Abstract
Phenotype is often correlated with resource use, which suggests that as phenotypic variation in a population increases, intraspecific competition will decrease. However, few studies have experimentally tested the prediction that increased intraspecific phenotypic variation leads to reduced competitive effects (e.g., on growth rate, survival or reproductive rate). We investigated this prediction with two experiments on wood frogs (Rana sylvatica). In the first experiment, we found that a frog’s size was positively correlated with the size of its preferred prey, indicating that the feeding niche of the frogs changed with size. In the second experiment, we used an experimental design in which we held the initial mass of “focal” frogs constant, but varied the initial mass of their competitors. We found a significant quadratic effect of the average mass of competitors: focal frog growth was lowest when raised with similar-sized competitors, and highest when raised with competitors that were larger or smaller. Our results demonstrate that growth rates increase (i.e., competitive intensity decreases) when individuals are less similar to other members of the population and exhibit less overlap in resource use. Thus, changes in the amount of phenotypic variation in a population may ultimately affect population-level processes, such as population growth rate and extinction risk.
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Acknowledgments
This work was conducted on the University of Michigan’s E.S. George Reserve. We thank Leslie Cabrera, Brian Duchemin, and Sam Upton for logistical assistance with this experiment. Earl Werner, the Werner lab group and two anonymous reviewers provided valuable feedback on our manuscript. M.F.B. was supported in part by the Michigan Society of Fellows at the University of Michigan. J.M.M. was supported by the Edwin S. George Reserve Scholarship and the Helen Olsen Brower Memorial Fellowship at the University of Michigan. This work complies with the current laws of the United States of America.
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Communicated by Anssi Laurila.
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Benard, M.F., Middlemis Maher, J. Consequences of intraspecific niche variation: phenotypic similarity increases competition among recently metamorphosed frogs. Oecologia 166, 585–592 (2011). https://doi.org/10.1007/s00442-010-1896-6
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DOI: https://doi.org/10.1007/s00442-010-1896-6