Use of temporary wetlands by anurans in a hydrologically modified landscape

Abstract

We examined larval anuran assemblages at 12 temporary wetlands occurring on the MacArthur Agro-Ecology Research center (MAERC) in southcentral Florida. MAERC is an active cattle ranch, and the wetlands on the site are heavily influenced by an extensive series of ditches that drain the landscape. Ditching has resulted in a change from a historically extensive marsh system to a series of isolated wetlands surrounded by upland habitats. Because a majority of anurans in Florida breed exclusively or facultatively in wetlands whose drying regime excludes fish, we were interested in determining the value of these modified wetlands as breeding sites. We examined the effect of wetland size and hydrology on anuran use, and compared breeding activity across three summers that varied greatly in rainfall pattern. We sampled tadpoles from May 93 to August 93 and from May 94 to September 95. A total of 3678 tadpoles from 11 species was collected. Rana utricularia was the most abundant species and the only species found in every wetland Species richness was related positively to wetland size (r=0.65, p=0.023) but not hydroperiod (r=0.03, p=0.93). Tadpole abundance was not related to wetland size (r=0.35, p=0.29) nor hydroperiod (r=0.40, p=0.22). Annual variation in rainfall resulted in significant changes in species composition. A drought during 1993 resulted in no breeding. A high water table in the spring of 1995 resulted in localized flooding in early summer on part of the ranch. Wetlands in these areas were exposed to spillover of water from ditches containing fishes. Wetlands so impacted showed significant changes in species composition from the previous year (x2=1008, p < 0.0001), whereas wetlands that were not impacted did not differ in composition. The wetlands at MAERC provide dynamic habitats that offer varying breeding opportunities that are highly dependent on meteorological conditions.