Predicting reptile distributions at the mesoscale: relation to climate and topography

Aim To explore the respective power of climate and topography to predict the distribution of reptiles in Switzerland, hence at a mesoscale level. A more detailed knowledge of these relationships, in combination with maps of the potential distribution derived from the models, is a valuable contribution to the design of conservation strategies. Location All of Switzerland. Methods Generalized linear models are used to derive predictive habitat distribution models from eco‐geographical predictors in a geographical information system, using species data from a field survey conducted between 1980 and 1999. Results The maximum amount of deviance explained by climatic models is 65%, and 50% by topographical models. Low values were obtained with both sets of predictors for three species that are widely distributed in all parts of the country (Anguis fragilis, Coronella austriaca, and Natrix natrix), a result that suggests that including other important predictors, such as resources, should improve the models in further studies. With respect to topographical predictors, low values were also obtained for two species where we anticipated a strong response to aspect and slope, Podarcis muralis and Vipera aspis. Main conclusions Overall, both models and maps derived from climatic predictors more closely match the actual reptile distributions than those based on topography. These results suggest that the distributional limits of reptile species with a restricted range in Switzerland are largely set by climatic, predominantly temperature‐related, factors.     

Exploring the evolution of environmental sex determination, especially in reptiles

Environmental sex determination has been documented in a variety of organisms for many decades and the adaptive significance of this unusual sex-determining mechanism has been clarified empirically in most cases. In contrast, temperature-dependent sex determination (TSD) in amniote vertebrates, first noted 40 years ago in a lizard, has defied a general satisfactory evolutionary explanation despite considerable research effort. After briefly reviewing relevant theory and prior empirical work, we draw attention to recent comparative analyses that illuminate the evolutionary history of TSD in amniote vertebrates and point to clear avenues for future research on this challenging topic. To that end, we then highlight the latest empirical findings in lizards and turtles, as well as promising experimental results from a model organism, that portend an exciting future of progress in finally elucidating the evolutionary cause(s) and significance of TSD.     

Climate change impacts on body size and food web structure on mountain ecosystems

The current distribution of climatic conditions will be rearranged on the globe. To survive, species will have to keep pace with climates as they move. Mountains are among the most affected regions owing to both climate and land-use change. Here, we explore the effects of climate change in the vertebrate food web of the Pyrenees. We investigate elevation range expansions between two time-periods illustrative of warming conditions, to assess: (i) the taxonomic composition of range expanders; (ii) changes in food web properties such as the distribution of links per species and community size-structure; and (iii) what are the specific traits of range expanders that set them apart from the other species in the community—in particular, body mass, diet generalism, vulnerability and trophic position within the food web. We found an upward expansion of species at all elevations, which was not even for all taxonomic groups and trophic positions. At low and intermediate elevations, predator : prey mass ratios were significantly reduced. Expanders were larger, had fewer predators and were, in general, more specialists. Our study shows that elevation range expansions as climate warms have important and predictable impacts on the structure and size distribution of food webs across space.     

Taphonomy of the south Brazilian Triassic herpetofauna: fossilization mode and implications for morphological studies

Skulls and limb bones of reptiles from Mid-Triassic rocks in southern Brazil show striking morphological and volumetric differences among specimens from the same taxonomic group; this is caused by early calcite cementation. Petrographic analysis of 40 thin sections of selected fossil bones demonstrates that the main agent of fossilization was precipitation of calcite and minor hematite in the pores of bones during early burial mineralization. The framework of the bones has been broken and replaced by calcite (and hematite), beginning in the spongy inner part of the bone (the cancellous bone) and gradually extending into the compact external layers. Three taphonomic groups of fossil bones are recognized: I – those almost entirely retaining their original structure and shape; II – those whose internal structure is destroyed, but which still have solid outer 'bone surface', and III – those composed of fragments of bone apatite 'floating' in a carbonate matrix. Destruction of the bone structure was caused by the displacive force of calcite crystallization, which typically occurs at shallow burial, during early diagenesis. This process occurs in the vadose zone and requires markedly alternating wet and dry seasons, which indicates a semi-arid paleoclimate for the south Brazilian Mid-Triassic, an inference consistent with other paleoclimatic data. Diagenesis can significantly alter the shape and size of bones and cause considerable morphological variation within the same fossil group, possibly leading to taxonomic misinterpretation.     

In defence of the calcichordates

The cornutes and mitrates, collectively known as stylophorans or calcichordates, are the most controversial members of the traditional group of the 'carpoid echinoderms'. In a recent review, Philip has rejected Ubaghs' interpretation of them as aberrant echinoderms with a single feeding arm, has also rejected my own interpretation of diem as primitive chordates, and has made some tentative proposals of his own. The present paper answers Philip's criticisms of the calcichordate interpretation and discusses his own proposals and his comments on Ubaghs' views.     

Skeleton weight allometry in aquatic and terrestrial vertebrates

The relation of skeleton weight to body weight with increasing size is compared for aquatic and terrestrial vertebrates. Due to the buoyancy of water, the skeleton weights of aquatic vertebrates (fishes and whales) vary in nearly direct proportion (exponent 1.0) to body weight; while the skeletons of terrestrial vertebrates occupy an increasingly greater proportion of total body weight as size increases (exponent greater than i. i) due to the necessity of supporting their weight on land.     

Divide to conquer: a complex pattern of biodiversity depicted by vertebrate components in the Brazilian Atlantic Forest

The identification of northern and southern components in different vertebrate species led researchers to accept a two‐component hypothesis for the Brazilian Atlantic forest (BAF). Nevertheless, neither a formal proposal nor a meta‐analysis to confirm this coincidence was ever made. Our main objective here was therefore to systematically test in how many vertebrate components the BAF could be divided by analysing existing empirical data. We used two approaches: (1) mapping and comparing the proposed areas of vertebrate endemism in the BAF and (2) analysing studies mentioning spatial subdivisions in distinct forest‐dependent vertebrates within the biome, by the use of panbiogeography. The four large‐scale endemism area components together with the six small‐scale panbiogeographical ones allowed the definition of three BAF greater regions, subdivided into nine vertebrate components, latitudinally and longitudinally organized. Empirical time estimates of the diversification events within the BAF were also reviewed. Diversification of these vertebrates occurred not only in the Pleistocene but also throughout the Miocene. Our results confirm the BAF's complex history, both in space and time. We propose that future research should be small‐scale and focused in the vertebrate components identified herein. Given the BAF's heterogeneity, studying via sections will be much more useful in identifying the BAF's historical biogeography. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Phenotypic population divergence in terrestrial vertebrates at macro scales

Phenotypic divergence between populations, i.e. how much phenotypes within a species vary geographically, is critical to many aspects of ecology and evolution, including eco-geographical trends, speciation and coexistence. Yet, the variation of divergence across species with different ecologies and distributions and the relative role of adaptive causes remains little understood. We predict that genetic control vs. phenotypic plasticity of traits, geographical distance and (assuming adaptation) environmental differences should explain much of the phenotypic variability between populations. We tested these predictions with body sizes of 1447 populations in 98 terrestrial vertebrate species. Population phenotypic variability differs strongly across species, and divergence increases with increasing levels of clade-typical phenotypic plasticity, the area covered by populations and body size. Geographical distance and environmental dissimilarity are similarly important predictors of divergence within species, highlighting a potential role for biotic and environmental conditions. Increased availability of phylogeographical and ecological data should facilitate further understanding of population divergence drivers at broad scales.