The influence of drought,precipitation and fossorial mammal reintroduction on the density of fossorial arthropods and their burrows in arid Australia

The density and abundance of arid-dwelling taxa often change significantly in response to precipitation fluctuations and the abundance of their predators. The survival and density of burrowing arthropods and their burrows in arid environments following prolonged dry periods and subsequent rains is poorly understood, as is the potential influence of reintroductions of their predators, such as fossorial mammals. The persistence of these arthropods and their burrows may be important for other species that rely on them for food or use their burrows for shelter. In this study, we examined the density of burrowing and ground-nesting arthropods and their burrows in Australia's Strzelecki Desert over two years between 2019 and 2021. This period spanned the tail-end of the worst drought on record and subsequent drought-breaking rains. We employed a Before-After Control-Impact (BACI) study design to examine the short-term effects of a fossorial mammal reintroduction of the greater bilby (Macrotis lagotis) into predator-free fenced exclosures and used an inspection camera to detect the presence of spiders and other taxa within individually marked burrows. We observed the largest changes in arthropod abundance and burrow density between a period that encompassed a third consecutive summer in drought and the commencement of drought-breaking rains, with some taxa declining by as much as 77% (p < 0.001). While the density of harvester ant middens erupted over this time, the density of tarantulas, trapdoor spiders and scorpions declined significantly. The greater bilby reintroduction had no short-term effect on the densities of the arthropods or their burrows, but their arrival may have implications on their post-drought recovery. Further studies are needed to determine if the significant declines in arthropod populations and burrows are reflective of normal boom-bust population dynamics due to the poor natural history knowledge of the arthropods we examined.