Experimental and model analyses of the effects of competition on individual size variation in wood frog (Rana sylvatica) tadpoles
Article first published online: 23 JUN 2006
© 2006 The Authors. Journal compilation © 2006 British Ecological Society
Journal of Animal Ecology
Volume 75, Issue 4, pages 990–999, July 2006
How to Cite
PEACOR, S. D. and PFISTER, C. A. (2006), Experimental and model analyses of the effects of competition on individual size variation in wood frog (Rana sylvatica) tadpoles. Journal of Animal Ecology, 75: 990–999. doi: 10.1111/j.1365-2656.2006.01119.x
- Issue published online: 23 JUN 2006
- Article first published online: 23 JUN 2006
- Received 18 January 2006; accepted 27 March 2006
- density dependence;
- individual variation;
- growth depensation;
- growth autocorrelation
- 1Size variation is a ubiquitous feature of animal populations and is predicted to strongly influence species abundance and dynamics; however, the factors that determine size variation are not well understood.
- 2In a mesocosm experiment, we found that the relationship between mean and variation in wood frog (Rana sylvatica) tadpole size is qualitatively different at different levels of competition created by manipulating resource supply rates or tadpole density. At low competition, relative size variation (as measured by the coefficient of variation) decreased as a function of mean size, while at high competition, relative size variation increased. Therefore, increased competition magnified differences in individual performance as measured by growth rate.
- 3A model was developed to estimate the contribution of size-dependent factors (i.e. based on size alone) and size-independent factors (i.e. resulting from persistent inherent phenotypic differences other than size that affect growth) on the empirical patterns.
- 4Model analysis of the low competition treatment indicated that size-dependent factors alone can describe the relationship between mean size and size variation. To fit the data, the size scaling exponent that describes the dependence of growth rate on size was determined. The estimated value, 0·83, is in the range of that derived from physiological studies.
- 5At high competition, the model analysis indicated that individual differences in foraging ability, either size-based or due to inherent phenotypic differences (size-independent factors), were much more pronounced than at low competition. The model was used to quantify the changes in size-dependent or size-independent factors that underlie the effect of competition on size-variation. In contrast to results at low competition, parameters derived from physiological studies could not be used to describe the observed relationships.
- 6Our experimental and model results elucidate the role of size-dependent and size-independent factors in the development of size variation, and highlight and quantify the context dependence of individual (intrapopulation) differences in competitive abilities.