Anuran calling activity as an indicator of wetland health: The importance of including variation in landscape composition

Recent studies suggest that anuran (frog and toad) calling activity is an accurate predictor of wetland health and, therefore, useful for making management decisions about wetlands that are impacted by human activity. Anuran calling activity is affected by the composition of the landscape surrounding a breeding wetland, however, and often is strongly correlated with hydroperiod, which can vary greatly from year to year. We monitored anuran calling activity at 16 cypress domes located in active wellfields and 8 domes not subject to the direct influence of water extraction. Monitoring occurred from May - September in 2005 and 2006. Community ordination revealed differences in calling assemblages between years and among sites. These differences in calling assemblages were associated with the date of inundation, number of neighboring domes, area of upland forest, and area of human disturbance at each cypress dome. The activities of most anuran species were consistently associated with landscape composition. In both years, species could be divided consistently into two major groups, based on their responses to landscape features. Multiple regression trees suggest that the area of surrounding upland forest area within 5 km and the number of neighboring cypress domes within 2 km most strongly explain variation in calling activity among cypress domes. Area of surrounding upland forest within 5 km was strongly negatively correlated with the area of human disturbance within 5 km. The activities of only a few species were associated with hydroperiod, and these associations were not consistent between years. This inconsistency is likely because most cypress domes became inundated much later in the summer of 2006 than in 2005. Our results suggest that variation associated with surrounding land use must be considered when using anuran calling activity as an indicator of wetland health.