DNA metabarcoding of prey reveals spatial, temporal and diet partitioning of an island ecosystem by four invasive wasps

Abstract

Invasive alien species can cause detrimental changes in native ecosystems, but our understanding of the interactions between multiple exotic species is limited. To evaluate the joint effect of multiple sympatric invaders on an ecosystem, we must first understand how they interact with each other. Here, we quantified the spatial distribution, dietary composition and overlap of four invasive generalist vespid species (two Vespula and two Polistes) that co-occur on Ahuahu off the north-east coast of New Zealand. We used DNA metabarcoding of larval faecal material to identify prey species, and mapped the locations of nests. We observed clear spatial partitioning, with different wasp species aggregating in different habitats. Diet differed both among wasp species (diet partitioning) and among seasons (temporal partitioning). There was stronger competition (highest diet overlap) between Vespula germanica and Vespula vulgaris than between other wasp species, but partitioning resources minimised spatial and diet overlap between the four species. Additionally, we obtained high-resolution diet inventories that help assess the combined ecological impact of invasion by multiple wasps. These species consumed mostly native and endemic invertebrates from multiple trophic levels, but particularly herbivores (Lepidoptera). We provide direct evidence that in combination they exploited a wide range of endemic invertebrates. Synthesis and applications. Our study demonstrates resource partitioning among four invasive wasps, facilitating coexistence of these generalist invaders. We conclude that coexistence probably amplifies their ecological impact. Quantifying how multiple invaders exploit and partition resources provides insights into how communities assemble and helps to assess the cumulative effects of multiple invaders on the recipient community.