23Effective management and conservation of biodiversity requires understanding of 24 predator-prey relationships to ensure the continued existence of both predator and prey 25 populations. Gathering dietary data from predatory species, such as insectivorous bats, 26 often presents logistical challenges, further exacerbated in biodiversity hotspots 27 because prey items are highly speciose yet their taxonomy is largely undescribed. We 28 used high-throughput sequencing (HTS) and bioinformatic analyses to phylogenetically 29 group DNA sequences into molecular operational taxonomic units (MOTUs) to examine 30 predator-prey dynamics of three sympatric insectivorous bat species in the biodiversity 31 hotspot of south-western Australia. We could only assign between 4-20% of MOTUs to 32 known genera or species, depending on the method used, underscoring the importance 33 of examining dietary diversity irrespective of taxonomic knowledge in areas lacking a 34 comprehensive genetic reference database. MOTU analysis confirmed that resource 35 partitioning occurred, with dietary divergence positively related to the 36 ecomorphological divergence of the three bat species. We predicted bat species' diets 37 would converge during times of high energetic requirements, i.e., the maternity season 38 for females and the mating season for males. There was an interactive effect of season 39 on female, but not male, bat species' diets, although small sample sizes may have limited 40 our findings. Contrary to our predictions, females of two ecomorphologically similar 41 species showed dietary convergence during the mating season rather than the maternity 42 season. HTS-based approaches can help elucidate complex predator-prey relationships 43 in highly speciose regions, which should facilitate the conservation of biodiversity in 44 genetically uncharacterised areas, such as biodiversity hotspots. 45

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Summary1. Interspecific competition is a recognized but under-studied mechanism by which invasive species affect native fauna. 2. We experimentally reduced populations of the introduced black rat Rattus rattus in relatively undisturbed littoral rainforest in south-eastern Australia to test its competitive impact on populations of the native bush rat Rattus fuscipes. 3. Removal of R. rattus resulted in significant and sustained increases in populations of the native rodent due to immigration, juvenile recruitment and increases in residency of females. Native juveniles were particularly vulnerable to R. rattus, being largely absent from untreated populations despite indications of breeding in females, but responding rapidly to their removal. 4. The absence of changes in body condition and reproduction of adult R. fuscipes with long-term removal of R. rattus suggests that direct interference by R. rattus rather than competition for resources best explains the low densities and poor juvenile recruitment of R. fuscipes. 5. The behavioural dominance of R. rattus was not due to an inherent competitive ability because they did not re-establish post-removal as expected if competition was asymmetrical. Instead, competitive dominance seemingly shifted to R. fuscipes with changes in residency status of populations. Improved survivorship among native females reveals that they were particularly important in establishing resident populations following removal of R. rattus. 6. Synthesis and applications. These findings identify R. rattus as a significant competitive threat to native R. fuscipes. Removal of invasive rodents and active conservation of common native species is recommended to forest managers based on the potential for R. fuscipes to prevent re-invasion subsequent to pest control efforts and maintain invasion resistance.