Geology topics

Lisa L. Lyren

Publications and source records attributed to Lisa L. Lyren.

3 recordsLinked to original sources

USGS2020

An uncertain future for a population of desert tortoises experiencing human impacts

We evaluated the status of a population of Mojave Desert Tortoises ( Gopherus agassizii ), a threatened species, in the El Paso Mountains of the northwestern Mojave Desert in California, USA. The study area lies north of and adjacent to a designated critical habitat unit for the species, is adjacent to a state park, and is a short distance from the Desert Tortoise Research Natural Area. We randomly sampled 373 1-ha plots from a 239.1-km 2 area in the mountain range to determine demographic attributes of the population, vegetation associations, predator presence, and human uses. Live and dead G. agassizii and sign (burrows, scats, tracks) occurred on 35.7% of plots. Densities of adults were higher than in adjacent critical habitat, and threats (traumatic injuries, infectious and other diseases) were similar to those reported elsewhere in the geographic range. Signs of human use were evident on 98.4% of plots. We used a multimodel approach to determine distribution of G. agassizii in relation to vegetation, anthropogenic, and predator variables. Vegetation, predators, trash, mining activity, and vehicles were important factors affecting the distribution and intensity of tortoise sign. We concluded that this population is in a downward trend, like other populations in the western Mojave Desert. The high death rate of adults, low population density, high human visitor use, and ongoing decline in the adjacent critical habitat unit indicate that a viable population is unlikely to persist in the study area. The future for the population found in the El Paso Mountains might depend on survival in the adjacent roadless El Paso Mountains Wilderness Area.

California↗

USGS2020

Feral burros and other influences on desert tortoise presence in the western Sonoran Desert

Across the globe, conflicting priorities exist in how land and resources are managed. In the American West, conflicts are common on public lands with historical mandates for multiple uses. We explored the impacts of multiple uses of land in a case study of Agassiz's Desert Tortoises ( Gopherus agassizii ), a federally threatened species, in the western Sonoran Desert. The tortoise has declined for many reasons, most of which relate to management of land and habitat. Frequently cited causes are livestock grazing, roads, vehicle-oriented recreation, predators, and disease. In spring of 2009, we conducted a survey to evaluate relationships between desert tortoises, vegetation associations, topography, predators, and anthropogenic uses. We sampled a 93-km 2 area with 200 independent 1-ha plots. Density (± SE) of adult tortoises was low, 2.0 ± 1.0/km 2 , and the annualized death rate for adults during the 4 yr preceding the survey was high, 13.1%/yr. We observed tortoise sign, most of which was recent, on 22% of the 200 plots, primarily in the southwestern part of the study area. More tortoise sign occurred on plots with Brittlebush ( Encelia spp.) vegetation at higher elevations. Most plots (91.0%) had ≥1 human-related impacts: feral burro scat ( Equus asinus ; 84.0%), recent vehicle tracks and trails (34.0%), trash (28.0%), burro trails and wallows (26.5%), and old vehicle tracks (24.0%). We used a multimodel approach to model presence of tortoise sign on the basis of 12 predictor variables, and calculated model-averaged predictions for the probability of tortoise presence. Importance values revealed two apparent top drivers: feral burros and vegetation association. This is the first study to identify a negative association between presence of desert tortoises and feral burros.

Arizona, California↗

USGS2016

A synthetic review of notoedres species mites and mange

Notoedric mange, caused by obligately parasitic sarcoptiform Notoedres mites, is associated with potentially fatal dermatitis with secondary systemic disease in small mammals, felids and procyonids among others, as well as an occasional zoonosis. We describe clinical spectra in non-chiropteran hosts, review risk factors and summarize ecological and epidemiological studies. The genus is disproportionately represented on rodents. Disease in felids and procyonids ranges from very mild to death. Knowledge of the geographical distribution of the mites is highly inadequate, with focal hot spots known for Notoedres cati in domestic cats and bobcats. Predisposing genetic and immunological factors are not known, except that co-infection with other parasites and anticoagulant rodenticide toxicoses may contribute to severe disease. Treatment of individual animals is typically successful with macrocytic lactones such as selamectin, but herd or wildlife population treatment has not been undertaken. Transmission requires close contact and typically is within a host species. Notoedric mange can kill half all individuals in a population and regulate host population below non-diseased density for decades, consistent with frequency-dependent transmission or spillover from other hosts. Epidemics are increasingly identified in various hosts, suggesting global change in suitable environmental conditions or increased reporting bias.

Parasitology↗