Wildlife of Lancewood (Acacia Shirleyi) Thickets and Woodlands in Northern Australia. 2. Comparisons With Other Environments of the Region (Acacia Woodlands, Eucalyptus Savanna Woodlands and Monsoon Rainforests).

Abstract

Embedded in the extensive Eucalyptus open forests and savanna woodlands that dominate the northern Australian landscape are patches of monsoon rain forest and Acacia thickets and woodlands. In this paper, the vertebrate species composition of patches of lancewood (Acacia shirleyi) thickets and woodlands of the Northern Territory was compared with that of other environments of this region: pindan woodlands (A. eriopoda and A. tumida), gidgee woodlands (A. georginae), patches of monsoon rain forests and the extensive Eucalyptus open forests and woodlands. The vertebrate fauna of lancewood thickets is distinct for that of Eucalyptus open forests, and has fewer species. Differences in species composition and richness are associated with substantial differences in resource availability, with lancewood thickets having far less grass cover (and hence relatively few granivorous birds and rodents, but more ground-feeding insectivorous and omnivorous birds), fewer nectar-bearing flowers (and hence fewer nectarivorous birds) and lower structural and floristic diversity than Eucalyptus forests. There was little difference in species richness or total abundance between the three types of Acacia woodlands sampled. Lancewood thickets had fewer species than monsoon rain forests to coastal dry monsoon rain forests to inland dry monsoon rain forests to lancewood thickets to pindan woodlands to gidgee woodlands, in accord with the pronounced rainfall gradient of this region and with canopy cover and height. Within this broad continuum the three Acacia woodlands were most closely grouped. Species turnover along this gradient consisted of substantial decrease or loss of some foraging groups (e.g. frugivorous birds) or replacement of species within broad foraging groups. The faunal relationship of the monsoon rain forests and Acacia communities provides some support for considering these fire-sensitive environments as fragments of a formerly extensive continuum. Three species (Pomatostomus temporalis, Struthidea cinerea and Melanodryas cucullata), all ground-foraging insectivorous or omnivorous birds, were significantly associated with lancewood in this region, but all three have extensive ranges beyond this area.