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,r...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 short-lived animals.We examined the thermal ecology and reproduction of US federally threatened Mojave desert tortoises(Gopherus agassizii),long-lived and large-bodied ectotherms,at opposite ends of a 250-m elevation-related rainfall cline within Ivanpah Valley in the eastern Mojave Desert,California,USA.Biophysical operative environments in both the upper-elevation,“Cima,”and the lower-elevation,“Pumphouse,”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°C-cooler 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 larger-bodied 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 counter-gradient variation in reproductive success across the rainfall cline.Land-use 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 ecosystem-level responses to regional resource variation in assessments of habitat for prospective development and mitigation efforts.展开更多
基金E.Stauffer provided invaluable field and logistical assistance.V.Izzo,A.Curtin and numerous Earthwatch volunteers were important contributors to the dataset.E.Beever and D.Pyke kindly shared their original vegetation survey data.G.Freeman allowed us access to his property within the Pumphouse plot.A grant from Earthwatch and the Betz Chair for Environmental Science funded this research.All research was conducted under the Mojave National Preserve Scientific Research and Collecting Permit No.MOJA-2003-SCI-0068(Study No.MOJA-00116)the State of California Collecting Permit 801176-04the US Fish and Wildlife Service(10(a)1(A))Permit No.TE049000-0,following a protocol approved by the Drexel University IACUC(01059,Project No.689).
文摘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 short-lived animals.We examined the thermal ecology and reproduction of US federally threatened Mojave desert tortoises(Gopherus agassizii),long-lived and large-bodied ectotherms,at opposite ends of a 250-m elevation-related rainfall cline within Ivanpah Valley in the eastern Mojave Desert,California,USA.Biophysical operative environments in both the upper-elevation,“Cima,”and the lower-elevation,“Pumphouse,”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°C-cooler 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 larger-bodied 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 counter-gradient variation in reproductive success across the rainfall cline.Land-use 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 ecosystem-level responses to regional resource variation in assessments of habitat for prospective development and mitigation efforts.
