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

Abstract

Animal social behaviour is not static with regard to environmental change. Flexibility in cooperative resource use may be an important response to resource decline, mediating the impacts of resource availability on fitness and demography. In forest ecosystems, hollow trees are key den resources for many species, but are declining worldwide owing to forestry. Altered patterns of den sharing may mediate the effects of the decline of this resource. We studied den-sharing interactions among hollow-dependent Australian mountain brushtail possums to investigate how spatial variation in hollow tree availability affects resource sharing and kin selection. Under reduced den availability, individuals used fewer dens and shared them less often. This suggests increased territoriality in the presence of resource competition. Further, there was a switch from kin avoidance to kin preference with decreasing hollow tree availability. This was driven primarily by a change in den sharing among siblings. The inclusive fitness benefits of den sharing with kin are likely to increase under resource-limiting conditions, but are potentially outweighed by the benefits of associating with non-relatives (avoidance of inbreeding or pathogen transmission) where dens are abundant. We discuss how predictions from social evolutionary theory can contribute to understanding animal responses to landscape change.

Can Individual and Social Patterns of Resource Use Buffer Animal Populations against Resource Decline?

“…Even within the same study region (and species), different studies have revealed contradictory patterns in different populations. Mountain brushtail possums at Cambarville (within the broader region studied here) shared dens less often and used fewer trees where hollow trees were scarce [15], [23], [46]. These results contradict the present findings and are consistent with predictions from theoretical and empirical work suggesting that resource defence behaviour and intolerance of other individuals develops under resource competition [30].…”

“…Commonly, resource-based models of distribution or abundance assume a static relationship between populations and resources [6]. However, increasing evidence demonstrates that the kinds of resources that are used [11], [12], the frequency with which they are used (or avoided) in relation to their availability (the resource selection function) [13], [14], and the degree of resource sharing (cooperation) [15] can vary with resource availability or other changes such as human disturbance or predation pressure [16], [17]. An understanding of the mechanisms by which animals respond to variation in resource availability is essential if we are to predict how resource variation will affect animal populations [9], [18].…”

“…Alternatively, decreasing resource availability can lead to increasing resource competition, with increasing aggression, resource defence and territoriality [30], [31]. Indeed, one of the species studied here, the mountain brushtail possum ( Trichosurus cunninghami ) shared dens less often where dens were less abundant [15], suggesting that social mechanisms can exacerbate the effects of resource decline.…”

Adaptive responses and disruptive effects: how major wildfire influences kinship‐based social interactions in a forest marsupial

“…Disturbance events may affect social behaviour by mediating the key factors underlying the evolution of social systems, such as demography, genetic population structure and resource availability (Brockhurst et al. 2007, 2010; Banks et al. 2011a).…”

Temporal patterns of den use suggest polygamous mating patterns in an obligate monogamous mammal

“…For instance, mountain brushtail possums (Richosurus cunninghami) increased their level of territoriality when their number of dens declined due to habitat destruction (Banks et al 2011), and the availability and distribution of suitable den sites have been suggested to limit group size in Eurasian badgers (Meles meles) (Doncaster & Woodroffe 1993). Aardwolves are primarily nocturnal and dens are important as thermal refugia during periods of inactivity, particularly during the cold dry season when thermal and nutritional stresses are high (Williams et al 1997).…”