Spiders, spinifex, rainfall and fire: Long-term changes in an arid spider assemblage

Understanding the spatial and temporal patterning of biota is critical to conserving biodiversity in arid regions. For mammals and reptiles, rainfall and fire are important forces determining patterns. Few studies consider these factors for invertebrates and even fewer over an extended period. Spiders were pitfall trapped over 14 years (1989–2003) as part of an experimental fire study in the Great Victoria Desert, Western Australia. Spider abundance decreased immediately after fire, but yearly variation confounded the interpretation of results. Species richness showed no clear pattern in response to fire. Spider species composition showed significant changes between sampling months and between burnt and long unburnt samples within the months of March and December, but not October. Rainfall appears the dominant driving force in this system with less pronounced fire effects. High rainfall during the previous February–April was correlated with increased spider abundance in March samples the following year. Given the highly seasonal structure of spider assemblages, favourable weather during mating and juvenile development may increase recruitment the following season. We conclude that to be successful in conserving biodiversity in arid Australia by re-instating anthropogenic fire regimes, it is vital to understand the mediating impact of rainfall.