Biogeographic patterns, environmental correlates and conservation of avifauna in the Northern Territory, Australia

Biogeography of the Northern Territory of Australia is little studied. This paper describes a numerical analysis of avian distribution based on species presence/absence in 1°C cells covering the Northern Territory mainland and major islands. A. TWINSPAN analysis defines more or less geographically coherent regions comprising groups arranged in east-west bands. The avifaunal zonations echo a steep climatic gradient from the seasonally wet tropics in the north to arid central Australia. Positions of individual cells on the primary axis of a DCA ordination are most strongly correlated with rainfall in the wettest quarter (r=0.95) and are precisely predicted $(r^2=0.94)$ from a combination of climatic and vegetation structure variables. We interpret the close correlation of climate variables with avian species composition to reflect the generally unmodified condition of most of the Northern Territory landscape. This long and relatively intact biological gradient offers unique oppotunities to (i) design a conservation reserve system that preserves representative samples of all major ecosystems, (ii) assess the impact of climate change on biota under a broad range of conditions, and (iii) arrange protected areas along the gradient to maintain biological diversity in the face of adverse climate change.