Ecology of streams in a biogeographic isolate—the Queensland Wet Tropics, Australia

Abstract

Global studies of streams are needed to develop general ecosystem and management models. We reviewed research that tested ecological models in streams of the Queensland Wet Tropics bioregion (QWT), which makes up 0.26% of Australia but supports distinctive and high biodiversity, most of which is of Gondwanan or marine origin. QWT streams have seasonal but perennial flow, high insolation, and higher diversity of riparian vegetation, invertebrates, and fish than temperate streams. Consistent physical conditions sustain biological processes through the year, and predictable wet seasons, but unpredictable floods, have shaped a resilient and opportunistic biota. Stream food webs are dominated by predators, and prey turnover is rapid. Small streams are heterotrophic and become autotrophic as canopies open in larger streams. Predation and competition influence assemblage composition most in the dry season, when habitats contract and densities increase. Riparian clearing, weed invasion, and agricultural contamination affect table lands and floodplains. High temperatures exacerbate weed growth and eutrophication, but contaminants may be diluted by high flows from forested catchments. Climate change probably will cause warming and greater hydrological seasonality, threatening endemic species. The biophysical characteristics of QWT streams are found elsewhere in the tropics, but the species pool is not. QWT streams are important because of their insular and remnant nature. Patterns and processes can differ between QWT and comparable temperate systems because of biogeographic and biophysical characteristics and their interactions with anthropogenic effects, exacerbated by the tropical climate. Research in the QWT both affirms and contradicts theories of stream ecology, underpins conservation and management needs of tropical streams, and provides points of reference for comparative studies in stream ecology, conservation, and management.