Amphibian diversity in the Georgia Sea Islands
O'Hare, Nancy Kay
MetadataShow full item record
Amphibian declines have been noted worldwide, but recent inventories are lacking for many state and federal conservation lands. How can future changes be addressed if present-day species diversity is unknown? The Georgia Sea Islands is a region of islands isolated by tidal salt marshes and rivers; it includes 35 conservation units, ranging from small parcels to entire islands. Most islands have an extensive land-use history and limited freshwater resources to support amphibian breeding. This study integrated a herpetofaunal inventory from a previously unstudied site (Wormsloe, Isle of Hope) with recent amphibian trapping data for four federal parks in the region and literature records of amphibian diversity for seven other islands (12 islands total). Landscape characteristics, including microtopographic features influencing freshwater resources, were also determined. The islands supported 23 of the 26 amphibians occurring on the adjacent mainland, but individual islands supported between 5 and 19 species. Species occurring across more islands tended to have greater total reproductive output (longer life span, greater number of eggs) and a shorter tadpole/larval stage (<60 days). Larger islands supported more species; however, the relationship between island size and species diversity was more idiosyncratic on smaller islands. Island size, geological age, and habitat (gamma) diversity were correlated, so it was not possible to separate their effects. Dispersal was limited more by the matrix of freshwater rivers and tidal marshes separating islands rather than by distance. Canals at Wormsloe, a land-use legacy feature common across many other islands, allowed tidal influx inland into seasonal freshwater ponds approximately 50 days per year. Consequently, the ability of some species to persist at Wormsloe is uncertain if inland freshwater resources continue to be degraded by tidal influx along canals. Resources management for conservation areas should minimally include annual monitoring of amphibian breeding, establishment of surface water gages, especially on islands more likely to be influenced by adjacent development or water-intensive land-uses. Freshwater quality should be protected by preventing tidal influx along canals and quantity increased by slowing rainwater percolation by lining depressions, after the residual salts in the soil have been leached downward.