Desert Tortoise (Gopherus agassizii) Survival at Two Eastern Mojave Desert Sites: Death by Short-Term Drought?

Longshore, Kathleen M.; Jaeger, Jef R.; Sappington, J. Mark

doi:10.1670/0022-1511(2003)037[0169:dtgasa]2.0.co;2

Cited by 61 publications

(46 citation statements)

References 16 publications

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“…The information presented in the present study demonstrates that mortality events can occur in pulses that track the large-scale climatic fluctuations in the Mojave Desert. Mortality as a direct impact of drought has been reported for desert tortoises (Germano & Joyner 1989, Peterson 1994, Longshore et al 2003. However, while elevated mortality may be coupled to natural processes, we do not consider the levels of mortality we quantified to be possible naturally because they clearly would result in unsustainable population losses over the course of decades (Doak et al 1994, USFWS 1994.…”

Section: Discussionmentioning

confidence: 99%

Effects of subsidized predators, resource variability, and human population density on desert tortoise populations in the Mojave Desert, USA

Esque¹,

Nussear²,

Drake³

et al. 2010

Endang. Species. Res.

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Understanding predator-prey relationships can be pivotal in the conservation of species. For 2 decades, desert tortoise Gopherus agassizii populations have declined, yet quantitative evidence regarding the causes of declines is scarce. In 2005, Ft. Irwin National Training Center, California, USA, implemented a translocation project including 2 yr of baseline monitoring of desert tortoises. Unusually high predation on tortoises was observed after translocation occurred. We conducted a retrospective analysis of predation and found that translocation did not affect the probability of predation: translocated, resident, and control tortoises all had similar levels of predation. However, predation rates were higher near human population concentrations, at lower elevation sites, and for smaller tortoises and females. Furthermore, high mortality rates were not limited to the National Training Center. In 2008, elevated mortality (as high as 43%) occurred throughout the listed range of the desert tortoise. Although no temporal prey base data are available for analysis from any of the study sites, we hypothesize that low population levels of typical coyote Canis latrans prey (i.e. jackrabbits Lepus californicus and other small animals) due to drought conditions influenced high predation rates in previous years. Predation may have been exacerbated in areas with high levels of subsidized predators. Many historical reports of increased predation, and our observation of a rangewide pattern, may indicate that high predation rates are more common than generally considered and may impact recovery of the desert tortoise throughout its range.

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Section: Discussionmentioning

confidence: 99%

Effects of subsidized predators, resource variability, and human population density on desert tortoise populations in the Mojave Desert, USA

Esque¹,

Nussear²,

Drake³

et al. 2010

Endang. Species. Res.

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“…Prolonged droughts or exposure to extreme heat can cause high mortality [25,26], to which populations with low intrinsic growth rates are especially susceptible [27]. We used the Mojave desert tortoise (Gopherus agassizii) -a long-lived ectothermic herbivore native to the Mojave Desert -to examine potential effects of climate-mediated changes in precipitation on species in arid systems.…”

Section: Introductionmentioning

confidence: 99%

Precipitation quantity and timing affect native plant production and growth of a key herbivore, the desert tortoise, in the Mojave Desert

Nafus

Tuberville

Buhlmann

et al. 2017

Clim Chang Responses

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Background: Deserts may be disproportionately vulnerable to changes in precipitation that accompany global climate change due to complex evolutionary relationships of species to historical conditions. Based on current and projected climate scenarios for the southwestern United States, we manipulated rainfall timing and quantity and measured the response by plants and the growth and behavior of the desert tortoise (Gopherus agassizii) to precipitation in the eastern Mojave Desert. Results: We found that winter-dominant rain -the current prevailing pattern in the eastern Mojave Desert -and greater total rainfall correlated with greater cover and species richness of plants. Winter-dominant rain also correlated with a higher proportion of native plants flowering relative to invasive plants. Juvenile tortoises grew more rapidly when they were subjected to rainfall treatments that associated with increased plant abundance and species richness, while their behavior appeared more driven by water availability. Conclusions: Our results suggest that precipitation timing may be as important as rainfall quantity when considering total effects of climate change on arid-adapted systems. Further research should explore how the timing of rainfall may interact with aridity or temperature to influence total effects due to climate change on arid communities.

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“…What we assume to be predation of healthy tortoises could in fact be scavenging following mortality from disease or drought stress. Upper respiratory tract disease and drought can have serious impacts on adult tortoise survival (Jacobson et al 1991, Longshore et al 2003), though we observed few indications these stressors were involved. Tortoises were tracked on average every 10 d by a team of researchers intimately familiar with assessing physical condition and identifying clinical signs of disease in Agassiz's tortoise.…”

Section: Discussionmentioning

confidence: 76%

“…Alarmingly, periods of high mortality appear to be increasingly common, and are threatening to alter desert tortoise population dynamics (Turner et al 1984, Peterson 1994, Longshore et al 2003, Esque et al 2010, Medica et al 2012, Zylstra et al 2013. Although populations may occasionally be able to rebound from temporary periods of elevated mortality (Germano & Joyner 1988, Zylstra et al 2013, increasing intensity, frequency, and duration of mortality events, coupled with habitat loss and fragmentation and a more physiologically stressful climate (Zylstra et al 2013, Lovich et al 2014 pose serious threats to the persistence of tortoise populations (Brook et al 2008).…”

Section: Discussionmentioning

confidence: 99%

“…Common ravens Corvus corax, coyotes Canis latrans, and mountain lions Puma concolor have been implicated as significant predators on Agassiz's tortoises (Peterson 1994, Boarman 2002, Medica & Greger 2009, Esque et al 2010, and high mortality events, often attributed to drought or a combination of drought and predation, have been documented since the 1980s (Turner et al 1984, Germano & Joyner 1988, Peterson 1994, Longshore et al 2003, Esque et al 2010. Increased mortality can be caused by a combination of anthropogenic and natural factors, but specific causes of mortality need further clarification in order to effectively address population declines.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Severe mortality of a population of threatened Agassiz’s desert tortoises: the American badger as a potential predator

Emblidge¹,

Nussear²,

Esque³

et al. 2015

Endang. Species. Res.

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Desert Tortoise (Gopherus agassizii) Survival at Two Eastern Mojave Desert Sites: Death by Short-Term Drought?

Cited by 61 publications

References 16 publications

Effects of subsidized predators, resource variability, and human population density on desert tortoise populations in the Mojave Desert, USA

Effects of subsidized predators, resource variability, and human population density on desert tortoise populations in the Mojave Desert, USA

Precipitation quantity and timing affect native plant production and growth of a key herbivore, the desert tortoise, in the Mojave Desert

Severe mortality of a population of threatened Agassiz’s desert tortoises: the American badger as a potential predator

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