Effects of Drought on Desert Tortoise Movement and Activity

Duda, Jeffrey J.; Krzysik, Anthony J.; Freilich, Jerome E.

doi:10.2307/3802836

Cited by 97 publications

(111 citation statements)

References 39 publications

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“…Neonatal tortoises that experienced less rainfall also decreased their time spent above ground. Reduced activity in response to lowered water availability has also been found in adult tortoises and other aridadapted reptiles such as the Gila monster, Heloderma suspectum [2,56]. Lowered activity can benefit aridadapted species by reducing evaporative water loss and other metabolic expenditures when water is scarce [57,58].…”

Section: Discussionmentioning

confidence: 99%

“…We used two outdoor enclosures divided into nine pens (each pen was 81 m 2 ) that were open to natural conditions. Enclosures excluded predators of juvenile desert tortoises, including ravens, coyotes, and ground squirrels.…”

Section: Study Sitementioning

confidence: 99%

“…We thus focused on juvenile growth as a proxy for understanding possible demographic responses to altered climate because, it responds more quickly to changing resources and habitat quality than many other demographic metrics [37]. Desert tortoises also exhibit behavioral plasticity, which allow them to alter metabolic expenditures based on water availability [2]. Thus, by measuring tortoise activity in addition to growth, we studied behavioral plasticity that may reduce challenges posed by future climate scenarios.…”

Section: Introductionmentioning

confidence: 99%

“…Water availability can affect many aspects of ecological communities, from primary productivity to activity patterns in wildlife [1,2]. Through the effects of rainfall on reproduction and recruitment, precipitation patterns can influence population structure and inter-and intraspecies interactions [3,4].…”

Section: Introductionmentioning

confidence: 99%

“…Desert tortoises obtain much of their annual energy budget from short, intensive foraging seasons during the spring and late summer when seasonal plants flower and fruit [15,28]. Outside of those seasons or during droughts, tortoises must withstand prolonged resource scarcity [2,29], relying on behavioral and physiological traits to survive [2,30,31]. Overall, the natural history and ecology of desert tortoises are closely tied to rainfall-see Ernst and Lovich [32] for an extensive review.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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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Section: Discussionmentioning

confidence: 99%

Section: Study Sitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

View full text Add to dashboard Cite

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Discriminating patterns and drivers of multiscale movement in herpetofauna: The dynamic and changing environment of the Mojave desert tortoise

Sadoti

Gray

Farnsworth

et al. 2017

Ecology and Evolution

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Changes to animal movement in response to human‐induced changes to the environment are of growing concern in conservation. Most research on this problem has focused on terrestrial endotherms, but changes to herpetofaunal movement are also of concern given their limited dispersal abilities and specialized thermophysiological requirements. Animals in the desert region of the southwestern United States are faced with environmental alterations driven by development (e.g., solar energy facilities) and climate change. Here, we study the movement ecology of a desert species of conservation concern, the Mojave desert tortoise (Gopherus agassizii). We collected weekly encounter locations of marked desert tortoises during the active (nonhibernation) seasons in 2013–2015, and used those data to discriminate movements among activity centers from those within them. We then modeled the probability of movement among activity centers using a suite of covariates describing characteristics of tortoises, natural and anthropogenic landscape features, vegetation, and weather. Multimodel inference indicated greatest support for a model that included individual tortoise characteristics, landscape features, and weather. After controlling for season, date, age, and sex, we found that desert tortoises were more likely to move among activity centers when they were further from minor roads and in the vicinity of barrier fencing; we also found that movement between activity centers was more common during periods of greater rainfall and during periods where cooler temperatures coincided with lower rainfall. Our findings indicate that landscape alterations and climate change both have the potential to impact movements by desert tortoises during the active season. This study provides an important baseline against which we can detect future changes in tortoise movement behavior.

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Integrating telemetry data at several scales with spatial capture–recapture to improve density estimates

et al. 2021

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Accurate population estimates are essential for monitoring and managing wildlife populations. Mark-recapture sampling methods have regularly been used to estimate population parameters for rare and cryptic species, including the federally listed Mojave desert tortoise (Gopherus agassizii); however, the methods employed are often plagued by violations of statistical assumptions, which have the potential to bias density estimates. By incorporating spatial information into conventional density estimation models, spatial capture-recapture (SCR) models can account for common assumption violations such as spatially heterogeneous detection probabilities and temporary emigration when animals leave plots during a survey. We conducted mark-recapture surveys at 10 1-km 2 plots in and adjacent to the Ivanpah Valley of California and Nevada from 2015 to 2019. Locality data were collected concurrently using radio-telemetry and GPS data loggers. GPS data demonstrated that desert tortoises frequently exhibited temporary emigration outside a plot during the survey periods, thereby complicating standard approaches for closed-model density estimation. We integrated mark-recapture survey data for subadults and adults at each plot with corresponding spatial capture locations and supplementary spatial data using a modified SCR model fitted in a Bayesian framework. We compared density estimates modeled with conventional non-spatial methods, as well as three SCR models based on symmetrical usage areas described by various levels and types of supplementary spatial data. The conventional model consistently resulted in inflated estimates of density while the SCR models allowed us to generate spatially corrected estimates for a species where detectability and densities are low. However, we found that if not properly specified, the temporal scale of supplementary data may result in an unintended source of bias in parameter estimates. Integrating spatial data over a larger temporal scale than mark-recapture surveys were conducted resulted in higher detection probabilities and lower density estimates, due to an overestimation of space use. Our results not only demonstrate the importance of accounting for spatial information but also the value of understanding the potential for bias when integrating multiple data sets at different temporal resolutions. The methods presented can be used to enhance monitoring efforts for the Mojave desert tortoise and other species where mark-recapture methods are used.

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Effects of Drought on Desert Tortoise Movement and Activity

Cited by 97 publications

References 39 publications

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

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

Discriminating patterns and drivers of multiscale movement in herpetofauna: The dynamic and changing environment of the Mojave desert tortoise

Integrating telemetry data at several scales with spatial capture–recapture to improve density estimates

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