Land Cover Influence on South Carolina Alligator Densities Derived from Nightlight Surveys (1971-2013)


Abigail J. Lawson


Kate McFadden


Wildlife and Fisheries Biology (College of Agriculture, Forestry and Life Sciences)


The American alligator (Alligator mississippiensis) is an iconic species of the southeastern U.S. of cultural and ecological importance. In South Carolina, habitat loss and fragmentation are considered prominent threats to alligator populations. I identified habitat features that influence alligator abundance and evaluated temporal and demographic differences. Alligator nightlight surveys were conducted by boat on rivers and lakes between 1971-1977 and 2011-2013. I examined land cover patterns within 1, 3, 5, and 10 km of each survey route. I used linear regression to identify land cover categories that best described juvenile, adult, and total alligator densities for each time period. Average density increased from 0.48 ± 0.54 (SE) alligators per km during the 1970s to 2.84 ± 2.03 for current surveys. Urban land cover proportion within each route area during the 1970s positively influenced total alligator densities (β: 0.21, 95% CI: 0.16-0.26), though current total alligator densities were negatively influenced by agriculture (β: -0.60, 95% CI: -0.29 - -0.97). Interestingly, the best explanatory variables for juvenile density differed among survey periods, and from variables that best described adult and total densities. Identifying potential mechanisms that explain these observed patterns is essential for effective broad-scale alligator conservation planning in a changing landscape.

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