Biodiversity patterns and their conservation in wetlands of the Western Australian wheatbelt

WA Museum Records and Supplements | Updated 7 years ago

ABSTRACT – A total of 197 wetlands were sampled between 1997 and 2000 in a survey designed to record wetland biodiversity across the wheatbelt and south coast of Western Australia, an area of 205 000 km2. Altogether, 986 wetland-associated plant, 844 aquatic invertebrate and 57 waterbird species were recorded, with an average of 73 and a range of 10-174 species per wetland. Thirty-four per cent of species were found at only one wetland.

Sixteen types of wetland were recognized, based on their biological assemblages. Overall, salinity was the factor most responsible for differentiation between wetlands in terms of biodiversitv but differences between some freshwater wetland types, such as sedge swamps and granite rock pools, were largely attributable to other abiotic factors. Among saline wetlands, the biota of naturally saline (and usually very salty) seasonal playas was distinct from that of wetlands with longer periods of inundation. It was unclear whether differences related to inundation or salinity.

Using cluster analysis, 22 assemblages of co-occuring species were identified and the distributions of 18 of them were modelled. Between 33 and 86% of the species richness of each assemblage at a wetland was explained by two to four abiotic variables. The assemblages that modelled most poorly consisted of species that were widespread and had broad ecological tolerances, with ranges extending beyond the wheatbelt, so that the survey was unlikely to have circumscribed their ecological requirements. Most assemblages consisted of a mix of plant, invertebrate and (fewer) waterbird species. Factors affecting the distribution of plants and animals within a co-occurring assemblage often appeared to differ, especially for plants growing on the bank of a wetland. Riparian plants are probably exposed to different environmental factors, especially salinity patterns, than those influencing animals using the waterbody itself.

The dramatic increase in secondary salinisation that has been observed in the wheatbelt and south coast over the past 100 years, with associated loss of freshwater habitat and changes to naturally saline playas, is likely to lead to significant loss of biodiversity. Most assemblages (and species) were associated with particular salinity ranges and there was an inverse relationship between overall community richness and salimty, especially within the waterbody. Many species typical of naturally saline playas were rarely found at secondarily saline wetlands.

The predictable occurrence of some species assemblages, such as those characteristic of sedge swamps and saline playas of the north-eastern wheatbelt, makes it possible to identify wetlands that, if protected from secondary salinisation, will conserve large proportions of them. Some other assemblages occur at many wetlands and their conservation is assured by almost any strategy, even if they are unpredictably distributed. However, protection of rare species and assemblages that occur infrequently and somewhat randomly within the wheatbelt poses a significant challenge to wetland managers.