A central focus of ecology is understanding patterns of resource acquisition and use, and body size may be a primary driver of resource consumption rates. The energetic equivalence rule predicts that abundance and metabolism will scale inversely with body size, and that therefore energy consumption rates of size classes of animals in a foraging guild will be equal. This prediction has attracted intense interest among community ecologists, and has received theoretical backing from metabolic theory, yet remains controversial and has been difficult to test directly. Our objective was to test energetic equivalence, controlling for factors that have confounded previous studies by examining energy consumption at the community scale, quantifying energy consumption by size class, directly measuring energy consumption by all members of a foraging guild, and focusing on consumption of a set of shared food resources. We measured energy consumption by a guild of endemic vertebrate frugivores as they foraged on native fig (Ficus) trees in a tropical forest in northern Madagascar, during the dry season period when few other resources were available.
Results/Conclusions
Our results indicated large differences by frugivore species in visitation rates to a foraging patch, residency time at a patch, and consumption rates while present at a patch. Further, energy consumption rates varied by frugivore species over four orders of magnitude, and frugivore species exhibited strong preferences for fig species. However, despite these striking differences, energy consumption rates did not differ by frugivore size class. In short, the considerable variation at the species level masked an underlying symmetry at the size class level, a result that provides clear support for the energetic equivalence hypothesis. Since energy distribution in a community may influence densities, growth rates, and carrying capacities of populations, and also the diversity, composition, and assembly of communities, these findings have important implications for understanding population dynamics and community structure.
