Effects of surrounding land use and wetland spatial position on amphibian parasite communities

The conversion of natural forest or prairie to agricultural land has wide-reaching effects on the stability and composition of surrounding wildlife populations. For example, increased nutrient inputs associated with agriculture can alter the dynamics of aquatic snails, larval anurans, and their parasites. To evaluate the effects of land usage and wetland spatial position on amphibian parasite communities (trematodes: Ribeiroia and Echinostoma), we sampled 40 wetlands across central and northern Wisconsin. Study sites were selected at random along transects perpendicular to the Mississippi flyway, a regional bottleneck in the migratory routes of trematode-carrying birds. At each wetland we measured presence and abundance of snail and anuran parasite hosts, presence and abundance of Ribeiroia and Echinostoma, nutrient concentrations, and surrounding land usage. We found a positive relationship between anuran abundance and both the percentage of agricultural land and total trematode abundance. Snail density was positively related to both anuran abundance and trematode presence and abundance. Furthermore, wetlands that had no snails exhibited lower nutrient concentrations and lower trematode abundances. As expected, Ribeiroia infection exhibited a negative relationship with distance to the Mississippi flyway. These results indicate how land use shifts can alter host-parasite dynamics in aquatic communities with potentially important conservation implications.