Reproductive Ecology and Life History of Female Sonoran Desert Tortoises (<i>Gopherus morafkai</i>)

Averill‐Murray, Roy C.; Christopher, Terry E.; Henen, Brian T.

doi:10.1655/herpmonographs-d-18-00003.1

Cited by 9 publications

(4 citation statements)

References 92 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We found that, in general, there was a low probability of extinction of an occupied cell, and conversely, a relatively low probability of colonization, congruent with the biology of a long‐lived species with high adult survival and limited rates of adult emigration/immigration (Averill‐Murray et al, 2020). However, the average colonization probability (0.03) was three times higher than extinction probability (0.01), resulting in generally increasing probability of occupancy through time.…”

Section: Discussionsupporting

confidence: 70%

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

et al. 2023

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionsupporting

confidence: 70%

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

et al. 2023

View full text Add to dashboard Cite

show abstract

“…Consequently, female S. minor does not display condition‐dependent HLR in the field; unlike males, lack of competition among females may select for constant HLR (Figure 1). This suggests that female S. minor invest in capital resources, unlike males (Averill‐Murray et al, 2018). The energy that could be used to defend territories and resources is likely allocated into somatic growth, reproduction, or both to increase fitness.…”

Section: Discussionmentioning

confidence: 99%

Sex‐based trade‐offs in the innate and acquired immune systems of Sternotherus minor

2020

View full text Add to dashboard Cite

Longevity patterns in most vertebrates suggest that females benefit most from maintenance investment. A reversed longevity pattern in loggerhead musk turtles (Sternotherus minor) allowed us to test trade‐offs between maintenance and survivorship. We tested the hypothesis that the sex with greater longevity has greater maintenance than the sex with shorter longevity. We also compared the following parameters between sexes: Bactericidal ability (BA) and heterophil:lymphocyte ratios (HLR). Baseline blood samples were collected from turtles in the field; a subset of turtles was returned to a laboratory for experiments of acquired immune responses to sheep red blood cells (SRBC). We found no support for the original hypothesis of reversal in sex‐dependent immune trade‐offs (difference between sex SRBC titers: p = .102; interaction between treatment and sex: p = .177; difference between treatments: p < .001; effect of sex on BA: p = .830; effect of sex on HLR: p = .717). However, we did find support for sex‐dependent differences in immunity in the relationship between HLR and body condition (BCI) (effect of BCI on HLR: p = .015). In field conditions, we found that males with higher body condition indices express stressed phenotypes more than males with lower body condition indices (p = .002). However, females expressed similar stress loads across all body conditions (p = .900). Testosterone concentrations were assayed in free‐living turtles and were not related to any of the immune parameters. Our results suggest that the immune systems play an important role in balancing sex‐specific responses to different selective pressures in S. minor.

show abstract

“…To calculate an area from the MCP, we removed tortoises with <3 unique locations. Traditional methods like MCP were recommended for studies of herpetofauna, even though these methods may include areas of unusable habitat or underestimate areas of habitat use (Row and Blouin-Demers, 2006;Fleming et al, 2015;Averill-Murray et al, 2020).…”

Section: Movements and Home Rangementioning

confidence: 99%

Variations in climate drive behavior and survival of small desert tortoises

2023

View full text Add to dashboard Cite

In the Mojave Desert, timing and amounts of precipitation profoundly affect the availability of water and annual plant foods necessary for the threatened Agassiz’s desert tortoise (Gopherus agassizii) to survive, especially during prolonged droughts. As part of recovery actions to increase declining populations, we translocated 83 juvenile and young desert tortoises raised in head-start pens for 4–10 years to a new location 15 km away during the fall of 2013 and 2014. We tracked them for 9 years during a megadrought, during multiple years of low rainfall, and a few years when precipitation neared or exceeded long-term norms. We evaluated behaviors and how precipitation and forage availability affected survival. At the end of the study, 21.6% of tortoises were alive, and six had grown to adulthood. Annual models of survival indicated that tortoise size was the driving variable in most years, followed by the number of repeatedly used burrows during periods of temperature extremes. Other variables affecting survival in ≥1 year were vegetation, movements during the first 2 years post-translocation, and condition index, a measure of health. Tortoises moved more, expanded home ranges, and grew rapidly in years when winter rainfall approached or exceeded long-term norms and annual plants were available to eat. During dry years, movements and growth were limited. Exceptions to this pattern occurred in the last year of study, a dry year: tortoises grew and moved more, and home ranges increased. The increase in size and approaching adulthood may have stimulated greater traveling. Some left the study area, indicating a need for large release areas. We may have aided survival by offering water twice yearly when handling because some tortoises drank and increased in mass up to 40%. Prolonged droughts and hotter temperatures can limit the recovery of populations, reduce the survival of young tortoises, and increase the time to maturity.

show abstract

Reproductive Ecology and Life History of Female Sonoran Desert Tortoises (Gopherus morafkai)

Cited by 9 publications

References 92 publications

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

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

Sex‐based trade‐offs in the innate and acquired immune systems of Sternotherus minor

Variations in climate drive behavior and survival of small desert tortoises

Contact Info

Product

Resources

About