Limits...
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.

Show MeSH

Related in: MedlinePlus

A subset of the decay stages of mountain ash trees used by arboreal marsupials (based on [33], [40].The dark arrows show the range of tree forms (TF1-8) preferred by each species, including the mountain brushtail possum (MBP), the greater glider (GG), the agile antechinus (AA) and the Leadbeater’s possum (LP). The thinner grey arrows are tree forms used less frequently by each species. Although there is overlap between species in the preferred tree decay stages, the species differ in their specific requirements for hollow size. Mountain ash trees may take up to 150 years from germination to reach the TF1 stage, when suitable hollows for arboreal marsupials first begin to form. Tree form 9 is not shown and represents trees that have completely collapsed. Generally, younger trees (within the range shown) may hollows in the main stem and broken branches, while older trees have hollows in a highly decayed main stem.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3539978&req=5

pone-0053672-g001: A subset of the decay stages of mountain ash trees used by arboreal marsupials (based on [33], [40].The dark arrows show the range of tree forms (TF1-8) preferred by each species, including the mountain brushtail possum (MBP), the greater glider (GG), the agile antechinus (AA) and the Leadbeater’s possum (LP). The thinner grey arrows are tree forms used less frequently by each species. Although there is overlap between species in the preferred tree decay stages, the species differ in their specific requirements for hollow size. Mountain ash trees may take up to 150 years from germination to reach the TF1 stage, when suitable hollows for arboreal marsupials first begin to form. Tree form 9 is not shown and represents trees that have completely collapsed. Generally, younger trees (within the range shown) may hollows in the main stem and broken branches, while older trees have hollows in a highly decayed main stem.

Mentions: We conducted our research in the Victorian Central Highlands of south-eastern Australia, an area covering approximately 60×80 km (37°20′– 37°55′S and 145°30′–146°20′E). The data were collected at 160 one hectare sites that were situated predominantly in mountain ash (Eucalyptus regnans) forest. This species is the world’s tallest angiosperm and is the dominant overstorey tree species between 800 m and 1100 m altitude in this area. The number of hollow-bearing trees at each site ranged from one to 31 and were identified on the basis of visual identification of hollows. Each marsupial species studied has specific (and largely non-overlapping) hollow requirements, and the total number of hollow trees per site is likely to be an overestimate of the number of hollow trees available to each species, as not all hollows are suitable for each species. Nevertheless, the type and size of tree hollows (related to their suitability for each species) in a tree is strongly related to its decay stage [32], and we used this as an explanatory covariate in our models. The sites were surveyed repeatedly on an overlapping and rotating sampling design from 1997 to 2007 [33]. During each survey of a site, we counted the number of individuals of each species of arboreal marsupial emerging from every hollow tree on the site for a period of one hour after dusk [33]. All of the species we surveyed are nocturnal. They shelter during daylight hours in tree hollows and typically emerge shortly after dusk to forage. This is the most effective method available for estimating the abundance of each species of arboreal marsupial at a site. We recorded nine species of arboreal marsupial in our surveys [33] but focussed on the four most commonly recorded species for these analyses. These were (1) the mountain brushtail possum (Trichosurus cunninghami) a large (2.5–4 kg) nocturnal arboreal marsupial that shelters in large tree hollows; (2) Leadbeater’s possum (Gymnobelideus leadbeateri), an endangered small (∼140 g) marsupial with a colonial social system that dens in hollow trees and typically favours small ‘keyhole’ entrances to large hollows inside dead standing mountain ash trees; (3) the greater glider (Petauroides volans), a large (1.35 kg) gliding marsupial that feeds exclusively on eucalypt leaves and prefers to den in hollows high in live trees; and (4) the agile antechinus (Antechinus agilis) a small (20–40 g) marsupial carnivore that predominantly forages at ground level but dens communally in a range of types of tree hollows. We provide a basic background to the biology of these species in Appendix S1 and a diagrammatic representation of the tree form preferences of each species in Figure 1.


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)

A subset of the decay stages of mountain ash trees used by arboreal marsupials (based on [33], [40].The dark arrows show the range of tree forms (TF1-8) preferred by each species, including the mountain brushtail possum (MBP), the greater glider (GG), the agile antechinus (AA) and the Leadbeater’s possum (LP). The thinner grey arrows are tree forms used less frequently by each species. Although there is overlap between species in the preferred tree decay stages, the species differ in their specific requirements for hollow size. Mountain ash trees may take up to 150 years from germination to reach the TF1 stage, when suitable hollows for arboreal marsupials first begin to form. Tree form 9 is not shown and represents trees that have completely collapsed. Generally, younger trees (within the range shown) may hollows in the main stem and broken branches, while older trees have hollows in a highly decayed main stem.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0053672-g001: A subset of the decay stages of mountain ash trees used by arboreal marsupials (based on [33], [40].The dark arrows show the range of tree forms (TF1-8) preferred by each species, including the mountain brushtail possum (MBP), the greater glider (GG), the agile antechinus (AA) and the Leadbeater’s possum (LP). The thinner grey arrows are tree forms used less frequently by each species. Although there is overlap between species in the preferred tree decay stages, the species differ in their specific requirements for hollow size. Mountain ash trees may take up to 150 years from germination to reach the TF1 stage, when suitable hollows for arboreal marsupials first begin to form. Tree form 9 is not shown and represents trees that have completely collapsed. Generally, younger trees (within the range shown) may hollows in the main stem and broken branches, while older trees have hollows in a highly decayed main stem.
Mentions: We conducted our research in the Victorian Central Highlands of south-eastern Australia, an area covering approximately 60×80 km (37°20′– 37°55′S and 145°30′–146°20′E). The data were collected at 160 one hectare sites that were situated predominantly in mountain ash (Eucalyptus regnans) forest. This species is the world’s tallest angiosperm and is the dominant overstorey tree species between 800 m and 1100 m altitude in this area. The number of hollow-bearing trees at each site ranged from one to 31 and were identified on the basis of visual identification of hollows. Each marsupial species studied has specific (and largely non-overlapping) hollow requirements, and the total number of hollow trees per site is likely to be an overestimate of the number of hollow trees available to each species, as not all hollows are suitable for each species. Nevertheless, the type and size of tree hollows (related to their suitability for each species) in a tree is strongly related to its decay stage [32], and we used this as an explanatory covariate in our models. The sites were surveyed repeatedly on an overlapping and rotating sampling design from 1997 to 2007 [33]. During each survey of a site, we counted the number of individuals of each species of arboreal marsupial emerging from every hollow tree on the site for a period of one hour after dusk [33]. All of the species we surveyed are nocturnal. They shelter during daylight hours in tree hollows and typically emerge shortly after dusk to forage. This is the most effective method available for estimating the abundance of each species of arboreal marsupial at a site. We recorded nine species of arboreal marsupial in our surveys [33] but focussed on the four most commonly recorded species for these analyses. These were (1) the mountain brushtail possum (Trichosurus cunninghami) a large (2.5–4 kg) nocturnal arboreal marsupial that shelters in large tree hollows; (2) Leadbeater’s possum (Gymnobelideus leadbeateri), an endangered small (∼140 g) marsupial with a colonial social system that dens in hollow trees and typically favours small ‘keyhole’ entrances to large hollows inside dead standing mountain ash trees; (3) the greater glider (Petauroides volans), a large (1.35 kg) gliding marsupial that feeds exclusively on eucalypt leaves and prefers to den in hollows high in live trees; and (4) the agile antechinus (Antechinus agilis) a small (20–40 g) marsupial carnivore that predominantly forages at ground level but dens communally in a range of types of tree hollows. We provide a basic background to the biology of these species in Appendix S1 and a diagrammatic representation of the tree form preferences of each species in Figure 1.

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
Related in: MedlinePlus