Concepts & Synthesis
CONCEPTS & SYNTHESIS EMPHASIZING NEW IDEAS TO STIMULATE RESEARCH IN ECOLOGY Ecological Monographs, 81(3), 2011, pp. 349–405 Ó 2011 by the Ecological Society of America Regulation of animal size by eNPP, Bergmann’s rule, and related phenomena 1,3 2 MICHAEL A. HUSTON AND STEVE WOLVERTON 1Department of Biology, Texas State University, San Marcos, Texas 78666 USA 2University of North Texas, Department of Geography, Denton, Texas 76203-5017 USA Abstract. Bergmann’s rule, which proposes a heat-balance explanation for the observed latitudinal gradient of increasing animal body size with increasing latitude, has dominated the study of geographic patterns in animal size since it was first proposed in 1847. Several critical reviews have determined that as many as half of the species examined do not fit the predictions of Bergmann’s rule. We have proposed an alternative hypothesis for geographic variation in body size based on food availability, as regulated by the net primary production (NPP) of plants, specifically NPP during the growing season, or eNPP (ecologically and evolutionarily relevant NPP). Our hypothesis, ‘‘the eNPP rule,’’ is independent of latitude and predicts both spatial and temporal variation in body size, as well as in total population biomass, population growth rates, individual health, and life history traits of animals, including humans, wherever eNPP varies across appropriate scales of space or time. In the context of a revised interpretation of the global patterns of NPP and eNPP, we predict contrasting latitudinal correlations with body size in three distinct latitudinal zones. The eNPP rule explains body- size patterns that are consistent with Bergmann’s rule, as well as two distinct types of contradictions of Bergmann’s rule: the lack of latitudinal patterns within the tropics, and the decline in body size above approximately 608 latitude.
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