The signature of human pressure history on the biogeography of body mass in tetrapods

Abstract

Aim Examining the biogeography of body size is crucial for understanding how animal communities are assembled and maintained. In tetrapods, body size varies predictably with temperature, moisture, productivity seasonality and topographical complexity. Although millennial‐scale human pressures are known to have led to the extinction of primarily large‐bodied tetrapods, human pressure history is often ignored in studies of body size that focus on extant species. Here, we analyse 11,377 tetrapod species of the Western Hemisphere to test whether millennial‐scale human pressures have left an imprint on contemporary body mass distributions throughout the tetrapod clade. Location Western Hemisphere. Time period Contemporary. Major taxa studied Tetrapods (birds, mammals, amphibians and reptiles). Methods We mapped the distribution of assemblage‐level median tetrapod body mass at a resolution of 110 km across the Western Hemisphere. We then generated multivariate models of median body mass as a function of temperature, moisture, productivity seasonality and topographical complexity, as well as two variables capturing the history of human population density and human‐induced land conversion over the past 12,000 years. We controlled for both spatial and phylogenetic autocorrelation effects on body mass–environment relationships. Results Human pressures explain a small but significant portion of geographical variation in median body mass that cannot be explained by ecological constraints alone. Overall, the median body mass of tetrapod assemblages is lower than expected in areas with a longer history of high human population density and land conversion, but there are important differences among tetrapod classes. Main conclusions At this broad scale, the effect of human pressure history on tetrapod body mass is low relative to that of ecology. However, ignoring spatial variation in the history of human pressure is likely to lead to bias in studies of the present‐day functional composition of tetrapod assemblages, at least in areas that have long been influenced by humans.

Geographic variation of body size in New World anurans: energy and water in a balance

“…Even after deconstructing our analyses into the two major biogeographical realms in the New World (Nearctic and Neotropics), results remained consistent with predictions of the heat and water conservation hypotheses (Olalla-Tárraga and Rodríguez 2007). We also found evidence for a role of water availability, in accordance with previous findings in Nearctic amphibians (Olalla-Tárraga et al 2009, Gouveia and Correia 2016, Rapacciuolo et al 2017). The patterns we observe are detectable along the whole American continent even if part of the variance may be related to other factors.…”

“…This general pattern could be interpreted as indicative of an influence of heat and water conservation dynamics on body size, as predicted by the heat balance and water conservation hypotheses (Olalla-Tárraga and Rodríguez 2007, Ashton 2002). Furthermore, the joint role of energy and moisture that becomes apparent in separate analyses for the Neartic and Neotropics is indicative of the inherent difficulties to tease apart thermal and hydric constraints in shaping anuran body size variation across water-limiting environments (Olalla-Tárraga et al 2009, Gouveia and Correia 2016, Rapacciuolo et al 2017. Larger body size confers better abilities to retain metabolic heat due to the smaller surface-to-volume ratio (Bergmann 1847, James 1970.…”

Geographical patterns and environmental drivers of functional diversity and trait space of amphibians of Europe

“…Human pressures (like agriculture or urbanization) explain a small but significant portion of geographical variation of traits that cannot be explained by ecological constraints alone. The median body mass of tetrapod assemblages is lower than expected in areas with a longer history of high human population density and land conversion (see Rapacciuolo et al, 2017). Additionally, functionally dissimilar species were more prone to be lost as a result of agricultural intensification than the functionally similar species perhaps implying that human influence acts as an environmental filter (Flynn et al, 2009).…”

Anuran 3D models reveal the relationship between surface area‐to‐volume ratio and climate

“…Faced with the task to predict how environmental changes will affect the interactions of species with their surroundings, researchers felt the urgency to better understand how the morphology of animals responds to climatic variation (Bradshaw & Holzapfel, ; Ficetola et al., ; Rapacciuolo et al., ). Our results show that variation in body geometry may be linked with better water economy, while body length was linked with variation in environmental temperature.…”

“…Faced with the task to predict how environmental changes will affect the interactions of species with their surroundings, researchers felt the urgency to better understand how the morphology of animals responds to climatic variation (Bradshaw & Holzapfel, 2010;Ficetola et al, 2016;Rapacciuolo et al, 2017).…”