Tuesday, August 7, 2007

PS 33-164: Integrating the ecological and metabolic significance of body size: The energetic niche of species

Hamish A. Wilman and Walter Jetz. University of California, San Diego

Energy is a core ecological currency and modeling its fluxes has helped address fundamental questions in ecosystem and community ecology.  We offer a perspective that combines principles regarding ecological niche and core energetic fluxes by considering a species “metabolic niche” in an assemblage.  We quantify species’ individual energy use relative to other members of a community to characterize this metabolic niche. Combined with respective abundances it determines total energy flux, yielding a core ecological signature of species and communities.  Extending this perspective to total energy requirements from the environment allows the assessment of potential constraints at the ecosystem level. We quantify these requirements using primary productivity required (PPR), which accounts for a species’ metabolic rate, diet, and the inherent inefficiency of energy transfer across trophic levels.  We analyze and compare body size, field metabolic rate (FMR), and PPR distributions for over 12,800 vertebrate endotherms across guilds, taxa, and scales. We show that as distributions of energy use become more inclusive of species ecology (Mass to FMR to PPR) their shapes change from being left-skewed to being centrally distributed in log space. We proceed to evaluate the utility of PPR in predicting species abundances. We find that by accounting for differences between feeding guilds PPR is a better and more parsimonious predictor of species abundance than body size.  Utilizing this measure of energetic needs, understanding the drivers shaping its distribution across species, and further exploring its ecological relevance to species abundances may help reconcile the perspectives of ecosystem and community ecology.

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