Document: KIM-3-49-7

Allometric scaling exponents: A test with invertebrates.

CUDDINGTON, K.* ¹, D.VASSEUR ², W.CURRIE ² and P.YODZIS ²

University of Connecticut, Storrs, CT 06269 ¹
University of Guelph, Guelph, ON N1G2W1, Canada ²

Abstract:
Allometric relationships are claimed to be general laws for biology, in some sense comparable to laws in physics and chemistry. Many characteristics of animals such as metabolic rate, reproductive rate and movement rate scale with body size according to the allometric relationship, Y=CM^b , where the constant, C, is determined by the ecological type of the organism (e.g. homeotherm vs. poikilotherm) and b is the scaling exponent. Empirical data, calculated for a variety of physiological rates across a range of body sizes, supports the claim that this scaling factor ranges from 0.5 to 0.75. Recently, a theoretical argument has been used to predict a scaling exponent of 0.75. We address two points: The dearth of data focusing on scaling relationships for small-bodied invertebrates, and the appropriate scaling exponent to describe these relationships. Quite often scaling exponents are estimated from datasets which lump many species, and which normally have a preponderance of homeotherm vertebrates (e.g. mammals and birds). Where ecological types are separated to generate scaling relationships, large-bodied invertebrates make up the majority of data points for poikilotherms. While such lumping of data and generalization across ecological types may be appropriate for some uses of allometric relationships, for other applications this degree of generalization could lead to grossly erroneous predictions. We collected data from a wide range of sources and generated allometric relationships for metabolic, reproductive and feeding rates of invertebrates from terrestrial and aquatic environments. We tested the claim that the scaling exponent of 0.75 is a general relationship for physiological rates. Our data suggest a 0.75 scaling exponent is the best description of allometric relationships for small-bodied invertebrates.

Keywords: allometry, scaling laws, invertebrates

This abstract is being presented at: 8:30 AM in session:
Oral Session #4: Herbivore Responses to Plants.