Synthesizing studies of plastic responses to pond drying in amphibians: a meta-analysis

Background/Question/Methods

Phenotypic plasticity allows organisms to respond to environmental change and persist in unpredictable environments. Hydroperiod is a critical driver of the ecology of aquatic habitats. Understanding how organisms respond to variation in hydroperiod is especially critical since climate change is expected to alter temperature and precipitation regimes worldwide. Amphibians reproduce in highly ephemeral environments and can display phenotypic plasticity by accelerating development to escape drying ponds. Despite more than 20 years of research on the effects of pond drying on amphibian development, these studies have not been quantitatively synthesized. We compiled 30 laboratory and field studies from 1987-2011 which directly manipulate water levels in experimental venues. These studies include 36 different species from 9 different families across desert, temperate and tropical regions. From each study, we calculated effect sizes as the log response ratio on time, size and survival to metamorphosis. We ask whether responses to pond drying are related to phylogeny, experimental venue (lab versus field), tadpole density, and taxa specific variation in life history traits.  

Results/Conclusions

Amphibian taxa vary in their response to pond drying, with leiuperids, hylids and ranids exhibiting larger proportional reductions in larval duration in response to dry down treatments than bufonids and pelobatids. These differences may be attributed to variation among experimental methods and/or in life history traits. Across taxa, faster drying rates resulted in larger reductions in larval period, supporting the idea that reductions in vertical swimming volume may act as an important cue for pond drying. Studies conducted at higher densities observed smaller reductions in larval duration in drying treatments, suggesting that species may be unable to plastically accelerate metamorphosis in food limited conditions.  Interestingly, species with longer larval periods displayed more plasticity in the time required to reach metamorphosis. Species with relatively fast development rates under constant water conditions exhibited weaker proportional response to drying compared to taxa with longer larval duration. While reductions in larval duration were wide spread among amphibian lineages, effects of drying on size at metamorphosis were variable. Many taxa emerged earlier with no apparent cost in size or survival. This synthesis contributes to our understanding of how life history and phylogeny may impact the ability of species to plastically respond to changing climatic conditions.