Species Removal Studies. I. Dispersal Strategies of Sympatric Sigmodon hispidus and Reithrodontomys fulvescens Populations

Abstract

Sigmodon hispidus and Reithrodontomys fulvescens are the codominant rodent species of the Texas coastal prairie. Eight isolated 1.6 hectare replicated plots were used to study dispersal strategies of these rodents. Each replicate was live-trapped for nineteen months. For two control replicates all captured individuals were identified, sexed, weighed, marked, and released. In two perturbed replicates all Reithrodontomys were removed, in two perturbed replicates all Sigmodon were removed, and in two other perturbed replicates both species were removed. Monthly dispersal of individuals into plots where that species was previously removed was measured. The number of dispersers of both sexes of Sigmodon and Reithrodontomys were positively correlated with monthly changes in control (resident) density. Sex ratio comparisons between dispersers and residents reflected nonsignificant differences for both species. The rank-order of weight (age) classes of dispersers was positively correlated with the classes found in control plots for female Sigmodon and male Reithrodontomys entering both types of perturbed conditions. Pre-emption by Reithrodontomys appeared to inhibit the immigration of the larger (adult) classes of Sigmodon males. Higher proportions of Reithrodontomys females, compared to males, invaded both types of perturbed plots. Resident populations of both species appeared to inhibit conspecific immigration. The rank-order templated dispersal strategy found during this study has the advantage of introducing a stabilized age structure into newly acquired habitat space.