Amphibian persistence in isolated wetlands in an agricultural landscape

Background/Question/Methods

Geographically isolated wetlands provide key habitat for amphibians associated with the endangered longleaf pine ecosystem in the southeastern U.S. Amphibians that breed in these wetlands generally spend the non-breeding season in surrounding upland habitats, thus an intact landscape is important for persistence of populations.  Today, the longleaf pine ecosystem has been reduced to a small fraction of its original extent and remaining tracts of forest and the isolated wetlands embedded within them are fragmented by roads, development, and large-scale agriculture.  The effects of habitat fragmentation on amphibians in isolated wetlands in the Southeast have not been described, largely because there are few sites available as references for comparison to impacted sites.  We examined amphibian species richness at reference isolated wetlands located within an 11,700 ha managed longleaf pine forest as compared to wetlands in an agricultural setting in southwestern Georgia.  Sampling methods included dip netting and frog call surveys using automated recording systems.  Data were collected at 10 reference wetlands and 10 agriculturally impacted wetlands in spring and summer of 2009 and 2010. Reference sites were all located in a forested landscape, whereas agricultural wetlands had <25% forest within a 1 km buffer. 

Results/Conclusions

We detected 20 amphibian species in reference wetlands (mean= 6.4, SD= 3.06, range= 1-12) and 18 in agricultural wetlands (mean= 8.0, SD= 2.54, range= 5-12).  Species unique to reference wetlands included mole salamander (Ambystoma talpoideum), dwarf siren (Pseudobranchus striatus), greater siren (Siren lacertina), striped newt (Notophthalmus perstriatus), and the Florida gopher frog (Lithobates capito).  We observed spring peeper (Pseudacris crucifer), pig frog (Lithobates grylio) and eastern spadefoot (Scaphiopus holbrookii) only in agricultural wetlands.  The striped newt and Florida gopher frog breed only in isolated wetlands and are considered longleaf pine forest specialists.  Mole salamanders also rely heavily on forest habitat during the non-breeding season.  Thus, it is not surprising that these species were observed only in reference wetlands. The occurrence of other longleaf pine associated amphibians such as the pinewoods treefrog (Hyla femoralis) and barking treefrog (Hyla gratiosa) in both reference and agricultural wetlands may be related to high dispersal ability of these species.