1 research outputs found
Mojave desert tortoise (Gopherus agassizii) thermal ecology and reproductive success along a rainfall cline
Desert resource environments (e.g. microclimates, food) are tied to limited, highly localized rainfall regimes which generate microgeographic variation in the life histories of inhabitants. Typically, enhanced growth rates, reproduction and survivorship are observed in response to increased resource availability in a variety of desert plants and shortâlived animals. We examined the thermal ecology and reproduction of US federally threatened Mojave desert tortoises (Gopherus agassizii), longâlived and largeâbodied ectotherms, at opposite ends of a 250âm elevationârelated rainfall cline within Ivanpah Valley in the eastern Mojave Desert, California, USA. Biophysical operative environments in both the upperâelevation, âCima,â and the lowerâelevation, âPumphouse,â plots corresponded with daily and seasonal patterns of incident solar radiation. Cima received 22% more rainfall and contained greater perennial vegetative cover, which conferred 5°Câcooler daytime shaded temperatures. In a monitored average rainfall year, Cima tortoises had longer potential activity periods by up to several hours and greater ephemeral forage. Enhanced resource availability in Cima was associated with largerâbodied females producing larger eggs, while still producing the same number of eggs as Pumphouse females. However, reproductive success was lower in Cima because 90% of eggs were depredated versus 11% in Pumphouse, indicating that predatory interactions produced counterâgradient variation in reproductive success across the rainfall cline. Landâuse impacts on deserts (e.g. solar energy generation) are increasing rapidly, and conservation strategies designed to protect and recover threatened desert inhabitants, such as desert tortoises, should incorporate these strong ecosystemâlevel responses to regional resource variation in assessments of habitat for prospective development and mitigation efforts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111753/1/inz212132.pd