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Can individual and social patterns of resource use buffer animal populations against resource decline?

Banks SC, Lindenmayer DB, Wood JT, McBurney L, Blair D, Blyton MD - PLoS ONE (2013)

Bottom Line: 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.Notably, the relationship between abundance and hollow tree availability was significantly less than 1:1 for all species.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.

View Article: PubMed Central - PubMed

Affiliation: The Fenner School of Environment and Society, The Australian National University, Canberra, Australian Capital Territory, Australia. Sam.Banks@anu.edu.au

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.

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The proportion hollow-bearing trees on each site that are live trees (Tree forms 1–2 in Figure 1), early-decay stage dead trees (Tree forms 3–6) or late-decay stage dead trees (Tree forms 7–8) plotted in relation to the number of hollow-bearing trees per site.
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pone-0053672-g002: The proportion hollow-bearing trees on each site that are live trees (Tree forms 1–2 in Figure 1), early-decay stage dead trees (Tree forms 3–6) or late-decay stage dead trees (Tree forms 7–8) plotted in relation to the number of hollow-bearing trees per site.

Mentions: We used binomial GLMMs with a logit link function to analyse the probability of occupancy of each tree by each arboreal marsupial species. Site and year were included in the models as random terms. The candidate explanatory variables (fixed terms) included the number of trees per site (untransformed and log-transformed), forest age category and tree form (Figure 1). Tree form was included because past work indicates that each species has a preference for particular kinds of tree forms [21], and the decay stage of hollow trees that predominate at a site is not independent of the number of trees at that site (Figure 2). For instance, old growth forest stands contain many hollow-bearing trees that are usually alive (Tree forms 1 and 2 in Figure 1). Younger regrowth forests typically contain few hollow trees, and those that are present are often highly decayed ‘legacies’ of an older cohort of trees from before the previous fire (Tree forms 6–8 in Figure 1). Further, the number and type of hollows found in the different tree forms can vary, with the earlier decay classes (Figure 1) often having a number of hollows in broken branches and the later decay classes having fewer, but larger, hollows in a highly decayed main stem [32]. We commenced our analyses with tree form represented as a categorical variable with all nine decay classes (Figure 1). However, after initial exploratory analyses, the tree forms were often condensed to two or three subsets based on the habitat use of each species. For example, for greater gliders we reclassified the tree forms (Figure 1) into a binomial variable distinguishing live trees (Tree forms 1–2) from dead trees (Tree forms 3–8). We included interactions between the number of hollow trees per site and tree form to test for shifts in the kinds of hollow trees selected as dens under variation in den availability (i.e. Is there a ‘relaxation’ of tree form preference as hollow trees become more scarce?).


Can individual and social patterns of resource use buffer animal populations against resource decline?

Banks SC, Lindenmayer DB, Wood JT, McBurney L, Blair D, Blyton MD - PLoS ONE (2013)

The proportion hollow-bearing trees on each site that are live trees (Tree forms 1–2 in Figure 1), early-decay stage dead trees (Tree forms 3–6) or late-decay stage dead trees (Tree forms 7–8) plotted in relation to the number of hollow-bearing trees per site.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3539978&req=5

pone-0053672-g002: The proportion hollow-bearing trees on each site that are live trees (Tree forms 1–2 in Figure 1), early-decay stage dead trees (Tree forms 3–6) or late-decay stage dead trees (Tree forms 7–8) plotted in relation to the number of hollow-bearing trees per site.
Mentions: We used binomial GLMMs with a logit link function to analyse the probability of occupancy of each tree by each arboreal marsupial species. Site and year were included in the models as random terms. The candidate explanatory variables (fixed terms) included the number of trees per site (untransformed and log-transformed), forest age category and tree form (Figure 1). Tree form was included because past work indicates that each species has a preference for particular kinds of tree forms [21], and the decay stage of hollow trees that predominate at a site is not independent of the number of trees at that site (Figure 2). For instance, old growth forest stands contain many hollow-bearing trees that are usually alive (Tree forms 1 and 2 in Figure 1). Younger regrowth forests typically contain few hollow trees, and those that are present are often highly decayed ‘legacies’ of an older cohort of trees from before the previous fire (Tree forms 6–8 in Figure 1). Further, the number and type of hollows found in the different tree forms can vary, with the earlier decay classes (Figure 1) often having a number of hollows in broken branches and the later decay classes having fewer, but larger, hollows in a highly decayed main stem [32]. We commenced our analyses with tree form represented as a categorical variable with all nine decay classes (Figure 1). However, after initial exploratory analyses, the tree forms were often condensed to two or three subsets based on the habitat use of each species. For example, for greater gliders we reclassified the tree forms (Figure 1) into a binomial variable distinguishing live trees (Tree forms 1–2) from dead trees (Tree forms 3–8). We included interactions between the number of hollow trees per site and tree form to test for shifts in the kinds of hollow trees selected as dens under variation in den availability (i.e. Is there a ‘relaxation’ of tree form preference as hollow trees become more scarce?).

Bottom Line: 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.Notably, the relationship between abundance and hollow tree availability was significantly less than 1:1 for all species.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.

View Article: PubMed Central - PubMed

Affiliation: The Fenner School of Environment and Society, The Australian National University, Canberra, Australian Capital Territory, Australia. Sam.Banks@anu.edu.au

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.

Show MeSH