Many organisms utilize different habitats at different periods of their life.  Identification of which habitat a species’ population is regulated is fundamentally important for understanding both the basic ecology of that species, and for determining optimal conservation strategies.  Amphibians are an excellent example of this:  many have an aquatic larval stage and a terrestrial post-metamorphic stage.  However, very little work has investigated whether the size of most amphibian populations are regulated in the larval or post-metamorphic stage. Using over a decade of detailed survey data on multiple ponds in Michigan, we tested for the presence of density-dependent survival in both the larval stage and the post-metamorphic stage of the wood frog (Rana sylvatica).  We also incorporated this data into a demographic model of wood frog population dynamics. 

Results/Conclusions

We found strong evidence for larval-stage density-dependence, but little evidence for post-metamorphic density-dependence in survival. Similarly, the size of adult populations at each pond was significantly related to the size of the larval habitat, but not related to the size of the post-metamorphic habitat.   Thus, these wood frog populations are regulated in the larval stage, but not the post-metamorphic life stage.  Further, our demographic model revealed that the sensitivity of amphibian extinction risk to changes in specific vital rates (e.g., fecundity, maximum larval survival, adult survival) could be strongly affected by the life-stage in which density-dependence was the strongest.   Many studies of amphibians and other organisms focus on only a single-life stage; our study highlights the importance of studying to entire life-cycle to determine the factors that most strongly affect population dynamics.