Data from: Multiple stressors and the cause of amphibian abnormalities

The repeated occurrence of abnormal amphibians in nature points to
ecological imbalance, yet identifying causes of these abnormalities has
proved complex. Multiple studies have linked amphibian abnormalities to
chemically contaminated areas, but inference about causal mechanisms is
lacking. Here we use a high incidence of abnormalities in Alaskan wood
frogs to strengthen inference about the mechanism for these abnormalities.
We suggest that limb abnormalities are caused by a combination of multiple
stressors. Specifically, toxicants lead to increased predation, resulting
in more injuries to developing limbs and subsequent developmental
malformations. We evaluated a variety of putative causes of frog
abnormalities at 21 wetlands on the Kenai National Wildlife Refuge,
south-central Alaska, USA, between 2004 and 2006. Variables investigated
were organic and inorganic contaminants, parasite infection, abundance of
predatory invertebrates, UVB, and temperature. Logistic regression and
model comparison using the Akaike information criterion (AIC) identified
dragonflies and both organic and inorganic contaminants as predictors of
the frequency of skeletal abnormalities. We suggest that both predators
and contaminants alter ecosystem dynamics to increase the frequency of
amphibian abnormalities in contaminated habitat. Future experiments should
test the causal mechanisms by which toxicants and predators may interact
to cause amphibian limb abnormalities.