Population ecology of the ground skink, Lygosoma Laterale [say]

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Population ecology of the ground skink, Lygosoma Laterale say
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Population ecology of the ground skink, Lygosoma Laterale say
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Brooks, Garnett Ryland,

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University of Florida
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Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
        Page iv
    List of Tables
        Page v
    List of Figures
        Page vi
        Page vii
    Introduction
        Page 1
        Page 2
    Methods and materials
        Page 3
        Page 4
        Page 5
        Page 6
    Description of the study area
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Spatial relationships
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
    Growth
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
    Ecology of reproduction
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
    Population size and density
        Page 55
        Page 56
        Page 57
        Page 58
    Population dynamics
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
    Activity
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
    Discussion
        Page 87
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
    Summary
        Page 93
        Page 94
        Page 95
        Page 96
    Literature Cited
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
    Biographical sketch
        Page 102
        Page 103
    Copyright
        Copyright
Full Text











POPULATION ECOLOGY OF THE GROUND

SKINK, LYGOSOMA LATERAL [SAY]











By

GARNETT RYLAND BROOKS, JR.


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY










UNIVERSITY OF FLORIDA
April, 1963















ACKNOWLEDGEMENTS


I wish to express appreciation to Dr. Coleman J. Goin,

Chairman of my Supervisory Committee, for his direction of my

graduate program and research, and to the other members of my

committee, Drs. Yoneo Sagawa, A. M. Laessle, B. McNab, and E. R.

Jones, for their suggestions concerning the study and for read-

ing and correcting the manuscript.

I also appreciate the help of the following people at the

University of Florida: Mr. George Zug who supplied several speci-

mens; Dr. Carter Gilbert for a valuable specimen and for construc-

tive criticism of portions of the manuscript; Dr. A. M. Laessle and

Mr. Timothy Brown for identification of the plants on the study

area; and Dr. J. N. Layne for the use of his data on the activity

of Lygosoma laterale and for helpful discussions concerning questions

on density and home range.

Finally, I wish to thank the Department of Biology, the

College of Arts and Sciences, the Graduate School of the University

of Florida, and my wife for granting me the privilege of graduate

work.
















TABLE OF CONTENTS


Page

ACKNOWLEDGEMENTS ................................................. ii

LIST OF TABLES .................................................. v

LIST OF FIGURES .................................................. vi

Chapter

I. INTRODUCTION ............................................. 1

II. METHODS AND MATERIALS .................................... 3


III. DESCRIPTION OF THE STUDY AREA ...............


............ 7


IV. SPATIAL RELATIONSHIPS .................................... 14
Distribution Within the Plot ........................... 14
Home Range ............................................. 16
Territory .............................................. 24
Dispersion ............................................. 30

V. GROWTH ......... .................. ....................... 38


VI. ECOLOGY OF REPRODUCTION ..........................
Sexual Maturity ................................
Breeding Season ................................
Sex Ratio ......................................
Reproductive Potential .........................


........ 43
........ 43
........ 44
........ 48
........ 49


VII. POPULATION SIZE AND DENSITY .............................. 55

VIII. POPULATION DYNAMICS ...................................... 59
Method of Determining Year Classes ..................... 59
Age Structure .......................................... 64
Survivorship ........................................... 66
Causes of Mortality .................................... 72

IX. ACTIVITY ................................................. 78
Temperature ............................................ 7P
Moisture ............................................... 82
Time of Day ............................................. S
Season ................................................. R6














Chapter Page

X. DISCUSSION ............................................... 87

XI. SUMMARY .................................................. 93

LITERATURE CITED................................................. 97

BIOGRAPHICAL SKETCH............................................. 102














































iv















LITS OF TABLES


Table Page

1. A list of amphibians and reptiles in addition to
Lygosoma laterale found on the study plot............... 13

2. Poisson analysis of the spatial distribution of the
lizards on the plot during June and July, 1961.......... 15

3. Comparison of the number of adults found in pine-
influenced areas with the number in nonpine areas
during June and July, 1961.............................. 18

4. Selected records showing permanence of home range....... 22

5. List of occasions when two lizards were caught at the
same time in the same place............................. 28

6. List of individuals which made a change in their
spatial position........................................ 31

7. List of individuals which evaded capture for an un-
usually long period of time between successive captures. 36

8. The instantaneous relative growth rates (k) for both
sexes of the 1960 hatchling group....................... 42

9. The reproductive potential of the female population on
the plot during the breeding season of 1961............. 53

10. Records of capture-recapture data of the 1961 hatchling
group from July, 1961, to March, 1962................... 54

11. Number and density of skinks on plot between July, 1960,
and August, 1961, by month............................... 57

12. The age composition of the population on the plot from
July, 1960, to March, 1962, listed by sex .............. 65

13. Life table for the 1960 hatchling group of Lygosoma
laterale based on data derived from Figure 14........... 70

14. List of predators of Lygosoma laterale recorded in the
literature.............................................. 76















LIST OF FIGURES


Figure Page

1. Diagramatic sketch of lizard feet to illustrate the
numbering system used in this study..................... 4

2. A map of the study plot showing major features of the
vegetation................... ........... ..... . ..... 8

3. Rainfall, average temperature, and number of ground
skinks active per field trip for each month from July,
1960, to March, 1962 ................................... 12

4. Position of adults on the plot captured during June and
July, 1961 ..................................... ...... 17

5. Home ranges of mnles living in an area of the plot bor-
dered by stakes 6A-6C-3C-3A during June, July, and
August, 1961........................................ ... 26

6. Home ranges of females living in an area of the plot bor-
dered by stakes 6A-6C-3C-3A during June, July, and
August, 1961 ............................................ 27

7. Percentage of new lizards in the total catch per month.. 37

8. Theoretical growth curves based on growth rates of the
hatchling group of 1960................................ 41

9. Yearly changes in the size of testes.................... 46

10. Growth of ovarian follicles and the size of oviducal
eggs. ................................................ . 47

11. Snout-vent length at month of first capture of females.. 62

12. Snout-vent length at month of first capture for males... 63

13. The progressive decrease in number of the 1960 hatch-
ling group.............................................. 69

14. Survivorship curve of the 1960 hatchling group of
Lygosoma latcrale...................................... 71

15. Number of ground skinks captured at each recorded field-
shade temperature.............................. ....... 80














LIST OF FIGURES continued


Figure Page

16. Average number of ground skinks captured per field
trip at selected temperature ranges..................... 81

17. The relationship between shade temperature, moisture,
and number of active ground skinks...................... 84















CHAPTER I

INTRODUCTION


Until recently very little was known about the dynamics of

natural populations of lizards. Gordon's (1956) work on the popu-

lation ecology of Anolis carolinensis, Fitch's (1954) paper on the

life history of Eumeces fasciatus, and Blair's (1960) detailed study

of a population of Sceloporus olivaceous are the major articles con-

taining data on the population ecology of these animals. The last

of these, which is the result of five years of work, well illustrates

the information obtained from such studies. Recent papers concerning

populations of other herptiles are those of Stickel (1950) and Sexton

(1959) on turtles, Pearson (1955), Martof (1956a, 1953b, 1956a, 1956b),

Turner (1960a), Jameson (1955), Bannikov (1950) and Pyburn (1958) on

anurans, Carpenter (1952) on snakes, and Organ (1961) on salamanders.

The present study was undertaken to further our knowledge re-

garding natural populations of lizards. The main objectives were

to investigate the spatial relationships, growth rate, reproductive

potential, age structure, density, and activity of a small population

of Lygosoma laterale (Say). This lizard, the ground skink, was chosen

as the object of study for several reasons: it is extremely abun-

dant in local areas, it is easily captured and marked for future

recognition, it is active the year round in Florida, and it has a

relatively short life span.











The ground skink is one of the more abundant and widely

distributed members of the Scincidae in the southeastern United

States. It is found in deciduous, mesophytic forests, pine woods,

gardens, wooded fields, at the edge of pasture and forest, and in

general, in most wooded areas where there is sufficient cover,

food, and moisture. In these habitats it feeds on the small insects

and spiders which live in the litter layer.

No detailed study of the life history of Lygosoma laterale

has yet been published, although Lewis (1951) studied certain features

of its biology in central Texas, and Johnson (1953) has determined

its reproductive cycle in Louisiana. Several other papers have ap-

peared concerning food habits (Slater, 1949; Hamilton and Pollack,

1961), parasites (Harwood, 1933), population size (Turner, 1960b),

and distribution (Carr, 1940; Smith, 1946; and Conant, 1958).

A statement from Turner's (1960a) study on a frog population

is especially applicable: "Data from such studies," i.e., population

studies on amphibians and reptiles, "are sorely needed, for our

knowledge of vertebrate population ecology is based almost exclusively

on studies of fish, birds, and mammals."














CHAPTER II

METHODS AND MATERIALS


Field work, involving the capture, mark, and recapture of

lizards, was carried on from July 22, 1960, to April 14, 1962.

During this period collections were made from nearby populations

and preserved for a study of food habits, parasites, and the

reproductive cycle. All lizards were captured exclusively by

hand. Specimens were marked for future recognition by clipping

toes with manicure scissors, and since this species of skink has

five toes on each limb, a large number of different combinations

was available. Toes on the right, rear foot stood for units,

with the first, or most medial, toe representing number one; the

second toe, number two, etc. Combinations of toes were used for

numbers higher than five. Toes on the left, rear foot stood for

tens, with the first representing the number ten; the second,

twenty, etc. Combinations of toes were used for numbers larger

than fifty. Similarly fingers on the right front limb repre-

sented hundreds, and those on the left front limb, thousands.

The numbering system is illustrated in Figure 1. No more than two

toes were removed from one limb, and usually only four or five were

removed from the entire animal. Toes lost by natural conditions

were incorporated as well as possible into the numbering system.

Individuals which had lost other toes after being marked could be

identified by a combination of sex, location, body length, tail
















2000

\ A 1000


100


FORE
FEET


LEFT


200 300
v/400
I /, 500


RIGHT


HIND
FEET


Figure 1. Diagrammatic sketch of lizard feet to illustrate the

numbering system used in this study.


3000
4000

5000 0,











length, and length of regenerated tail data. No regeneration of

clipped toes was observed. The loss of toes did not seem to hamper

the lizards in their normal activity. In fact, several individuals

were collected on the plot and from other locations which had lost

entire limbs, seemingly with no detrimental effects. An attempt

was made early in the study to mark specimens with paint spots in

addition to clipping toes, but since the paint wore off too quickly

this method of marking was abandoned.

Three body measurements were made in the field: 1) snout-vent

length or the distance from the tip of the snout to the anterior

margin of the vent; 2) tail length or the distance from the posterior

margin of the vent to the tip of the tail; and 3) the length of any

regenerated portion of the tail. Measurements, to the nearest mm,

were made by suspending the lizard near the front limbs between thumb

and index fingers of the collector, and applying a clear mm rule

against the body of the lizard.

The sex of adults was determined by applying gentle pressure

to the region just posterior to the vent. If the individual was

a male, the hemipenes were easily detected, the absence of hemipenes

indicating a female. There is no easily observed difference in

scalation or color between males and females. Because of size the

sex of hatchlings and juveniles could not be determined.

The plot was visited 115 times during the course of the

study. The procedure followed during a trip was to start at either

the north or south border, and work horizontally back and forth











(eastward and then westward) over the plot, thus scrutinizing the

entire area. The location of a lizard, its sex, body measurements,

the air temperature, micro-habitat, time, and weather were recorded

in a field notebook and later transferred to McBee Key Sort cards

(type Ks371N). Temperature was recorded by a centigrade thermometer

placed in the shade one inch above the litter layer.

Statistical methods used in the following analyses were taken

from Snedecor (1956) and Simpson, et al. (1960). The following

abbreviations are used in the text; standard error of the mean as

S.E.m, number as N., and mean as T.

The botanical nomenclature follows that in "Gray's Manual of

Botany" (Fernald, 1950).














CHAPTER III

DESCRIPTION OF THE STUDY PLOT


The plot was located in a wooded portion of the University

of Florida campus, Gainesville, Florida. The large number of

ground skinks present, the type of habitat, and convenience made

this area an ideal one for study. The plot was approximately one

and one-fourth acres in size, and measured 120 yards by 50 yards, with

the long axis in a north-south direction (Fig. 2). A grid system,

composed of quadrats 10 yards by 10 yards, was laid out over the

plot. Grid lines running north-south were labeled with letters

(A to F) and lines running east-west by numbers (1 to 13). Wooden

stakes, each bearing a letter and a number, marked the intersections

of grid lines. The stake in the extreme southeast corner of the

plot was selected as 1A. Moving north from this stake, the numbers

went up to 13 (a distance of 120 yards). Moving west, the letters

progressed to F (a distance of 50 yards). Thus stake SC, for example,

was 40 yards due north of line 1, and 20 yards due west of line A.

The plot was bordered on the east side by a dirt road; on the south,

by a paved campus road; and on the southwest, by a thicket of small

trees and shrubs. The north and northwest edges had no natural

barrier but were continuous with further woods.

Large pignut hickories (Carya glabra megacarpa), sweet gums

(Liquidambar styraciflua), laurel oaks (Quercus laurifolia) and a








P C1 N ,


01n




> \


0
I o


0

> o


0




* 1X
XC
'C


- -


0 0


>


0 -'Xx


0

X\
>


0
0


0 0


0 o o


3


Figure 2.


4


12


A map of the study plot showing major features of the vegetation. Dots show position of
grid stakes; oak trees are indicated by circles, pines by crosses, hickories by triangles, and
gums sy squares. The letters and numbers designate grid lines. The lines represent logs.


0
P,


0.o


S0"\


2


p


&











few loblolly pines (Pinus taeda)dominated the canopy of the forest.

Approximately 20 per cent of the canopy was made up of the two ever-

greens, laurel oak and loblolly pine. Other trees scattered through-

out the plot were a few water oaks (Q. nigra), live oaks (. virginiana),

and a spanish oak (a. falcata). The canopy was continuous during the

warm months except for an opening at 7A and 7B. As in most deciduous

forests in Florida, the epiphyte, spanish moss (Tillandsia usneoides),

was present on most of the trees.

Smaller trees such as dogwood (Cornus florida), winged elm

(Ulmus alata), cow oak (Q. michauxii), a few ashes (Fraxinum caroliniana),

hop-hornbeam (Ostrya virginiana), and young pignut hickory made up the

understory. Shrubs present consisted of stiff dogwood (C. foemina),

hackberry (Celtis laevigata), red mulberry (Morus rubra), hawthornes

(Crataegus sp.), and a few southern black-haw (Viburnum rufidulum),

sparkleberry (Vaccinium arboreum), and strawberry-bush (Euonymus

americanus).

Vines present on the plot were Virginia creeper (Parthenocissus

quinquefolia), grape (Vitus rotundifolia), and laurel-leaved green-

brier (Smilax laurifolia). A dense covering of herbaceous vegetation

dominated by Virginia creeper and poison ivy (Rhus radicans) carpeted

the forest floor in most of the northern and eastern quadrats. Other

herbs were violets (Viola walteri) predominantly in the southeast

sector, scattered panic grasses (Panicum spp.), and a few sedges

(Scleria spp.).

Since Lygosoma laterale is a ground inhabiting skink, the

litter layer assumes great importance. This layer was composed of











leaves, pine needles, twigs and sticks of assorted sizes, clumps of

fallen spanish moss, and decaying logs. The depth and composition

of the litter layer varied throughout the year; the greatest depth

of leaves occurred during the winter months. Microbial decomposi-

tion increased as spring arrived and by late fall some areas of

forest floor were exceedingly bare. Around the pines, however, a

fairly constant depth of litter was present the year round. The surface

soil of this region, a mixture of Arredondo loamy fine sand and fine

sand, is light brown in color, loose, and well drained (U.S.D.A.

Soil Survey, Alachua County, 1954).

Since the greatest portion of the canopy was deciduous, the

forest floor during the winter months was exposed to the sun, per-

mitting some activity of lizards on warm days. For a review of the

climate of the Gainesville region see Pearson (1955). The rainfall

and average temperature for each month of the study period is given

in Figure 3.

In addition to Lygosoma, a number of other species of reptiles

and amphibians were noticed in the study area. These species are

listed in Table 1.






















Figure 3. Rainfall, average temperature, and number of ground skinks active per field trip for each
month from July, 1960, to March, 1962.





















--4
0
10-1
I-
-9

8

i-
r-
7
z
6z

5 m


1962


MONTHS


w 0
4 cr-
ID
I-
z 30 w
u U-
LL.
28
w
w
m w
(D 26 >
w -

z 244
w co)
cr 22 c


cr 20 -
w IJ-
a. 0
I- 18 c


< z
w w
1 4

w 12Wu


1960


1961











Table 1. A list of amphibians and reptiles in addition to
Lygosoma laterale found on the study plot.


Scientific Name


Common Name


Amphibians


Acris gryllus
RanaT-pipiens
=Buo terrestris
Buto quercicus
I-crohyla carolinensis
Hyla cinerea
lil crucifer
Eleutherodactylus ricordi

Reptiles
Eumeces laticeps
Eumeces inexpectatus
Anolis carolinensis
Cnemidophorus sexlineatus
Ophisaurus ventralis


Tantilla coronata
Coluber constrictor
Thamnophis sauritus
Thamnophis sirtalis
laphe guttata
iadophus punctatus
Opheodrys aestivus
Micrurus fulvius

Terrapene carolina


cricket frog
southern leopard frog
southern toad
oak toad
narrow-mouth toad
green tree frog
spring peeper
green-house frog


broad-headed skink
southeastern five-lines skink
anole
six-lined race runner
glass lizard


crowned snake
black racer
ribbon snake
garter snake
corn snake
ring-necked snake
rough green snake
coral snake


box turtle


Scientific Name














CHAPTER IV

SPATIAL RELATIONSHIPS


Distribution Within the Plot


After several months of field work it became evident that

the skinks were not uniformly distributed over the plot but were

captured more frequently in certain sectors. To examine the spatial

distribution, the position of 159 adults captured during June and/or

July, 1961, were recorded on a map of the plot (Fig. 4). These

months were chosen because of the large number of adults present,

and because hatching of the 1961 eggs had not yet begun in force.

The number of quadrats containing 0, 1, 2, 3, ..., n number of lizards

was then compared to a Poisson series (Table 2). One characteristic

of a Poisson series is that its variance is equal to its mean. Thus,

if the variance of the counts made on the quadrats is larger than the

mean per plot, a tendency toward aggregation is revealed (Dice, 1952).

Examination of Figure 4 clearly reveals that the lizards were

more abundant in the lower, eastern quadrats and that very few were

found along the southern and middle-western borders. Although the

chi-square value is not significant (P.<.05), a tendency toward ag-

gregation is indicated by the large variance (Table 2). Since there

were habitat differences, as will be pointed out below, within the

plot, a concentration of skinks in favorable locations would be















Table 2. Poisson analysis of the spatial
lizards on the plot during June


distribution of the
and July, 1961.


Number of Number Number
Lizards of Poisson (A E)2 of
Per Quadrat Quadrats Series E Lizards

0 9 4.24 5.344 0
1 11 11,35 0.011 11
2 10 14.89 1.596 20
3 10 13.15 0.755 30
4 11 8.71 0.602 44
5 4 4.62 0.083 20
6 18
7 5 3.04 1.264 7
8 0
9 9


Total 60 60.00 9.655 159


Mean 2.65


Variance 3.96











expected, The nonsignificant chi-square value might be due to chance,

that is, by chance the distribution of quadrats containing 0, 1, 2,

..., n number of skinks was not statistically different from that

of a theoretical Poisson series based on 60 quadrats.

To see if vegetational differences influenced distributions,

the plot was divided into areas which contained loblolly pines,

and areas which did not. The portions influenced by pines were arbi-

trarily selected as those areas in which pine needles comprised

most of the litter layer. These different regions are shown in

Figure 4. The area of pine-influenced regions was measured by a

compensating polar planimeter. This area was then subtracted from

the total area of the plot to obtain the nonpine area. A comparison

of the number of skinks living in each region during June and/or

July, 1961, is given in Table 3. The results indicate that in the

study plot, pine-influenced areas provided a more favorable habitat for

ground skinks than nonpine areas.

A comparison of the first recorded position of the hatchlings

of 1961, which in most cases indicates the site of hatching, with a

Poisson series indicated (X2 = 8.54) that the young were nonrandomly

distributed (P. = .01). As was found for the adults, the great

majority of hatchlings were found in the northern and eastern sectors.


Home Range

The concept of home range has been defined as the area in which

an individual animal normally travels while engaged in its usual daily

activities (Dice, 1952; Burt, 1940). Dice (Ibid.) included breeding






































3 4 7 9 10

4. Position of adu and July, 1961.
are enclosed by arked by a cross.
designate grid














Table 3. Comparison of the number of adults found in pine-influenced
areas with the number in nonpine areas during June and July,
1961.


Area in Actual Number Expected Number Chi-
Square Yards of Lizards of Lizards Square

Pine -
1519.7 60 40.3 9.63

Nonpine -
4480.3 99 118.7 3.27


Total Chi-square 12.90*


*A significant value.











sites as a part of the individual's home range, but in this study

movement to a breeding site, or to an egg-laying site, was not included

in the measurement of any home range.

The method for determining size of home range is that described

by Mohr (1947). In this method, each capture point of an individual

is plotted on a map of the area, and the peripheral points are then

connected to form an irregular polygon. The area enclosed by the

polygon represents the "minimum home range." This method is subject

to error for, depending on the worker, polygons of different size can

be constructed by connecting different sets of points of one individual.

There is no definite rule to determine which polygon is most accurate,

but by studying the terrain and vegetational cover, a reasonable

facsimile of the true home range can be obtained. The size of a plotted

home range was determined by the use of a planimeter. Other methods

for estimating the size of home range can be found in Hayne (1950),

Calhoun and Casby (1958), Davis (1953), and Stickel (1954).

Before the average size of a home range can be calculated for

these lizards it must be first determined whether or not they possess

and utilize a definite AREA, i.e., a home range. To do this it is

necessary to find out whether or not the area in which captures are

made increases with an increase in the number of captures. If the

area does increase with an increase in number of captures no measure-

ment of home range is possible and there would be some question as to

whether or not there was any definite "home range" area. If, however,

after a certain number of captures, the area does not increase in size












with an increase in number of captures, a plateau has been reached

and use of the home range concept is justified.

Since in many other studies (Fitch, 1954, 1958; Blair, 1960;

and Tinkle, et al., 1962) it has been found that males and females

have different home range sizes, each sex will be considered separately.

In males, it was found by use of a correlation test that be-

ginning with at least five captures within a 12-month period, the

number of captures and the area over which the captures were made was

positively correlated (r = 0.559; P. = .01). In other words, the

more times an individual was captured, the larger was the area in

which the captures occurred. However, when these data were plotted

on a graph with size of area covered on the ordinate axis and number

of captures on the abcissa, it was noted that a curve drawn through

the points leveled off after reaching the point associated with

eight captures and remained level beyond this point. A correlation

test was then run comparing the area covered with the number of cap-

tures beginning with at least eight captures and ranging to 16. An

r value of 0.100 (P. .05) was obtained, which indicates no correla-

tion between these parameters.

Thus after eight captures of a male the area over which sub-

sequent captures were made remained constant and could be called a

home range. The average size of a home range determined from the

records of 16 males captured eight or more times during a 12-month

period was 62.5 square yards (S.E.m = 6.8).











In females, a correlation test between area covered and

number of captures starting with five captures gave an r value of

0.045 (P. <.05) which indicates no correlation. Thus the home range

of females can be determined from those individuals captured five

or more times. The average size of a home range determined from the

records of 36 females captured five or more times.during a 12 month

period was 17.2 square yards (S.E.m = 2.4).

The difference in home range size between males and females is

significant. The result of a "t" test (t = 2.51; P. = .05) indicates

that males have larger home ranges than females. The average size of

a male home range was 3.6 times as large as that for a female.

Comparisons of home range size between juvenile males and

juvenile females, and between juveniles and adults would have been

interesting, but could not be determined due to the small number of

recaptures of individual juveniles. Only 12 were captured more than

three times as juveniles out of 293 juveniles tagged. Blair (1960)

found that the home range size for juveniles of Sceloporus olivaceous

was small at first but as the individual grew, the size of its home

range also expanded.

Once a home range was established, a skink tended to remain

there throughout its life. Table 4 is a list of selected data show-

ing the permanence of some home ranges. A shift in home range did

occur in a few cases as indirectly indicated by Nos. 483 and 62. A few

individuals, No. 43 for example, tagged at the beginning of the study,

were still in the same range when field trips ended.

















Table 4. Selected records showing


permanence of home range.


Time in Same Time Under
Home Range: Observation:
Number Sex Months Days Months Days


483*
93
26
84
25
1500
485
463
465
87
477
70a

39
43
304
40b
473
302
446
428
62*
489
305
45


female
I
to
it

it
it
it
to
If
It




male
It



It

It
It
It

of
"i


* Indicates a shift in


position.












The advantages to an individual possessing a home range

have been attributed to the protective value offered by its familiar-

ity with the terrain, sources of possible danger, location of food

and water supplies, and shelter spots. Factors such as food

and water supplies probably play a small role in the advantages of

a home range for Lygosoma since these supplies are not usually lo-

cated at definite points within the home range. The protective

value, however, of knowing the position of shelter spots and the

shortest route to these spots is well illustrated by the behavior

of individual skinks.

Many times on the study plot skinks were observed before

they were startled. When startled they would unhesitatingly run

for a shelter spot at the base of a tree or under a log. Only in

rare instances would a skink attempt to hide under leaves, making

no attempt to seek shelter elsewhere. That this was not merely

chance choosing of the nearest shelter spot is evidenced by the

observation that on many times a certain skink, easily recognized

due to its stumped tail, would always run, no matter where its posi-

tion in its home range, to a certain tree where it had a shelter

spot between two exposed roots. This behavior was noticed in many

other skinks which could be recognized as certain individuals. A

few had several spots of refuge within their home range and would

run, when startled, toward the one closest in sight.

Other observations which bear out the importance of a home

range revolve around the behavior of liberated skinks. On several











occasions skinks were taken to the laboratory for identification.

When they were returned, always on the following day, and dropped

in their home range, they would immediately run for a shelter spot

previously utilized. On the other hand skinks when captured on

collecting trips off the plot and then released in foreign sur-

roundings would appear hesitant and in most instances burrow under

the leaf mold where dropped. It thus appears that the most obvious

advantage of a home range for the ground skink lies in its protective

value.


Territory

In a great variety of animals a portion, or occasionally

all, of a home range is defended by the inhabitant against entry

by other members of the species. The particular method of defense

varies, some animals relying on bluff, others on actual combat.

The area defended is known as a territory and except in a few rare

cases, only the male of the species is known to show this trait.

The best evidence for the presence of a territory is, of course,

direct observation of defense of a home range, but the absence of

overlap between adjacent home ranges can be used as evidence also

(Dice, 1952).

To determine if home ranges overlapped, all home ranges of

adults living within a crowded portion of the plot at a given time

were mapped, and the amount of overlap measured. A three-quadrat

square in the eastern sector, 6A-6D-3D-3A, was chosen because of












the large number of lizards known to exist in this area during

June, July, and August, 1961. If a lizard was known to live in one

of these quadrats for two of the three months, its home range was

plotted. Figures 5 and 6 show the results for males and females

respectively. It is readily observed that there was considerably

less overlap in the home ranges of females than in males. Out of

23 female ranges mapped, there were only nine points of overlap,

with only eight square yards being shared. Of 22 male ranges,

however, there were 28 points of overlap. The area contained in

these regions of overlap was approximately 153 square yards, some

19 times more than in females.

One objection to the above procedure is that a few of the

home ranges are based on only three or four captures. The exten-

sive overlap of male home ranges can be illustrated, however, in

another way. If the number of each sex in this area is multiplied

by their respective average size of home range, it is found that

males cover an aggregate of 1375 square yards, whereas females

cover only 396 square yards. Since there are only 900 square

yards in these nine quadrats, the males undoubtedly shared more

space than females.

Further evidence indicating the isolation of individual females

is given in Table 5. This table lists the occurrences when two lizards

were caught in the same place at the same time. Of these 30 pairs,

the sex of both partners was known in 25. Only one of these 25 pairs

was female-female.


























































Home ranges of males living in an area of the plot bordered
by stakes 6A-6D-3D-3A during June, July, and August, 1961.
Capture points are represented by dots. The letters and
numbers designate grid lines.


Figure 5.


















































D C B A


Figure 6. Home ranges of females living in an area of the plot bordered
by stakes 6A-6D-3D-3A during June, July, and August, 1961.
Capture points are represented by dots. The letters and num-
bers designate grid lines.








Table 5. List of occasions when two lizards were caught at the same time in the same place.

Type of Distance Apart
Interaction in Feet Date Microhabitat


Female with Female
83 443


Female
485
26
26
442
379
15
38
327
87
739
590
87
35
56

Female
440
525


with















with


Nov. 5, 1960


Male
386
304
304
92
566
473
39
545
62
738
592
57
92
92


Aug.
Aug.
Aug.
Apr.
Jun.
Jan.
Aug.
Jul.
Feb.
Sep.
Jul.
Aug.
Aug.
Apr.


Hatchling
73
99


Female with Unknown Sex
344 456

Female with Unknown
375 ???


1961
1961
1961
1961
1961
1962
1960
1961
1962
1961
1961
1960
1960
1961


Sep. 24, 1961
Sep. 24, 1961


Mar. 2, 1961


Apr. 16, 1961


under stick matted with spanish moss


in leaves near log
in mat of spanish moss and sticks
in mat of spanish moss and sticks
in leaves at edge of spanish moss mat
in sticks and leaves
in leaves near sticks
in leaves in open
in leaves beside log
in leaves at base of tree
under mat of spanish moss
in copulation in leaves
in mat of spanish moss
in leaves near base of tree
in leaves and twigs


in leaves along side of log
in small brush pile


in leaves in open


in leaves fighting








Table 5 continued.


Type of Distance Apart
Interaction in Feet Date Microhabitat


Male with Male


on top of
in leaves
in leaves
in leaves
in leaves
under mat
under mat
in leaves
in leaves
in leaves


mat of spanish moss
under vines
beside log
at base of tree
beside log
of spanish moss
of spanish moss
beside log
under vines
and sticks


Male with Hatchling
495 493


Nov. 5, 1960 in pine needles near stick


596
40b
473
386
468
394
86
43
3c
506


428
302
727
559
469
393
452
408
72
72


Dec.
Mar.
Feb.
Oct.
Aug.
May
Oct.
Dec.
Jun.
Sep.


1961
1962
1962
1960
1961
1961
1960
1960
1961
1961












Ohly one instance of fighting was noticed in the field and

only one of the combatants, a female, was captured. Skinks of both

sexes, when confined in terraria, invariably began to fight, one of

them, a large female in most cases, assuming dominance over the

others.


Dispersion

Dispersion within the plot and dispersion outward or inward

from peripheral areas have entirely different effects on the popula-

tion. The first type of movement merely shuffles the lizards within

the plot, while the second type increases or decreases the popula-

tion size. For this reason the two types are reported separately

below.

Dispersion within the plot. As mentioned above, the great

majority of home ranges were permanent. A few cases were recorded,

however, of a shift in home range or movement from one point in the

plot to another. In analysing movement only individuals with two or

more captures at least two months apart were used in calculating

percentages. All movements were assumed to have been in a straight

line.

A distinction was made regarding the age at which dispersion

was detected. Three categories were devised: 1) dispersion of the

lizard after reaching adult size, 2) dispersion as it grew from

juvenile to adult, and 3) dispersion of hatchlings. Table 6 lists

the individuals for which data on dispersion within the plot were

available.















Table 6. List of individuals
position.


which made a change in their spatial


Type of Distance Direction
Number Sex Movement Moved in Yards Moved

4a female A-A* 83.5 S.E.
38 30.7 S.
67 34.1 S.E.
483 28.3 N.W.
69 67.7 N.E.N.
36 37.4 S.E.S.
441 37.4 E.N.E.
14 male 42.7 W.N.W.
308 31.7 S.E.S.
27 20.2 N.W.N.
302 29.8 S.E.S.
62 19.7 N.W.N.

50a female J-A** 29.3 N.W.
447 37.0 E.S.E.
40a 62.4 S.E.S.
426 20.2 S.W.
400 male 37.9 N.
484 53.8 N.

55b unknown H-H*** 27.4 S.E.S.
3098 37.9 S.


*A-A
**J-A
***H-H


represents
represents
represents


category
category
category


see text.
see text.
see text.












Dispersion of adults. Of 181 records for adults taken from

the entire study period, only 12, or 6.6 per cent, showed a shift in

their spatial position. This is undoubtedly a low estimate, for some

movements were probably not detected. The average distance moved

was 38.6 yards. There was little difference in the number of females

and males moving; five of 89 males (5.6 per cent) moved an average

distance of 28.8 yards, and seven of 93 females (7.5 per cent)

moved an average distance of 45.6 yards.

Dispersion of juveniles. A change in position of a lizard

while growing from juvenile size to adult occurred in six of 51

specimens (11.8 per cent). The average distance moved was 40.1 yards.

Dispersion of hatchlines. Only two records out of 24 (8.3 per

cent) revealed movement of hatchlings. One hatchling moved 27.4

yards; the other, 53.8 yards.

The direction of dispersion did not seem to follow any natural

lane, but was essentially random. Seven movements were southeast;

two were northeast; one was southwest; five were northwest; two

were north; one was south, and none were east or west. Any extensive

movement to the east or west would have carried the lizard out of

the plot.

All movements were one way; no lizard was detected moving

from one spot to another and then later returning to the original

position. This type of travel might occur, however, during the

breeding season by both sexes.












The speed of dispersion could not be measured since in all

but one case, described below, a considerable length of time separ-

ated the successive captures which indicated a change in position.

A gravid female, No. 36, captured 20 feet northwest of stake SC on

June 28, 1961, was found spent four days later, July 2, 1961, four

feet southeast of stake 2B. She had moved 37.5 yards on what might

have been a search for an egg laying site.

Emigration and immigration. Several field trips were de-

voted to marking skinks outside the boundaries of the plot, and

searching for marked lizards which might have emigrated from the

plot. A total of 37 were marked at different times during the

study from areas surrounding the plot. Eight individuals were

marked in the region bordering the northwestern boundary, 14 in the

region bordering the northern boundary, and 15 in the woods on the

eastern side of the dirt road. None of these individuals were ever

recovered within the plot. Likewise no skinks marked within the plot

were ever discovered outside, except for a few individuals whose home

ranges overlapped both regions.

The only nonrestricted pathways available for dispersion were

along the northwestern and northern borders. At these points the plot

was adjacent to further woodland. The paved road at the southern bor-

der prevented movement in this direction. The eastern border, a dirt

road used and maintained by the cross country track team, was kept

free of branches, weeds, etc., and was probably a partial barrier.

No skinks were ever observed in this road, although movement across











it might have occurred whenever a fallen branch or vine provided a

pathway. The small trees and shrubs along the upper southwestern edge

were a partial barrier due to the differences in vegetation structure.

As pointed out by Pearson (1955) one means of detecting im-

migration is to study the percentage of new specimens taken at each

trip. After a period of time one would expect that all the residents

would be marked, and the percentage of new animals would approach

zero. The appearance, therefore, of any unmarked individual would

indicate immigration. This type of analysis has one major drawback;

that is, at what time are all of the permanent residents marked? By

chance, some individuals, fulltime residents of the area, might be

active only during times when the plot was not being searched. One

skink, No. 424 for example, was first marked October 16, 1960, and

was not recaptured until January 23, 1962, still in the same area in

which it was first captured. Table 7 is a list of such lizards in

which an unusually long time separated successive captures. Undoubtedly

these lizards were active between the two dates listed, but this activity

was not observed. Lewis (1951) reported that one Lygosoma he had under

under observation in a study plot was active almost daily for several

months.

The percentage of new skinks in the total catch per month,

plotted against successive months, is shown in Figure 7. The hatchlings

of 1961 were omitted.

The curve drops rapidly at first, but levels off beginning in

August, 1961, and remains fairly level for the remaining months. Assuming







35




that the great majority of the skinks were tagged in the first year

of study, Figure 7 indicates that immigration was constant, averaging

approximately 8.9 per cent, or about 5.2 lizard immigrants per month.

The high number of new animals taken from March, 1961, to July, 1961,

were composed mostly of young of 1960 which had not been tagged before

winter.














Table 7. List of individuals which evaded capture for an unusually
long period of time between successive captures.


Date of First Date of Second Number of Days
Number Sex Capture Capture Between Captures

87 female Aug. 26, 1960 Sep.. 3, 1961 373
26 Aug. 26, 1960 Aug. 15, 1961 354
477 Oct. 9, 1960 July 9, 1961 273
424 Oct. 16, 1960 Jan. 23, 1962 464
402 Dec. 18, 1960 Jan. 25, 1962 403
447 Oct. 1, 1960 Oct. 30, 1961 394

29 male July 29, 1960 June 28, 1961 334
62 Oct. 16, 1960 Oct. 30, 1961 379
445 Sep. 23, 1960 Dec. 17, 1961 420
484 Nov. 5, 1960 Feb. 15, 1962 467










z
V 100
4
90
,.J

o 80
0
I-


So


s50
w4

z 40
0
.30

0 20-

I0


7 8 9 10 I 12 1 2 3 4 5 6 7 8 9 10 11 12 1 23
1960 1961 1962

MONTHS
Figure 7. Percentage of new lizards in the total catch per month. The hatchlings of 1961 were
omitted.














CHAPTER V

GROWTH


The growth rate of Lygosoma lateral has never been determined

from field data. Johnson (1953) presented two graphs containing

measurements of preserved specimens from monthly collections, but

made no conclusions concerning rate of growth. Barwick (1959) de-

termined the growth rate of Leiolopisma zelandica, a closely related

form from New Zealand, and the growth rate of several species of

Eumeces has been determined by Fitch (1954), Rodgers and Memmler

(1943), and Breckenridge (1943).

In determining the growth rate, capture-recapture data from the

hatchling group of 1960 were used exclusively; no measurements from lab-

reared young were utilized. A chart for each sex was compiled which

listed the body length of each individual for each month it was cap-

tured. The sample size for each month for each sex is given in Table 8.

If an individual was captured more than once in a month and the snout-

vent measurements were different, an average value was substituted into

the chart. The average snout-vent length for each month was then ob-

tained, and these values used to calculate a second-degree equation to

represent the rate of growth (see Snedecor, 1952, for methods).

The equation which describes the growth curve for females is

Y = 21.2308 + 2.0691X 0.0480X2; that for males is Y = 20.7713 +

1.9473X 0.0491X2. Snout-vent length in mm is represented by Y,












age in months by X. The curves derived from these equations are

shown in Figure 8.

The calculated values of Y from the above equations were used

to determine the instantaneous growth rate between successive time

intervals (Brody, 1945). For convenience each month was considered

to consist of 30 days.

The instantaneous relative growth rate is obtained from the

equation


k = Log Ll Log L2 where
T2 Tl


Log L2 and Log Ll are the natural logarithms of snout-vent length,

T2 and T1 are units of time associated with the L's, and k is the

instantaneous relative growth rate. The instantaneous relative

growth rate for each sex is given in Table 8.

As Brody states; "The constant k has a perfectly definite

meaning. It is the instantaneous relative rate of growth for a

given unit of time. Thus, for the growth of a fetus of the albino

rat, from 14 days to birth, the value of k is 0.53; this means that

the instantaneous percentage rate of growth is about 53 per cent

per day."

In the months just after hatching, growth is relatively fast

in both sexes (Fig. 8). Females, however, soon began growing at

a faster rate than males, and by adulthood, averaged 3 to 5 mm more

in snout-vent length. Growth continues throughout life, although the






40




increase in body length is relatively small. Several old females

attained 50 mnun in body length. Although not indicated in the curves

(Fig. 8), very little growth occurred during the winter months.









































0 I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22
AGE IN MONTHS


Figure 8.


Theoretical growth curves based on growth rates of the hatchling group of 1960. The upper
curve is that of females; the lower, males.















Table 8. The instantaneous relative growth rates (k) for both
sexes of the 1960 hatchling group.




k value

Age Sample Size Males Females

Months Days Males Females Months Days Months Days

1- 2 30- 60 27 31 0.08 0.003 0.08 0.003
2- 3 60- 90 11 9 0.07 0.002 0.07 0.002
3- 4 90-120 16 27 0.06 0.002 0.06 0.002
4- 5 120-150 9 9 0.05 0.002 0.06 0.002
5- 6 150-180 12 8 0.05 0.002 0.05 0.002
6- 7 180-210 7 5 0.04 0.001 0.04 0.001
7- 8 210-240 11 3 0.04 0.001 0.04 0.001
8- 9 240-270 11 12 0.03 0.001 0.04 0.001
9-10 270-300 15 8 0.03 0.001 0.03 0.001
10-11 300-330 12 7 0.03 0.001 0.03 0.001
11-12 330-360 17 16 0.02 0.001 0.03 0.001
12-13 360-390 19 24 0.02 0.001 0.02 0.001
13-14 390-420 15 9 0.02 0.001 0.02 0.001
14-15 420-450 13 10 0.01 0.02 0.001
15-16 450-480 3 4 0.01 0.01 *
16-17 480-510 3 2 0.01 0.01 *
17-18 510-540 5 1 0.01 0.01 *
18-19 540-570 12 8 ** 0.01 *
19-20 570-600 15 8 ** ** *
20-21 600-630 8 4 ** ** *
21-22 630-660 2 2 ** ** *


* Less than 0.0005.
** Less than 0.005.















CHAPTER VI

ECOLOGY OF REPRODUCTION


Sexual Maturity

Sexually mature males are defined as those producing sperm,

as evidenced by enlarged testes; sexually mature females are those

which contain enlarged ovarian follicles or oviducal eggs. In

Florida both sexes become sexually mature at approximately 35 mm in

snout-vent length. Ground skinks in Louisiana also reach sexual

maturity at 35 mm snout-vent length (Johnson, 1953). Johnson used

the presence of spermatozoa in the testes and/or ducts, and the

presence of enlarged ovarian follicles and/or oviducal eggs as cri-

teria for sexual maturity.

These results do not imply, however, that all individuals

35 mm and above in snout-vent length were sexually mature. Four

females preserved during the breeding season with snout-vent lengths

of 35, 36, 36, and 38 mm were found to have undeveloped follicles.

The same situation is probably applicable in males although no

smears were made to detect sperm. Therefore only a percentage of

those 35 mm and slightly larger contribute to the reproductive pool.

Of 19 female specimens 35-39 mm in snout-vent length preserved during

the breeding season, 15 or 78.9 per cent, were sexually mature. All

specimens 40 mm and over were sexually mature.












Sexual maturity is reached in less than a year in those

hatched in late June, July, or August. Those hatching later in

the year do not enter the reproductive pool until the succeeding

breeding season. Assuming the same hatching date, females will be-

come sexually mature earlier than males since females grow faster

(Fig. 8).

There was no indication of a loss of reproductive powers as

a female aged. On the contrary, larger (older) females produced

more eggs than smaller (younger) females (see below). Blair (1960)

found that females Sceloporus olivaceous reached a reproductive

peak at about four to five years of age, after which their repro-

ductive potential regressed.


Breeding Season

The breeding season, or period of sexual activity, for Lygo-

soma in Florida was determined from measurements of the gonads of

preserved specimens. Figure 9 shows the cyclic enlargement and re-

gression of the testes; Figure 10, that of the ovarian follicles.

From this data the breeding season was estimated to occur from Jan-

uary through July for males, and from February through July for

females. Johnson (1953), also from a study of preserved specimens,

concluded that the breeding season in Louisiana was from January

through August for males, and from December through August for females.

Field observations of sexual activity in this lizard have never been

recorded in the literature. The absence of dimorphic pigmentation












may be one of the reasons why this information is lacking. In other

species of skinks, Eumeces laticeps and E. egregius for example, the

males show a change in degree of pigmentation when sexual activity

begins. Thus a handy, external guide to their sexual activity is

available.

Copulation was observed only once. On July 14, 1961, a

copulating pair was noticed on top of the leaves near stake 5E. Air

temperature was 270C, there was a slight breeze, and the sun was

shining brightly. When first observed (9:08 A.M.) the right hemi-

penis was inserted; three minutes later (9:11 A.M.) they broke apart

and started to burrow into the leaves. The male was 39 mm in snout-

vent length and the female was 42 mm. The copulatory position was

similar to that depicted by Barwick (1959) for Leiolopisma zelandica.

Ovarian follicles start to enlarge just after the end of the

breeding season (August-September), but do not increase rapidly in

size until the middle of February (Fig. 10). Between February and

April the follicles increase four fold in width. Oviducal eggs are

present from April through August although by August most have been

laid.

Seven of 21 specimens preserved in June and July, 1961, con-

tained enlarged ovarian follicles and extremely extended and thin-

walled oviducts. This condition of the oviducts is characteristic

of females which have just laid eggs. All seven were 42 mm or above

in snout-vent length. The follicles of those from June averaged 1.94

mm in width; those from July, 2.99 mm in width. From Figure 10 it










6.00-




5.50-


5.00-


4.50-




4.00-




3.50-




3.00-


2.50-




2.00-




I.50


JAN FEB MAR
(14) (15) (II)


APR MAY
(17) (14)


JUN
(14)


JUL AUG SEP OCT NOV DEC
(11) (9) (8) (7) (8) (13)


MONTHS


Figure 9.


Yearly changes in the size of testes. Data taken from pre-
served specimens. The number enclosed by parentheses below
each month is the number of specimens examined. Line 1 re-
presents the length of the right testis; line 2, length of
left testis; line 3, width of right testis; and line 4,
width of left testis.


1 1 1







5.00-



4.50-



4.00-



3.50-



3.00



2.50-



2.00-



1.50-



1.00-



0.50-


Figure 10.


Growth of ovarian follicles and the size of oviducal eggs.
Data taken from preserved specimens. The numbers) enclosed
in parentheses is the number of specimens examined. In April
through August, the first number represents the number of
specimens examined to determine width of follicles; the second,
of oviducal eggs. The upper line represents width of oviducal
eggs; the lower line, width of ovarian follicles.


JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
(8) (12) (6) (6-3) (3-4) (7-4) (6-3) (6-4) (16) (9) (9) (7)
MONTHS


ql












appears possible that these follicles could have developed into

oviducal eggs by late August. Johnson found in several females 44 mm

or more in snout-vent length both oviducal eggs and ovarian follicles

2 mm or more in diameter. Number 432 on the plot was recorded as

gravid on March 23 and 27, 1961, and again on July 21, 1961. Four

months separated these dates, which is ample time to lay one clutch

and develop another. From these data it is evident that a small per-

centage of the larger females do produce two clutches of eggs per

breeding season.


Sex Ratio

Of 303 adults sexed in the study area, 152 were males and 151

were females, an almost perfect 1:1 ratio. The sex ratio of young

was determined from specimens 34 mm or below in snout-vent length

collected from July, 1961, to November, 1961. There were 41 males

and 39 females.

The number of males and females within the hatchling group

of 1960 for 20 consecutive months is given in Table 12. The number

of males and females decreased at approximately the same rate, neither

sex showing a higher mortality rate than the other. In contrast, a

differential mortality rate between the sexes has been found for

several other species of lizards. Blair (1960) observed that male

Sceloporus olivaceous suffered higher attrition than females. Hirth

(1962) found a higher mortality rate among male sub-adults than

among females for Ameiva quadrilineata and Basiliscus vittatus.












Reproductive Potential

To determine the reproductive potential of the population

two main types of data were required: 1) the number of sexually

mature females alive on the plot during the breeding season, and 2)

the average number of eggs produced per female. The first was obtained

from capture-recapture results and preserved material; the second, ex-

clusively from preserved material. Of secondary consideration is the

possibility of a female producing more than one clutch of eggs in one

breeding season.

Reproductive potential of the 1961 breeding population. There

were 54 females from the 1960 hatchling group present on the plot in

the spring of 1961. Possibly all had reached sexual maturity. Thirteen

of these 54 were gravid, and eight of these were 40 mm or above in

snout-vent length, the other five were 39 mm or less. This left 41

individuals whose sexual maturity was in doubt. Eight of these 41

were over 39 mm in snout-vent length and thus may be presumed to have

been sexually mature. The other 33 were between 35 and 39 mm in snout-

vent length. As indicated before, 78.9 per cent of those females

with a snout-vent length of 35 mm to 39 mm which were dissected proved

to be sexually mature. Hence it will be assumed that 26 or 78.9 per

cent of the 33 under consideration were sexually mature. Thus out of

the 54 females, 47 are estimated to have been sexually mature in the

spring of 1961.

There were 57 females present on the plot which had hatched

prior to 1960. Since all were 40 mm or above in snout-vent length,












all were assumed to have been sexually mature. Of these 57, 30 were

recorded as being gravid, and the other 27 were alive for a consider-

able length of time during the breeding season. Fifteen individuals

over 42 mm in snout-vent length could possibly have laid two clutches

of eggs.

The distinction made between the two size groups is important

because the average number of eggs produced by individuals of the two

groups was different. The 15 preserved specimens between 35 mm and

39 mm in snout-vent length, all hatched in 1960, contained an average

of 2.13 eggs, whereas the average for specimens over 39 mm was 2.82

eggs. This separation of body sizes is arbitrary and does not imply

complete separation of those lizards hatched in 1960 (1960 young)

from those hatched in preceding years (pre-1960 young). Some of

those 40 mm in snout-vent length were 1960 young, but none below 40

mm were pre-1960 young. The average number of eggs in those individuals

which indicated a developing second clutch was 2.57.

A positive correlation (r = 0.640; P. = .01) was found to

exist between snout-vent length and number of eggs. That is, larger

females tend to produce more eggs than smaller females. Johnson (1953)

found no correlation between body length and number of eggs, but he

did not include in his computation (as determined from Figure 13 in

his paper) any specimen 39 mm or less in snout-vent length.

The estimated number of eggs produced by each group of females,

and the total number of eggs produced in the 1961 breeding season is

given in Table 9.












There were no data available concerning mortality of Lygosoma

eggs. A measure of egg survival, however, was obtained by dividing

the number of young tagged in the fall of 1961 by the potential number

of eggs laid in the preceding summer. Between August, 1961, and March,

1962, 109 hatchlings were tagged. The survival rate based on this

figure was 35.2 per cent, that is, a little over one out of every

three eggs hatched and the hatchling survived till capture.

The number of hatchlings tagged is probably a low estimate of

the true number on the plot. There were 183 individuals hatched dur-

ing 1960 that were tagged during the study, yet 79 were tagged after

March, 1961. In other words only 104 of these 1960 young were tagged

between July, 1960, and March, 1961.

The modified Lincoln index described by Ilayne (1949) was used

to achieve an estimate based on the capture-recapture data of the

young hatched during 1961. In this method the population estimate is

based upon the increase in the proportion tagged which appear in suc-

ceeding catches. The capture-recapture results are given in Table 10.

The reader is referred to Ilayne's paper for methods and also for pos-

sible sources of error. A population estimate of 130 hatchlings was

computed. Using this estimate the survival rate of the eggs was about

41.9 per cent.

In comparison with the survival rate found for eggs and young

of Sceloporus olivaceous by Blair (1960) both of the above estimates

are extremely high. Blair found that under normal conditions the po-

tential production was about 4000 individuals but only about 160 were












required to reach adulthood to maintain a stable population. Verte-

brate predators were the most important cause of nest failure, but

desiccation of the eggs, failure of the young to escape from the shell,

and failure of eggs to hatch also were instrumental in causing egg

mortality (Blair, 1960). These factors were probably responsible for

egg mortality in this study also. In the laboratory only two eggs out

of 27 incubated were lost, both from a fungus infection. None were

infertile.















Table 9. The reproductive potential of the female population
on the plot during the breeding season of 1961.


Number of Sexually Average Number of Number of Eggs
Mature Females Eggs Produced Produced by Group

Females hatched during 1960

40 mm and above
16 2.82 45.12

39 mm and below
31 2.13 66.03

Females hatched prior to 1960

Number laying one clutch
57 2.82 160.74

Number laying a second clutch
15 2.57 38.55


Estimated number of eggs produced in 1961 310.44















Table 10.


Records of capture-recapture data of the 1961 hatchling
group from July, 1961, to March, 1962. The formulae be-
low were taken from Hayne (1949); P represents population
size, the other symbols are defined in the headings of the
table.


Proportion of Total Number
Month Number of Captures Catch Previously Previously
of Previously Total Handled Handled
Capture New Handled (w) (Y) (x)

July -
August 17 0 17 0.00 0

September 44 6 50 0.12 17

October 10 15 25 0.60 61

November 12 15 27 0.56 71

December 2 14 16 0.88 83

January 10 14 24 0.58 85

February 7 13 20 0.65 95

March 5 8 13 0.62 102


Sx2w


= 842958.0


Y xyw = 6499.5


P x2

P = 129.7















CHAPTER VII

POPULATION SIZE AND DENSITY


One of the objectives of this study was to determine the

density of Lygosoma in a favorable habitat and to compare this den-

sity with that of other populations of Lygosoma and with that of other

lizards.

In determining density two different figures were computed.

One, minimal density, was based on the entire area of the plot plus

a buffer strip (explained below). The other, maximal density, was

based on the area remaining after subtracting regions of unfavorable

habitat from the area of the plot plus buffer strip.

In computing maximal density, unfavorable areas were considered

as those quadrats or portions of quadrats, in which no lizards, or only

one or two, were captured. Six quadrats (1A-2A-2D-1D, 1F-2F-2E-1E,

6F-7F-7E-6E, 7A-8A-8B-7B), or 600 square yards, were so designated.

The importance of adding a buffer strip to a study area was

was proposed by Dice (1938). This buffer stip is equal to one-half

of the diameter of the average home range and should be added to the

plot at points Ohere the plot is bordered by continuous habitat. By

adding this strip, the extension of home ranges of individuals living

on the inner periphery onto area outside the plot is considered in

computing density. Along the southwestern, northwestern, northern,

and northeastern edges of the plot, the wooded habitat was continuous












along the border. Skinks residing along these edges could possibly

range out of the plot at these points. One-half of the diameter of

the average home range was added between 13A and 13F, 7F and 13F, 1F

and 5F, and between 8A and 13A. The diameter of the average home

range was determined by averaging the male and female data used in

the section on home range. The diameter was 6.3 yards.

The minimal density computation was based on the area of the

plot (6000 square yards) plus the area of the buffer strip (640 square

yards), or on a total of 6640 square yards. The maximal density

computation was based on the total area minus the unfavorable area

(600 square yards) or on 6040 square yards.

The number of individuals estimated to have been alive on the

plot for each month from July, 1960, to August, 1961, is given in the

fourth column of Table 11. The number of lizards per 100 square yards

and per acre is also given in Table 11. At the end of the study, 499

lizards had been tagged within the plot.

As would be expected, the population underwent a cyclic change

in number of individuals. A peak density occurred in August when most

of the hatchlings appeared. The population then started to decline

in numbers, the most drastic loss occurring during the spring months

(see the section on Survivorship). The low point in population size

occurred in July. The highest density recorded on the plot was in

August, 1960, when there were 263 lizards per acre.

Turner (1960b), in a study in which different methods for de-

termining population size were compared, used Lygosoma laterale as the







Table 11. Number and density of skinks on plot between July, 1960, and August, 1961, by month.


Uncorrected* Density Corrected** Density
Number Number per 100 sq. yds. per 100 sq. yds. acre
of of
Month Adults Young Total Adults Young Total Adults Young Total Total

1960
July 178 178 2.68 2.68 2.95 2.95 131
August 174 183 357 2.62 2.76 5.38 2.88 3.03 5.91
September 327 4.92 5.41 240
October 321 4.83 5.31 236
November 284 4.28 4.70 209
December 278 4.19 4.60 204

1961
January 272 4.10 4.50 200
February 270 4.07 4.47 199
March 263 3.96 4.35 193
April 247 3.72 4.09 182
May 230 3.46 3.81 169
June 213 3.21 3.53 157
July 185 185 2.79 2.79 3.06 3.06 136
August 147 130*** 277 2.21 1.96 4.17 2.43 2.15 4.59 204


*Density based on entire area of plot plus buffer strip, see text.
**Density based on favorable area of plot plus buffer strip, see text.
***Based on estimate derived from Hayne's method, see Table 10 and text.












test animal. He used two methods, a capture-recapture analysis known

as the Schumacher method (see Schumacher and Eschmeyer, 1943, and also

DeLury, 1958) and a removal method described by Zippin (1958), to es-

timate the size of an isolated population of the ground skink in Louis-

iana. An estimate of 175 lizards and 100 lizards was obtained from the

two methods respectively. Although the size of the study area was not

mentioned, a very crude approximation of the area involved was obtained

by utilizing Figure 1 in his paper. From this approximation an estimate

of the density was computed using both estimates of population size.

The area of the habitat around the skinks was estimated to be

1160 square meters or about 1388 square yards. Using the population

size determined by Schumacher's method, a density of 12.6 lizards per

100 square yards is found.

Turner (1960b) stated that the removal method probably gave

a low estimate of the population size. Thus the actual density was

probably closer to 12 lizards per 100 square yards than to 7. Both

densities, however, are much higher than that observed in this study.

In a study of Leiolopisma zelandica by Barwick (1959) a popula-

tion of at least 200 individuals were found within a small cemetery.

This population size was equivalent to a population of about 900 skinks

per acre, some four and one-half times as many as found in any one month

in this study (see Table 11). It is not clear, however, whether 200

individuals were alive at one period of time or whether this number

represents the total number of skinks tagged throughout the study. Even

if the second suggestion is correct, Barwick's population was still

larger than the one observed in this study.














CHAPTER VIII

POPULATION DYNAMICS


The importance of survivorship and life table information in

population studies has been well emphasized by Deevey (1947). Very

little of this type of information can be found, however, in ecological

studies of reptiles and amphibians. Bannikov determined the population

structure for the toad, Bombina bombina (1950), and the salamander,

Ranodon sibiricus (1949). Turner (1960a) was able to compute minimal

survival rates for Rana pretiosa, and Organ (1961) successfully pre-

pared survivorship curves and life tables for five species of the sala-

mander genus Desmognathus. The survival rate for the lizard Sceloporus

olivaceous was determined by Blair (1960) but he did not include in his

book survivorship curves or life tables.


Method of Determining Year Classes

As Organ (1961) has pointed out, size-frequency histograms have

been used in the past in an attempt to separate age classes within a

given sample. This method easily separates young or newly hatched in-

dividuals from adults, but in most cases it is less successful in separ-

ating older year classes within the adult size group. The danger in

this method is illustrated by the mistake of Taylor (1935) who divided

a large preserved sample of Eumeces skiltonianus into 16 age groups.

It was later found by Rodgers and Memmler (1943) that the normal life

span of this lizard was only five to six years.












In this study an attempt was made to separate year classes by

correlating the snout-vent length at first capture, the month of first

capture, and the known growth rate.

In examining the growth rate of the female hatchlings of 1960

it was found that it took, on the average, 18 months to reach 42.4 mm

in snout-vent length. Thus if it takes 18 months to reach 42.4 mm, an

individual 44 mm or above tagged in August-October, 1960, must have

been hatched in August, 1958, or before, not in 1959. Those individuals

between 36 mm and 42 mm tagged in August-October, 1960, were 1959 young.

For male 1960 hatchlings it took 18 months to reach 40.0 mm in snout-

vent length. Thus any individual 41 mm or above tagged in August-

October, 1960, was hatched in August, 1958, or before, and any between

36 mm and 39 mm would be 1959 young.

By utilizing these growth data the longevity can also be estimated.

As mentioned above, it is possible to show that some individuals were

hatched in 1958, or before. These individuals would have been at least

24 months old when tagged in August, 1960. Six of these individuals

were still alive in March, 1962, 43 months after hatching. Since field

trips ended in early April, 1962, it is possible that a few individuals

hatched prior to 1959 might have lived for several more months. There-

fore the minimal estimate of the life span of Lygosoma laterale is be-

tween three years and seven months and four years. The longevity

record for Lygosoma casuarinae, the Tasmanian Skink, in the Philadel-

phia Zoological Garden was five years and four months (Conant and

Hudson, 1949).












To determine how many year classes were represented, and how

many specimens were in each, the sexed, pre-1960 hatchlings, each sex

separately, were taken and individual snout-vent lengths at the time

of first capture plotted against month of first capture. The results

are shown in Figures 11 and 12 for females and males respectively.

Two size groups are recognizable in Figure 11, the larger size group

composed of individuals hatched prior to 1959, and the smaller group

composed of 1959 hatchlings. Those specimens enclosed in the trapezoid

were considered as borderline cases. The record of each was closely

examined in respect to future growth. On the basis of this examina-

tion each specimen was assigned to either one or the other of the two

groups. In Figure 12 there were more borderline cases, but two main

groups were still discernable. Those enclosed in the trapezoid were

treated as in Figure 11. The group designated as pre-1959 hatchlings

contained mostly individuals hatched in 1958, a few hatched in 1958,

and possibly a few hatched in 1956. The hatchlings of 1960 were easily

separated from pre-1960 hatchlings on the basis of size.

A small group of pre-1960 hatched individuals whose sex was not

determined in the field was assigned to year classes and sex by compar-

ing their size and time of capture with Figures 11 and 12. Only 11

were unassignable as to sex. These 11 were divided so that six were

considered as females and five as males. All 11 were hatched in 1959.

One other small group of individuals remained to be classified.

This group consisted of those captured for the first time after July,

1961. Those individuals tagged as new through July, 1961, were






o= PRE-1959 YOUNG
*= 1959 YOUNG
50 o o x= BORDER LINE CASE, SEE TEXT

49 o o

48 0 0 o o o

| 47 o

2
- 46 oo00 o o o oo
"I-
0 45 o0 oo oo ooo oo 0
2
uj
-.J 44 o 0 oo 0o o o o 0 0

2
,W 43- x xxx x xxx * *
> /1

-- 42- ** 0

th 41- eeee 0 ee e

40 *O


JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG
1960 1961
MONTHS

Figure 11. Snout-vent length at month of first capture of females.












o= PRE-1959 YOUNG

*= 1959 YOUNG

x = BORDER LINE CASE, SEE TEXT



o


44-


0 0


0 00000


0 0000 0 000


/ X xxX xxx

****


o




x


x xx x x x


x x xx 90


0** *


* 99


* ***** *


* **


JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG
1960 1961

MONTHS

Figure 12. Snout-vent length at month of first capture for males.


0 0


41-


40-


39-


38-


37-


36-


9.


* *












considered to have been residents on the plot since the study began

in July, 1960. July, 1961, was chosen as the cut-off month since

after this month the per cent of new individuals appearing in the

total catch was fairly constant for the remainder of the study

(Fig. 7). Those assigned to the pre-1959 or 1959 groups (as above)

were considered as immigrants. Those assigned to the 1960 group

were examined as to their position in the plot when tagged. Indi-

viduals which were tagged on the inner periphery of the plot were

considered as immigrants, whereas those found well within the plot

were considered as residents which had, by chance, evaded previous

capture. All individuals delegated as immigrants were counted as

part of the population at the month of their first capture.

There are many sources of error in the above methods, especially

in the allocation of individuals to age groups. The chance of error

concerning the placement of immigrants is somewhat less because

there was no evidence that immigration occurred more frequently than

emigration. Immigration and emigration were probably of equal magni-

tude. The results based on the above methods, however, provide the

best estimates of the age structure of the population available from

the data.


Age Structure

The age composition of the population from July, 1960, to

March, 1962, is given in Table 12. Of the 357 individuals estimated

to have been alive in August, 1960, 16.8 per cent were pre-1959












Table 12. The age composition of the population on the study
area from July, 1960, to March, 1962, listed by sex.


Pre-1959 1959 1960 1961
Month Male Female Male Female Male Female Unsexed Unsexed Total


57 59
57 57
49 51
47 49
44 41
43 41


43 40
42 40
40 39
35 37
32 36
29 34
25 30
16* 25
15 22
12 21
9 20
9 20


8 18
8 17*
5 13


68 62
68 62
68 62
68 62
68 62
68 62


68 62
68 62
67 62
66 61
63 58
58 56
52 51
46* 41*
41 36
34 32
33 28
28 25


27 25
28 23
20 16


* Indicates insertion point of immigrantss.
** Data insufficient to warren inclusion.


29
28
26
26
23
22


22
22
21
19
17
14
12
9
9*
6
6
6


1960
Jul
Aug
Sep
Oct
Nov
Dec

1961
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

1962
Jan
Feb
Mar












hatchlings, 31.9 per cent were 1959 hatchlings, and 51.3 per cent

were 1960 hatchlings. In August, 1961, there were only 277 lizards

estimated to have been alive; 6.9 per cent were pre-1959 hatchlings,

14.8 per cent were 1959 hatchlines, 31.4 per cent were 1960 hatch-

lings, and 46.9 per cent were 1961 hatchlings. In both years the

hatchling group comprised approximately one half of the population.

Also the one year old age group at each August comprised 31 to 32 per

cent of their respective populations. Even though the population

decreased in size, the percentage of corresponding age groups, when

compared between years, remained fairly constant.

During the breeding season at least three and possibly four

year classes contribute to the reproductive pool. In 1961, for

example, lizards hatched in 1960, 1959, 1958, and possibly 1957 were

available for reproductive functions.

The sex ratio within each age group remained constant at one

to one.


Survivorship

The turnover, or survival, of different age groups within the

population, and of the original population itself, may be calculated

by dividing the original number of marked lizards into the number re-

covered after a period of time. The quotient, expressed as a percen-

tage, is an estimate of the minimal rate of survival over the period

of time selected. To compute an absolute rate of survival the number

of marked lizards lost from the original population by emigration and












the number of marked individuals inactive at the time of census would

have to be known. Mortality rates may, of course, be obtained by sub-

tracting the figure for rate of survival from 100. Minimal survivor-

ship rates of the population can be determined from the data given in

Table 12.

The overall survival rate of the original population from August,

1960, to August, 1961, was 41.2 per cent. The survival rate of the

population including the 1961 hatchling group was 77.6 per cent. A

survival rate of 100 per cent would indicate a constant population

size from year to year. The rate of survival for the different year

classes between August, 1960, and August, 1961, was 31.7 per cent for

the pre-1959 group, 35.9 per cent for the 1959 group, and 47.5 per cent

for the 1960 group.

If the study had been continued for several more months the

survival rate of the population would probably have been much higher

than 77.6 per cent, since more hatchlings of 1961 would have been dis-

covered (see page 51).

The effect of sex on rate of survival was not consistent within

the different age groups. The rate of survival of females and males

from August, 1960, to August, 1961, was 31.3 per cent and 32.1 per

cent respectively within the pre-1959 group, and 43.9 per cent and 28.1

per cent respectively within the 1959 group. The rate of survival for

each sex in the 1960 hatchling group was determined by dividing the

group of unsexed individuals so that 26 were considered as males and

27 as females. The resultant survival rate for females was 46.1 per












cent; that for males, 48.9 per cent. The rate of survival of all

females (including 27 of the unsexed individuals) from August, 1960,

to August, 1961, was 42.7 per cent. The rate of survival of all males

(including 26 of the unsexed individuals) over the same period of time

was 39.7 per cent.

A graph of the progressive decrease in numbers of the 1960

hatchling group, based on an initial population of 1000, is given in

Figure 13. Only the data for the first 19 months are based on field

observations, the rest of the curve is speculative, being based on

the assumptions that the average life span is 3.8 years (see page 60)

and that the population decreased at a constant rate. A life table

for the 1960 hatchling group based on the data obtained from Figure

13 is given in Table 13. The abbreviations employed in the headings

of Table 13 are defined as follows: x represents age in months, x' re-

presents age as per cent deviation from the mean length of life, dx

represents the number dying in age interval of 1000 hatched, lx repre-

sents the number surviving to beginning of age interval out of 1000

hatched, l000qx represents the mortality rate per 1000 alive at the

beginning of age interval, and ex represents the expectation of future

life in months. For methods of preparing a life table see Dublin, cte

al. (1949). A survivorship curve based on the data in Table 13 is

given in Figure 14.

The survivorship curve of the 1960 hatchling group given in

Figure 14 closely approaches the Type II curve described by Deevey

(1947). A Type II curve was defined by him as being "diagonal (when




































2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46


Figure 13.


AGE IN MONTHS
The progressive decrease in number of 1960 hatchling group. The data for the first 19 months are
based on field observations. The remainder of the curve is speculative, based on an estimated
3.85 year life span and a constantly declining population.


1000-

900-










Life table for a hatchling group
on data derived from Figure 13.
months. Headings of columns are


of Lygosoma laterale based
Mean length of life, 13.29
defined in the text.


x x' dx lx l000qx ex


0- 1
1- 2
2- 3
3- 4
4- 5
5- 6
6- 7
7- 8
8- 9
9-10
10-11
11-12
12-13
13-14
14-15
15-16
16-17
17-18
18-19
19-20
20-21
21-22
22-23
23-24
24-25
25-26
26-27
27-28
28-29
29-30
30-31
31-32
32-33
33-34
34-35
35-36
36-37
37-38
38-39
39-40
40-41
41-42
42-43
43-44
44-45
45-46


-100
- 92
- 85
- 77
- 70
- 62
- 55
- 47
- 40
- 32
- 25
- 17
- 10
- 2
+ 5
+ 13
+ 20
+ 28
+ 35
+ 43
+ 50
+ 58
+ 66
+ 73
+ 81
+ 88
+ 96
+103
+111
+118
+126
+133
+141
+148
+156
+163
+171
+178
+186
+193
+201
+209
+216
+224
+231
+239


60
11
119
22
22
6
16
33
43
44
71
88
54
60
28
43
6
5
34
32
31
26
31
23
18
16
8
9
6
5
5
5
5
3
4
3
2
2
2
2
2
2
1
1
1


1000
940
929
820
798
776
770
754
721
678
634
563
475
421
361
333
290
284
279
245
213
182
156
125
102
84
68
60
51
45
40
35
30
25
22
18
15
13
11
9
7
5
3
2
1
0


60
12
117
27
28
8
21
44
60
65
112
156
114
143
78
129
21
18
122
131
146
143
199
184
176
190
128
150
118
111
125
143
167
120
182
167
133
154
182
222
286
400
333
500
1000


Table 13.


13.29
12.75
12.71
12.51
11.83
11.03
10.17
9.47
8.93
8.46
8.17
8.28
8.43
8.51
8.47
8.13
7.94
7.07
6.53
6.33
6.19
6.05
6.06
6.31
6.45
6.67
6.73
6.55
6.48
6.26
5.82
5.72
5.39
4.73
4.85
4.53
4.29
3.83
3.40
3.00
2.67
2.50
2.00
1.50
1.00
0.00














1000


500


100


50






10


5


-100 -50 0 +50 +-100 4150 +200 +250


PER CENT DEVIATION FROM MEAN

LENGTH OF LIFE (X')


Figure 14.


Survivorship curve of the 1960 hatchling group of
Lygosoma laterale.












the logarithm of the number of survivors is plotted against age),

implying a constant mortality rate for all age groups, or no one

age as a favorable time of dying." In comparison a Type I curve,

"the negatively skew rectangular, is shown by members of a cohort

which, having been born at the same time, die more or less simul-

taneously after a life span which is presumably characteristic of

the species." A Type III curve, "the positively skew rectangular,

shows extremely heavy mortality beginning early in life, but the

few individuals which survive to advanced ages have a relatively high

expectation of further life." In order to compare survivorship curves

of different species the age should be expressed as percentage devia-

tion from the mean (Deevey).

The survivorship curve of Lygosoma laterale is not typically

diagonal but shows a slight shift towards a Type I curve.

An individual which survives the first year has an expectation

of eight more months of life; one which survives the first two years

has an expectation of six more months of life (Table 13). Thus, if

an individual survives the first breeding season it has a good chance

of partaking in another.


Causes of Mortality

Actual occurrences of mortality are difficult to observe in

any field study since only a fraction of the life span of any one

individual is spent by the collector in the individual's home range.

The small size and secretive behavior of Lygosoma make observations












of this kind even more difficult. Evidence of predation pressure,

however, is more easily detected. In most lizards the tail is

broken when seized by a predator or other organism, a new tail being

regenerated from the stump if the individual escapes. In the ground

,skink a regenerated portion is easily detected due to a difference

in color and scalation between it and the stump. The presence of a

regenerated portion of the tail would thus indicate either unsatisfied

aggression by a predator, or autophagy.

The possibility of some ground skinks feeding on their own

tails (autophagy) or on the tails of other individuals (canabalism)

will be considered first. Carr (1940) reported finding "tails in the

stomachs of 4 specimens," of Lygosoma, "each of which recently lost

its tail," and furthermore, "the stub remaining on the animal plus

the portion in the stomach constituted a tail of the proper facies

and dimensions." lie interpreted these findings as evidence for auto-

phagy. No evidence was found in this study to support such a conclusion.

Over 100 individuals were maintained in the laboratory during the period

of the study, with, in some cases, ten or more in a single terrarium,

and no evidence of one lizard ever breaking its own tail, or that of

another, was ever observed even though numerous fights were noticed.

Also, 381 intestinal tracts of ground skinks taken from varied habitats

and collected over the period of a year were examined, and none contained

any portion of a Lygosoma. Two tracts did contain patches of shed skin

from the limbs.












This leaves the possibility that predators are responsible

for lost portions of tails. On the plot, 90.5 per cent of all speci-

mens with a snout-vent length of 35 mm or more possessed regenerated

tails. Only 22.2 per cent of the individuals below 35 mm had regener-

ated tails. The probably reason for the difference in percentages is

that larger lizards because of their age had been exposed to predators

more often than juveniles. One of two ring-necked snakes, Diadophus

punctatus, collected on the plot contained remains of a Lygosoma tail

in its intestine, but no other body part was found. As further evi-

dence of predation, many specimens, both preserved and on the plot,

were missing toes, and in a few cases an entire limb was missing.

Corollary evidence as to the effect of predation on the numbers

of lizards possessing regenerated tails may be found in a study by

Rand (1954). In a study of an island and a mainland population of

Cnemidophorus lemniscatus he found that the ratio of regenerated tails

on the island population to those from the mainland was 1:8. He at-

tributed this ratio to greater predation pressure on the mainland.

Literature records of predation on Lygosoma laterale are listed

in Table 14. Those species of predators known to occur on or near the

plot are marked by an asterisk. Other species not recorded previously

as predators of Lygosoma are the armadillo, Dasyipus noviemcencyus (W.

Wirtz, personal communication), and the milk snake, Lampropeltis

doliata (T. Brown, personal communication). Animals that are known

to feed on other small lizards and which might occasionally prey on

Lygosoma include bluejays, Cyanocitta cristata, mockingbirds, Mimus












polyglottos, young rat snakes, Elaphe obsoleta quadrivittata, coral

snakes, Micrurus fulvius, moles, Scelopus aquaticus, shrews, Blarina

brevicauda, opossums, Didelphis marsupiolis, and the house cat, Felix

domesticus.

Emigration should also be considered as a form of mortal ity

since it results in the loss of individuals from the population.

During the course of field work on the plot one adult ground

skink was found dead of undeterminable cause under a log, and one

adult and two hatchlings were killed in capture.

There was no evidence to consider parasitism as a cause of death.

Tapeworms, Cyclotaenia americana, were found in 53.2 per cent of all

preserved specimens 35 mm and above in snout-vent length. Nematodes,

consisting of two or three unidentified species, were found in 50.9

per cent, and 27.5 per cent were parasitized by a digenetic fluke,

Brachyocoelium sp. All of the above parasites were found in the in-

testinal tract. Three lizards on the plot were parasitized by unidenti-

fied ticks. In no case did a host seem to have been adversely affected

by the presence of one or more species of parasite. f S A












Table 14. List of predators of Lygosoma lateral recorded
literature. Those known to inhabit the area of
plot are marked by an asterisk.


Predator


in the
the study


Literature Source


Hamilton and Pollack (1956


Diadophus punctatus*
(ring-necked snake)

Heterodon platyrhinos
(eastern hognose snake)

Coluber constrictor*
(black racer)

Masticophis flagellum
coachwhipp snake)

Elaphe guttata*
(corn snake)

Lampropeltis getulus
(king snake)

Cemophora coccinea
(scarlet snake)

Ancistrodon contortrix
(copperhead snake)


Sistrurus miliarius
(pygmy rattle snake)

Crotalus horridus
(canebrake rattle snake)

Ophisaurus ventralis*
(glass lizard)

Eumeces laticeps*
(broad headed skink)

Eumeces inexpectatus*
(southeastern five-lined skink)


Bush (1959)

Hamilton and


Pollack (1956)


Hamilton and Pollack (1956)


Hamilton and Pollack (1956)


Hamilton and Pollack (1956)


Hamilton and Pollack (1956)


Hamilton and Pollack (1956)


Hamilton and
Bush (1959)
Fitch (1960)

Hamilton and


Pollack (1955)



Pollack (1955)


Hamilton and Pollack (1955)


Hamilton and Pollack (1961)


McConkey

Hamilton


(1954)

and Pollack


(1961)


Hamilton and Pollack (1961)


- I IIlII II -- ------ I -~-- I-I---- I













Table 14. Continued.


Literature Source


Lygosoma laterale
(ground skink)

Cryptotis parva floridana
(Florida short-tailed shrew)

Latrodectus mactans
(black widow spider)

Lanius ludovicianus
(loggerhead shrike)


Lewis (1951)


Pearson (1951)


Neill (1948)


Lewis (1951)


Predator


I I


_~__















CHAPTER IX

ACTIVITY


The common name of Lygosoma laterale, the ground skink, is very

appropriate since this lizard spends its entire life cycle in associa-

tion with the litter layer and surface soil. When not active, an in-

dividual remains quiescent under a mat of spanish moss, a rotting log,

fallen leaves, or had burrowed into loose soil beneath the litter layer.

The most favorable retreat is under leaf mold at the base of trees and

logs. When active, a ground skink prowls over and under leaves, twigs,

mats of spanish moss, and vines in search of small insects and spiders.

The presence or absence or activity is, of course, determined

by a complex of factors, both internal and external. Only those environ-

mental factors which were easily correlated with activity in the field

will be considered; the effect of environmental changes on the hormonal

regulation of the body is beyond the scope of this study.

Field trips were nonrandom in nature. Most trips were made only

when success was expected. Thus the quantitative results given in com-

paring amount of activity and different factors must be regarded as

only estimated.


Temperature

Since lizards are ectothermic, environmental temperatures are

important in regulating their activity. To determine the preferred











temperature range for activity, the number of skinks captured at each

recorded field, shade temperature was counted. The results are given

in Figure 15. Figure 16 shows the average number of active skinks

per field trip for arbitrarily selected temperature ranges.

From both figures it is evident that most activity occurred

between 250 and 300 C. Fitch (1956b) found an average cloacal tempera-

ture of 28.80 C for 16 ground skinks in Kansas. In his study the air

temperatures ranged from 22.8* C to 28.50 C with but one exception;

one skink was active at an air temperature of 14.70 C.

The activity of skinks at low shade temperatures was probably

due to higher temperatures in sunlit spots. All skinks active on

days when the shade temperature was 120 C to 180 C were captured in

sunny spots where the air temperature, one inch above the litter

layer, was always 19 C or above. Basking was observed only on sunny

and partly cloudy days during late fall and winter.

The number of active skinks decreased considerably more when

the shade temperature reached above 300 C than when it dropped below

250 C (Fig. 15). This might be explained by the fact that in lizards

the preferred optimum body temperature is closer to the critical

maximum than to the critical minimum (Cowles and Bogert, 1944). Also

at lower shade temperatures an individual could bask at intervals and

thus raise its body temperature to its optimum for activity.

It must be realized that the shade temperature at the point

of highest activity does not represent the ecological optimum tempera-

ture of Lygosoma laterale. Cole (1943) has shown that the body






80












200-

180-

160-

140-

S120-

S100-

U-
0 80-
w-
m 60-

40-


20- Yi H( T

I I
12 14 16 18 20 22 24 26 28 30 32 34
SHADE TEMPERATURE TWO INCHES ABOVE
GROUND IN DEGREES CENTIGRADE





Figure 15. Number of ground skinks captured at each recorded shade
temperature.








































F


0- 16- 19-
15 18 21


1
22-
24


1 1
25- 28-
27 30


n R


31-
33


I
34-
36


SHADE TEMPERATURE TWO INCHES
ABOVE GROUND IN DEGREES
CENTIGRADE








Figure 16. Average number of ground skinks captured per' field trip
at selected temperature ranges.


k I I ,I I , I I I I ,


U












temperature of a lizard is very little affected by that of the sur-

rounding air; the substratum and incident radiation being the more

important temperature determining factors. However, since the average

body temperature found by Fitch (1956b) falls within the range of

shade temperature which contained the greatest amount of activity,

the ecological optimum temperature of Lygosoma lateral probably occurs

within the temperature range of 250 C to 300 C.


Moisture

At each field trip the moisture content of the litter layer

was recorded in one of two ways: 1) "moist," if the litter layer

contained any moisture as judged by touch, and 2) "dry." if the litter

layer was dry down to the surface soil.

The average number of active lizards per field trip under

"moist" conditions was 21.5 (S.E.m = 1.5); under "dry," 11,1 (S.E.m = 1.5).

The average number active per hour of field trip was 8.2 for "moist" and

6.7 for "dry."

Figure 18 shows the relationship between shade temperature,

moisture content of the litter layer, and the number of ground skinks

active. Between 25* C and 300 C (the area blocked off in the graph)

there were 34 "moist" trips with an average of 25.8 skinks active

(S.E.m = 1.5), and 15 "dry" trips with an average of 15.3 active

skinks (S.E.m = 2.1). Within this temperature range "moist" conditions

were much more favorable for activity than "dry." Whether moisture

affects the individual directly, or indirectly by affecting the





























Figure 17. The relationship between shade temperature, moisture,
and number of active ground skinks.











o = DRY
* = MOIST


*


0


* 0


0*
*
*
*
*
*



0 a



0 *


* *S*
0


* 0


0

0


* *


0 o


oOo


S


O0* *


ILJ
- 26
I-

<24

20
iE22
N
.j 20
u.
0 18

m16
z14
z 14


8 10 12 14 16 18 20 22 24 26 28 30 32 34

SHADE TEMPERATURE IN DEGREES CENTIGRADE












activity of food items, is not known. At temperatures below 250 C

the difference in number of active skinks between "moist" and "dry"

conditions was less. "Moist" conditions, however, still resulted

in more active skinks; an average of 12.3 S.E.m = 2.7) were active

under "moist" trips, 7.2 (S.E.m = 1.6) "dry."

Lygosoma laterale thus seems to prefer warm-moist conditions

over warm-dry, cool-moist over cool-dry, but warm-dry over cool-moist

or cool-dry.

The data shown in Figure 3 indicated that there is some cor-

relation between activity and rainfall in a few months (October and

December, 1960; February, October, and November, 1961) but the more

obvious correlation is between activity and temperature.


Time of Day

Observations during the course of the study indicated that

throughout the year more skinks were active during the afternoon than

during the morning. Lizards were active though at all times of the

day at all seasons. In general, skinks were active throughout the

day in spring, mostly in the morning and later afternoon in summer,

and usually in the afternoon during fall and winter. Four field

trips were made to the plot at night in 1961; one in April, two in

June, and one in July. No skinks were found active on the surface but

several were uncovered when logs were being moved. These individuals

immediately ran for cover.

The earliest recorded time of activity on the plot was at 810

on July 14, 1961, in the southeastern corner; the latest, at 1820 on












June 15, 1961, in the southwestern corner. Individual ground skinks

have been observed by Dr. J. N. Layne (personal communications) to

be active at 615 in June, 1958, at 615 on July 5, 1962, at 640 on

September 19, 1958, at 700 on April 21, 1959, and before sunup on

May 27, 1958. One was observed active at 2000 on June 28, 1959. All

of these observations were made in his study plot located in a turkey

oak woods. Myers (1959) observed a ground skink in Missouri crawling

in leaves after midnight on June 13, 1954.


Season

The average number of active lizards per field trip for each

of the seasons was as follows: spring, 26.0 (S.E.m = 3.2, N. = 12);

summer, 21.3 (S.E.m = 1.7, N. = 28); fall, 12.8 (S.E.*m = 2.2, N. = 27);

and winter, 16.2 (S.E.m = 2.3, N. = 22). A large number of skinks

active during an exceptional warm spell in February raised the winter

average (Fig. 3). The large number of skinks active during spring

months was probably due to a combination of factors, chief of which

were suitable temperature and moisture conditions and the influence

of the breeding season. That the reproductive urge influenced activity

is indicated by the differential number of males and females active in

winter and spring (Table 16). The low number of skinks active during

the fall was due to unfavorable temperatures. As one example, on

October 21, 1961, the shade temperature was 170 C and no lizards were

active. The next day, October 22, 1961, the shade temperature was 240 C

and 12 lizards were captured. Both trips were recorded as being "moist."















CHAPTER X

DISCUSSION


An interesting discovery during this study was the unusual

distribution of individuals within the plot. A large number of skinks

were found associated with areas characterized by a litter layer com-

posed mainly of oak, hickory, and pine leaves. Fewer skinks than ex-

pected were found in other types of litter.

This difference in concentration may be due to one or many of

several reasons. As was mentioned on page 16, the litter layer beneath

pine trees was much more constant in depth throughout the year in com-

parison with that beneath oaks and hickories. The mixture of pine

needles, oak, hickory, and other leaves was also much less compacted

than other litters. Skinks escaped much easier in pine-oak-hickory

litter than in other types. The constancy in depth alone undoubtedly

provided more favorable cover, a more dependent supply of food items,

and a more stable moisture content to individual ground skinks.

A difference in the p1H of the humus might also have influenced

the skink density either by affecting the skinks directly or by af-

fecting the supply of certain food items. Unfortunately no chemical

determinations were made of the humus during the study. Heatwole (1961),

however, found a difference in the pH between surface samples of an

oak-pine-aspen forest and an oak-hickory forest. The pH of the former,

taken at a depth of 2.5 cm was 4.7; that of the latter, taken at the

surface, was 6.0. Both forests were in Michigan.

87











The distribution of the skinks may also be approached from

another point of view. The oak-hickory-pine litter as opposed to

other types of litter might cautiously be regarded as analogous to

an ecotonal effect. An ecotone is the transition or tension zone

between two major communities (Allee, et al., 1949). In this analogy

the two major communities would be pine litter and oak-hickory litter.

There is a tendency in an ecotone for an increased variety and density

of organisms over that found in the adjoining communities (Odum, 1959).

The reasons behind this effect have been described by Allee, et al.:

"The ecological reality of the ecotone is attested by the fact that,

in addition to organisms penetrating this boundary area from both

communities involved and living therein for all or a regular part of

their lives, there are other organisms that find the biotic and

physical environment of the ecotone more stimulating than the condi-

tions prevailing in either community." Thus in the plot, the mixture

of different leaves possibly resulted in a greater variety and density

of food items being available which, in combination with the increased

cover, resulted in a high density of ground skinks.

It is interesting to speculate on the future of the lizard

population if the woods remain unmolested. If undisturbed the woods

will probably succeed to a mesic hammock or similar vegetation. The

present vegetation is dominated by loblolly pines, various oaks and

pignut hickory. No small pines or pine seedlings were found in the

area yet both Quercus and Carya were represented by seedlings and

saplings. The trend toward a more mesic habitat was indicated by the











presence of seedling magnolias, Magnolia grandiflora, scattered

throughout the plot.

As the pines die and are replaced by other trees will the

population density of skinks rise, fall, or remain stable? A vague

answer can be supplied by comparing the amount and character of the

litter layer between the present and the future woods. Dominant

trees of a mesic hammock are magnolias, pignut hickory, and laurel

oak (C. Monk, personal communication). Decomposition of magnolia

leaves is relatively slow and the litter layer remains deep the

year round (A. M. Laessle, personal communication; personal observa-

tion). Thus perhaps a decrease in density might occur during a transi-

tion period but an increase would probably occur once the magnolias

became dominant.

In connection with the above, a mesic hammock dominated by

oaks and magnolias was visited several times and was found to have

a very high density of ground skinks. On one trip lasting 35 minutes,

12 skinks were captured and approximately that many escaped. Subse-

quent trips to this hammock revealed large numbers of skinks in an

area much smaller than the study plot.

The difference in the average size of home range between males

and females is not unique among lizards. The home ranges of adult

males of Eumeces fasciatus (Fitch, 1954), Uta stansburiana (Tinkle,

et al., 1962), Sceloporus olivaceous (Blair, 1960), and Anolis carolinen-

sis (Gordon, 1956) were found to be larger than those of females. Bar-

wick (1959), however, found that the home range of Leiolopisma












zelandica did not differ in size or shape between adult males and

females, and Fitch (1958) found that females of Cnemidophorus sexlineatus

had a slightly larger home range than males.

The behavior of males in searching for mates is thought by

Blair (1960) to be the basic reason for adult males having larger

ranges than females. Another possibility will be discussed below.

The nonoverlapping of female home ranges indicated female terri-

toriality. This evidence, however, is not conclusive; observation of

actual defense of an area by the female inhabitant is needed for de-

finite proof.

The possibility of females and not males exhibiting territorial-

ity is without precedence among the Scincidae. A thorough search of

the literature failed to reveal any record of territoriality by females

of scincoid species.

Many examples of territoriality by males among iguanid lizards

have been reported (Fitch, 1940, 1956a; Blair, 1960; Evans, 1951;

Schmidt, 1935) and it is among the iguanids that the only cases of

female territoriality have been found. Evans (1938) reported that

both females and males of the Cuban lizard, Anolis sagrei, defend a

territory. The presence of a foreign female within the territory

elicits defense behavior by the resident female. The resident male,

however, prevents any attack and courts the strange female. Rodolfo

Ruibal (personal communication) has observed females of Anolis

sagrei and of A. allisoni showing aggressive behavior.











The biological advantage bestowed upon a female because of a

territorial habit might basically be one of energy conservation.

Dice (1952) believes that "the habit of living in territories results,

... in a minimum amount of fighting among the members of a species

compared to what might take place if each individual roamed about

widely over the habitat." A territorial habit also is a regulatory

mechanism in the community. A territory "prevents the over utiliza-

tion and depletion of food and other sources in the ecosystem, thereby

lessening for the species concerned the danger of recurrent crises

caused by lack of one or more items essential for its existence"

(Dice, 1952).

The apparent lack of a territory among males may in part be

responsible for the larger size of male home ranges. An individual

male should require more space than a territorial female since he

shares space with other males and with females.

The above discussion adequately expresses the need for further

study on the spatial relations of individuals within a high density

population.

The position of Lygosoma in the trophic structure of the com-

munity is of importance since it occurred in such large numbers. The

four other species of lizards on the plot were not nearly as abundant

as Lygosoma. Anolis carolinensis was common along the southern edge

of the plot but only a few individuals were noticed elsewhere. The 10

to 15 individuals of Cnemidophorus sexlineatus observed were confined

to the southern border. A few individuals of Eumeces laticeps and E.

inexpectatus were observed in the interior of the plot.












Lygosoma filled a niche in the community as a secondary and

tertiary consumer. A study of the intestinal tracts of 328 skinks

revealed a diet composed of a wide variety of organisms. Insects, be-

longing to 10 orders, were found in 90 per cent of the tracts. Coleop-

terans found in 24 per cent of the guts, dipterans in 20 per cent,

hemipterans in 22 per cent, collembolans in 17 per cent, and lepidop-

teran larvae in 18 per cent comprised the greater portion of the in-

sects eaten. Other types of insects taken were: hymenopternas, orthop-

terans, isopterans, neuropterans, and dermapterans. Spiders were a

large source of food, being found in 48 per cent of the tracts. Other

inhabitants of the litter layer were also eaten: snails were found in

10 per cent of the guts, isopods in 19 per cent, and millipedes,

centipedes, earthworms, and acarinids all in less than four per cent.

Ground skinks in return served as a food supply for many other animals

(see Table 14).















CHAPTER XI

SUMMARY


The population ecology of Lygosoma laterale, the ground skink,

was studied from July, 1960, to April, 1962, a period of 22 months.

The study plot, 120 yards by 50 yards in size, was located

in a wooded area on the campus of the University of Florida, Gaines-

ville. A mixture of hardwoods, mostly oaks and hickory, and loblolly

pines dominated the vegetation.

All captures of skinks were made by hand. Lizards were marked

by removing toes; each individual having a different number. A total

of 115 field trips were made during the study. Collections were made

from other populations for study of the reproductive cycle and para-

sites.

Within the plot, ground skinks were more abundant in pine-

influenced areas than in nonpine-influenced areas. Areas in which

the litter layer contained a mixture of pine needles and other leaves

were considered as pine influenced. Areas in which the litter con-

tained no pine needles were considered as nonpine-influenced regions.

Litter containing pine needles provided a more favorable habitat due

to the constancy in depth, moisture content, and possibly food supply.

Skinks were found to occupy home ranges throughout their lives.

The average size of a home range for males was more than three times