Sexual and density dependent behavior in two neotropical small mammals

Abstract

1. Home range and resource selection are important ecological approaches to understand how animals occupy the space and use the resources available. Sex is an important intrinsic factor that can mediate or change how the individual uses the habitat and selects the resources. Another important factor is the population density that can limit or facilitate both the formation and use of the home range and the selection of resources. 2. Here, we present two studies, one related to the home range of the opossum Didelphis albiventris in an urban area and the other related to resource selection of the rodent Thrichomys fosteri in a region of the Pantanal. In the first study, we investigated the relationship between body mass and sex influencing the home range size. We hypothesized that males should have larger home ranges than females and larger animals should have larger home ranges. In the second study, we hypothesized that the main resource for the rodent should be the density of bromeliad stands, which protects spiny rats from predators, being potentially more important for females than males. We also hypothesized that the abundance of conspecifics should lead females to a negative selection and, lead males to a positive selection due to different sexual behaviors related to sexes. 3. We did not find any relationship between sex and weight with the home range size of D. albiventris. However, females showed a lower overlap of their core areas when compared to male-male overlap. The bromeliad cover was the main resource for T. fosteri, with an almost double selection force for females than for males. Females selected for areas with lower density of conspecifics, while male selected for higher densities. We also hypothesized that the abundance of conspecifics should lead females 8 to a negative selection and, lead males to a positive selection due to different sexual behaviors related to sexes. 4. Spatial limitation and urban barriers may explain the absence of effect of mass and sex on the home range of opossums. In addition, supplementary feeding with human waste and generalist habits can also limit the movement of urban animals. The low overlap of female core areas may be a response to reproductive behavior, where females need more exclusive areas for the care of their offspring. The higher selection of T. fosteri females for bromeliads can also be explained by the higher need of females for protection to maximize their reproductive success by survival of the offspring. In the same way, females tend to avoid areas with high density of conspecifics. On the other hand, males should maximize their reproductive success by covering a larger number of females, so they should not avoid areas with high density of individuals, even when it entails being more exposed to predators.