Population Structure of Everglades Rodents: Responses to a Patchy Environment

Abstract

This study investigated (1) how individuals respond to patchy environments, and (2) how these responses may collectively produce attributes that characterize local and regional populations. Mark-recapture trapping was used to monitor populations of Peromyscus gossypinus, Sigmodon hispidus , and Oryzomys palustris occurring on a constellation of six discrete patches (tropical hardwood hammocks) in the Everglades of south Florida. In the wet season the populations were compressed onto the hammocks where the three species occurred together at high densities in 1975. In 1976 there were fewer Peromyscus and Sigmodon in the wet season than in the other years, while the density of Oryzomys matched its 1975 level. All reproduction occurred in the wet season. In the dry season Sigmodon moved off the hammocks and occupied the prairie, Oryzomys disappeared (presumably to seek refuge in mesic sites off the study area), and Peromyscus remained on the hammocks (although frequently caught on the prairie). Sigmodon and Oryzomys recolonized the hammocks at the beginning of the wet season, although no individuals captured on the hammocks in 1975 returned in 1976. Of the three species, Oryzomys showed the greatest degree of interhammock movements; Peromyscus was the least vagile. Interhammock movements by individual Peromyscus were dependent on sex, season, and hammock size. The largest hammock, 0.25 ha, apparently promoted and accomodated fewer vagrant Peromyscus than the smaller hammocks. Saturation of habitat appears determined by the interplay of the size and spacing of the hammocks and the structure of each species population.