Landscape-scale species richness of earthworms in the Porongurup Range, Western Australia: influence of aspect, soil fertility, and vegetation type

Abstract

Indigenous Australian earthworms comprise a patchily collected taxon that is likely to have high γ diversity and pose difficulties for systems of biodiversity prediction or monitoring that use surrogates. This is because surrogates for earthworm diversity have scarcely been identified at landscape scales in Australian contexts. In the present paper we examine the diversity of earthworms in a 26 km2 remnant of native vegetation. Comparison of α diversity within the Porongurup Range to diversity of other earthworm faunas demonstrates the sampling intensities required to adequately sample regions of 100–101 km2. In addition β diversity patterns were examined in relation to habitat as described by landscape context, vegetation cover and soil characteristics. Species accumulation in samples from the northern aspect of the Porongurup Range was less than expected from a random distribution of species. Combined Karri-, and Marri- and Karri-vegetated sites supported significantly more earthworm species on the southern aspect of the Porongurup Range than expected from accumulation in randomly ordered samples. Sites carrying Jarrah as the only dominant canopy had fewer earthworm species than would be expected from accumulation in randomly ordered samples. Jarrah overstorey sites and southern aspect Karri sites correspond to extremes in a continuum of soil and landscape characteristics. Earthworm responses to landscape and vegetation units in the region warrant further investigation.