Of all shapes and sizes: a theoretical framework for animal-mediated terrestrial heterogeneity across scales

Abstract

Animals redistribute elements throughout their lives by depositing wastes and carcasses. Growing evidence shows that these zoogeochemical processes enhance landscape diversity and heterogeneity worldwide. We provide a descriptive framework for understanding how direct animal depositions (i.e. fecal matter, urine, carcasses, and other body materials) contribute to element heterogeneity across scales, with particular focus on how a species' contributions differ relative to one another. In this framework, we identify mean body mass and population density as the main predictors of element heterogeneity. Secondary predictors, including population strategy, overabundance, habitat preference, elemental composition and predation, are nested within and influenced by body size and density. We then demonstrate how animals can play unique roles within communities, leading to multiscale patterns of elemental heterogeneity within an ecosystem. In doing so, we highlight the importance of studying zoogeochemistry through both an ecosystem ecology and community ecology lens. We illustrate our framework using three spatial scales of animal communities (100 cm², 100 m², 100 km²) within an eastern temperate forest, considering both individual species traits and their community interactions at each scale. The community heterogeneity framework provides a theoretical understanding of how individual species and animal communities collectively drive element heterogeneity, allowing a predictive mechanism for the ecosystem contributions of animals across systems and scales.