2011 ). I classified habitat types into five main groups as described in SJRWMD (2008) for analysis. Hardwood s wamp (HS) was wetland s dominated by deciduous hardwood species subject ed to seaso nal periods of flooding. Shrub s wamp (SS) was dominated by willows ( Salix sp.), buttonbush (Cephalanthus occidentalis) or similar appearing vegetation. Transit ional s hrub (TS) was dominated by vegetation typical of hydric transition zones in Florida such as wax myrtle ( Myrica cerifera ) and Baccharis halimnifolia Shallow m arsh (SM) was comprised of herbaceous or graminoid communities with species such as sawgrass ( Cladium jamaicense ), maidencane ( Panicum hemitomon ), cattails ( Typha spp.), pickerel weed ( Pontederia cordat a ), and arrowhead ( Sagittaria spp.). Floating m arshes (FF) are communities of free floating plants, such as, water hyacinth ( Eichhornia crassipes ), water lettuce ( Pistia stratiotes ), and/or duckweed ( Lemna Spirodella ); or floating mats of rhizomatous/stol oniferous species, such as, alligator weed ( Alternanthera philoxeroides ), pennywort ( Hydrocotyle spp.); or various graminoids, such as Paspalum spp. and sedges.
36 I chose habitat ma trices that might be associated with immature alligators to be used in conjun ction with the vegetation classification. Class proportion represents an evaluation of the proportionate amount of dominant vegetation types in a particular area (Elkie et al. 1999). This allow ed me to consider if there was some selection by alligators for certain vegetation types. Number of patches was the total number of patches for an individual class (Elkie et al. 1999). There has been considerable attention given to patch size and resource use, and depending on the environment, number of patches of a p articular class is an important factor in habitat use by animals (MacArthu r and Pianka 1966). This measure allow ed comparison of areas with large contiguous patches to areas with small interspersed patches. Edge density was the amount of edge relative to t he landscape area (Elkie et al. 1999). I included edge as a component because it has been shown to be an important microhabitat variable for many species (MacArthur and Pianka 1966), and potentially for immature alligators (Rodda 1984 a ). However, edge may also mean susceptibility to predators (Yahner 1988) particularly if it includes open water (Rootes and Chabreck 1993 b relative patch diversity (Elkie et al. 1999). The index will equal zero when there is only one patch in the landscape and will increase as the number of patches increase s I included this matrix because it has been shown that the juxtaposition and interspersion of habitat types is important for immature all igators (McNease and Joanen 1974 ). I hy pothesize that immature alligators will be more likely to move if they are in or near deep, open water and if the vegetation is too homogenous or if the area has been
37 Biological factors : I use d the biological parameters, sex, snout vent length (SVL) and body condition for assessing factors that might prompt movement The onset of sexual maturity of alligators occurs when they reach approximately 100 cm SV L ( Joanen and McNease 1975, Wilkinson and Rhodes 1997). T hough this study focused on immature alligators there is some hormon al expression at that age (Rooney et al. 2004, Milnes and Guillette 2008) which might influence their propensity to dis perse. H ome range patter n s of immature alligators have been observed to differ between the sexes (McNease and Joane n 1974 Rauschenberger et al. 2010). Although all my study animals were in the same size class (43 75 cm SVL) I includ ed SVL as a parameter because I suspected alligators near er to 43 cm SVL may select different habitat alligators at the upper end of the size range (75 cm SVL) In addition to having different habitat preferences, I hypothesized that it that smaller alligators would be more li kely to move than larger alligators because they are still in an exploratory stage of life, whereas alligators at the upper end of the size range which are nearing maturity would be less likely to move Body condition directly relates to the amount and q uality of food consumed (Joanen and McNease 1976 Fujisaki et al. 2009 ) which is indirectly related to food availability and subsequently habitat quality. I hypothesized that a lligators with lower relative body condition at initial capture would be more l ikely to make significant movements while they a re searching for better habitat (Benard and McCauley 2008). I hypothesize that alligators near 43 cm SVL will make more significant movements than alligators nearer to 75 c m that alligators with a low er rela tive body condition index ( BCI ) will be more likely to move, and that sex of the animal will not significantly influence movement.
38 CHAPTER 3 METHODS Study A rea The study site was located in central Florida along the north shore of Lake Apopka and the North Shore Restoration Area (NSRA) which consisted of multiple impoundments managed by the St. Johns River W ater Management D istrict (Fig. 3 1) Note: Adapted from Rauschenberger, R. H., C. B. Carter, R. W. D. Throm, and A. R. Woodward. 2010. Alligat or and amphibian monitoring on the Lake Apopka North Shore Restoration Area assessing organochlorine pesticide levels and potential biomonitors. St. Johns R iver Water Management District Special Publication SJ2010 SP8 Palatka, Florida, USA Figure 3 1 Location of the north shore restoration area (NSRA) in relation to Lake Apopka in central Florida.
39 These individual impoundments were similar in that they all were formerly farmed and were being restored to marsh and they contained an extensive levee/can al system. The majority of research was conducted on four study units; Lake Apopka, Duda, West Marsh, and Phase 1 (Fig. 3 2 ). Selection of the four units was based primarily on a gradient of pesticide levels detected in the soils by the SJRWMD ( Sepulveda e t al. 2005 ) and occupancy by alligators. We also did a small amount of work on an additional area, Phase 2 (Fig. 3 2 ), which was flooded in the summer of 2009 near the end of our study. Duda (1203 ha) is located between the West Marsh and Uni t 2. It has tw o retention ponds about 30 cm deep with surrounding cattail and willow. Water depth range was 0 60 cm, with the deepest areas located in i rrigation ditches that transect the unit. Duda represented an area of lower OCP contamination, and it has been flooded or saturated since 2003. Dense cattail stands and willow heads are the predominant vegetation components on Duda, with a few open areas containing smartweed The predominant soil type is Everglades, which co mprises about half the area. Terra Ceia and Gato r soils make up the remainder of Duda. West Marsh (cells G and H) is a 290 ha area north of the marsh flow way and west of the Apopka Beauclair Canal. Water depths ranged from 30 150 cm, with the shallowest areas in cell H. West Marsh soils represent highe r OCP contamination relativ e to the other two study areas, and most of the unit has been flooded since 1994. Willow and catta il stands border the site, with the center comprised of dense hydrilla water hyacinths and open water. Half of the underlying soi l type is Everglades and the rest is a mixture of nine other types. Phase 1 is a 719 ha site located in the northwest corner of Unit 2. Water depth s ranged from saturation to around 150 cm, with the deepest water i n the northern sections and the
40 shallowest areas along the southern edge. Abrupt changes in dept h occurred throughout the unit due to a network of old irrigation ditches. Phase 1 represents an area of intermediate OCP contamination, and has been flooded since 2008 Water depths range from saturati on to about 150 cm Clumps of will ow and cattail are interspersed throughout the site, with open water areas and a few sca ttered patches of alligatorweed and duckweed The predominant soil type is Gator, with a few patches of Canova and Terra Ceia types.
41 Note: Adapted from Rauschenberger, R. H., C. B. Carter, R. W. D. Throm, and A. R. Woodward. 2010. Alligator and amphibian monitoring on the Lake Apopka North Shore Restoration Area assessing organochlorine pesticide levels and potential biomonitors. S t. Johns R iver Water Management District Special Publication SJ2010 SP8 Palatka, Florida, USA Figure 3 2. Locations of the study units, West Marsh, Duda, Phase 1 and Phase 2, on the Apopka North Shore Restoration Area in central Florida (Rauschenberger 2 010). Field Techniques We conducted night light surveys similar to those described by Woodward and Marion (1978) during June and J uly from 2007 2009 to determine distribution and relative densities of alligators Capture efforts in 2008 consisted of 2 da y and 7 night
42 catches, alligators were captured by hand at night, as described by Chabreck (1963), from an airboat. Capture efforts in 2009 consisted of 2 day light and 9 night catches. We recorded standard body measurements, sex, and GPS location for each alligator, and we marked alligators with #3 Monel web tags as described by Woodward et al. (1987). We outfitted 96 immature alligators with radio transmitters (Advanced Telemetry Systems, Isanti, MN) attached with a backpack style harness (Fig. 3 3 ) O nly alligators within the 43 75 cm SVL size class received transmitters. Radio transmitters were 7.5 cm long, 4.3 cm wide, 3 .0 cm high, and weighed 63 g. Once outfitted with radio transmitters, we released alligators at their capture sites. Movements one wee k after a transmitter had been attached were greater than the rest, suggesting that the capture and handling may have had a short term effect the movements of movements (Beaupre et al. 2004) I assumed that the radios did not influence alligator behavior because they were not heavy (63 g) compared to the weight of the alligators about 1.8% of their me an body mass I monitored each marked alligator weekly by triangulation using a truck mounted null peak antenna system and a R4000 ATS model receiver. I collected location information once a week and alternated tracking times every week between day and ni ght periods to ensure complete temporal coverage. I defined day as sunrise to sunset, and night as sunset to sunrise. I also rotated l ocation time s for each animal so that the same animal was not located at the same hour too frequently. I typically tracke d alligators from a pick up truck using the digital equipment described above. When I
43 tracked from an airboat, I used a handheld GPS, a handheld antenna, and a manual compass. I used a n electronic digital compass mounted on the antenna to take azimuth read ings, and I checked calibration weekly. I used a digital GPS receiver, set for Universal Transverse Mercator (UTM) grid coordinates and wirelessly linked to a Palm Figure 3 3 Radio transmitter mounted on an immature alligator in the NSRA on Lake Apopka, Florida during the 2008 field season. Pilot (Palm Inc., Sunnyvale, CA). I used program Locate III software (Nams 2006) loaded on a Palm Pilot to record and plot weekly locations of radio outfitted alligators. A minimum of 3 directional bearings were reco rded for individual alligator locations. When I calculated a location an error ellipse was also calculated. If the error ellipse was greater than the maximum acceptable error, I took additional bearings Acceptable elliptical error was maintained under 10 ,000 m 2 but the majority of locations were well under 2,000 m 2 In addition, I collected all directional bear ings used for one location within 40 minutes of each other, with the assumption that the alligator would not move
44 an appreciable distance during t hat time period. I separated successive lo cations for each individual by one week and collected location data over a one year span; thereby reducing autocorrelation (Swihart and Slade 1997). Location data were loaded into the windows version of Locate III after each tracking session. Data P rotocols I used the average of daily air temperature between two c onsecutive movements as the temperature measurement. Temperature data were obtained from the NOAA website ( http://www.nws.noaa.gov/climate/index.php?wfo=ml b ) I used the sum of daily precipitation at the NSRA between two consecutive movements as the measure of rainfall Rainfall data were obtained from the SJRWMD website ( http://webapub.sjrwmd.com/agws10/imageviewer/ ). I derived m oon data using http:// starda te.org. I cla ssified moon phase by quarters, waxing crescent (moon phase 1) waxing gibbous (moon phase 2) waning crescent (moon phase 3), waning gibbous (moon phase 4) I recorded the number of days in each quarter bet ween locations I used water level da ta collected from the SJRWMD ga ge located in the center of Lake Apopka. Because water le vels in the NSRA are reasonably well correlated (Fig 3 4 ) with the lake water level (Rauschenberger et al. 2010), I only us ed this one source to indicate water fluctu ations. I considered anything flooded < area because Bennett (1971) described decreased production in reservoirs after 6 years I assigned the locations that fit this description a 1 and flooded locations years a 0.
45 Note: Ad apted from Rauschenberger, R. H., C. B. Carter, R. W. D. Throm, and A. R. Woodward. 2010. Alligator and amphibian monitoring on the Lake Apopka North Shore Restoration Area assessing organochlorine pesticide levels and potential biomonitors. St. Johns R i ver Water Management District Special Publication SJ2010 SP8 Palatka, Florida, USA Figure 3 4 The relation between the water level on the lake with water levels in the north shore restoration impoundments from June 2008 through June 2009. The abbreviati ons are: West Marsh (WM), Duda (DU), Phase 1 (P1), Lake (LA), and Phase 2 (P2).
46 to calculate the body condition index (BCI) (Zweig 2003), and is described by the following equation: K = W/L 3 10n; Where W = weigh t of alligator in kg, L = SVL in cm, and the constant n = 5 Because some alligators were captured in the fall and some alligators were captured in the spring, their initial BCIs might not have be en consistent Therefore the BCIs were standardized by div iding the individual fall animal BCI by the average fall BCI, and the individual spring BCI by the average spring BCI so that all the BCIs are on a 2 to 2 scale. Indices close to 2 indicate better body condition. Adult density data were collected during n ight light surveys conducted in 2008 and 2009 in all accessible areas of the study area. Densities w ere expressed as alligators/ha and reflected average adult densities between years 2008 and 2009. I then classified densities <0.1/ha as low, 0.1/ha 0.2/ ha as medium and >0.2/ha as high based on the relative densities of alligators throughout the study area There were some locations that were not accessible during surveys. In these cases I classified the adult density as low, medium, or high based on ha bitat type and length of time flooded (Rauschenberger 2010 et al ). I also based the low, medium, and high classifications of these unsurveyed units on habitat, length of time flooded and personal observation I felt t his was reasonable because I was very familiar with all the units and I was aware of relative adult population densities among those units. Data Analyse s I deemed a ny movement 2 standard deviations greater than the median distance moved per animal as a significant move. The median was a mo re representative measurement than the mean because movements would not meet normal theory. Two or more standard deviations encompass ed most of the major m ovements Movements made during the first week of tracking were not included due to
47 potential effects of being handled and the potential of instrumented alligators moving due to disturbance I used Patch A nalyst (Northwest Science T echnology, Thunder Bay, Ontario, Canada) an ArcGIS package that analy zes vegetation related matri ces, to assess habitat st ructure. Patch analyst is a tool for quantifying landscape structure used in conjunction with ArcGIS (Elkie et al. 1999). Median distance moved by each animal was buffered around the locations. M a trix class proportion, number of patches, edge density, and S I used the 2008 GIS vegetation overlay of the Lake Apopka NSRA (Fig 3 5 ) to qualify habitats (SJRWMD 2008). I used a g eneralized linear mixed model with a binomial distribution using the G LMER function in the R statistical program to conduct the analysis. I used a m ixed model to account for repeatedly tracking individual alligators thus I included the alligator ID as a random variable. I used Akaike Information Criterion (AIC) (Bu rnham and Anderson 2002 ) to rank the models based on the most parsimonious fit. For modeling purposes, I made the probability of an alligator making a significant move to an area a function of one, or a combination of, the following variables; moon phase, precipita tion, index, length of time flooded, adult density, snout vent length, sex, and body condition. I also used R to make the graphs. Lines for the two discrete variables, sex and adult density, were shown on every graph. I displayed the probability of movement as a function of the individual continuous variables. O nly one continuous parameter of
48 interest was displayed at a time, all other variables were set to mean in the graphing code Note: Adapted from Rauschenberger, R. H., C. B. Carter, R. W. D. Throm, and A. R. Woodward. 2010. Alligator and amphibian monitoring on the Lake Apopka North Shore Restoration Area assessing organochlorine pesticide levels and potential biomonitors. St. Johns R iver Water Management District Special Publication SJ2010 SP8 Palatka, Florida, USA Figure 3 5 T he 2008 GIS vegetation overlay of the Lake Apopka NSRA that was used to qualify habitats (SJRWMD 2008)
49 CHAPTER 4 RESULTS During 2008 and 2009 we outfitted 96 alligators with radio transmitters throughout the study site (Fig 4 1) The average number of days between fixes was 10 (median = 8, SD = 5). Only 53 of the 96 alligators radio tagged were monitored for 52 consecutive weeks. This was primarily due to several harnesses coming off shortly after deployment and actual or presumed early battery failure. In a few cases I suspect that the animals moved out of the study area. Therefore the effective sample size used in analysis was 53 Note: Adapted from Rauschenberger, R. H., C. B. Carter, R. W. D. Throm, and A. R. Woodward. 2010. Alligator and amphibian monitoring on the Lake Apopka North Shore Restoration Area assessing organochlorine pesticide levels and potential biomonitors. St. Johns R iver Water Management District Special Publication SJ2010 SP8 Palatka, Florida, USA Figure 4 1 A erial image of the Apopka n or th shore restoration a rea in central Florida with initial capture locations of the 53 alligators analyzed in the stu dy
50 Seventeen percent of recorded moves were considered significant. Of the entire model set (Appendix A) only two models had any weight at all. Both of these models contained second moon phase, average air temperature, rain, body condition, length, sex, predator density and water level. The top model carried 82 % of the weight of the model set, and included two additional parameters: number of s h allow marsh patches, and number of floating marsh patches. Together these two models comprised 100% of the mode l weight (T able 4 1 ). Immature alligators moved most often during warmer months (Fig 4 2) and when there was the m ost cumulative rainfall (Fig 4 3 ). Table 4 1 AIC and relative weights of top two models in the model set examining f actors affecting movement of immature alligators on the Apopka NSRA. Model # AIC Weight Parameters 1 1304 0.82 Second moon phase Air temperature Cumulative rainfall Body condition index Snout vent length Sex Predator density Water level Number of shallow marsh patches Number of floating marsh patches 2 1307 0.18 Second moon phase Air temperature Cumulative rainfall Body condition index Snout vent length Sex Predator density Water level
51 Fig ure 4 2. C umulative rainfall related to time of year during t he 2008 09 field season. Figure 4 3 S ignificant moves made by immature alligators on the Lake Apopka NSRA as they relate to the 2008 09 field season P robabil ity of movement was increased with moon phase 2 average air temperature, cumulative precipi tation, number of shallow marsh and floating marsh patches, and body condition (Figs. 4 3 through 4 1 0 ) The p robability of movement was decreased with wate r level and snout vent length. The probability of movement increased substantially as the number of days in moon phase increased ( Fig. 4 3 ). The p robability of movement was increased as a ir temperature s increased ( Fig. 4 4 ) 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jun 09 Jul 09 Aug 09 Sep 09 Oct 09 Nov 09 Dec 09 Average cumulative rainfall (cm) month and year rainfall 0 10 20 30 40 50 60 Oct 08 Nov 08 Dec 08 Jan 09 Feb 09 Mar 09 Apr 09 May 09 Jun 09 Jul 09 Aug 09 Sep 09 Oct 09 Nov 09 Dec 09 Perent of moves that were significant month and year % of sig moves
52 ranging from a probability of movement near 0.1 during cooler temperatures to near 0.4 during warmer temperatures. The p robabil ity of movement increased from 0.2 at 0 cm of rainfall to almost 0.5 at 35 cm of rainfall ( Fig. 4 5 ). The p robability of movement also increased with number of shallow marsh patches ( Fig. 4 7 ) from a probability of approximately 0.2 at 0 patches to almost 1.0 with 40 patches. The probab ility of movement increased as the n umber of patches of floating marsh increased ( Fig. 4 8 ) from around 0.2 at 0 patches to almost 0.4 with 12 patches. The p robability of movement increased as b ody condition increased ( Fig. 4 9 ) from 0.2 at a BCI of 2 to 0.4 at a B CI of 2 Movement declined as water level increased ( Fig. 4 6 ) with a probability of approximately 0.3 for lower water levels decreas ing to approximately 0.2 as water levels rose The probability of movement decrea sed as alligator size increased (Fig. 4 10 ) from P = 0.3 for alligators with SVL 45 cm to P < 0.2 for alligators with SVL = 75 cm. These correlations are also illustrated in table 4 2. I attempted to run a global model containing all parameter s but having 14 parameters in the model made it too complicated to successfully converge.
53 Figure 4 4 The probability of male and female immature alligators in the NSRA of Lake Apopka making a significant move to a new area under high, medium and low predator den sities, based on the second moon phase during the 2008 and 2009 field seasons.
54 Figure 4 5 The probability of male and female immature alligators making a significant move to a new area in high, medium and low predator densities, based on air temperatu re in the Lake Apopka NSRA during the 2008 and 2009 field seasons.
55 Figure 4 6 The probability of male and female immature alligators making a significant move to a new area in high, medium and low predator densities, based on rainfall in the Lake Apop ka NSRA during the 2008 and 2009 field seasons.
56 Figure 4 7 The probability of male and female immature alligator s making a significant move to a new area in high, medium and low predator densities, based on water level in the Lake Apopka NSRA during th e 2008 and 2009 field seasons.
57 Figure 4 8 The probability of male and female immature alligator s making a significant move to a new area in high, medium and low predator densities, based on number of shallow marsh patches in the Lake Apopka NSRA duri ng the 2008 and 2009 field seasons.
58 Figure 4 9 The probability of male and female immature alligator s making a significant move to a new area in high, medium and low predator densities, based on number of floating marsh patches in the Lake Apopka NSRA during the 2008 and 2009 field seasons.
59 Figure 4 10 The probability of male and female immature alligator s making a significant move to a new area in high, medium and low predator densities, based on body condition in the Lake Apopka NSRA during the 2008 and 2009 field seasons.
60 Figure 4 11 The probability of male and female immature alligator s making a significant move to a new area in high, medium and low predator densities, based on length in the Lake Apopka NSRA during the 2008 and 2009 field seasons.
61 Table 4 2 T he fixed effects from the top model of alligator movements in the NSRA of Lake Apopka during the 2008, 2009 field season. Slope Stand. Error Z value Pr (>|z|) Intercept 22.3 8.45 2.6 5 0.00 Moon phase 2 0.07 0.02 3.0 4 0.00 Air 0 .0 6 0.0 2 3.49 0.00 Rain 0.04 0.01 3.60 0.00 Body Cond. 0.16 0.1 2 1.39 0.16 S VL 0.0 2 0.0 2 0.94 0.3 5 Sex m 0.2 2 0.23 0.9 4 0.3 5 Pred l ow 0.06 0.2 6 0.2 6 0. 80 Pred m ed 0.6 1 0.36 1.6 9 0. 10 W a t e r 0.3 9 0.13 2.95 0.00 S hallow msh 0.04 0.0 2 2.3 2 0.02 Floating msh 0.0 6 0.0 5 1.29 0. 20
62 CHAPTER 5 DISCUSSION I found that movements of immature alligators on a restored marsh in central Florida were more likely to occur in the warmer months during periods of full moon, with low water levels and after rain events when there was potentially new habitat available. Alligators were more likely to move to areas where there was abundant shallow marsh and /or floating marsh patches. Environmental E ffects Chabreck ( 1965) and other researchers observed that a lligator movement is closely associated with environmental factors such as moon phase, air temperature, and cumulative rainfall T hose observations were supported in this study However, it should be noted that those variables probably do not influence where the a lligator decides to go, but rather what stimulates them to move. Moon phase : R esults indicate that lunar cycles may stimulate alligators to move This is concurrent with lunar effects found on cricket frogs ( Ferguson et al. 1965 ) sea turtles (Gyuris 1994) and caiman (Gorzula 1978 Silveira et al. 2008 ). Similarly, Woodward and Marion ( 1978) concluded that alligators were more likely to be counted and they assumed that this was because they were more active during certain lunar cycles I cla ssified moon pha se by quarters, waxing crescent (moon phase 1) waxing gibbous (moon phase 2) waning crescent (moon phase 3), waning gibbous (moon phase 4) Alligators seem to be most active during full moon phases par ticularly in The apparent significan ce of in the models indicates that immature alligators are more likely to move during this phase of the moon cycle than any other. This phenomenon has been shown for many other animal including
63 humans (Zimecki 2006), and has been attributed to the increased gravitational pull and the electromagnetic fields that are activated during that moon phase (Weaver 1974). It is possible that illumination during full moon phases has some bearing on animal behavior, however, I did not measure the amount of nocturnal light emitted during this study. Based on other studies (Gyuris 1994, Zimecki 2006) I suspect that the effect of moon phase on alligator movements has more to do with the gravitational forces from the moon than illumination. Air temperature : The best model indicated that the probability of a n immature alligator making a significant move increased with air temperature. Because alligators are ectothermic (Spotila et al. 1972), they are more likely to be dormant during cooler months when their n eed for food and space declines. However, when temperatures are warmer and their metabolism speeds up their requirements for food and space can be expected to increase (Spotila et al. 1972 Howarter 1999 ). T herefore I attribute the observed increase in m ovements of immature alligators during warmer weather to their greater foragin g requirements or their need to avoid larger alligators whose foraging activities have also increased. Rainfall : The best model indicated that the probability of a n immature alli gator making a significant move increase d with cumulative rainfall. The rainy season in Florida occurs from June through September and these are also some of the hottest months in Florida. So although the top model in my analysis indicate d that the probab ility of movement was greater during high er temperatures, this result may have been partly due to the expanded aquatic habitat available during the hot rainy season. Movement of crocodilians into newly flooded areas, especially immature s, has been well
64 doc umented (Kushlan 1974, Ouboter and Na nhoe 1988, Tucker et al. 1996 Spratt 1997, Munoz and Thorbjarnarson 2000, Kay et al. 2004, Campos et al. 2006, Brien et al. 2008). Newly flooded areas are often more productive than areas that have been constantly floo ded, partly due to the oxygenated soil (Novak et al. 2004, Aldous et al. 2005 ; 2007, Montgomery and Eames 2008). This also has been documented in fisheries studies which show that individual fish grow at exponential rates for the first five years after a r eservoir is formed (Bennett 1971) Similarly, immature alligators may be selecting newly flooded areas due to their increased productivity and the resulting increased abundance of prey Biological E ffects T he physical condition of each alligator, its lengt h and its sex were also influential factors influencing movement. The se biological variables were probably more indicative of why the alligator moved, whether it was for dispersal purposes, lack of food etc than to where it moved. Body condition index : B ody condition index is a relative measure of alligator health based on amount of body fat and muscle tissue The best model indicated that the probability of a n immature alligator making a significant move increased with body condition. I t seems unlikely that it would be energetically efficient to spend extensive energy finding a better feeding area i f adequate food was available in the existing site This indicates that the significant movements were probably not foraging trips but perhaps more explorato ry in nature Size : The best model indicates that the probability a n immature alligator making a significant move decreases with SVL This may be because smaller immature alligators are more likely to move than larger immature s because they are not able to
65 out compete the larger alligators for food and space. Perhaps, as immature alligators grow closer to maturity they start t o establish more predictable home ranges and are less prone to wandering T his behavior could suggest that the significant movements made by immature alligators in my study were probably more exploratory in nature, as immature alligators disperse and search for more suitable home ranges (Chabreck 1965, Deitz 1979). Sex : I t has been shown, even as immature s, the genders may behave diff e rently (McNease and Joanen 1974 Rauschenberger et al. 2010). Twenty percent of the moves by females were significant, whereas 15% of the moves by male were significant. The best model indicated that there was a higher probability of significant moves amo ng female alligators. Howard (1960) proposed that, as a general principle, male animals were naturally more prone to exploring than females One possible explanation for female alligators having a higher probability of movement in my study is that they ar e actively searching for an area to set up a permanent home range F emales typically have home ranges in shallow marshes as adults, where as males usually occupy open water areas as adults (Chabreck 1965, Joanen and McNease 1972, Goodwin and Marion 1979) an d most of the significant moves in my study were toward shallow marshes. Ecological E ffects It is likely that the main impetus for immature alligator movements is the quality of their current habitat. However, it is difficult to distinguish which ecologica l processes are contributing to habitat suitability. The best model in my study identified several variables that seem ed to effect movement and within the hierarchical levels of habitat selection, helped to identify macrohabitat selection by immature allig ators.
66 Water level : The best model indicated that the probability of a n immature alligator making a significant move decreased as water level increased. This is fairly intuitive because at low water levels prey may be concentrated in certain areas and aft er those resources are depleted, alligators are more likely to move to new pools to forage ( Kushlan 1990, Mazzotti and Brandt 1994). Also, when water levels are low, adult and immature alligators are often concentrated in a small area which make s immature s more susceptible to predation (Rootes and Chabreck 1993b Mazzotti and Brandt 1994 ). It can be difficult for alligators to find refuge from the heat as existing pools of water dry during the summer months requiring them to seek either shade or deep wate r holes (Howarter 1999) When water levels are low, the water line is typically far receded from the natural vegetated shoreline in lakes and impoundments Therefore, alligators rely on deep er areas or holes, which they maintain to a degree, or may need to move to a more suitable water refuge during drying cycles Number of shallow marsh patches : The best model indicated that the number of shallow marsh patches w a s an important variable influencing immature alligator movement. T he probability of movement wa s highe r when alligators were leaving an area with less shallow marsh and going to an area with more shallow marsh. It seems likely that immature alligators would prefer sha llow marsh because generally larger alligators are in open deep water (Chabreck 196 5, Joanen and McNease 1972, Goodwin and Marion 1979) and immature alligators can find more abundant cover and food resources in shallow marshes (Delany 1990). Number of floating marsh patches : The probability of movement was highest when alligators were l eaving an area with less floating marsh and going to an area with
67 more floating marsh. It seems likely that this type of habitat characteristic would be favorable to immature alligators because even in areas of deep water, floating marsh provides cover fro m predators and food abundance may be expected to increase Floating mar s h is often used by immature s for basking, so it may be especially important in vast marshes, where other nearby basking structures such as levees and logs are not available. Shallow m arsh and floating marsh habitats appear to be more suitable for immature alligators than the other habitat types studied. This may be a function of the vegetation structure, because these two habitat types have vegetation that is directly on, or near, the cover for prey that is easily accessible to immature alligators. Shrub swamp and transitional shrub habitat may harbor prey species but the type and density of the prey is likely to be different than that of shallow and floa ting marsh. Also, the structure of the vegetation is elevated sometimes a few in shrub swamp and transitional shrub habitats, which does not allow for easy access to the prey for alligators. Emergent vegetation is sparse or a bsent from hardwood swamp because of the shade. Without cover close to the water, the density of immature alligator prey is likely reduced. So whereas hardwood swamp is probably suitable habitat for travelling, it is not the most ideal habitat for immatur e alligators. Edge : This is an important parameter for generalist species because it typically indicates high productivity areas ( Robinson and Bolen 1989 ), which is where generalist species like alligators tend to thrive ( MacArthur and Pianka 1966) T he s hallow marsh and floating marsh habitats that were in this study are inherently high productivity areas
68 (Mit s ch and Gosselink 2000) so the edge density or diversity was not an important factor to the immature alligators in this study That is probably why models with edge density pa rameters did not rank very high S ince immature alligators prey on almost any animal they can physically consume, and can survive in practically any aquatic environment, having large expanses of marsh, with high quantities of fo od and cover gives more space for the immature alligators to set up home ranges. Edges with certain vegetation types also showed a negative correlation ( A ppendix A 2 ), though these did not carry enough weight to be included in the final model. Therefore si nce the edge density parameter in this study did not carry much weight ; it would be difficult to detect the importance of these parameters to alligators, even if they are commonly important to other species. Predator density : T he models containing predator density consistently had more weight. Indeed the best model indicated that predator density was an influential variable regarding immature alligator movement. I predicted that immature alligators would probably move more from areas that have high predator densities H owever areas with the highest probability of immature alligators moving were considered to have medium predator densities suggesting that the number of predators might n ot be as important as the cover. Or it may indicate that any level of am ount of predator alligators in the area will stimulate t hem to move If there is adequate cover for protection from larger alligators, then immature s may be able to persist in areas with high densities of predator alligators. Length of time flooded : M y h ypothesis that the length of time an area is flooded is important was supported to a degree by the model Newly flooded areas have a surge
69 of primary productivity and are less likely to h ave larger predatory alligators. Th erefore immature alligators would likely colonize newly flooded units. M odels that contained parameters of a specific habitat type carried more weight than the newly flooded unit (new) parameter by itself and this parameter was not included in either of the top two models. Therefore there is an indication that length of time flooded is not an important determinate of habitat selection. Management I mplications Insight into alligator behavior can help explain some variability in alligator nightlight surveys. After rain events, I found an inc rease in the probability of immature alligators leaving main water bodies and explor ing newly available habitat in adjacent wetlands Therefore, when alligator surveys have uncharacteristically low counts of immature alligators, managers should take into c onsideration the possibility that they have moved into adjacent wetlands. This migration has been demonstrated for adult alligators (Spratt 1997). Accounting for variability in the availability of alligators to be counted can increase the precision of nig htlight surveys ( Woodward and Marion 1978 Carter 2010). Use of immature alligators as indicators of environmental contaminant levels may be problematic when impoundments are adjacent to permanent water bodies. Alligators can readily move between the two systems, and our study indicated a substantial proportion of the population may shift among water management units. If immature alligators are used as indicators of contaminant exposures, I recommend using animals that are located within units that have a substantial amount of shallow marsh and floating marsh patches. Alligators in t hese units are less likely to move among impoundments. Immature alligators that have greater body condition, or that are in the
70 60 75 SVL range are less prone to moving and wou ld make better indicators of environmental contaminant levels than smaller alligators in poorer condition My findings may also be usefu l for making decisions about alligator translocation or reintroductions. The release of immature alligators into less su itable habitat may increase their chances of being preyed upon. In my study, s hallow marsh and patches of floating marsh were preferred immature alligator habitat and these two variables far outweighed other seemingly important habitat variables such as d iversity, edge, patch shape, and dominant vegetation The preferred habitat types may provide high quality food and/or cover for immature alligators. Therefore, to improve survival rates, it would be prudent for managers to select such habitat before relea sing immature alligators. Having knowledge of immature alligator macro habitat preferences may aid in discouraging immature alligator use of some wetlands. When planners are designing retention ponds around neighborhoods or airports they can create habitat that is relatively unfavorable to immature alligators. For example, ponds that are deep and vo id of vegetation, particularly lacking floating and shallow marsh type habitats, would not be ideal areas for immature alligators to reside. If an immature allig ator did happen into these ponds, there is a good chance that they would not remain for a long period of time.
71 CHAPTER 6 THE MECHANISMS BEHIND IMMATURE ALLIGATOR MOVEMENT Backgr o u n d M ovement of immature animals from natal habitats to the breeding location s is considered natal dispersal (Howard 1960, Kenward et al. 2001). There are three basic steps involved with dispersal. First there is the impetus to move which may be determined innately or environmentally (Benard and McCauley 2008). Second is the transi ence phase, and third is the selection of new habitat. While there is evidence to explain the first and last steps, little is known about the second step ( Ronce et al. 2001, Mayer et al. 2002). The area between the natal habitat and the habitat where the a nimal settles is a landscape matrix with various associated costs and benefits (Wiens 2001). M ovement of the animal is determined by the costs and benefits it encounters as it crosses the landscape matrix How it perceives these costs and benefits are depe ndent on its heredity and natal habitat (Benard and McCauley 2008). The way in which an animal navigates through this landscape is also dependent on stimuli for dispersal, whether they are innate or environmental. I explored the possibility of discerning whether immature alligators moved b ecause on either innate or environmental stimuli by using the best fit model from my study on habitat selection (C hapters 4 and 5). The parameters in this model consisted of environmental, ecological, and biological varia bles. I hypothesized that if immature alligators moved solely because of innate stimuli, then they would disperse even during moon). While this would support the hypoth esis of true innate dispersal, I thought it was unlikely that instincts would drive alligators to do something that would put them at high
72 risk of overheating or predation. I thought it was much more likely that movement during favorable weather conditions (i.e. high cumulative rainfall, moon phase 2, etc.) but with little incentive based on preferred habitat (i.e. low amounts of shallow and flo ating marsh patches), would indicate that immature alligators moved due to innate factors. Conversely, if alligato rs moved to find better habitat, then it seems likely that alligators would move regardless of weather conditions if their current habitat conditions were unfavorable (i.e. low amounts of shallow and floating marsh habitat). I tested 9 hypotheses based on information obtained from my data set and using my best fit model. Hypotheses 1 3 directly address innate dispersal, hypotheses 4 6 address habitat selection, and hypotheses 7 9 address non random movement by immature alligators. Dispersal It is difficult to characterize the directional movement of innate dispersers because the purpose of dispersal may not always be for individual benefit (Tinbergen 1951, Wilson 1975, Barton 2001). As a result, animals may move into unfavorable habitat and ignore nearby sui table habitat (Fretwell and Lucas 1970). Evolutionary reasons for dispersal may include facilitating range expansion an d genetic mixing (Dawkins 1976 Nosil and Crespi 2004), so the instinctive behavior is often more advantageous to the species than the in dividual. Immature alligators may make natal dispersal movements based on innate stimuli. Dodson (1975) proposed that the mechanical properties of the femoral retractor muscles and the longer limb lengths in immature alligators indicate a higher propensity for terrestrial locomotion of immatures relative to adults. This suggests that alligators may be physically predisposed to disperse over a diverse matrix at a young age. If this is the case, then immature
73 alligators make significant movements regardless of environmental conditions. The first 3 models specifically address the question of innate dispersal. M od eling Method s Best fit model: Moon phase 2 + Air temperature + Cumulative rainfall + Body condition index + Snout vent length + Sex + Predator densi ty + Water level + Number of shallow marsh patches + Number of floating marsh patches. (Chapter 3 pages 41 43) Hypothesis 1: Immature alligators move as a function of innate dispersal. Based on this hypothesis, if immature alligators are innate dispersers they should move regardless of habitat conditions. I tested this hypothesis by using my best fit model to test for probability of moving during scenarios that would indicate innate dispersal. Since I had a binomial distribution, I use d the Inverse Logit E quation to back transform my data from the logit scale. Inverse Logit E quation: P= / 1+ I manipulated the variables by setting cumulative rainfall, water level, and moon phase t o their respective minimums. I set air temperature at average because I suspect that even innate dispersers are unlikely to move during cold weather due to their endothermic nature. I set the predator density, shallow and floa ting marsh parameters 1). Then I averaged the probabilities between males and females because the difference in male and female movements was so slight in the best model that any difference in estimated movement
74 probabilities would have been insignificant. I used a chi square d test to identify differences between estimations. Hypothesis 2: Immature alligators move as a function of innate dispersal during condition s favorable for travel. Even i f alligators were predisposed to disperse, they would be unlikely to expend energy dispersing during harsh environmental conditions (i.e. low water level s), which is what I modeled in H ypothesis 1. I suspect that if water levels were conducive to alligator movement then immature alligators would be more likely to follow their instinct to move If immature alligators are innate dispersers they will have a high probability of moving, regardless of what the habitat characteristics are, but especially if water levels are high. I tested this hypothesis the same way as I tested H ypothesis 1, except I set the rain parameter to maximum and the water level at average. I set the rain parameter at maximum because it is likely that standing water will be available in be tween pools, which seems ideal for alligator movement. I set the water level at average or normal levels which I considered as not too high where movement could be enhanced by current s and not too low that alligators could sense that there might not be w ater elsewhere. Hypothesis 3: Immature alligators move as a function of innate dispersal during high I hypothesize that if immature alligators are going to make exp loratory ventures, regardless of habitat, they are most likely to do so during high water levels, high temperatures, and with the maximum amount of days during moon phase 2. I tested a
75 m odel using the same methods as H ypothesis 1, with the following change s to parameter settings; maximum amount of rain, water level, moon phase 2 days and maximum body condition, while the rest of the parameter settings were set to average. I set body condition at maximum because healthy alligators are more likely to explore than unhealthy alligators. Movem e nt Probabili t ie s I estimated that immature alligators are most likely to move under hypothesis number 3 and least likely to move under H ypothesis 1 Under H ypothesis 1 t he probability of moving ( P ) was 0.38 (Fig 6 1). Th is estimated probabi lity of moving are low er than that of hypothesis 2 ( P = 0. 59) and 3 ( P = 0. 76) It seems that if immature alligators do have an instinctual need to disperse, it does not override their basic affinity for water. If they do indeed have an instinct to disperse it is not strong enough to push them out into unknown territory when conditions are unfavorable for travelling i.e. low water conditions. It is likely, that when water level reaches a certain minimum where resources are diminished, a lligators will move regardless of any other variable. However, the alligator movements analyzed in this study did not contain any movements from areas where water levels were considered below adequate for alligator survival. Hypothesis 2 is still not a str ong indication that immature alligators are innate dispersers, but it does show some evidence that immature alligators may have moved for reasons other than habitat. Based on H ypothesis 3, it seems likely that immature alligators moved because of instinct, but only during conditions that allow for easy travel. It also seems that the moon influences their propensity for movement.
76 Tabl e 6 1. Parameters settings for H ypotheses 1, 2, and 3 and the probability of the maximum, and avg. indicates that the average for the parameter w as used. Model 1 Innate d ispersal 2 Innate disp. w/water 3 Innate disp. w/water and moon Moon phase 2 Air temperature Avg Avg Cumulative rain Body cond. SVL Avg Avg Avg Pred. density Avg Avg Avg Water level Avg Shallow marsh Avg Avg Avg Floating marsh Avg Avg Avg Probability of moving 0. 38 0.59 0.76 Home Range and Habitat Selection Animals not only depend on certain habitat types, but also the interspersion of habitat types within the cruising radius of the home range of an individual (Leopold 1933 Kie et al. 2002 Yarrow 2009 ). The resources available in each habitat type can vary with season, age, and time (Leopold 1933 Kie et al. 2002, Yarrow 2009 ). An animal may use certain areas within the home range disproportiona lly to other areas. These differential use patterns are usually rel ated to resource availability. Kernohan et e specified time period is key because home ranges can change throughout the lifetime for many species of fish, reptiles and amphibians (Chabreck 1972, Werner and Gilliam 1984, Burke et al. 2009) as their ontogenetic niches change. Although it is possible to broadly identify habitats that are selected or avoided, it is difficult to assign habitat preference based on one
77 variable because preference is often a function of interaction among many factors (Hedger et al. 2005). Because of the complexity of correl ating density with habitat quality, habitat suitability can be gauged based on the success of the individual and population dynamics (Hobbs and Hanley 1990, Krohn 1992, Winker et al. 1995). The best fit model indicated that macrohabitat selection for imma ture alligators consisted of wetlands with high amounts of shallow and floating marsh habitat. Based on this finding, I wanted to examine the probability of movement based on habitat makeup. Hypotheses 4 6 were set up specifically to address the question of habitat selection. M od eling Method s Hypothesis 4: Moving to better habitat. Based on the notion that immature alligators uphold their fitness through habitat selection, I hypothesized that the probability of movement will be high if alligators are movi ng to areas with high amounts of shall ow and floating marsh (i.e. preferred habitat ). Also, alligators with lower body condition index will be less likely to move to find higher quality habitat, because they do not have as much energy reserves as alligator s with greater body condition index. I used the same methods to tes t this hypothesis as I did for H ypothesis 1, with the following changes; I set the shallow and floating marsh variables to high, body condition index to low, and all other variables at aver age. Hypothesis 5: Predator avoidance Based on the notion that immature alligators move to avoid predation by larger alligators, I hypothesized that there is a high probability of immature alligators moving to a new area, with low predator density. I hypo thesize that this probability will be high even if the habitat and body condition parameters are not ideal for moving. I used the
78 same methods to tes t this hypothesis as I did for H ypothesis 1, with changes to the following parameters; I set the shallow an d floating marsh variables to low, to nullify the effect of alligators moving for different habitat structure, b ody condition index to low because animals with lower body condition would be less likely to expend energy on exploring and predator density to low. Hypothesis 6: Alligators move to avoid predators and for better habitat structure Based on the theory that immature alligators uphold their fitness through habitat selection and predator avoidance I tested a hypothesis to see if alligators were sele cting for shallow and floating marsh habitat as a source of cover. I tested this hy pothesis the same way I tested H ypothesis 1, except I set the shallow and floating marsh parameters to high, predator density to low, and all other parameters to average. M ov e ment Probabilitie s I estimated that immature alligators are most likely to mov e under H ypothesis number 4 and least likely to move under hypothesis 5 ( = 52.60, P < 0.001) Under H ypothesis 4, t he probability of moving is 0.73, while P = 0.07 for hypothesis 5 and P = 0.61 for hypothesis 6 (Fig. 6 2). Based on these probabilities, it seems likely that better habitat, based on vegetation, explains so me of the drive behind immature alligator movement but has little to do with predator avoidance.
79 Tabl e 6 2. Parameters settings for H ypotheses 4, 5, and 6 and the probability of parame the maximum, and avg. indicates that the average for that parameter was used. Model 4 Selecting for habitat based on veg. 5 Predator avoidance 6 Selecting for better veg./ less predators Moon phase 2 Avg Avg Air temperature Avg Avg Avg Cumulative rain Avg Avg Avg Body cond. SVL Avg Avg Avg Pred. density Avg Water level Avg Avg Avg Shallow marsh Floating marsh Probability of moving 0. 73 0.07 0.61 Direct ional M ovement The ability of the animal to transverse the landscape matrix also has a bearing on which direction it choose s to disperse (Mayer et al. 2002) and is a function of its natal habitat quality and phenotypic traits (Benard and McCauley 2008). P r evious studies of wild animals have demonstrated that some animals that perform innate natal dispersal, take direct routes to suitable habitat. Studies of field mice have shown that there seemed to be little trial and error searching for appropriate habita t as young deer mice dispersed (Howard 19 60 Wecker 196 4 ). Hatchling sea turtles instinctively use light cues and wave action, followed by magnetic navigation to leave their natal beaches for the open ocean where they find rafts of sargassum weed ( Sargassu m sp.) (Lohmann and Lohmann 1998). Animals that are stimulated to move to find batter habitat, would theoretically stop once they reached desirable habitat. However it is unclear whether alligators can sense where desirable habitat is, or if they wander r andomly throughout
80 the landscape until they find it. There may be some level of randomness associated with the direction of dispersal. Therefore, I wanted to test if immature alligators moved with a purposeful direction during dispersal or if their moveme nts were random. Hypotheses 7 9 were set up specifically to address the question of directional movement. M od eling Method s/ Movement Probabilities Hypothesis 7: Immature alligators know where they are going. I wanted to test the hypothesis that alligators d isperse non randomly disregarding stimuli behind their movement. I did this by setting all the parameters to average except for the shallow and floating marsh variables which were set to high. I predicted that if there was a high probability of moving to a location that was desirable habitat then it was not a random movement. The probability of males moving under these conditions is 0.79 and the probability of females moving under these conditions is 0.82 (Fig. 6.3). These probabilities suggest that when i mmature alligators moved, they moved to good habitat which indicates non random movement. Hypothesis 8: Immature alligators moved randomly. I wanted to test the hypothesis that alligators disperse randomly. I did this by setting all the parameters to avera ge except for the shallow and floating marsh variables which were set to low. I predicted that if there was a high probability of moving to a location that was undesirable habitat then they arrived at that location by chance. The probability of males movin g under these conditions is 0.18 and the probability of females moving under these conditions is 0.22 (Fig. 6.3). These probabilities indicate that it is unlikely that immature alligators moved in a random direction. Hypothesis 9: Alligators moved non rand omly and used the moon for navigation.
81 I wanted to test the hypothesis that alligators disperse non randomly, and they use the moon to help aid their navigation. I did this by setting all the parameters to average except for the shallow and floating marsh variables which were set to high, and the moon phase 2 variables which were also set to high. I predicted that if there was a high probability of moving to a location that was desirable habitat then it was not a random movement, and if this probability was higher than H ypothesis 7, then they used the moon to assist with navigation The probability of males moving under these conditions is 0.89 and the probability of females moving under t hese conditions is 0.91 (Fig. 6 3). This indicates that there is a hig h probability that immature alligators moved in a non random direction and the movements are strongly influenced by the moon, possibly using it for navigation. Hypothesis 8, alligators move randomly, was much less likely than hypothesis 7 or 9 ( = 4 5 56 P < 0.00 1 ). Tabl e 6 3. Parameters settings for H ypotheses 7, 8, and 9 and the probability of the maximum, and avg. indicates that the average for the parameter was used. Model 7 Non random movement 8 Random movement 9 Non random movement using moon Moon phase 2 Avg Avg Air temperature Avg Avg Avg Cumulative rain Avg Avg Avg Body cond. Avg Avg Avg SVL A vg Avg Avg Pred. density Avg Avg Avg Water level Avg Avg Avg Shallow marsh Floating marsh Probability of moving male 0.79 0.18 0.89 Probability of moving female 0.82 0.22 0.91
82 C onclu sion s Based on these findings I surmise that immature alligators are predisposed to disperse, but will most likely do so under certain favorable environmental and biological conditions. When they disperse, they move non randomly to a location with desirable habitat. It seems that alligators moved as a course of instinct, rather than desperation, thus it makes sense that individuals with higher BCIs would be more prone to move. It periods when cumulative rainfall is high because it would increase their chances of encountering standing water and facilitate their travel. Because the probability of moving is low er with high er densities of large alligators, it is unlikely that immature alligators are being excluded from desirable habita t by dominant adults, as some density depend ent theories would suggest, but more likely that they are selecting for shallow marsh habitat. It is interesting that full moon phases increased the probability of travel by immature alligators Although this is in concert with other findings of animal behavior during full moons (Zimecki 2006, Grant et al. 2012) it is difficult to separate whether movement was related to increased illumination or if gravitational pull or magnetic field stimulated movements If th e moon effect does have to do with illumination, it is possible that immature alligators could be using a kind of lunar compass, which is an indication of type 2 navigation, as described by Able (2001). Based on the high probability of alligator movement t o favorable habitat, it is also possible that alligators are capable of type 3 navigation prey particularly anurans which are a source of food for immature alligators (Delany
83 1990) Perhaps alligators key in on frog calls when they are trying to locate a habitat that has an abundance of food. Pig frog calls may be especially useful because they have a frequent, low frequency call that can be heard from some distance and typically fa vor habitat that is structurally similar to preferred immature alligator habitat. If an alligator hears the calls from pig frogs, it may signal to the alligator that there is suitable habitat with food in that direction. Alligators use a wide range of voca lizations for communication such as mating (Garrick and Lang 1977) and distress calls or pod calls from immatures (Garrick and Lang 1977). They also are able to key in on audio cues from prey such as barking dogs (pers. obs). Alligators use more vocal sign als than other crocodilians during breeding season, perhaps due to the lack of visibility in the systems they occupy (Garrick and Lang 1977). T hus they may be highly responsive to audible cues. There is some support that other crocodilians may use frog ca lls as an indicator of suitable pools during the dry season. In Venezuela where caimans move between pot holes in a prairie region, Gorzula (1978) found that out of 21 species of frogs that breed in the lagoons during the wet season only three species were commonly found in the stomachs of caiman, and all three species call and breed in the shallow water at the edge of the pond. It seems unlikely that animals move because of a single cause, and more likely iates movement. Significant movements made by some immature alligators are the result of certain habitat factors driving the need for movement. Biological factors affect how the ecological factors will influence the alligator, and environmental factors enh ance or hinder the conditions that are favorable for alligators to make movements. I found that movements of immature
84 alligators on a restored marsh in central Florida were more likely to occur in the warmer months during periods of full moon, with low wa ter levels and after rain events when there was potentially new habitat available. Alligators were more likely to move to areas where there was abundant shallow marsh and /or floating marsh patches. However, w hile it is possible to broadly identify habitat s that are selected or avoided, it is difficult to assign habitat preference based on one variable because preference is often a function of interaction between many important factors.
85 APPENDIX A MODELS
86 Appendix A 1 model ranking Model # Neg LogLik K n AIC AIC Weight Parameters Ex7 639 13 1418 1304 0 1.00 0.82 moon2+air+rain+bci+svl+sex+pred+wtr+smnump+ffnump Ex2 642.5 11 1418 1307 3 0.22 0.18 Moon2+air+rain+bci+svl+sex+pred+wtr 56 653.4 10 1420 1327 23 0.00 0.00 moon2 + air + rain + alled + bci 63f 676.4 11 1419 1338 34 0.00 0.00 moon2+wtr+bci+sex+ssed+pred+wnump+alled 61f 1341 10 1420 1341 37 0.00 0.00 moon2 + alled + hsed + smcp + pred + sex + svl 55 668.8 8 1461 1354 50 0.00 0.00 moon2 + air + rain + pred + bci 67f 796.9 9 1460 1355 51 0.00 0.00 air+moon2+wtr+svl+pred+alled 68f 672 7 1461 1358 54 0.00 0.00 air+moon2+svl+pred 64f 681.9 8 1461 1369 65 0.00 0.00 pred + wnump +hsed+ air+svl+bci 58 678.2 8 1460 1372 68 0.00 0.00 moon2 + wtr + wnump + smcp + pred 62f 679 9 1460 1376 72 0.00 0.00 moon2+wtr+wnump+smcp+alled+pred 19 680.5 7 1460 1377 73 0.00 0.00 bci + ffnump 65f 797.2 9 1460 1382 78 0.00 0.00 wtr + alled + pred+bci+smcp+smnump 14 682.1 10 1460 1384 80 0.00 0.00 wtr + pred + new + allsdi + wed + allnump + ssnu 15a 688.1 5 1461 1384 80 0.00 0.00 pred 16 686.5 7 1461 1387 83 0.00 0.00 pred + wnump + new + allpssd 53 768.8 7 1752 1552 248 0.00 0.00 moon2 + air + rain + sex + bci Ex6 780.8 8 1793 1578 274 0.00 0.00 moon2+air+rain+bci+smnump+ffnump 42 782.4 7 1793 1579 275 0.00 0.00 moon3 + moon2 + moon1 + moon4 + air + allsdi + bci 100 782.5 7 1814 1579 275 0.00 0.00 wtr+smnump+rain+air+moon2 Ex5 780.5 9 1793 1579 275 0.00 0.00 moon2+air+rain+bci+smnump+svl+ffnump Ex9 782.1 8 1793 1580 276 0.00 0.00 moon2+ai r+rain+bci+smnump+allsdi Ex4 782.3 8 1793 1581 277 0.00 0.00 moon2+air+rain+bci+smnump+svl 6 787.5 4 1752 1583 279 0.00 0.00 bci+sex 57 785.2 7 1793 1584 280 0.00 0.00 moon2 + air + rain + allsdi + bci 61 785.9 6 1793 1584 280 0.00 0.00 moon2+alled +hsed+smcp+alled+pred+sex+svl Ex1 785.9 6 1793 1584 280 0.00 0.00 moon2+air+rain+bci 1 787.4 5 1752 1585 281 0.00 0.00 svl + sex + bci 54 785.8 7 1793 1586 282 0.00 0.00 moon2 + air + rain + svl + bci 60 785.9 7 1793 1586 282 0.00 0.00 moon2 + air + rain + allpssd + bci 52 790.1 5 1793 1590 286 0.00 0.00 air + rain + bci 11 788.2 8 1816 1592 288 0.00 0.00 moon1 + moon2 + moon3 + moon4 + air + rain 32 786.9 9 1816 1592 288 0.00 0.00 moon3 + air + rain + allnump + allsdi + bci 12 789.9 7 1816 15 94 290 0.00 0.00 moon1 + moon2 + moon3 + moon4+ air 31 788.7 9 1793 1595 291 0.00 0.00 moon3 + moon2 + moon1 + moon4 + bci + allnump + rain
87 3 795.3 3 1775 1597 293 0.00 0.00 sex 2 795 4 1775 1598 294 0.00 0.00 svl + sex Model # Neg LogLik K n AIC AIC Weight Parameters 10 797.8 4 1816 1604 300 0.00 0.00 air + rain 13 795 7 1816 1604 300 0.00 0.00 moon1 + moon2 + moon3 + moon4+ rain 69f 796 5 1816 1604 300 0.00 0.00 air+moon2+svl+pred 8 798.4 6 1816 1609 305 0.00 0.00 moon1 + moon2 + moon 3 + moon4 66f 797.5 8 1814 1611 307 0.00 0.00 smcp+ssed+hsed+wtr+rain+wnump 7 803.5 3 1816 1613 309 0.00 0.00 air 9 804.7 3 1816 1615 311 0.00 0.00 rain 17 800.7 8 1793 1617 313 0.00 0.00 bci + ffnump + allnump + tsnump + smnump+ new 5 806.4 3 17 93 1619 315 0.00 0.00 bci 18 805.6 4 1793 1619 315 0.00 0.00 bci + allnump 30 805.6 4 1793 1619 315 0.00 0.00 bci + ffnump 8b 807 3 1816 1620 316 0.00 0.00 moon2 28 805.6 5 1793 1621 317 0.00 0.00 allsdi + bci + new 8c 810.1 3 1816 1626 322 0.00 0.00 moon3 8d 811 3 1816 1628 324 0.00 0.00 moon4 8a 811.8 3 1816 1630 326 0.00 0.00 moon1 25 810.6 5 1814 1631 327 0.00 0.00 moon3 + bci + new 14a 812.5 3 1814 1631 327 0.00 0.00 wtr 29 811.3 5 1814 1633 329 0.00 0.00 allsdi + wtr + new 4 814.4 3 1816 1635 331 0.00 0.00 svl 16a 814.4 3 1816 1635 331 0.00 0.00 new Appendix A 2 model intercepts *****Model23***** Edge density of hardwood swamp Estimate Std. Error z value Pr(>|z|) (Intercept) 1.3882209 0.0609449 22.778 <2e 16 *** *****Model22*****
88 Edge density of transitional shrub Estimate Std. Error z value Pr(>|z|) (Intercept) 1.423997 0.062583 22.754 <2e 16 *** *****Model21***** Edge density of shrub swamp Estimate Std. Error z value Pr(>|z|) (Intercept) 1.2536556 0.0978842 12.808 <2e 16 *** *****Model20***** Edge density of water Estimate Std. Error z value Pr(>|z|) (Intercept) 1.3403055 0.0816267 16.420 <2e 16 ***
89 APPENDIX B BEST MODEL OUT PUT
90 Model Ex7 > ModelEx7< glmer(yes ~ (moon2+air+rain+bci+svl+sex+pred+wtr+smnump+ffnump+ (1 | tag)),family=binomial("logit")) > summary(ModelEx7) Generalized linear mixed model fit by the Laplace approximation Formula: yes ~ (moon2 + air + rain + bci + svl + sex + pred + wtr + smnump + ffnump + (1 | tag)) AIC BIC logLik deviance 1304 1372 639 1278 Random effects: Groups Name Variance Std.Dev. tag (Intercept) 0.2291 0.47864 Number of obs: 1418, groups: tag, 42 Fixed effec ts: Estimate Std. Error z value Pr(>|z|) (Intercept) 22.36226 8.45153 2.646 0.008146 ** moon2 0.07174 0.02361 3.039 0.002374 ** air 0.05660 0.01620 3.493 0.000478 *** rain 0.04116 0.01143 3.602 0.000316 *** bci 0.16320 0.11725 1.392 0.163943 svl 0.01690 0.01798 0.940 0.347317 sexM 0.21699 0.23161 0.937 0.348814 predL 0.06622 0.25617 0.259 0.796006 predM 0.61420 0.36384 1.688 0.091388 wtr 0.38553 0.13049 2.954 0.003133 ** smnump 0.04492 0.01938 2.318 0.020453 ffnump 0.05939 0.04588 1.294 0.195507 --
91 Co rrelation of Fixed Effects: (Intr) moon2 air rain bci svl sexM predL predM wtr moon2 0.052 air 0.228 0.016 rain 0.031 0.062 0.286 bci 0.016 0.003 0.043 0.032 svl 0.190 0.012 0.012 0.043 0.267 sexM 0.102 0.017 0.054 0.011 0.330 0.098 predL 0.250 0.004 0.097 0.075 0.104 0.390 0.193 predM 0.026 0.002 0.061 0.056 0.159 0.060 0.043 0.390 wtr 0.993 0.058 0.273 0.020 0.003 0.08 3 0.078 0.219 0.036 smnump 0.074 0.007 0.050 0.036 0.054 0.009 0.086 0.123 0.210 0.059 ffnump 0.026 0.017 0.074 0.015 0.030 0.066 0.070 0.163 0.053 0.027
92 APPENDIX C HYPOTHESES EQUATIONS The 9 theory scenario models were buil t using the output from the top model (Ex7) and the inverse logit equation. P= / 1+ Where the probability of an immature alligator moving = log of the intercept+(slope of variable 1 the average of variable 1)+ +(slope of variable 2 the average of v
93 Scenario 1 Males =EXP(22.75947+0.07174*0+0.0566*22.4+0. 04116*0+0.1632*2.86 0.0169*53.4 0.38553*63.44+0.04492*3.98+0.05939*0.9)/(1+EXP(22.75947+0.07174*0+0.0566*22.4+0.04116*0+0.1632*2.86 0.01 69*53.4 0.38553*63.44+0.04492*3.98+0.05939*0.9)) Females =EXP(22.97646+0.07174*0+0.0566*22.4+0.04116*0+0.1632*2.86 0.0169*53.4 0.38553*63.44+0.04492*3.98+0.05939*0.9)/(1+EXP(22.97646+0.07174*0+0.0566*22.4+0.04116*0+0.1632*2.86 0.0169*53.4 0.38553*63.44+0.0 4492*3.98+0.05939*0.9)) Scenario 2 Males =EXP(22.97646+0.07174*0+0.0566*22.4+0.04116*30.56+0.1632*2.86 0.0169*53.4 0.38553*64.7+0.04492*3.98+0.05939*0.9)/(1+EXP(22.97646+0.07174*0+0.0566*22.4+0.04116*30.56+0.1632*2.8 6 0.0169*53.4 0.38553*64.7+0.04492*3.98 +0.05939*0.9)) Females =EXP(22.97646+0.07174*0+0.0566*22.4+0.04116*30.56+0.1632*2.86 0.0169*53.4 0.38553*64.7+0.04492*3.98+0.05939*0.9)/(1+EXP(22.97646+0.07174*0+0.0566*22.4+0.04116*30.56+0.1632*2.8 6 0.0169*53.4 0.38553*64.7+0.04492*3.98+0.05939*0.9)) Sce nario 3 Males =EXP(22.74947+0.07174*13+0.0566*22.4+0.04116*30.56+0.1632*2.86 0.0169*53.4 0.38553*64.7+0.04492*3.98+0.05939*0.9)/(1+EXP(22.74947+0.07174*13+0.0566*22.4+0.04116*30.56+0.1632*2. 86 0.0169*53.4 0.38553*64.7+0.04492*3.98+0.05939*0.9)) Females =EX P(22.97646+0.07174*13+0.0566*22.4+0.04116*30.56+0.1632*2.86 0.0169*53.4 0.38553*64.7+0.04492*3.98+0.05939*0.9)/(1+EXP(22.97646+0.07174*13+0.0566*22.4+0.04116*30.56+0.1632*2. 86 0.0169*53.4 0.38553*64.7+0.04492*3.98+0.05939*0.9)) Scenario 4 Males =EXP(22.7 5947+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)/(1+EXP(22.75947+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12))
94 Females =EXP(22.97646+0.07174*2.5+0.0566 *22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)/(1+EXP(22.97646+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)) Scenario 5 Males =EXP(22.1149+0.07174*0+0.0566*22.4+0.04116*3. 6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*0+0.05939*0)/(1+EXP(22.1149+0.07174*0+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*0+0.05939*0)) Females =EXP(22.42846+0.07174*0+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.385 53*64.7+0.04492*0+0.05939*0)/(1+EXP(22.42846+0.07174*0+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*0+0.05939*0)) Scenario 6 Males =EXP(22.14527+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*47+ 0.05939*12)/(1+EXP(22.14527+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)) Females =EXP(22.42846+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)/(1+EXP(22.4 2846+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 2.68 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)) Scenario 7 Males =EXP(22.75947+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)/(1+EXP(22.75947+0.07174 *2.5+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)) Females =EXP(22.97646+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)/(1+EXP(22.97646+0.07174*2.5+0.0566*22.4+0.04 116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)) Scenario 8
95 Males =EXP(22.75947+0.07174*13+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)/(1+EXP(22.75947+0.07174*13+0.0566*22.4+0.04116*3.6+0.163 2* 0.011 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)) Females =EXP(22.97646+0.07174*13+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*47+0.05939*12)/(1+EXP(22.97646+0.07174*13+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0. 38553*64.7+0.04492*47+0.05939*12)) Scenario 9 Males =EXP(22.75947+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*0+0.05939*0)/(1+EXP(22.75947+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0. 04492*0+0.05939*0)) Females =EXP(22.97646+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*0+0.05939*0)/(1+EXP(22.97646+0.07174*2.5+0.0566*22.4+0.04116*3.6+0.1632* 0.011 0.0169*53.4 0.38553*64.7+0.04492*0+0.05939*0))
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111 BIOGRAPHICAL SKETCH Rio is a native Floridian from Cocoa in Brevard County. She received her B.S. in Wildlife Ecology and Conservation from UF in 2007. Her current person al best alligator capture was a 12.8 footer from Lake Apopka, captured in part by Cameron Carter. She resides in Tallahassee, FL.