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For animals exhibiting range residency, the home range is a useful framework to quantify space use. Some reptiles can live decades in the wild and experience extreme environmental variation that influences patterns of habitat use. Individuals may modify their use of space over time, reducing the utility of single‐year home range estimates. Very high frequency (VHF) telemetry data were collected for Gila monsters (Heloderma suspectum) at three Mojave Desert sites in Clark County, Nevada, and home range utilization distributions were calculated using an autocorrelated kernel density estimator. Home range size was consistent within individuals and populations, and home range size did not vary across years at any site. To measure home range fidelity (year‐to‐year reuse), we calculated Bhattacharyya's coefficient (BC) for each combination of years in which an individual was tracked and averaged estimates across individuals and populations. The average BC score was 0.86 (scale from 0 to 1; 0 = no overlap and 1 = complete overlap) and did not vary among populations. We modeled home range area accumulation to estimate the minimum sample size needed for asymptotic stability and found home range accumulation to be dynamic and variable within and across years and individuals. Analysis of the frequency of movement by individuals, average distance traveled per movement, and cumulative distance traveled per active season revealed that movement patterns vary considerably by year. Heterogeneity of space use among populations and individuals suggests that individual and local environmental variation, rather than annual variation in resource availability, may drive home range size and movement patterns of Gila monsters in southern Nevada. Annual variability in movement patterns did not translate to variability in home range size or location, and the species exhibits extremely high philopatry, using the same areas for periods of at least 3–5 years. [ABSTRACT FROM AUTHOR]

The distribution and abundance of human-caused disturbances vary greatly through space and time and are cause for concern among land stewards in natural areas of the southwestern border-lands between the USA and Mexico. Human migration and border protection along the international boundary create Unauthorized Trail and Road (UTR) networks across National Park Service lands and other natural areas. UTRs may cause soil erosion and compaction, damage to vegetation and cultural resources, and may stress wildlife or impede their movements. We quantify the density and severity of UTR disturbances in relation to soils, and compare the use of previously established targeted trail assessments (hereafter -- targeted assessments) against randomly placed transects to detect trail densities at Coronado National Memorial in Arizona in 2011. While trail distributions were similar between methods, targeted assessments estimated a large portion of the park to have the lowest density category (0-5 trail encounters per km2), whereas the random transects in 2011 estimated more of the park as having the higher density categories (e.g., 15-20 encounters per km2 category). Soil vulnerability categories that were assigned, a priori, based on published soil texture and composition did not accurately predict the impact of UTRs on soil, indicating that empirical methods may be better suited for identifying severity of compaction. While the estimates of UTR encounter frequencies were greater using the random transects than the targeted assessments for a relatively short period of time, it is difficult to determine whether this difference is dependent on greater cross-border activity, differences in technique, or from confounding environmental factors. Future surveys using standardized sampling techniques would increase accuracy. [ABSTRACT FROM AUTHOR]

We challenged the common practice of using a single mean absorptance based on unfiltered skylight spectra to model operative temperature for reptiles in filtered light habitats by examining the effects of plant canopies on light transmittance. To assess differences in light filtration over a range of microhabitats, spectra were recorded under canopies of desert plants, tropical plants, and under unfiltered skylight. Spectra were then integrated with absorptivity curves of desert reptiles to determine if differences in light quality among microhabitat types changed integrated mean absorptance. Finally, we used the desert tortoise (Gopherus agassizii) as a case study to investigate the effects of filtered microhabitats on paint choice for physical operative temperature models and determined the magnitude of error that could result from discrepancies between paint and animal absorptance. We found that light energy was partitioned similarly among microhabitats with like canopy types and that most variation was explained by differences in transmittance between the visible and near infrared wavelengths. Mean absorptance for reptiles was similar among microhabitats with the greatest differences observed between animals in unfiltered skylight and under tropical canopies. In most microhabitats paint and tortoise absorptances differed, but operative temperatures were nearly identical within microhabitats no matter the absorptance used in the model. The findings of this study support the use of a single mean absorptance in modeling operative temperature for reptiles in a variety of habitats., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Our experiments were designed to test the hypotheses that dietary lipids can affect whole-animal physiological processes in a manner concordant with changes in the fluidity of cell membranes. We measured (1) the lipid composition of five tissues, (2) body temperatures selected in a thermal gradient (T(sel)), (3) the body temperature at which the righting reflex was lost (critical thermal minimal [CTMin]), and (4) resting metabolic rate (RMR) at three body temperatures in desert iguanas (Dipsosaurus dorsalis) fed diets enriched with either saturated or unsaturated fatty acids. The composition of lipids in tissues of the lizards generally reflected the lipids in their diets, but the particular classes and ratios of fatty acids varied among sampled organs, indicating the conservative nature of some tissues (e.g., brain) relative to others (e.g., depot fat). Lizards fed the diet enriched with saturated fatty acids selected warmer nighttime body temperatures than did lizards fed a diet enriched with unsaturated fatty acids. This difference is concordant with the hypothesis that the composition of dietary fats influences membrane fluidity and that ectotherms may compensate for such changes in fluidity by selecting different body temperatures. The CTMin of the two treatment groups was indistinguishable. This may reflect the conservatism of some tissues (e.g., brain) irrespective of diet treatment. The RMR of the saturated treatment group nearly doubled between 30 degrees and 40 degrees C. Here, some discrete membrane domains in the lizards fed the saturated diet may have been in a more-ordered phase at 30 degrees C and then transformed to a less-ordered phase at 40 degrees C. In contrast, the RMR of the unsaturated treatment group exhibited temperature independence in metabolic rate from 30 degrees to 40 degrees C. Perhaps the unsaturated diet resulted in membranes that developed a higher degree of disorder (i.e., a certain phase) at a lower temperature than were membranes of lizards fed the saturated diet. Our study demonstrates links between dietary fats and whole-animal physiology; however, the mechanistic basis of these links, and the general knowledge of lipid metabolism in squamate reptiles, remain poorly understood and warrant further study.