Mammalian body size is determined by interactions between climate, urbanization, and ecological traits

Maggie M Hantak,Daijiang Li,Bryan S Mclean,Robert P Guralnick

doi:10.1038/s42003-021-02505-3

Abstract

Anthropogenically-driven climate warming is a hypothesized driver of animal body size reductions. Less understood are effects of other human-caused disturbances on body size, such as urbanization. We compiled 140,499 body size records of over 100 North American mammals to test how climate and human population density, a proxy for urbanization, and their interactions with species traits, impact body size. We tested three hypotheses of body size variation across urbanization gradients: urban heat island effects, habitat fragmentation, and resource availability. Our results demonstrate that both urbanization and temperature influence mammalian body size variation, most often leading to larger individuals, thus supporting the resource availability hypothesis. In addition, life history and other ecological factors play a critical role in mediating the effects of climate and urbanization on body size. Larger mammals and species that utilize thermal buffering are more sensitive to warmer temperatures, while flexibility in activity time appears to be advantageous in urbanized areas. This work highlights the value of using digitized, natural history data to track how human disturbance drives morphological variation.

Highlights

Anthropogenically-driven climate warming is a hypothesized driver of animal body size reductions
With increasing Mean Annual Temperature (MAT), species with any hibernation ability and non-hibernators decrease in body mass, but the strength of the decrease is stronger for species that use torpor compared to species that hibernate (Estimate = 0.008, 95% CI = 0.004 – 0.011) and that do not hibernate (Estimate = 0.019, 95% CI = 0.017 – 0.021; Table 1, Fig. 2b)
Species that use habitat buffering and non-buffered species decrease in body mass with increasing MAT, but the strength of the decrease is stronger for species that facultatively use habitat buffers compared to species that do not use habitat buffers (Estimate = 0.026, 95% CI = 0.021 – 0.030) and species that are obligated to use buffers (Estimate = 0.016, 95% CI = 0.012 – 0.021; Table 1, Fig. 2c)

Summary

Introduction

Anthropogenically-driven climate warming is a hypothesized driver of animal body size reductions. We tested three hypotheses of body size variation across urbanization gradients: urban heat island effects, habitat fragmentation, and resource availability. Schmidt and Jensen[26,27] suggested that species that experience landscape fragmentation driven by urbanization and an increased human footprint should either go extinct or adapt through changes in traits, namely increasing body size for smaller species and decreases for larger species. Each of these hypotheses have clear, alternate predictions about the overall effects of urbanization, and can be emplaced in the broader context of overall climatic gradients

Methods

Results

Conclusion