Local extinction and nestedness of small-mammal faunas in fragmented forest of central Victoria, Australia

A survey of small mammals was undertaken in eight forest fragments of three sizes (2.5, 10 and 40 ha) and in five 'pseudofragments' within a large area of State Forest. The latter were used to provide 'reference' results against which the fragments could be compared. There was a paucity of dasyurid marsupials in fragments and pseudofragments, but arboreal 'herbivores' (possums and a glider) were 7.5 times more abundant in fragments than in pseudofragments. The Short-beaked Echidna Tachyglossus aculeatus was recorded in both fragments and pseudofragments. All sites were impoverished, with a maximum of four native species of small mammals recorded at any one site, and six native species recorded overall. There was significant faunal 'nesting' as a function of fragment size, with the small-mammal fauna of smaller fragments being subsets of larger fragments. The extant fauna in fragments appears to be a result of a sequence of local extinctions such that some species are more vulnerable to habitat loss, fragmentation and degradation and become locally extinct earlier than other, hardier species. The impoverishment within pseudofragments seems to be a function of broad-scale habitat modifications and especially timber harvesting, which maintains the forest as a dense array of small, pole-sized trees with few large, old trees. Several of the arboreal mammals are dependent on hollows found in larger trees, so the absence of the latter probably constrains the occurrence and density of the hollow users.