Invertebrate community structure helps explain the distribution of amphibian chytrid in Eastern Missouri

Background/Question/Methods

The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), is an emergent infectious disease that threatens amphibian biodiversity at a global scale.  Bd has caused declines, extirpations, and extinctions on several continents, but is also known to exist in an enzootic state across much of the world.  Despite the rapid accumulation of knowledge about Bd when it is emergent and causes declines, relatively little is known about the ecology of Bd in regions where it is not emergent.  In particular, few studies have investigated factors that explain and predict the pattern of occurrence of this pathogen among sites within a region.  We present an exploratory analysis of abiotic and biotic factors that might influence the incidence of Bd in fifty-four ponds in Eastern Missouri.  We consider physical factors (pond isolation, temperature, etc. ), biological factors (amphibian, macroinvertebrate, and zooplankton community diversity), and chemical factors (Nitrogen, Phosphorus, etc.).  

Results/Conclusions

Bd was found in approximately 1/3 of our ponds.  Ponds that contained newts (Notophthalmus viridescens) were more likely to contain Bd, but no other factors (alone) correlated with presence of Bd.  When ponds were ordinated according to water chemistry or macroinvertebrate diversity (using non-metric multidimensional scaling), ponds with Bd were found to occupy a subset of the parameter space occupied by the non-Bd ponds.  That is, Bd was restricted to ponds with a restricted range of water chemistry and macroinvertebrate community structure.  The results of a structural equation model then revealed that the effect of water chemistry on Bd was indirect and mediated by macroinvertebrate community dissimilarity, whereas macroinvertebrate dissimilarity had a direct, emergent effect on Bd presence.  

Our results can be used to generate numerous hypotheses regarding Bd’s specific ecological requirements in this region.  Furthermore, we can use our results to inform predictions of high-risk sites in regions where Bd is already epidemic.  Understanding more about the ecology of Bd in regions where it is enzootic may ultimately help us mitigate and predict further epidemics in the future.