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Oecologia

, Volume 153, Issue 4, pp 879–889 | Cite as

Density dependence in the terrestrial life history stage of two anurans

  • Elizabeth B. HarperEmail author
  • Raymond D. Semlitsch
Population Ecology

Abstract

Populations of species with complex life cycles have the potential to be regulated at multiple life history stages. However, research tends to focus on single stage density-dependence, which can lead to inaccurate conclusions about population regulation and subsequently hinder conservation efforts. In amphibians, many studies have demonstrated strong effects of larval density and have often assumed that populations are regulated at this life history stage. However, studies examining density regulation in the terrestrial stages are rare, and the functional relationships between terrestrial density and vital rates in amphibians are unknown. We determined the effects of population density on survival, growth and reproductive development in the terrestrial stage of two amphibians by raising juvenile wood frogs (Rana sylvatica) and American toads (Bufo americanus) at six densities in terrestrial enclosures. Density had strong negative effects on survival, growth and reproductive development in both species. We fitted a priori recruitment functions to describe the relationship between initial density and the density of survivors after one year, and determined the functional relationship between initial density and mass after one year. Animals raised at the lowest densities experienced growth and survival rates that were over twice as great as those raised at the highest density. All female wood frogs in the lowest density treatment showed signs of reproductive development, compared to only 6% in the highest density treatment. Female American toads reached minimum reproductive size only at low densities, and male wood frogs and American toads reached maturity only in the three lowest density treatments. Our results demonstrate that in the complex life cycle of amphibians, density in the terrestrial stage can reduce growth, survival and reproductive development and may play an important role in amphibian population regulation. We discuss the implications of these results for population regulation in complex life cycles and for amphibian conservation.

Keywords

Population regulation Amphibian Reproductive development Growth Survival 

Notes

Acknowledgments

We thank T. Altnether, D. Patrick, L. Rehard, and T. Rittenhouse for their assistance in the field. C. Galen, D. Patrick, T. Rittenhouse, B. Rothermel, J. Vonesh and two anonymous reviewers provided useful comments on earlier drafts of the manuscript. This research was supported by a grant from the National Science Foundation DEB 0239943. Eggs and larvae were collected under Missouri Department of Conservation Wildlife Collector’s permits 12,227 and 12,696, and maintained under University of Missouri Animal Care and Use Protocol 3368.

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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Division of Biological SciencesUniversity of MissouriColumbiaUSA

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