Patterns in the biodiversity of terrestrial environments in the southern Carnarvon Basin, Western Australia

Abstract

-Sixty-three quadrats each of 16 ha were chosen to represent the geographical extent and diversity of terrestrial environments in a 75 000 km 2 area of the Carnarvon Basin, Western Australia. A total of 626 plant and 456 animal species were recorded from the quadrats, an average of 120 (s.d. = 22.1) species per quadrat.After species that occurred at only one quadrat and species for which the sampling methods were unreliable (e.g. snakes and raptors) were removed from the data-set, 730 species remained, an average of 108.6 per quadrat (s.d. = 20.1). These comprised 81 herpetofauna, 13 small ground mammals, 85 birds, 9 scorpions, 12 centipedes, 122 ground-dwelling spiders and 408 plants.The data were compiled into a single matrix comprising the presence or absence of the 731 species at the quadrats. When the species were classified according to their co-occurrences, thirteen assemblages were distinguished. Each assemblage could be characterised in terms of the Australia-wide habitat preferences of its component species. Also, quadrat similarity matrices were generated for each of the seven types of organism sampled and 1000 random matrices. These were output as linear similarity vectors so that the differences in their biodiversity patterns could be quantified as a single matrix of correlation coefficients.Analyses revealed that: 1. Geographical patterns in species composition derived from the combined matrix correlated with processes operating at both biogeographical and local (ecological) scales: the compositional structure of each assemblage was related to a different set of climatic plus soil and/or topographic attributes. Poisson error models with logarithmic links fitted the gradient in species richness of each assemblage across the study area. Similar environmental attributes emerged whether an assemblage's composition or its richness was analysed. Since these attribute-sets were also consistent with the assemblages' Australia-wide characterisations, they are unlikely to be artifacts of quadrat positioning or study area extent. 2. Each of the seven ecologically different types of organism had a distinct influence on the biodiversity model; cross-taxon congruence levels were low. To be representative, a Carnarvon Basin reserve system should sample the geographical range of the various climatic, soil and topographic gradients identified by the analyses. It should also be designed using a biodiversity model that incorporates a wide range of organisms.

Some gaps in the reserve system of the southern Carnarvon Basin, Western Australia

“…Herein, these assemblages are termed 'communities', and the broad-scale characterisation of their environmental niches 551 provided by McKenzie et al (2000a) was used as a basis for enhancing the reserve system's comprehensiveness. This was feasible in this instance because most of the scaled deviance in community richness could be explained in terms of climatic and other mapped environmental attributes (McKenzie et al, 2000a). There were four steps in the process.…”

“…Although the species richness gradients of the communities were related to combinations of climatic and substrate factors (the GLM equations are listed in Table 5 in McKenzie et al, 2000a), substrates were expressed as local soil-mozaics within regional climatic patterns. Thus, we could suppress the localised influence of the soil attributes on the contour maps by basing the interpolations on the maximum communityrichness value recorded from the quadrats in the vicinity of each campsite, excluding singletons (Table 2).…”

“…The patterns are summarised by Halse et al (2000) and Gibson et al (2000a) for wetland communities, and by McKenzie et al (2000a) for terrestrial communities. This paper should not be used without prior reference to all three of these publications.…”

“…Data-sets on three additional terrestrial groups were analysed individually -mygalomorph spiders (Main et al, 2000), millipedes (Harvey et al, 2000b) and bats (McKenzie and Muir, 2000). Additional analyses of wetland data undertaken in this paper are comparable to those of McKenzie et al (2000a), and aimed at showing patterns in the whole wetland community. Together, the terrestrial and aquatic community analyses provide a basis for identifying major gaps in the 'comprehensiveness' of the reserve system in the study area, but provide no data on either its 'adequacy' or its 'representativeness'.…”

“…Thus, ecological niches of wetland species in the southern Carnarvon Basin cannot be characterised in the way that McKenzie et al (2000a) characterised requirements of terrestrial species. This precluded using gradients in the composition of wetland species assemblages in reserve design, although this approach has been used successfully for terrestrial ecosystems elsewhere in Western Australia (McKenzie et al, 1989;McKenzie and Belbin, 1991).…”