Long-term patterns of invertebrate abundance and relationships to environmental factors in arid Australia

Resource pulses are a key feature of semi-arid and arid ecosystems and are generally triggered by rainfall. While rainfall is an acknowledged driver of the abundance and distribution of larger animals, little is known about how invertebrate communities respond to rain events or to vegetative productivity. Here we investigate Ordinal-level patterns and drivers of ground-dwelling invertebrate abundance across 6years of sampling in the Simpson Desert, central Australia. Between February 1999 and February 2005, a total of 174381 invertebrates were sampled from 32 Orders. Ants were the most abundant taxon, comprising 83% of all invertebrates captured, while Collembola at 10.3% of total captures were a distant second over this period. Temporal patterns of the six invertebrate taxa specifically analysed (Acarina, ants, Araneae, Coleoptera, Collembola and Thysanura) were dynamic over the sampling period, and patterns of abundance were taxon-specific. Analyses indicate that all six taxa showed a positive relationship with the cover of non-Triodia vegetation. Other indicators of vegetative productivity (seeding and flowering) also showed positive relationships with certain taxa. Although the influence of rainfall was taxon-dependent, no taxon was affected by short-term rainfall (up to 18days prior to survey). The abundance of Acarina, ants, and Coleoptera increased with greater long-term rainfall (up to 18months prior to survey), whilst Araneae showed the opposite effect. Temperature and dune zone (dune crest vs. swale) also had taxon-specific effects. These results show that invertebrates in arid ecosystems are influenced by a variety of abiotic factors, at multiple scales, and that responses to rainfall are not as strong or as predictable as those seen for other taxa. Our results highlight the diversity of invertebrates in our study region and emphasize the need for targeted long-term sampling to enhance our understanding of the ecology of these taxa and the role they play in arid ecosystems.