Ecological controls on the diversity and morphology of eastern Australian spiders
Spiders are an extraordinarily diverse group of organisms found virtually everywhere on the planet. Australian spiders present a broad array of hunting strategies and come from a wide variety of environments. However, the details of their diversity patterns and the relationships between their ecological roles and their overall body plans are not fully understood. The aim of this thesis is to address these matters. Firstly, species diversity estimates for the whole of eastern Australia were calculated using multiple measures (Chao 1, Fisher's ɑ and Simpson's index) based on an occurrence dataset spanning 9483 quarter degree cells within New South Wales, Victoria and Queensland. Comparisons of estimated richness in well-sampled areas to environmental conditions based on multiple regressions suggest that temperature and precipitation are equally important drivers of spider diversity, as opposed to the older finding that temperature is more important in many other groups. The increasing aridity of Australia resulting from global climate change likely means that the local-scale diversity of spiders will decline instead of increasing. Further analyses were based on measurements of 25 body plan components of 553 species found in eastern Australia. These measurements were of body segment dimensions and lengths of leg components ranging from the femur to the tarsus for each leg pair. The measurement data were then subjected to principal coordinates analysis to see how morphology varies across environments, hunting methods, and phylogenetic groupings. Spatial autoregressions were used to control for autocorrelation, and k-means cluster analysis was used to see how the major morphological groupings compared with phylogenetic and hunting method groupings. The morphospaces show that phylogenetic relatedness and sharing of hunting methods are equally important drivers, and that environmental signatures have little impact on spider size or shape. The results also show that the uniformity of diet across this insectivorous clade does not translate into uniformity of morphology. Despite that, representatives of individual species vary little in their morphology, and families or other groups of spiders can be separated from each other readily based on their body plans. The data therefore provide rich information regarding ecology and phylogeny.