Demographic Analysis 
231 
The habitat of the area included a loose 
sand and gravel substrate, sparsely vegetated 
with grasses and other annual weeds. Small 
cottonwood, mulberry, and elm trees were 
distributed across the area, occasionally 
forming small groves. The study area was 
bordered on the north by a pond, on the south 
by a riparian forest and ditch, and on the 
east and west by plastic drift fences. Thus 
the population was relatively confined. 
Several other vertebrates inhabited the 
area. Some of these that are potential lizard 
predators were: birds (blue jays, brown 
thrashers, catbirds, shrikes, cuckoos, sparrow 
hawks, kingbirds) ; mammals (deermice, 
shrews, moles, raccoons, opossums, skunks, 
badgers, and coyotes) ; amphibians (western 
toads, bullfrogs, leopard frogs) ; and lizards 
(racerunners, prairie skinks, and plains 
skinks). No snakes known to prey on lizards 
were observed in the area. 
We began a census of the population in 
May 1971 and, for the purposes of this re- 
port, terminated it October 1972. The census 
methods were similar to those reported by 
Tinkle (1967). Processing of individual 
lizards included capturing; measuring and 
recording snout-vent length; clipping toes 
of individuals and recording the toe-clip 
patterns for future identification; recording 
location and recording habitat; painting tail 
base; and then releasing individuals at the 
location of their capture. The area was 
searched systematically. On the first search 
all lizards seen were captured and processed. 
On subsequent searches all lizards lacking a 
paint mark were captured and processed, 
while those with a paint mark were merely 
tallied. After six to eight sweeps, the pro- 
portion of “new” lizards was usually less 
than 10 percent, and the census was con- 
sidered complete. Population sizes were esti- 
mated by use of the Haynes index (Hayne, 
1949). Due to the high rate of hatching in 
the period from July 23, 1971 through Sep- 
tember 7, 1971, and the low manpower avail- 
able during that time, that entire 47-day 
period was considered a single census. Sub- 
sequent census periods were shorter and in- 
cluded for purposes of this report: Septem- 
ber 27 through October 10, 1971; July 10 
through July 17, 1972; July 31 through 
August 8, 1972; August 21 through August 
23, 1972; and September 26 through October 
11, 1972. 
Data from these census periods analyzed 
in this report included density change for 
each of the 24 sectors. Each sector was a 
square composed of four adjacent quadrats. 
The total area was considered large enough 
(6400 square feet) to include the home range 
of a large number of juvenile lizards and 
small enough to generate a number of in- 
dividual sectors for analysis of the effect 
of population density on survivorship. A 
few sectors were not included in the analysis 
because they contained marginally suitable 
habitats and did not support juveniles for 
more than a few days. In order to assess 
density change for a given sector over a 
time interval, the number of juveniles regis- 
tered during a census period “to” at the be- 
ginning of the interval was compared to that 
registered on the same sector during a later 
census period “tx” at the end of the interval. 
A ratio ti/ta of less than one indicated a de- 
crease in population density in the sector 
between the two census periods ; a ratio 
greater than one, indicated an increase in 
density. 
Survivorship of marked lizards was also 
analyzed for each sector by noting the pro- 
portion of individuals marked on a sector 
at “to” and still alive somewhere on the total 
study area at “ti”. The effect of density on 
both density change and survivorship was 
analyzed by comparing the 24 sectors, which 
had variable “to” densities. 
Insect food available to lizards on the study 
area was estimated during the summer of 
1972. An 8 Y 2 X 11 inch sheet of paper was 
affixed to a wooden clipboard and coated with 
“stickum special,” a commercially available 
petroleum compound. These “insect traps” 
were placed on the ground throughout the 
study area in microhabitat regions suitable 
for lizards. Traps were set in place for 2 
hours and after removal were immediately 
replaced with a fresh trap. On each “insect 
census day” traps were in place from 0700 
