Distribution patterns of the desert horned lizard (Phrynosoma platyrhinos): the influence of biotic and abiotic factors.
Newbold, Scott*,1, MacMahon, James1, 1 Utah State University, Logan, UT
ABSTRACT- Elucidating the critical ecological factors that determine patterns of species abundance and distribution has been a fundamental human pursuit for centuries. Community ecologists debate whether species are more strongly influenced by biotic or abiotic factors. We explore this question using a shrub-steppe community of desert horned lizards (Phrynosoma platyrhinos), ants, and vegetation distributed along an elevational gradient in northwestern Utah, U.S.A. We first examined desert horned lizard-habitat associations to evaluate the determinants of lizard occurrence using transect surveys along a shrub-steppe bajada. Lizard response to abiotic attributes of shrubs (shade and soil conditions) was assessed using a manipulative study in an enclosed arena (30 x 30 m). Unvegetated intershrub spaces and the percent cover of cryptobiotic crust were the best predictors of lizard occurrence. Lizards had strong preference for high-shade model shrubs during the day (82% of day selections). Microsites with soil mounds were favored over sites with no soil mounds (85% of total selections). Our findings support the contention that organisms in arid systems are constrained by abiotic factors. Biological interactions operate secondarily. This work is consistent with research that suggests the physical structure of vegetation plays a fundamental role in the organization of ecological communities.
Key words: habitat associations, biotic/abiotic factors, Phrynosoma platyrhinos
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