Geology topics

Chris E. Lowrey

Publications and source records attributed to Chris E. Lowrey.

5 recordsLinked to original sources

USGS2017

Tolerance to disturbance regulated by attractiveness of resources: A case study of desert bighorn sheep within the River Mountains, Nevada

Human activity may mimic predation risks for wildlife by causing abandonment of foraging sites and increasing expenditure of energy. Animals that can tolerate nonlethal disturbance may minimize these fitness costs. We examine this aspect of the risk—disturbance hypothesis by first analyzing recent habitat use of desert bighorn sheep relative to areas of attraction and disturbance. We then compare and contrast sheep responses to differing levels of anthropogenic disturbance between 2 time periods, 30 years apart. Desert bighorn sheep were tolerant of suburban activity when a consistent forage resource (municipal grass) was provided. Males were more tolerant than females, and females returned to natural, steep areas during the birthing season. Increased recreation activity, specifically mountain bike use, may have resulted in avoidance by sheep of otherwise suitable habitat that had been occupied decades earlier, thereby reducing availability of limited habitat. Tolerance increased only when attractiveness was relatively high and decreased as perceived fitness decreased, supporting risk—disturbance theory.

Nevada↗

USGS2016

Foraging at the wildland–urban interface decouples weather as a driver of recruitment for desert bighorn sheep

A growing number of ungulate populations are living within or near the wildland–urban interface. When resources at the interface are of greater quality than that of adjacent natural habitat, wildlife can be attracted to these developed areas. Little is known about how use of the wildland–urban interface by wildlife may affect vital rates. Under natural conditions, recruitment by desert bighorn sheep ( Ovis canadensis nelsoni ) correlates with variation in the timing and amount of rainfall that initiates and enhances growth of annual plant species. However, for populations that forage in developed areas, this relationship may become decoupled. In the River Mountains of Nevada, USA, desert bighorn sheep have been feeding in a municipal park at the wildland–urban interface since its establishment in 1985. Approximately one-third of the population now uses the park during summer months when nutritional content of natural forage is low. We hypothesized that use of this municipal area, with its abundant vegetation and water resources, may have decoupled the previous relationship between precipitation and lamb recruitment. We assessed variables known to affect lamb recruitment before (1971–1986) and after (1987–2006) establishment of the park using linear regression models. Our top candidate model for the pre-park period indicated that total November precipitation was the greatest driver of lamb recruitment in this population. After park establishment, this relationship became decoupled because lamb recruitment was no longer driven by weather variables. These results raise questions about the effects of decoupling drivers of population growth and maintaining natural populations near urban areas.

Nevada↗

USGS2016

Ecology, distribution, and predictive occurrence modeling of Palmers chipmunk ( Tamias palmeri ): a high-elevation small mammal endemic to the Spring Mountains in southern Nevada, USA

Although montane sky islands surrounded by desert scrub and shrub steppe comprise a large part of the biological diversity of the Basin and Range Province of southwestern North America, comprehensive ecological and population demographic studies for high-elevation small mammals within these areas are rare. Here, we examine the ecology and population parameters of the Palmer’s chipmunk ( Tamias palmeri ) in the Spring Mountains of southern Nevada, and present a predictive GIS-based distribution and probability of occurrence model at both home range and geographic spatial scales. Logistic regression analyses and Akaike Information Criterion model selection found variables of forest type, slope, and distance to water sources as predictive of chipmunk occurrence at the geographic scale. At the home range scale, increasing population density, decreasing overstory canopy cover, and decreasing understory canopy cover contributed to increased survival rates.

Nevada↗

USGS2015

Habitat selection and survival of pronghorn fawns at the Carrizo Plain National Monument, California

On the Carrizo Plain National Monument (CPNM), California, little is known about survival rates and habitat characteristics of pronghorn fawns (Antilocapra americana). A marked decline in pronghorn numbers on the CPNM (from approximately 200 to <30 individuals from 1989 to 2011) prompted a study of fawn habitat use and fawn survival from 2009 to 2011. Only 45 fawns were born during this period. We attached GPS collars to 44% of these fawns (<5 days-of-age). We then used the locations of collared fawns to develop two separate binary logistic regression models to explore the best combination of micro- and macrohabitat-scale environmental variables for predicting (1) fawn habitat selection and (2) fawn survival. Model results for habitat selection showed that fawn locations were associated with increased concealment at close distances (5 m and 50 m) and decreased concealment at far distances (100 m). Fawn locations were on lower sloped terrain and closer to available drinking water and saltbush (Atriplex spp.). Model results for fawn survival showed that increased survival time was associated with higher sloped terrain, proximity to available drinking water and saltbush, and increased distance from high-use roads. Collectively, these results demonstrate that fawn habitat selection is scale-dependent and likely influenced by the combined spatio-temporal needs of both females and their young. The results of this study can be used to inform critical management actions on the CPNM.

California↗

USGS2009

Nocturnal movements of desert bighorn sheep in the Muddy Mountains, Nevada

Adequate management of a species requires complete knowledge of its ecology, including both nocturnal and diurnal behavior. Knowledge of the movement behavior of bighorn sheep can provide insight for understanding spatial population processes as the combined result of individual behavior, physiological constraints, and fine-scale environmental influences. However, because of past difficulties in tracking radio-collared animals in the dark, little is known about nocturnal movements of many ungulates, including desert bighorn sheep (Ovis canadensis nelsoni). The use of GPS collars that supply sequential location records over a 24-hour period has provided new opportunities for recording movements of animals. We report findings from a preliminary analysis of data on nocturnal movements of desert bighorn sheep wearing GPS collars in the Muddy Mountains, Nevada. The study is part of a larger research project on movement patterns aimed at assessing the connectivity of bighorn sheep populations that comprise the metapopulation in southern Nevada. We recorded nighttime locations at 2100 and 0400 PST and calculated a total of 8,758 nocturnal movement distances for 12 ewes and 16 rams. Nocturnal movements were characteristic of all individuals. Bighorn sheep varied in the magnitude of movement from night to night and there were significant differences among individuals in the mean distance moved. Females had a greater proportion of short movement distances when compared to males; males had the greatest proportion of long distance movements. Movement distances were affected by sex, season, and percent of the moon’s surface illumination. Mean movement distances of males were greater than those of females. For both males and females, mean movement distances were shortest during the late spring months (April-June) and greatest during summer (July–September). Mean movement distances were greatest when the moon was brightest for all seasons except late spring, when movement distances for both sexes were shortest. We also describe movement distances >1 km (19% ewes, 81% rams) relative to movements within or between 50% core use areas, and nighttime intermountain and intra-mountain travel.

Black Mountain, Muddy Mountain↗