Habitat and Community Patterns of Tropical Australian Hydradephagan Water Beetles (Coleoptera: Dytiscidae, Gyrinidae, Noteridae)

Abstract

Water beetle communities have been investigated in northern regions of the Northern Hemisphere but similar studies have not been conducted within the tropics. Thus, a study was undertaken to describe patterns of water beetle co‐occurrence in a tropical environment and to compare these with water beetle community structure in temperate regions. Hydradephagan water beetles (Dytiscidae, Noteridae and Gyrinidae) were sampled quantitatively and qualitatively from a variety of habitats in the Atherton Tableland region of tropical Queensland from September 1990 to February 1991. Principal component analysis (PCA), using species occurrence in samples, supported a primary classification of sites as lotic, lentic and closed‐forest lotic. Closed‐forest lotic sites were tightly grouped in the PCA ordination, whereas the lotic and lentic groups of sites were more diffuse. Through analysis of species distributions in the PCA ordination it was inferred that factor 1 corresponded to habitat stability (e.g. permanence, water level fluctuation), especially among lotic sites, whereas factor 2 corresponded to the interrelated variables of water flow, substratum and vegetation. Quantitative samples taken from the shorelines of reservoirs showed that water beetle densities dropped sharply from the dry to the wet times of the year. Also, densities decreased and faunal mix changed with distance from shoreline. Quantitative samples from rice fields and a temporary pond demonstrated that a suite of species were quick to colonise and breed in newly formed habitat. Many of these species breed before other predators such as fish or Odonata become established. the lack of defined communities is due largely to the high mobility of many species which retreat to watered refuges during dry periods and opportunistically colonise new habitat as it is available. This mobile element obscures community boundaries, although characteristic species occur in certain habitat types such as closed‐forest streams, permanent vegetation‐rich ponds and particular regions along habitat continua. Patterns in size and habits of species of permanent habitats, and colonisation patterns of species occurring in temporary habitats, suggest that these represent mechanisms that reduce predation from other aquatic predators.