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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.

Many sea turtle nesting colonies are in decline worldwide, and a common conserva- tion practice maximizes hatchling production by translocating eggs from threatened nests to pro- tective beach hatcheries. Typically, translocated eggs are 'doomed', or at risk of death due to tidal inundation, predation, or poaching. Sea turtles exhibit temperature-dependent sex determination. We determined how primary sex ratios, estimated from incubation temperatures, were affected by egg clutch translocation to a beach hatchery. We monitored incubation temperatures of eastern Pacific leatherback turtles Dermochelys coriacea in hatchery and in situ clutches at Playa Grande, Costa Rica, throughout each nesting season from 1998 to 2007. In situ clutches were estimated to be 90% female, whereas hatchery clutches (9% of clutches) were estimated to be 64% female. Taking into account differences in hatching success of in situ and hatchery nests, the overall sex ratio was 83% female. The Playa Grande hatchery abiotic environment (sand temperatures, water inputs) was similar to that in situ. However, metabolic heating was significantly reduced in hatch- ery clutches. The most likely explanation is that temperatures in hatchery clutches were cooler (less female-biased) due to decreases in the number of metabolizing embryos since hatchling suc- cess was lower in hatchery clutches than in situ clutches. Alteration of both primary sex ratios and hatching success is the tradeoff for reducing the risk of death to egg clutches by translocation to a hatchery. This tradeoff is not unique to Playa Grande leatherback turtles, and it is a strong indica- tion that hatchery translocation should be used cautiously.

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.

The recently proposed metabolic theory of ecology (MTE) claims to provide a mechanistic explanation for long known allometric relationships between mass and metabolic rate. The MTE postulates that these patterns of allometry are driven by the primary selective constraint of transport of energy and materials. However, recent evidence along several different lines has called into question both the adequacy and the universality of this mechanism. We review the accumulating body of literature on this subject, adding our own concerns and criticisms. In addition to other difficulties, we argue that MTE fails as a mechanistic explanation of mass versus metabolic rate allometries because: 1) circulatory cost minimization is not a tenable criterion for evolutionary optimization, 2) the Boltzmann type relationships on which MTE depends are inadequate descriptors of complex metabolic pathways, and 3) most of the hypotheses advanced by the MTE do not, in fact, depend on the proposed mechanism and therefore cannot be used to test the theory. We conclude that the MTE should be abandoned as a monolithic explanation for allometric patterns, and that a more realistic path toward a better understanding of allometry would be to consider multiple explanatory mechanisms for physiological allometries.

We present an approach to delineating physiological effects on population level processes by modeling the activity and resource budgets of animals. Physiology and its environmental forcing functions are assumed to affect both the total time available for activity and foraging and the resource budgets by affecting resource acquisition, costs, and handling. We extend the earlier model of Dunham and others (1989) and translate it into a computational algorithm. To satisfy conservation needs for accuracy, wide applicability, and rapid deployment, the model is relatively simple, uses as much data on the focal organism as possible, is mechanistically driven, and can be adapted to new organisms by using data for the new species, or the best available approximations to those data. We present 2 applications of the modeling approach. First, we consider a system with substantial information available, canyon lizards (Sceloporus merriami) studied by Dunham and colleagues in west Texas. In this case the focus is on integration of numerous inputs and the ability of the model to produce predictions that approximate counterintuitive empirical patterns. By using the wealth of specific data available, the model outperforms previous attempts at explanation of those patterns. Next, we consider a system with much less available information (forest-dwelling semi-fossorial frogs). The question here is how hydric conditions can become limiting. A model of evaporation from frogs buried in leaf litter was incorporated and it demonstrates how rainfall patterns can both supply water and put the frogs at risk of critical dehydration.

The possibility of nest site fidelity of leatherback turtles, Dermochelys coriacea, raises concerns about the merit of translocating poorly located clutches to a safe hatchery. Specifically, if some females habitually nest in areas where the probability of egg survival is low because of tidal inundation, nest relocation may inadvertently select for turtles that make poor nest site selections. We investigate the nest site fidelity of leatherbacks by studying consecutive nest site selections by leatherbacks at Playa Grande, Costa Rica, from 1993 to 2001. Along the ocean-to-vegetation axis, consecutive nest placements were independent (G42=4.737, P=0.315). Regardless of previous zone choices, leatherbacks typically nested in the open beach above the high tide line and away from vegetation. Thus, concerns about translocation of poorly located nests are unfounded. Along the coastal axis, however, an independence model was rejected (G362=145.179, P 0.001 ). The log-linear model-based analysis we developed and applied indicated that the pattern of dependence in nest site locations is more consistent with a hypothesis of spatial proximity in which leatherbacks simply nest close to the site of the previous nest than it is with a hypothesis of intrinsic fidelity to a specific location on the beach. Our model-based approach is suitable for other settings where longitudinal nesting data are available.

Limb preference is a behavioral indicator of lateralized brain function that was recently elucidated experimentally in lower vertebrates. We assessed natural spontaneous limb use of nesting eastern Pacific leatherback turtles by recording which hindlimb flipper was extended overtop the cloaca to cover the egg chamber during oviposition. We found a population level right bias in 1889 observations of 361 individuals. This is the first report of a limb preference in Testudinata.