Threatened stick-nest rats preferably consume invasive boxthorn over native vegetation on Australia’s Reevesby Island

Abstract

Due to an abundance of feral predators on the mainland, native rodent species Leporillus conditor (greater stick-nest rats) live almost exclusively on small islands off the coast of South Australia. Many of these islands are heavily degraded novel ecosystems, overrun with African Boxthorn. African boxthorn (Lycium ferocissimum) is an aggressive invasive plant that negatively impacts biodiversity by outcompeting native vegetation and degrading habitat. However, it can also provide habitat and food sources for vulnerable native species. To understand if boxthorn is an important dietary component of the stick-nest rat, we used point-intercept vegetation surveys to estimate relative availability for each plant species in areas inhabited by stick-nest rats. We then collected faecal pellets from the study site and used micro-histological faecal analysis to measure plant use by the animals. This allowed us to calculate the “selection ratio” of plant use (abundance in faecal pellets)/plant availability. We found a strong preference of the stick-nest rat for the highly invasive African boxthorn, with a selection ratio of 4.397. This is valuable information as it suggests that other heavily degraded, African boxthorn-infested ecosystems have the potential to provide suitable habitat for the greater stick-nest rat. However, due to the potential of African boxthorn to continue to invade and inflict damage on the greater ecosystem, further research is crucial to ensure a context specific management plan that maximises the resilience of the greater stick-nest rat, as well as the other native species that rely on these island habitats.