Resource distribution influences mating system in the bobuck (Trichosurus cunninghami: Marsupialia)

Abstract

Mammalian mating systems are thought to be shaped by the spatial distribution and abundance of key resources, which in turn influence the spacing behaviour of individuals. In particular, female home range size is predicted to reflect the availability of key resources. We documented the availability and distribution of food and shelter resources for two neighbouring populations of bobucks, or mountain brushtail possums, Trichosurus cunninghami, that were characterised by different mating systems: our "forest population" was socially monogamous, whereas the "roadside population" was polygynous. Both silver wattle, Acacia dealbata, the main food resource for bobucks, and den-trees, which provided shelter, occurred at significantly higher density at the roadside site. The pattern of distribution of these two resources also differed between the sites. Both food and den-trees were scattered evenly throughout the roadside habitat. In contrast, den-trees were located predominantly at one end of the forest site, while silver wattle trees were located at the other. There was no significant difference in the amount of silver wattle, or in the number of den-trees, located within the home ranges of individual females at the two sites. However, forest females had home ranges, on average, almost three times the size of those of roadside females. At the roadside site, the size of female home ranges varied inversely with the density of silver wattle, indicating that these females ranged over as large an area as necessary to gain access to sufficient silver wattle trees. There was no such relationship among forest females. These populations provide a clear example of resource distribution determining female home range size. This influenced the number of female home ranges a male's home range overlapped with, which in turn determined the mating system. Such clear links between resource availability and mating system have not previously been established in a marsupial.

Kin selection in den sharing develops under limited availability of tree hollows for a forest marsupial

“…Because mountain ash trees are the only trees at this site large enough to form hollows suitable for mountain brushtail possums, the varying age of the mountain ash overstorey results in spatial heterogeneity in the availability of den resources (figure 1). Mountain brushtail possums are predominantly solitary, although they occasionally share dens with other individuals and a proportion of individuals form 'socially monogamous' pairs, the rate of which varies between populations [31,33]. At our Cambarville study site, the rate of sequential (between years) monogamy was approximately 46 per cent for females and 60 per cent for males, which is higher than expected random mating (M. D. J. Blyton, S. C. Banks, D. B. Lindenmayer & R. Peakall 2010, unpublished data).…”

“…At our Cambarville study site, the rate of sequential (between years) monogamy was approximately 46 per cent for females and 60 per cent for males, which is higher than expected random mating (M. D. J. Blyton, S. C. Banks, D. B. Lindenmayer & R. Peakall 2010, unpublished data). Females produce a single offspring per year [33].…”

Resting and nesting in a small mammal: sleeping sites as a limiting resource for female grey mouse lemurs

“…The highly skewed use of sleeping sites suggests that sleeping site trees are restricted in the study area and may thus represent a limiting resource for female grey mouse lemurs as has been reported for other mammals (e.g. Du Plessis 1992; Doncaster & Woodroffe 1993;Martin & Martin 2007;Walker et al 2007). The importance of large trees for the study species is further indicated by the uneven distribution of grey mouse lemurs in the study area that has previously been linked to vegetation features such as a lack of large trees and cover with plant creepers (Rendigs et al 2003).…”

“…Day & Elwood 1999;Sedgeley & O'Donnell 1999;Martin & Martin 2007). In addition, the availability of suitable sleeping sites can limit population density and affect a species' space use and social interactions (Du Plessis 1992;Doncaster & Woodroffe 1993;Chaverri et al 2007b;Martin & Martin 2007;Walker et al 2007;Kerth 2008).…”

“…In addition, female mammals require well-insulated and protected sites for dependent young (Soderquist 1993;Radespiel et al 1998;Henner et al 2004;Chaverri et al 2007a). The importance of this resource for female mammals is illustrated in a study of bobucks, Trichosurus cunninghami (Martin & Martin 2007) where females increased their home range size by three times in habitats where den trees were rare compared to habitats were they were common, even though food abundance was comparable between the sites.…”