Effect of plant composition on epigeal spider communities in northern New Zealand forest remnants

Te Paki Ecological District (TPED) in northern Northland, New Zealand, is well known as an ecologically significant centre of endemism. However, due to extensive anthropogenic habitat degradation, native forest has been reduced to small, isolated remnants and many of its endemic species are threatened with extinction. Epigeal spider communities (species living on or near the ground) were surveyed within TPED by pitfall trapping at seven native forest remnants differing in plant composition and apparent seral stage to investigate how spider communities varied within them. Surveys were conducted four times over a 12-month period coinciding with winter, spring, summer and autumn. Changes in spider communities were related to differences in plant composition, which were in turn associated with differences in apparent seral stage of the vegetation. Spider communities in forests at later seral stages were dominated by species such as Rinawa sp., Porrhothele sp. and Uliodon sp., whereas Euryopis nana, Cambridgea reinga, Stanwellia hollowayi and Hypodrassodes apicus were most prevalent in remnants at earlier seral stages. These species could potentially serve as useful bioindicators of ecological succession or restoration. Apart from soil organic matter content none of the predictor variables tested, including plant species richness, were significantly correlated with spider richness or diversity. Spider richness and diversity are most likely determined by a complex interaction of environmental and temporal factors that operate at different spatial scales. This study has increased our understanding of the ecological associations of spider communities and established that TPED is an important centre of endemism for spiders in New Zealand. We have also demonstrated the importance of forest remnants as reservoirs of indigenous spider diversity and helped resolve several historical taxonomic issues. Furthermore, we demonstrate the need for taxonomic research in this region of New Zealand and highlight the value of such biodiversity surveys.