Effects of Vegetation Structure and Elevation on Lower Keys Marsh Rabbit Density



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The Lower Keys marsh rabbit (Sylvilagus palustris hefneri, LKMR), 1 of 3 subspecies of Sylvilagus palustris, is endemic to the Lower Florida Keys. The LKMR is listed as an endangered species due to predation by feral and free roaming domestic cats (Felis catus) and raccoons (Procyon lotor), road mortality, effects of storm surges, sea level rise, the small declining metapopulation size, and possible habitat loss from hardwood encroachment. The purpose of this study was to determine the current LKMR density on lands managed by the United States Navy, Naval Air Station Key West and evaluate how vegetation structure and patch elevation effect LKMR population density. I conducted fecal pellet counts to determine LKMR density, collected vegetation data using percent composition of ground cover, Robel range pole, and point-centered quarter methods, and obtained data on patch area and elevation. I used simple linear regression to assess the relationship between LKMR density and 9 measured vegetation characteristics, patch area, and patch elevation to determine which variables have an influence on LKMR density and the relationship between them.

In my examination of the simple regression models, 6 out of the 11 variables appeared to influence LKMR population density. The average per patch percent composition of nonliving material and grasses, maximum height of vegetation at the range pole, distance to nearest woody vegetation, patch elevation, and visual obstruction readings (VOR) individually accounted for 26.4%, 30.4% , 18.1%, 8.5%, 6.8%, and 1.4% of the variability in LKMR density, respectively. According to the regression models, LKMR density increased in patches with greater amounts of grasses and with greater distance to woody vegetation. Habitat management is vital to the recovery of the LKMR and needs to focus on providing greater amounts of grasses and reducing the amount of woody vegetation encroachment to enhance LKMR population density.