Tree Islands of the Everglades

Chapter 14.
Effects of Tree Island Size and Water on the Population Dynamics of Small Mammals in the Everglades

Michael S. Gaines¹, Christopher R. Sasso¹, James E. Diffendorfer², and Harald Beck¹
email: m.gaines@miami.edu
¹University of Miami, Department of Biology, Coral Gables, FL 33124.
²San Diego State University, Department of Biology, 5500 Campanile Dr, San Diego, CA 92104.

From Tree Islands of the Everglades edited by Fred H. Sklar (South Florida Water Management District) and Arnold G. van der Valk (Iowa Lakeside Laboratory)

Abstract

Tree islands in the Everglades prairie provided a unique opportunity to study how patch dynamics affect population processes in two small mammal species, the marsh rice rat and hispid cotton rat. We assessed the effect of island size and water on density, survivorship, reproduction, and movement in both these species. Rice rats had the highest densities on the small islands, while survivorship and reproductive activity was not affected by island size. Cotton rats had the highest densities and reproductive activity on large islands, while survivorship and reproduction was not affected by island size In both species, the highest proportion of animals moved from small islands.

The semi-aquatic rice rat was not affected by the presence of water. In contrast, the presence of water had a negative effect on the cotton rat, which is generally found in upland habitat. Abundance, survival and reproduction of cotton rats were all lower on the islands when there was water in the prairie matrix. We concluded that tree islands are crucial for the persistence of both species. Tree islands may provide resources such as food, nest sites, and refugia from water. The interaction of island size, presence or absence of water in the prairie, and the movement of individuals may give insight into the long term survival of these species in the Everglades.

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