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

Abstract

Species in many ecosystems are facing declines of key resources. If we are to understand and predict the effects of resource loss on natural populations, we need to understand whether and how the way animals use resources changes under resource decline. We investigated how the abundance of arboreal marsupials varies in response to a critical resource, hollow-bearing trees. Principally, we asked what mechanisms mediate the relationship between resources and abundance? Do animals use a greater or smaller proportion of the remaining resource, and is there a change in cooperative resource use (den sharing), as the availability of hollow trees declines? Analyses of data from 160 sites surveyed from 1997 to 2007 showed that hollow tree availability was positively associated with abundance of the mountain brushtail possum, the agile antechinus and the greater glider. The abundance of Leadbeater’s possum was primarily influenced by forest age. Notably, the relationship between abundance and hollow tree availability was significantly less than 1∶1 for all species. This was due primarily to a significant increase by all species in the proportional use of hollow-bearing trees where the abundance of this resource was low. The resource-sharing response was weaker and inconsistent among species. Two species, the mountain brushtail possum and the agile antechinus, showed significant but contrasting relationships between the number of animals per occupied tree and hollow tree abundance. The discrepancies between the species can be explained partly by differences in several aspects of the species’ biology, including body size, types of hollows used and social behaviour as it relates to hollow use. Our results show that individual and social aspects of resource use are not always static in response to resource availability and support the need to account for dynamic resource use patterns in predictive models of animal distribution and abundance.

Relationships between tree size and occupancy by cavity-dependent arboreal marsupials

“…Our analyses revealed that, for all species of arboreal marsupial, the probability of occupancy of an individual hollow-bearing tree was lowest in old growth stands (Figure 2; Appendix 1). Earlier research (Banks et al, 2013) found that the relationship between animal abundance and hollow-bearing tree abundance was positive, but less than 1:1. This was due primarily to a significant increase by all species in the proportional use of hollow-bearing trees where the abundance of this resource was low (Banks et al, 2013).…”

“…Earlier research (Banks et al, 2013) found that the relationship between animal abundance and hollow-bearing tree abundance was positive, but less than 1:1. This was due primarily to a significant increase by all species in the proportional use of hollow-bearing trees where the abundance of this resource was low (Banks et al, 2013). These earlier results also suggest that other resources or social constraints become limiting for arboreal marsupials under conditions of high hollow-bearing tree availability, such as that found in old growth forest.…”

“…Potentially, the proportion of hollow trees used per animal may vary with hollow tree availability (for instance, due to changes in resource sharing; (Banks et al, 2011) or due to resources other than the availability of hollow trees limiting animal occurrence (Banks et al, 2013). For example, the probability of occupancy of individual hollow-bearing trees may be reduced in old growth forests where animals have access to many alternative trees; that is, the marginal value of a given tree will be lower where there are already many hollow-bearing trees (Fischer et al, 2010).…”

“…These earlier results also suggest that other resources or social constraints become limiting for arboreal marsupials under conditions of high hollow-bearing tree availability, such as that found in old growth forest. Conversely, low levels of abundance of hollow-bearing trees in younger aged forests mean that cavity-dependent arboreal marsupials have little choice other than to occupy the fewer remaining nest trees in these kinds of forests where alternative nesting resources are depleted (see Banks et al, 2013). That is, the marginal value of a given large hollow-bearing tree for occupancy may be higher in stands dominated by otherwise much younger-aged forest and where such important nesting and denning resources are uncommon or rare (Fischer et al, 2010).…”

Landscape connectivity and conservation prioritization for an old forest species with limited vagility

“…Reduction in forests containing large, old trees poses pervasive conservation challenges because many species depend on trees with complex structural characteristics that take decades or centuries to develop (Banks et al, 2013). What remains of forested landscapes, including the distribution and extent of remnant old-forest patches and intervening cover types, is a primary driver of the capacity of these landscapes to support populations of old-forest dependent species (Lindenmayer et al, 1999;.…”