[Show abstract][Hide abstract] ABSTRACT: Hydrologic conditions are critical to the nesting behavior and reproductive success of crocodilians. In South Florida, USA, growing human settlement has led to extensive surface water management and modification of historical water flows in the wetlands, which have affected regional nesting of the American alligator (Alligator mississippiensis). Although both natural and anthropogenic factors are considered to determine hydrologic conditions, the aspects of hydrological patterns that affect alligator nest effort, flooding (partial and complete), and failure (no hatchling) are unclear. We deconstructed annual hydrological patterns using harmonic models that estimated hydrological matrices including mean, amplitude, timing of peak, and periodicity of surface water depth and discharge and examined their effects on alligator nesting using survey data from Shark Slough, Everglades National Park, from 1985 to 2005. Nest effort increased in years with higher mean and lesser periodicity of water depth. A greater proportion of nests were flooded and failed when peak discharge occurred earlier in the year. Also, nest flooding rates were greater in years with greater periodicity of water depth, and nest failure rate was greater when mean discharge was higher. This study guides future water management decisions to mitigate negative impacts on reproduction of alligators and provides wildlife managers with a tool for assessing and modifying annual water management plans to conserve crocodilians and other wetland species.
Journal of Wildlife Management 01/2013; · 1.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tree islands—small, wetland forest communities imbedded in a matrix of freshwater marsh—characterize Arthur R. Marshall Loxahatchee National Wildlife Refuge in South Florida. The establishment and spread of invasive exotic plant species were hypothesized to alter tree-island communities and prolong recovery times from hurricane disturbances. During the fall of 2004, two hurricanes, Frances and Jeanne, caused damage to these tree islands. We examined the spatial extent of damage to tree islands and tree species across the Refuge by sampling 74 islands. Each tree island was assigned an overall damage rating based on both the openness of the canopy and the type and quantity of damage received. Distance from the eye-wall of the hurricanes, tree-island size, average tree height on the island, and relative abundance of invasive exotic plants were examined as predictors of damage. Over 85% of the sampled tree islands had damage, with most of the damage occurring in the center of the Refuge. Most tree islands were found to have moderate damage, (i.e., snapped large branches and less than 50% canopy cover removed). Persea palustris (swamp bays) had more snapped trunks than Ilex cassine (dahoon holly) and Myrica cerifera (wax myrtle). Islands with larger trees had heavier damage than islands with shrubs or smaller trees. Fifty-eight percent of the tree islands sampled had either Lygodium microphyllum (lygodium) and/or Melaleuca quinquenervia (melaleuca). The only island with severe damage had abundant lygodium that appeared to have caused the entire canopy to collapse. These hurricanes present a unique opportunity to investigate recovery patterns of tree islands in an ecosystem impacted by invasive exotics. They also provide an opportunity to examine patterns of spread and recruitment of lygodium and melaleuca.
[Show abstract][Hide abstract] ABSTRACT: The Pig Frog (Rana grylio) is an aquatic frog that is an abundant component of the Everglades ecosystem. South Floridians recreationally and commercially hunt pig frogs in marshes throughout Water Conservation Areas (WCA) and Big Cypress National Preserve (BCNP) in South Florida. Most of these areas are under fish consumption advisories because of high levels of methylmercury present in game fish tissues. It is important to understand how mercury is distributed throughout Pig Frog populations because their consumption from certain areas may present a risk to human health. We sampled 88 pig frogs along a north-south transect through the Florida Everglades. There were substantial differences in total mercury (THg) concentrations from leg muscle tissue among sites. Total mercury in frog leg tissue was highest from areas protected from harvest in Everglades National Park (ENP), with a maximum concentration of 2051 ng/g wet mass. The THg levels in R. grylio leg tissue from most harvested areas are below Federal advisory limits. However, many pig frogs collected near Frog City, and one from WCA 3B and 3AN, harvested sites, had THg levels above the USEPA 0.3 mg/kg Fish Tissue Residue Criterion. Spatial patterns in the mercury found among pig frogs were similar to those of other wildlife species from the Everglades. We found frogs to have high THg levels in areas where alligators and mosquito fish also have high THg. THg in ENP frogs had an exponential relationship to SVL, we found no other relationship in frogs from other sites. Our data suggests that pig frogs should not be harvested or consumed from sites that exceed federal limits.
Science of The Total Environment 07/2005; 345(1-3):51-9. · 3.26 Impact Factor