Range‐wide occupancy trends for the Mojave desert tortoise (<i>Gopherus agassizii</i>)

Kissel, Amanda M.; Wallace, Bryan P.; Anderson, Jesse J.; Dickson, Brett G.; Neste, Kristen Van; Landau, Vincent A.; Averill‐Murray, Roy C.; Allison, Linda; Fesnock, Amy

doi:10.1002/ecs2.4462

Cited by 5 publications

(3 citation statements)

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“…Gopher tortoises ( Gopherus spp. ), for example, are considered as keystone species due to their propensity to dig burrows that other animals could then use as refugia (Catano & Stout, 2015), and populations of the Mojave Desert tortoise ( G. agassizii ) have declined dramatically over the course of the late 20th and 21st centuries (Kissel et al., 2023).…”

Section: Discussionmentioning

confidence: 99%

“…Here we conduct a resistance‐based community viability analysis (Eichenwald & Reed, 2021) of the terrestrial community of the Mojave Desert, a well‐studied ecosystem in the southwest United States (e.g., Iknayan & Beissinger, 2018; Kissel et al., 2023; Rundel & Gibson, 1996a, 1996b, 1996c, 1996d, 1996e). We did this by first constructing a food web and then examining the potential cascading loss of species following initial species losses.…”

Section: Introductionmentioning

confidence: 99%

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Potential extinction cascades in a desert ecosystem: Linking food web interactions to community viability

Eichenwald,

Fefferman,

Reed

2024

Ecology and Evolution

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Desert communities are threatened with species loss due to climate change, and their resistance to such losses is unknown. We constructed a food web of the Mojave Desert terrestrial community (300 nodes, 4080 edges) to empirically examine the potential cascading effects of bird extinctions on this desert network, compared to losses of mammals and lizards. We focused on birds because they are already disappearing from the Mojave, and their relative thermal vulnerabilities are known. We quantified bottom‐up secondary extinctions and evaluated the relative resistance of the community to losses of each vertebrate group. The impact of random bird species loss was relatively low compared to the consequences of mammal (causing the greatest number of cascading losses) or reptile loss, and birds were relatively less likely to be in trophic positions that could drive top‐down effects in apparent competition and tri‐tropic cascade motifs. An avian extinction cascade with year‐long resident birds caused more secondary extinctions than the cascade involving all bird species for randomized ordered extinctions. Notably, we also found that relatively high interconnectivity among avian species has formed a subweb, enhancing network resistance to bird losses.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Potential extinction cascades in a desert ecosystem: Linking food web interactions to community viability

Eichenwald,

Fefferman,

Reed

2024

Ecology and Evolution

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“…Due to these threats, the Mojave desert tortoise is currently listed as a threatened species under the U.S. Endangered Species Act and conservation efforts are ongoing to protect remaining habitat, monitor populations, and minimize other threats to the species as it continues to decline 24 – 26 .…”

Section: Introductionmentioning

confidence: 99%

Indirect impacts of a highway on movement behavioral states of a threatened tortoise and implications for landscape connectivity

Harju,

Cambrin,

Berg

2024

Sci Rep

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Roads have often been identified as barriers to the movement of free-ranging animals. However, whether restoration of landscape connectivity across roadways can mitigate barriers to movement is insufficiently understood in light of indirect effects of roads on wildlife movement. We GPS-tagged free-ranging Mojave desert tortoises (Gopherus agassizii) to quantify movement behavioral states using hidden Markov models in relation to a major highway and to document use of existing, permeable culverts. We then used the observed movement behaviors to parameterize simulations of tortoise movement to evaluate alternative culvert designs and placements for enhancing connectivity across the roadway. Tortoises were most active during mid-day, in warm temperatures, and when close to the highway. The highway affected transition probabilities between movement states, as females were more likely than males to switch to an energy-demanding traveling movement state, remain in that state, and move farther than usual within that state. In contrast, males were more likely than females to continue in the low-energy resting state when close to the highway, but if traveling, to travel farther than usual. We observed two highway crossings by a tagged tortoise, which was a higher rate of crossing than in simulated tortoises. Simulated crossing rates increased with culvert size and culvert density, and size and density appeared more important for crossing than if culverts were placed singly or in pairs. Existing culvert densities across the region appeared potentially sufficient for long-term genetic connectivity, but only if retrofitted to allow for tortoise access and passing. We concluded that existing highway traffic may indirectly depress tortoise populations adjacent to the highway, particularly via negative impacts to female movements, and that existing culverts in washes should be retrofitted to allow for periodic tortoise crossings to improve structural connectivity for occasional passage.

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Range‐wide occupancy trends for the Mojave desert tortoise (Gopherus agassizii)

et al. 2023

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Data from long‐term monitoring programs, such as the US Fish and Wildlife Service (USFWS) line distance sampling (LDS) program for Mojave desert tortoises (Gopherus agassizii), are increasingly being used in new ways to elucidate trends in population dynamics. We used the USFWS LDS data in a novel way to generate range‐wide predictions of occupancy, colonization, and local extinction rates from 2001 to 2018. We developed a dynamic occupancy model to answer fundamental questions posed by Bureau of Land Management personnel regarding how G. agassizii are distributed across the landscape over space and time. We transformed the LDS data into detection/nondetection data and constructed a Bayesian dynamic occupancy model using several time‐varying (e.g., temperature, precipitation, normalized difference vegetation index, fire, and a proxy for invasive grasses) and static covariates (e.g., soil properties, topography, distance to roads, distance to urban areas) hypothesized to influence G. agassizii occupancy dynamics. We estimated that over the entire time series (2001–2018) the probability of G. agassizii occupancy is declining in over one quarter (26%) of the range, largely in the northeastern part of the range, but that from 2011 to 2018, 77% of the range has a declining trend. Drawing on these model outputs, we developed an interactive, web‐based tool for exploring trends in dynamic occupancy across the species range, allowing users to focus on areas of management interest or concern.

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Range‐wide occupancy trends for the Mojave desert tortoise (Gopherus agassizii)

Cited by 5 publications

References 50 publications

Potential extinction cascades in a desert ecosystem: Linking food web interactions to community viability

Potential extinction cascades in a desert ecosystem: Linking food web interactions to community viability

Indirect impacts of a highway on movement behavioral states of a threatened tortoise and implications for landscape connectivity

Range‐wide occupancy trends for the Mojave desert tortoise (Gopherus agassizii)

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