Positive edge effects for arboreal marsupials: an assessment of potential mechanisms
Elaine K. Harding A B and Shirin Gomez AA School of Tropical Environment Studies and Geography, James Cook University, PO Box 6811, Cairns, Qld 4870, Australia.
B Corresponding author. Email: elaine.harding@jcu.edu.au or eharding@wildwatch.com.au
Wildlife Research 33(2) 121-129 https://doi.org/10.1071/WR04059
Submitted: 9 July 2004 Accepted: 14 February 2006 Published: 12 April 2006
Abstract
In this study we examined the potential for positive edge effects on folivorous arboreal marsupials inhabiting upland rainforest in the Wet Tropics region of far north Queensland, Australia. We predicted that the folivores should have increased densities at edges relative to interior forest 90 m from the edge owing to the following causal factors, either separately or in combination: (a) increased foliar biomass, measured as vertical foliage density; and/or (b) increased abundance of preferred food trees. To test these hypotheses, we conducted surveys of the lemuroid ringtail possum (Hemibelideus lemuroides), the green ringtail possum (Pseudochirops archeri), the Herbert River ringtail possum (Pseudochirulus herbertensis) and the coppery brushtail possum (Trichosurus vulpecula johnstonii) at two remnant rainforest sites with ‘hard’ edges such as roads or pasture. Because arboreal species are often difficult to survey accurately within forests, we utilised pellet counts as an index of the population and compared this to the common survey technique of night spotlighting. Our results indicated that pellet counts, combined over all species, were positively and strongly correlated with spotlighting results. Using pellet counts as a relative index of arboreal folivore populations, we found that edge transects contained a higher abundance of all species combined than did interior transects. Further, total foliage density in the 10–30-m vertical transect was found to be significantly correlated with total pellet counts at edge transects. Total preferred tree species was not significantly different between edge and interior transects. From these results we propose that foliage density, as a surrogate for biomass, is a possible mechanism explaining the higher abundance of arboreal marsupials at the edges of these two highland rainforest sites in north Queensland.
Acknowledgments
The authors thank James Cook University for providing funding for this study and Jonathan Munro for plant identification. Catherine Pohlman and two anonymous reviewers provided insightful comments on the draft manuscript.
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