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Body mass–abundance relationships reveal uneven global energy distribution across body size classes in vertebrates

Luis F. Camacho,M. Araújo

Published 2026 in Frontiers of Biogeography

ABSTRACT

The relationship between species body mass and abundance (MAR-SPP) is a fundamental feature of ecosystems, reflecting whether energy is accumulated in few large organisms or dispersed amongst several smaller ones. While larger species are generally less abundant than smaller ones, identifying broad patterns in this relationship – and the mechanisms shaping it – has been hindered by sparse spatial and taxonomic data. Here, we present a global assessment of MAR-SPP as a function of individual body-mass distribution and species richness, each representing how body size influences energy allocation and the ecological opportunity for diversification. Using extensive species abundance datasets, we model global abundances of 12,057 bird and mammal species at a one-degree resolution. This enables localised reconstructions of community structure and detailed examination of body-mass–abundance–richness relationships. We find that increasing ecosystem productivity and human activity are associated with a relative decline in the abundance of small species. This pattern arises because smaller organisms become more diverse, but not proportionally more abundant, effectively diluting individuals across an increasing number of species. Given that basal metabolic rate scales with body mass to the 0.75 power, our findings suggest that larger species, on average, capture more energy than smaller ones — particularly in productive ecosystems — despite general constraints on their energy acquisition and diversification. Our study demonstrates that energy distribution and ecological opportunity independently shape the functional space governing MAR-SPP. It also highlights the disproportionate impact of human activity on large organisms, revealing lasting consequences for the functional organization of ecological communities. Body mass–abundance–richness relationships reflect how energy is distributed across body size classes and the ecological opportunities available for diversification. Modelling species abundances helps bridge gaps in sparse empirical data, enabling more robust ecological inferences about the structure of body mass–abundance relationships. An analysis of these relationships in bird and mammal communities reveals a general constraint on large organisms: limited capacity to diversify and accumulate energy. Paradoxically, however, larger-bodied species tend to capture more energy, on average. High-productivity environments increase the relative energy contribution of large organisms, but simultaneously reduce their ecological opportunity for diversification. Body mass–abundance–richness relationships may serve as a functional metric for assessing the ecological impact of human activities on natural communities.

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