Mojave desert tortoise (Gopherus agassizii) thermal ecology and reproductive success along a rainfall cline

Desert resource environments (e.g. microclimates, food) are tied to limited, highly localized rainfall regimes which generate microgeographic variation in the life histories of inhabitants. Typically, enhanced growth rates, reproduction and survivorship are observed in response to increased resource availability in a variety of desert plants and short‐lived animals. We examined the thermal ecology and reproduction of US federally threatened Mojave desert tortoises (Gopherus agassizii), long‐lived and large‐bodied ectotherms, at opposite ends of a 250‐m elevation‐related rainfall cline within Ivanpah Valley in the eastern Mojave Desert, California, USA. Biophysical operative environments in both the upper‐elevation, “Cima,” and the lower‐elevation, “Pumphouse,” plots corresponded with daily and seasonal patterns of incident solar radiation. Cima received 22% more rainfall and contained greater perennial vegetative cover, which conferred 5°C‐cooler daytime shaded temperatures. In a monitored average rainfall year, Cima tortoises had longer potential activity periods by up to several hours and greater ephemeral forage. Enhanced resource availability in Cima was associated with larger‐bodied females producing larger eggs, while still producing the same number of eggs as Pumphouse females. However, reproductive success was lower in Cima because 90% of eggs were depredated versus 11% in Pumphouse, indicating that predatory interactions produced counter‐gradient variation in reproductive success across the rainfall cline. Land‐use impacts on deserts (e.g. solar energy generation) are increasing rapidly, and conservation strategies designed to protect and recover threatened desert inhabitants, such as desert tortoises, should incorporate these strong ecosystem‐level responses to regional resource variation in assessments of habitat for prospective development and mitigation efforts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111753/1/inz212132.pd

Data from: Mammalian metabolic allometry: do intraspecific variation, phylogeny, and regression models matter?

Power scaling relationships between body mass and organismal traits are fundamental to biology. Compilations of mammalian masses and basal metabolic rates date back over a century and are used both to support and to assail the universal quarter‐power scaling invoked by the metabolic theory of ecology. However, the slope of this interspecific allometry is typically estimated without accounting for intraspecific variation in body mass or phylogenetic constraints on metabolism. We returned to the original literature and culled nearly all unique measurements of body mass and basal metabolism for 695 mammal species and (1) phylogenetically corrected the data using the fullest available phylogeny, (2) applied several different regression analyses, (3) resampled regressions by drawing randomly selected species from each of the polytomies in the phylogenetic hypothesis at each iteration, and (4) ran these same analyses independently on separate clades. Overall, 95% confidence intervals of slope estimates frequently did not include 0.75, and clade‐specific slopes varied from 0.5 to 0.85, depending on the clade and regression model. Our approach reveals that the choice of analytical model has a systematic influence on the estimated allometry, but irrespective of the model applied, we find little support for a universal metabolic rate–body mass scaling relationship

High beach temperatures increased female-biased primary sex ratios but reduced output of female hatchlings in the leatherback turtle

Sex of offspring in most turtles is determined by temperature-dependent sex determination (TSD). In sea turtles, higher incubation temperatures produce female hatchlings and primary sex ratios are often highly female-biased. Because of the current rate of climate warming, highly female-biased sex ratios have raised concern among scientists and managers because populations might become too female biased for genetic viability.We tested the effects of higher incubation temperatures on embryo and hatchling mortality and on sex ratios in a population of leatherback turtles (Dermochelys coriacea) in the eastern Pacific. The long-term study provided a large sample size in a location influenced by El Niño Southern Oscillation that resulted in highly variable climatic conditions between seasons. High temperatures reduced emergence success. Output of female hatchlings increased with incubation temperature as it reached the upper end of the transitional range (range of temperatures that produce both sexes) (30. °C) and decreased afterwards because high temperatures increased mortality of 'female clutches'. Effect of temperature on female hatchling output lessened female-biased sex ratios from 85% female primary sex ratios to 79% secondary sex ratios (sex ratios of total number of hatchlings emerged). If male turtles reproduce more often than females, operational sex ratios will be closer to 1:1. Female-biased primary sex ratios should not raise concerns by default, but climate change may still threaten populations by reducing hatchling output and increasing frequency of seasons with 100% female production. Clutch relocation to cooler conditions may alter sex ratios and should be used cautiously unless temperatures are so high that no hatchlings survive. In addition, it is unknown what differential survival of male versus female hatchlings may have on the eventual adult sex ratio after they enter the ocean and disperse. © 2014 Elsevier Ltd.Funding was provided by the Earthwatch Institute, The Betz Chair Endowment of Drexel University, The Leatherback Trust, The Goldring Family Foundation, The Schrey Distinguished Professorship of Indiana University-Purdue University Fort Wayne, the Balearic Government (FEDER funds) and by a Marie Curie International Incoming Fellowship within the 7th European Community Framework ProgrammePeer Reviewe