Biodiversity of the freshwater invertebrates of the wet tropics region of northeastern Australia: patterns and possible determinants

Abstract

This chapter discusses the patterns of diversity and distribution of the stream invertebrates of the Wet Tropics and examines possible determinants of those patterns. The rainforest streams of tropical Queensland rise in mountains up to 1,600 m in elevation and descend across an ancient landscape of tablelands, gorges, and a coastal floodplain. These streams have probably remained permanent for millions of years. Physically, they are dominated by the flow regime, dictated by a summer wet season and a winter dry season, with mostly perennial flow. Increased wet-season flows are predictable, but cyclonic floods are not. Biologically, streams are characterized by high invertebrate diversity, despite climatic and habitat shifts probably causing historical extinctions of some species. Continuing descriptive and experimental studies are elucidating the determinants of this diversity, which include the geologic constancy of the streams, the equable temperatures, and the constancy of organic inputs, which facilitate constant breeding by many species and lead to evolutionary opportunities and increases in the species pool; seasonally and annually variable flows, which lead to sustained patchiness of habitats and species populations, providing maximum opportunities for colonization by a large proportion of the regional species pool; and random assemblages of species at the site or microhabitat scale, which allow for different assemblages on adjacent habitat patches.