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Spring Focus on Sustainability and the Environment : Predator-Prey Dynamics : Prey Responses to Heightened Risk of Nativ...
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Permanent Link: http://ufdc.ufl.edu/UF00091523/00623
 Material Information
Title: Spring Focus on Sustainability and the Environment : Predator-Prey Dynamics : Prey Responses to Heightened Risk of Native and Exotic Predators in Urban and Rural Environments
Series Title: Journal of Undergraduate Research
Physical Description: Serial
Language: English
Creator: Taylor-Hoar, Kira
Fletcher, Robert
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: Spring 2012
 Subjects
Subjects / Keywords: Tufted titmouse
predator-prey interactions
predation risk
native and exotic predators
urban and rural effects on prey behavior
Genre: serial   ( sobekcm )
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Abstract: Although the dynamics of predator-prey have fascinated scientists for several decades, factors influencing behavioral responses to predation risk remain relatively unknown. With ongoing environmental change, two key issues that may alter perceived risk by prey are the presence of non-native predators and if (and how) urban environments may alter perceived risk. We tested the tufted titmouse (Baeolophus bicolor) reactions toward similar sounding but non-native predator calls, as well as how they would react to differences in predation risk in urban and rural environments. Predator calls of two local and nonlocal species were broadcasted to titmice in both urban and natural areas and their behaviors recorded. Latency to approach and minimum distance were the two variables that produced significant results, showing that the titmice would generally come in closer and more quickly in rural areas. We found that titmice altered their behaviors in response to different predators and effects varied in rural and urban environments.
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Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: sobekcm - UF00091523_00602
System ID: UF00091523:00623

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University of Florida | Journal of Undergraduate Research | Volume 13, Issue 2 | Spring 2012 1 Predator Prey Dynamics: Prey R esponses to H eightened R isk of N ative and E xotic P redators in U rban and R ural E nvironments Kira Taylor Hoar and Dr. Robert Fletcher College of Liberal Arts and Sciences, University of Florida Although the dynamics of predator prey have fascinated scientists for several decades factors influencing behavioral resp onses to predation risk remain relatively unknown. With ongoing environmental change, two key issues that may alter perceived risk by prey are the presence o f non native predators and if (and how) urban environments may alter perceived risk. We tested the tufted titmouse ( Baeolophus bicolor ) react ions toward similar sounding but non native predator calls, as well as how they would react to differences in predati on risk in urban and rural environments Predator calls of two local and nonlocal species were broadcasted to titmice in both urban and natural areas and their behaviors recorded. Latency to approach and minimum distance were the two variables that produced significant results showing that the titmice would generally com e in closer and more quickly in rural areas. We found that titmice altered their behaviors in response to different predators and effects varied in rural and urban environments. I NTRODUCTION Predation can affect the fitness of organisms by both consumptive and non consumptive aspects. Aside from direct consumption of an individual, the habitat choice, foraging behavior, social behavior, reproductive effort and other behavioral characteristics may be altered in behavior due to the perception of predation risk can result in adverse effects on fitness (Parsons and Blumstein 2010, Travers et al. 2010, a nd Large et al. 2011). Many prey species have modified their behavior in accordance to predator specific cues (Ghalambor and Martin 2001, Rainey 2004, Orrock et al. 2004, Apfelbach 2005). While prey can alter their behavior in response to predation risk, the introduction of non native predators poses a formidable problem for native prey species (Case 1996). Non indigenous predators are becoming more frequent due to urbanization and shifting biogeographical ranges (Case 1996, Williamson, M 1996, Vitousek 19 97). Native prey may not immediately percieve a predation threat from foreign predator species, resulting in increased population vulnerability of prey It is unclear how these novel predator species will affect prey behavior and how they will react behavi orally to new predation pressures. The urban to rural gradient of landscapes can also have implications on the behaviors of prey species (Chace and Walsh 2006, Marzluff and Neatherlin 2006, Bodey et al. 2011). As an effect of increasing urbanization, more non native species are being introduced into urban areas, proliferating in these human dominated habitats (McKinney 2006). Urbanization can lead to an increase in several types of predators, such as some raptor species ( Chace and Walsh 2006, Stout and Ros enfield 2010) which could influence predation risk for prey living in increasingly urban environments For example, f itness of avian species in urban areas is directly related to predator occupancy (Chace and Walsh 2006). We performed a field experiment to test if nonnative predators have adverse e ffects on the behavior of the tufted titmouse ( Baeolophus bicolor ) as well as how urbanization may affect behavior Non native versus local predator calls may affect how the titmice respond behaviorally T he degree of human occupation may also affect the detection and behavioral response to these calls due to surrounding noise differences in canopy and matrix structure and potential differences in predator density in urban environments These factors may aff ect behavior because of their unnatural origin and relatively recent appearance in evolutionary time ( Chace and Walsh 2006 ) We expect the titmouse not to respond as strongly to the foreign predator calls as the native predator calls because they have not evolved with nonnative predators and would not as easily identify those calls as a threat. For the effect of urbanization we expect that the titmice will be more wary in the natural environment because they would be more habitualized to fo reign noises in an urban area. METHODS Study A rea This study was done in neighborhoods around Gainesville, Florida and at the Ordway Swisher Biological Station located in Melrose, Florida. These areas consist mostly of live oak ( Quercus virginiana ) hammocks, pine flatwoods, and riparian areas.

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KIRA TAYLOR H OAR AND D R ROBERT F LETCHER University of Florida | Journal of Undergraduate Research | Volume 13, Issue 2 | Spring 2012 2 Focal S pecies Tufted titmice are a passerine species and in northern Florida are found most commonly in the hardwood hammock habitat (Langham et al. 2006). The most common avian predators of this species incl ude Eastern Screech Owls ( Otus asio ) and ( Accipiter cooperii ). The tufted titmouse has very pronounced reactions to threats posed by predators and therefore is an ideal candidate for the study of predator prey interaction and the effects of urbanization on prey species. This species uses a mobbing behavior for protection from predators (Sieving et al. 2010). Detection of a predator may result in mobbing, in which the predator is chased away by all individuals, thus protecting the family unit. Experimental D esign I conducted a field experiment to test the effects of native and non native predator cues on behavioral responses of titmice in urban and rural environments. I manipulated predator cues of avian predators using a playback experiment ( Rainey et al. 2003, Templeton et al. 2005, Templeton and Greene 2007, Sieving et al. 2010). Playback experiments are effective designs for understanding the role of predation risk becau se they mimic examples of predation situations by broadcasting calls t h at prey species may encounter and allow the researcher to observe prey behavior. I collected calls of local frog species ( Acris gryllus Anaxyrus terrestris, Gastrophryne carolinensis, Hyla andersonii, Hyla cinerea, Hyla femoralis, Hyla gratiosa, and Hyla squirella ) Western Screech Owls ( Megascops kennicottii ) Eastern Screech Owls ( Otus asio ) Hawks ( Accipiter cooperii ), and Northern Goshawks ( Accipiter gentilis ) For each species I collected multiple examples of calls from various sources so t hat I could determine if one call had varying e ffects on prey behavior (Kroodsma 2001) I assigned playlists to be played randomly during each trial. The order of the playlist of the predator (treatment) and frog (control) calls were also randomly assigned. The playlists were set up as follows : 30 seconds silence, 30 seconds treatment/control, 1 minute silence, 2 minutes buffer silence, 30 seconds treatment/control, 1 minute silence. I took verbal notes i n the first 30 seconds of silence, the 30 sec onds of treatment/control and the 1 minute silences. The 2 minutes buffer silence between the first and second calls was to reduce carryover reaction from the first call (cf. Martin et al. 1996, Martin and Martin 2001) The experimental calls were produc ed through a speaker with a 5 meter long wire hooked up to an MP3 player. I would recognize an individual in either a wilderness area (The Ordway Swisher Biological Station) or suburban/urban environment (neighborhoods around Gainesville). I took verbal no tes on a voice recorder of the number of calls, the number of psh calls, the number of peter calls, the number of call types, the number of flights and the latency to approach the speaker. Titmice psh calls are used when they are mobbing a predator and he lp to draw in other passerines to force the predator to flee (Langham et al. 2006). If this call were used during a playback risk toward that call. Peter calls are the song call of the species and may be use d to assert territories or call to mates I f this call were made during a playback it would suggest that the individual did not assess the playback as a risk (Sieving et al. 2010). To ensure independence among replicate trials, all trials were > 100m apar t. I conducted 160 trials at both the Ordway Swisher Biological Station and in neighborhoods around Gainesville (80 trials for each habitat type) Analysis I used repeated measures analysis of variance to test for the effects of treatment, urban versus rural environment (hereafter referred to as location ) and their interaction on the six component behaviors described above. I initially checked if these behaviors measured were highl y correlated with each other but found no evidence for strong correlations ( r < 0.4), so I tested each behavior separately. This experimental design can be considered a cross over design due to the sequential nature of treatments and controls within a tria l I tested for potential cross over effects in the experiment, following Littell et al. (2006) and considered measurements within trials as repeated measures RESULTS None of the six variables tested varied greatly enough from the control value to be co nsidered statistically significant. F or all of the variables, F value <1.91 and P>0.09. DISCUSSION Percieved p redation risk directly relates to behavioral responses and results in changes in choices of habitat, foraging, and reproductive effort (Ghalambor and Martin 2001, Orrock et al. 2004) I observed varying responses of titmice to different predator cues, however, none were considered statistically significant. The hypothesis that n ative predator calls (Eastern would elicite more of a response than the non native predator calls (Western Screech Owl and Northern Goshawk), was not supported by the statistical evidence. This occurance could be explained by the timing of the experiment Avey (2011) found that black to season, and that one call type occurred more often in spring, the breeding season. The titmice calls that I

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PREY R ESPONSES TO H EIGHTENED R ISK OF N ATIVE AND E XOTIC P REDATORS University of Florida | Journal of Undergraduate Research | Volume 13, Issue 2 | Spring 2012 3 witnessed were observed during the breeding season, and the birds could ha ve been expending more energy on defending territories than searching for predators. If the experiment occurred during the non breeding season, results may have been more significant. More interest in breeding would lead to similar reactions to both native and non native predator calls. Parsons and Blumstein (2010) studied effects of novel predator cues on small mammals and found that the mammals had similar avoidance responses to both foreign and native cues. According to Sih et al. (2010), invading predat ors have a novelty advantage when it comes to the naivety of native prey species, and community similarities may increase this advantage. This may suggest that passerine prey species may be at higher risk to foreign predators due to the similarities in c ommunities selected by passerines and due to differences seen in the reactions of mammal prey species and passerine prey species to novel predator cues. More research should be conducted in order to more effectively determine behavioral effects of non nati ve predators on tufted titmice. The location effect was also not significant because there were only two examples of each area type (one urban area and one rural area). To actually determine a significant effect, multiple rural and urban areas would need to be studied. However, a bundance of bird species in urban areas has been shown to generally improve with a decrease in urban infrastructure, an increase in old growth trees, and an increase in the use of native shrubs in landscaping (Ortega Alvarez and Ma cGregor Fors 2010) This could mean that p redation risk ( perceived and actual) is higher in urban areas, and birds may stay further away from any sign of a predator. A ll vocal responses also had mostly inconclusive results. Though we expected to observe t he greatest reaction rate in the vocal response, we could have not accounted for impacts of the family group (such as dominance) or environmental factors. The vocal behaviors exhibited by titmice could be used mostly when the risk is visually recognized. T itmice may hear a predator, move in to assess the risk, and then after recognizing the predator visually, use auditory calls to drawn in other members to mob the predator. Lack of significant effects could also be explained by the lack of data or faulty r esearch design. The number of trials conducted resulted in nearly, but not quite significant results. If I had conducted more trials for each playlist, predator type, and habitat type, I may have seen more significance in the results. The playlist design a lso may have been too short or long to obtain appropriate behavioral responses. My presence also may have affected these individuals would not be as accustomed to humans as birds in urban environm ents. The results obtained cannot be used for management implications for all passerine species and can only be directly applied to tufted titmice in Northern Florida. There may be some continuations of this study that would help to solidify these results and provide more information on predator prey interactions and behavior of species in urban vs. rural environments. If in addition to the auditory cue a visual cue were added to this experiment, it could be determined if titmice use alarm calls more often for the visual representation of a predator. This study could also be expanded to include more urban and rural areas to ensure that the effects seen here can be applied to a broader region. More species may also be included to determine differences in rea ctions to risk posed by avian predators. Another direction for this study may include the use of more predators, including depredating predators such as corvids, snakes, and mammals. Predator prey interactions and urbanization are of great interest to ecologists because of their influences on multiple aspects of prey behavior. In this study we saw that tufted titmice will respond differently to the similar auditory cues of native and non native predators and also have varying responses to predators in urban and rural areas. These results may have implications for the management of urban areas and the introduction of novel predators to native prey ranges. Urban areas may be managed to provide enough cover for prey species, and prey species may not initia lly assess the risk level of novel predators, which may have its own implications in the ever changing ranges of species. ACKNOWLEDGMENTS I would like to acknowledge and thank Irina Skinner, the University Scholars Program, and th e Ordway Swisher Biological Station for making this project a possibility. LITERATURE CITED Apfelbach, R., C. D. Blanchard, R. J. Blanchard, R. A. Hayes, and I. S. McGregor. 2005. The effects of predator odors in mammalia n prey species: A review of field and laboratory studies. Neuroscience and Biobehavioral Reviews 29 :1123 1144. Artuso, C. 2009. Breeding and population density of the Eastern Screech Owl Megascops asio at the northern periphery of its range. Ardea 97 :525 5 33. Avey, M. T., A. Rodriguez, and C. B. 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