HABITAT AND COMMUNITY PATTERNS OF TROPICAL AUSTRALIAN HYDRADEPHAGAN WATER BEETLES (COLEOPTERA, DYTISCIDAE, GYRINIDAE, NOTERIDAE)

Water beetle communities have been investigated in northern regions of the Northern Hemisphere but similar studies have not been conducted w ithin the tropics. Thus, a study was undertaken to describe patterns o f water beetle co-occurrence in a tropical environment and to compare these with water beetle community structure in temperate regions. Hydr adephagan water beetles (Dytiscidae, Noteridae and Gyrinidae) were sam pled quantitatively and qualitatively from a variety of habitats in th e Atherton Tableland region of tropical Queensland from September 1990 to February 1991. Principal component analysis (PCA), using species o ccurrence in samples, supported a primary classification of sites as l otic, lentic and closed-forest lotic. Closed-forest lotic sites were t ightly grouped in the PCA ordination, whereas the lotic and lentic gro ups of sites were more diffuse. Through analysis of species distributi ons in the PCA ordination it was inferred that factor 1 corresponded t o habitat stability (e.g. permanence, water level fluctuation), especi ally among lotic sites, whereas factor 2 corresponded to the interrela ted variables of water flow, substratum and vegetation. Quantitative s amples taken from the shorelines of reservoirs showed that water beetl e densities dropped sharply from the dry to the wet times of the year. Also, densities decreased and faunal mix changed with distance from s horeline. Quantitative samples from rice fields and a temporary pond d emonstrated that a suite of species were quick to colonise and breed i n newly formed habitat. Many of these species breed before other preda tors such as fish or Odonata become established. The lack of defined c ommunities is due largely to the high mobility of many species which r etreat to watered refuges during dry periods and opportunistically col onise new habitat as it is available. This mobile element obscures com munity boundaries, although characteristic species occur in certain ha bitat types such as closed-forest streams, permanent vegetation-rich p onds and particular regions along habitat continua. Patterns in size a nd habits of species of permanent habitats, and colonisation patterns of species occurring in temporary habitats, suggest that these represe nt mechanisms that reduce predation from other aquatic predators.