RESULTS
Models that were painted to color-match in the urban environment had
higher COI scores than those that were not color-matched (urban gray vs
urban red, t = 2.59, df =18, P = 0.019), and models that were painted to
color-match on the ranch had higher COI scores than those that were not
color-matched (ranch gray vs ranch red), (t = 4.86, df = 18, P =
0.00013) (Fig. 3).
A total of 61 predation events were recorded over both sampling periods
representing 12.1% of all models. We found no difference in the total
number of predation events occurring between early summer (N = 30) and
late summer (N = 31) (P = 0.89) (Table 1). Four predation events
occurred on the controls over both sampling periods, all of which were
located on the ranch. Predation events were higher on the models than on
the controls, both overall (χ2 = 3.74, df = 1, P =
0.05) and on the ranch (χ2 = 3.24, df = 1, P = 0.04).
We observed more predation events on models at the ranch (N = 60) over
the two sampling periods than in the towns (N = 1) (P =
1.12x10-18) (Table 1). During the early summer, 1
model was attacked in town and 29 were attacked on the ranch (P =
1.05x10-8) (Table 1). During the late summer, no
models were attacked in town and 31 were attacked on the ranch (P =
1.13x10-10). Hatchling models were attacked less than
juvenile or adult models (χ2 = 7.08, df = 2, P =
0.029) (Table 1). Models that had evidence of being disturbed by
non-predators (i.e. hoof marks) (n=2) or went missing (n=6) were only on
the ranch and were not counted as predation events and excluded from the
analysis.
We found a significant difference in the number of predation events by
predation category: birds, rodent, other, and unknown
(χ2 = 33.24, df = 3, P = 2.86x10-7)
(Fig. 4). We also found that the number of attacks by birds in the early
summer (N = 13), when lizard models were not painted to color-match the
red soils on the ranch was significantly higher than during late summer
(N = 5) when models were painted to background color-match
(χ2 = 3.8, df = 1, P = 0.05) (Fig. 4). We did not see
any difference in color-matching in the remaining categories on the
ranch rodents:( χ2 =2.9 , df = 1, P = 0.09), other
(χ2 =1.5 , df = 1, P = 0.23) or unknown
(χ2 = 0.1, df = 1, P = 0.78) (Fig 4). The attack in
June on a control piece had distinct peck marks, whereas the three
remaining controls that were attacked in August had conspicuous
half-moon shape bite marks (Fig. 5). Our controls during the second
round were painted to color-match the soils on the ranch and as a result
resembled dried prickly pear (Opuntia spp.) pads and fruits;
which may have attracted Texas tortoises (Gopherus berlandieri )
(Fig. 5). We frequently encountered Texas tortoises eating both the
fruits and pads of Opuntia spp. on the Dimmit County ranch and
the bite marks on the controls were similar in size and shape to the
tortoise bites on cactus pads (Fig. 5).