Vascular Plant and Vertebrate Inventory of Saguaro ... - USGS

Cumulative number of species
50
40
30
20
10
0 20 40 60 80 100 120
Sample period
39
All survey methods
Extensive and intensive surveys
Figure 4.3. Species accumulation curve for herpetofauna surveys, Saguaro National Park, Rincon
Mountain District, 2001 and 2002. Each sampling period represents batches of 35 individuals, the
mean number of individuals observed in an eight-hour field day. “All survey methods” includes extensive,
intensive, road surveys, and incidental observations. The order of all sampling periods was randomized.
were detected in Turkey, Rincon, Chimenea, and
Wildhorse creeks.
We detected 24 species during extensive
surveys that were near randomly-selected
transects (n = 22) and 38 species in non-random
areas (n = 63) with only one new species
detected in random areas. Species richness in
non-random areas (5.1 ± 0.4) was similar to that
in random areas (5.3 ± 0.6; t 83 = 0.42, P = 0.81,
t-test), yet there was some evidence that richness
of amphibians was greater in non-random
areas (t 83 = 1.80, P = 0.075, t-test). Relative
abundance in non-random survey areas (41.9 ±
5.1 individuals/10 hrs) was also similar to that
in random areas (52.3 ± 8.6; t 83 = 1.04, P = 0.30,
t-test), yet there was some evidence that relative
abundance of lizards was greater in random areas
(t 83 = 1.89, P = 0.065, t-test).
Road Surveys
We detected 688 individuals of 19 species during
55 surveys totaling 46.3 hours of effort (Table
4.9). We detected four amphibian species (21%
of all species) totaling 515 individuals, 74.9%
of all individuals detected and proportionally
more amphibians than for other survey methods
(Table 4.7). Reptiles included eight lizard and
seven snake species; 20.8% (n = 143 of 688)
of individuals were lizards and 4.4% (n = 30 of
688) were snakes. Relative abundance averaged
17.5 ± 2.7 individuals/hr (range = 0– 85.3), the
majority of which were the Sonoran Desert and
red-spotted toads.
Relative abundance averaged 37.1%
higher in summer than in spring (t 53 = 1.92, P =
0.060, t-test) but was not necessarily attributable
to an increase in amphibians during summer
(t 53 = 0.79, P = 0.43, t-test). The desert spiny
lizard was the most common lizard detected (89
detections) and the western diamond-backed
(eight detections) and tiger (six detections)
rattlesnakes were the most common snake species
detected.
Incidental Observations
We recorded 1,226 incidental detections of 44
species between 3 April to 5 October 2001 and
2 May to 7 November 2002 (Appendix B).