Potential predation impacts of invasive non-native rodents (black rats) on plant species from a Pacific Island (Lord Howe Island, Australia)

Context Invasive non-native rodents pose a significant threat to a range of plants on oceanic islands, particularly where there are high levels of endemism. Aims On Lord Howe Island in the western Pacific Ocean, prior to rodent eradication measures, we used selective caging and cafeteria trials across several sites and over several fruiting seasons to infer predicted seed/fruit losses due to consumption by invasive non-native black rats (Rattus rattus). Methods We tested 27 native plant species (11 endemics) comprising 17 trees (including 2 palms), 5 shrubs, 4 climbers and 1 herb. Many of the study species are important structural dominants/components of lowland vegetation communities on the island. Key results Losses of seeds and fruits to black rats were moderate to high for 21 (78%) species and low in 6 (22%) species. We found no evidence that plant habit/life form influenced the likelihood of seed/fruit removal. Conclusion Seed and fruit losses to black rats were generally both ongoing (occurred repeatedly over different years) and widespread (consistent across different locations). This suggests that black rats have impacted many plant species across the island, particularly if our observed seed losses translate to impacts on population structure and growth. Many other species, as yet unsampled, are also likely to have been impacted. Implications The recent (2019–2022) eradication of black rats from the island should allow recovery of impacted species. Our results suggest several highly impacted taxa that should be prioritised for recovery monitoring, in particular, species also likely to be adversely affected by a warming climate.