title: Taxonomic variation in size-density relationships challenges the notion of energy equivalence.
abstract: The relationship between body mass and abundance is a major focus for research in macroecology. The form of this relationship has been suggested to reflect the partitioning of energy among species. We revisit classical datasets to show that size-density relationships vary systematically among taxonomic groups, with most variation occurring at the order level. We use this knowledge to make a novel test of the 'energy equivalence rule', at the taxonomic scale appropriate for the data. We find no obvious relationship between order-specific exponents for abundance and metabolic rate, although most orders show substantially shallower (less negative) scaling than predicted by energy equivalence. This finding implies greater energy flux among larger-bodied animals, with the largest species using two orders of magnitude more energy than the smallest. Our results reject the traditional interpretation of energy equivalence as a predictive rule. However, some variation in size-density exponents is consistent with a model of geometric constraints on foraging.
authors: NERC Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK. njbisaac@gmail.com
authors: Nick J B
authors: NJ
authors: Isaac
authors: David
authors: D
authors: Storch
authors: Chris
authors: C
authors: Carbone
mesh_terms: D000818:Animals; D049628:Body Size; D004734:Energy Metabolism; D011156:Population Density