Regional development and water management practices have drastically altered the spatial extent and traditional hydropatterns of the Greater Everglades. Proposed restoration plans will dramatically affect the Everglades ecosystem. Alligators are a keystone species that have an important role in the trophic dynamics of the Everglades by engineering trails, "gator" holes and caves that are important refugia for many species of plants and animals (especially fish and amphibians) during the dry season. Canals (one focus of restoration plans) serve as refugia for alligators throughout the Everglades. Alligator life history patterns (including movement and habitat selection) are expected to change in response to restoration efforts.

For this study, the American alligator was selected (Alligator mississippiensis) as an indicator of the success of restoration efforts. The objective was to collect information that can be used in ecological models for predicting and evaluating alternatives of the Comprehensive Everglades Restoration Plan (CERP). The success of restoration efforts will rely on models such as the Across-Trophic Level System Simulation that require valid estimates of alligator response to habitat restoration.

Radio telemetry was used to examine habitat selection and home range of alligators in the Greater Everglades. The size and shape of home ranges as well as selection of cover types within home ranges reflect the quality and condition of available resources. As canals are removed and alligators move back into adjacent marsh habitat, we anticipate that resource selection (and ultimately demography) will depend on where the alligator is located in the Greater Everglades. Therefore, alligators were observed inthree contrasting Everglades habitats: marsh in Water Conservation Area 3A North (WCA), marsh in the Everglades National Park (ENP), and canals in both the WCA and ENP (Canal). Weekly locations for 66 alligators (WCA = 11, ENP = 22, Canal = 33 alligators) and intensive daily locations for 31 alligators (WCA = 6, ENP = 7, Canal = 18 alligators) were recorded in the 3 habitats. Weekly locations were recorded using aerial telemetry, while the daily locations were recorded using ground-based telemetry.

Home range for all alligators was estimated using a 95 percent daptive kernel model, which is a more robust and conservative estimate of home range size. However, we used a 100 percent. Minimum Convex Polygon (MCP) to estimate the proportion of habitat available to alligators in our examination of habitat selection. A 100 percent MCP included all habitats used by each alligator. We used compositional analysis to examine the selection of cover types with the 100 percent MCP. We examined seven cover types for the daily locations. The number of cover types was restricted by sample size. Cover types for daily locations included: 1) sawgrass (Cladium jamaicense), 2) emergent vegetation - including spikerush (Eleocharis cellulosa) and cattails (Typha spp.), 3) uplands - tree islands and shrub islands, 4) floating vegetation - mainly water lilies (Nuphar spp., and Nymphaea spp.), 5) open water - areas with little or no vegetation, 6) "gator" hole, and 7) canal. For weekly locations the same 7 cover types included in the daily locations were examined, but levee break, gator trail and airboat trail were added.

Mean home range was larger for alligators in canals (111.2 ± 27.1 ha, ± SE) than either WCA (55.5 ± 17.7 ha) or ENP (79.7 ± 25.2 ha) marshes. There was no difference in home ranges for alligators in the marsh of WCA and ENP. Mean male home range (144.34 ± 22.3 ha) was larger than female home range (35.91 ± 16.76 ha).

Alligators frequently selected deeper water marsh in WCA (table 1) for both daily (P < 0.05) and weekly locations (P < 0.001). Floating vegetation was selected more than any other cover type for both daily and weekly locations. Weekly location data also indicated selection for emergent vegetation, levee breaks, and airboat trails that was greater than other cover types.

Alligators were frequently located in gator holes (table 1) in ENP during both daily (P < 0.01) and weekly locations (P < 0.0001). Daily locations also indicated a selection for emergent vegetation not observed for weekly locations. Spikerush and cattails often surround gator holes in ENP. More intensive daily locations were more likely to record locations in the surrounding emergent vegetation while alligators were using holes.

As expected, canal alligators strongly selected canals over all other cover types (table 1) for both daily (P < 0.0001) and weekly locations (P < 0.0001). The creation of canals in the Greater Everglades has influenced alligator movement and habitat selection. Canal alligators spend most of their time in canals and move greater distances (i.e., have larger, more linear home ranges) than alligators in WCA or ENP marshes. The response of alligators to the proposed removal of canals may depend on adjacent habitat. Alligators are able to restore abandoned alligator holes or create new holes in the peat dominated slough of ENP, but they may be drawn to deeper water marsh, such as found around floating vegetation or in levee breaks in the WCAs.

Contact: Michael L. Phillips, University of Florida, Ft. Lauderdale Research and Education Center, 3205 College Ave., Ft. Lauderdale, FL 33314-7799; Phone: 954-577-6306, FAX: 954-475-4125, mlphillips@usgs.gov

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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