projects > integrating monitoring and modeling of ecological responses to ecosystem in picayune strand and southwest florida: amphibian community component
Integrating monitoring and modeling of ecological responses to ecosystem in Picayune Strand and southwest Florida: Amphibian community component
Prior to extensive drainage, wetlands historically covered approximately 50% of Florida (Mulholland et al., 1997). The present-day landscape of southwest Florida still contains a matrix of diverse wetland types that vary in hydroperiod, ranging from permanent to seasonally ephemeral, isolated sites. The latter are important breeding sites for many amphibians, although ephemeral wetlands have received little or no mention in most summaries of the expected effects of climate change on freshwater systems (e.g., Mulholland et al., 1997; Meyer et al., 1999; Allan et al., 2005; Bates et al., 2008). Amphibians are important 'bioindicators' of habitat suitability and ecosystem restoration success (Waddle, 2006): they are sensitive to changes in the environment, especially those having to do with water quantity and quality. Because amphibian reproduction is so tightly tied with the aquatic habitat, changes in hydrology are perhaps the biggest threat to most species. Indeed, freshwater wetlands of varying types are considered 'optimal' habitat for 95% of the species of anurans and 64% of the species of salamanders found in the southeast U.S. (Bailey et al., 2006). Amphibians are also abundant and readily sampled with established methods. When several species of amphibians are evaluated together, the species composition is a good indicator of habitat quality.
The DOI Science Plan for CERP and the research areas outlined by the BAA request for proposals described a need for scientific research that will develop models that can be used as tools to evaluate restoration alternatives and assess restoration outcomes. Because hydrology is a major driving factor in Everglades habitats, our focus in prior funding was to create a model of amphibian occupancy in relation to hydrology and habitat, to be used as a restoration evaluation tool. We collected data on amphibian distributions by habitat and hydrology in Everglades National Park, Big Cypress National Preserve, Florida Panther National Wildlife Refuge, Fakahatchee Strand State Reserve and Picayune Strand State Forest. These data were collected for analysis, along with hydrological data, to produce an ecological model of occupancy of amphibian communities. The goal was for this community level occupancy rate to serve as an index, a target for restoration assessment and, in a spatial framework, as a tool for evaluation of alternatives.
This community index model of amphibians throughout southwest Florida, called the Stressor Response Model for Southwest Florida Amphibians, is currently being finalized. Estimates of the proportion of sites occupied by amphibian species in various habitats under different hydrologic conditions will elucidate patterns and lead to the creation of an amphibian community index. This index can then be used to predict the effects of various water management scenarios on the amphibian community.
This model also serves as a promising tool for assessing the potential impact of climate change on amphibians occupying a hydrologically modified/restored landscape. Climate change may influence the hydrology of freshwater wetlands by altering patterns of precipitation, groundwater levels, evapotranspiration, and the frequency and intensity of fires. Variation in these factors may interact with various community characteristics (e.g., community type, canopy cover) to further influence site hydroperiod. For instance, Mulholland et al. (1997) predicted that large increases in summer precipitation during the wet season in south Florida may lead to extensive pine flatwoods/cypress swamp areas becoming dominated by pond cypress, and extensive areas of sawgrass marsh being converted to open water. Modification of wetland hydroperiod ultimately affects the presence of fish and invertebrate predators on larval amphibians, larval growth, survival and, ultimately, the species richness of amphibians at a site. The Stressor Response Model can potentially be used to predict how amphibians may respond under different climate change scenarios.
Our long-term objective in the present study is to validate this newly-developed model with respect to predicted responses of an amphibian community to hydrologic and habitat restoration at a focal site. Two objectives in prior funding were (1) to define amphibian communities appropriate for evaluating restoration success and (2) to develop restoration targets for the amphibian community of southwest Florida. With that funding, we identified two anuran species (the Pinewoods treefrog, Hyla femoralis and the Barking treefrog, Hyla gratiosa) that are particularly sensitive as indicators of suitable pine flatwoods habitat. However, with encroaching climate change, the hydric pine flatwoods of south Florida are specifically predicted to be converted to sites dominated by pond cypress (Mulholland et al., 1997). Moreover, only approximately 12% of the historic (ca. 1940) pinelands in some regions of southwest Florida remains (Mazotti et al., 1992, sensu Pearlstine et al., 1995). During our prior effort we also identified the habitat targeted in CERPís Picayune Strand Hydrologic Restoration project as being well suited for testing the predictions of our model with regards to the potential responses of H. femoralis and H. gratiosa to restoration of the hydrologically degraded habitat in Picayune Strand State Forest. Our specific objectives are to: