Male group size, female distribution and changes in sexual segregation by Roosevelt elk.

Leah M Peterson,Floyd W Weckerly,Cheryl S Rosenfeld

doi:10.1371/journal.pone.0187829

Abstract

Sexual segregation, or the differential use of space by males and females, is hypothesized to be a function of body size dimorphism. Sexual segregation can also manifest at small (social segregation) and large (habitat segregation) spatial scales for a variety of reasons. Furthermore, the connection between small- and large-scale sexual segregation has rarely been addressed. We studied a population of Roosevelt elk (Cervus elaphus roosevelti) across 21 years in north coastal California, USA, to assess small- and large-scale sexual segregation in winter. We hypothesized that male group size would associate with small-scale segregation and that a change in female distribution would associate with large-scale segregation. Variation in forage biomass might also be coupled to small and large-scale sexual segregation. Our findings were consistent with male group size associating with small-scale segregation and a change in female distribution associating with large-scale segregation. Females appeared to avoid large groups comprised of socially dominant males. Males appeared to occupy a habitat vacated by females because of a wider forage niche, greater tolerance to lethal risks, and, perhaps, to reduce encounters with other elk. Sexual segregation at both spatial scales was a poor predictor of forage biomass. Size dimorphism was coupled to change in sexual segregation at small and large spatial scales. Small scale segregation can seemingly manifest when all forage habitat is occupied by females and large scale segregation might happen when some forage habitat is not occupied by females.

Highlights

Sexual segregation, or the differential use of space by males and females, is ubiquitous among size-dimorphic vertebrates [1]
Between 1997 and 2008, 91 percent or more of males were encountered in the Davison and the remaining 9 percent or less were sighted in the Boyes meadow complex
Our findings were consistent with the female avoidance hypothesis for small spatial scale—social or group level segregation—and the vacated female hypothesis for large-scale— habitat segregation

Summary

Introduction

The differential use of space by males and females, is ubiquitous among size-dimorphic vertebrates [1]. The degree of sexual segregation in mammals often varies seasonally, reflecting a lower degree of segregation during the mating season and a higher degree of segregation during parturition and lactation [5, 6]. These seasonal patterns are often attributed to the intersexual difference in requirements for achieving reproductive success [7]. The persistence of sexual segregation beyond parturition and mating seasons infers that what occurs outside of the times of reproductive events must be influential [8, 9].

Methods

Results

Conclusion