Diversity, endemism and species turnover of millipedes within the south-western Australian global biodiversity hotspot
To examine how current and historical environmental gradients affect patterns of millipede (Diplopoda) endemism and species turnover in a global hotspot of floristic diversity, and to identify regions of high endemism and taxonomic distinctness for conservation management. Location
South-western Australia. Methods
Museum database records of millipedes (subclasses Pentazonia and Helminthomorpha), supplemented with extensive fieldwork, were used to map species richness, species turnover (β-diversity), weighted endemism, average taxonomic distinctness and variation in taxonomic distinctness in half-degree grid squares (c. 2500 km2). Generalized linear models were used to examine relationships between these parameters with rainfall (present day and historical), topography and human disturbance (clearing for agriculture and urbanization). Results
Millipede species richness, particularly within the order Spirostreptida, and millipede endemism were positively associated with large within-cell differences in elevation (mountainous regions). Large variation in taxonomic distinctness (unevenness in the taxonomic tree) in higher-rainfall areas was mainly due to speciation within the Spirostreptida genus Atelomastix. Hotspots of millipede endemism and taxonomic distinctness were identified within three categories of importance: primary (Stirling Range East, Cape Le Grand, Cape Arid, Walpole, Porongurups), secondary (Mount Manypeaks, Bremer Bay, Stirling Range West, Duke of Orleans Bay, Ravensthorpe, Albany, Busselton) and tertiary (Nornalup). A species turnover boundary was positively associated with rainfall, broadly located in the transition zone of 300–600 mm year−1. Main conclusions
The current lack of knowledge on the endemism of invertebrates hampers their incorporation into conservation planning. With this knowledge we can identify global biodiversity hotspots and, at a smaller scale, significant conservation areas within a region. Here we have shown that weighted endemism and taxonomic distinctness are useful tools in identifying centres of high endemism and speciation for millipedes within the south-west Australian hotspot. Moreover, it is unlikely that either vertebrates or vascular plants will be useful surrogates for identifying significant areas for invertebrate conservation. While other workers have shown that vascular plants, mammals and frogs have different centres of endemism within south-west Australia, our results show that centres of endemism for millipedes encompass all of these plus other areas.