Invasive rat impacts on insular invertebrate biodiversity: investigating the selective mechanism of rat predation and the taxonomic and functional implications for island ecosystems

• Applicant: Sebastian Steibl
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 493936649

Oceanic islands contribute only 5% to the earth’s surface but harbour more than 20% of the total terrestrial biodiversity, bringing oceanic islands at a particular focus for conserving global biodiversity. The biggest threat to insular biodiversity are invasive species. Among those, invasive rats are the most widely distributed and detrimental invasive species for insular ecosystems. While the negative impacts of rats for insular mammal, bird, or reptile species have been well documented, comparably little is known about their impacts on insular invertebrates, although it is known that invertebrates form a significant proportion in the diets of invasive rats on islands. Therefore, this project aims to identify the impact of invasive rat species (Rattus rattus and R. exulans) on the diversity and community composition of insular invertebrates. This project will first investigate the selective mechanism behind rat predation, which causes the suppression of certain invertebrate species while others remain unimpaired from biological invasions. Recent advances in nutritional ecology thereby suggest that predators select their prey primarily based on their nutritional composition (i.e., carbohydrate, protein, and lipid content) to optimise and balance their nutrient intake targets. Therefore, the nutrient intake targets of the two investigated invasive rat species will be investigated. Based on the intake targets of the two invasive rat species, it will then be tested whether invasive rats consume predominantly those invertebrate species that have a macro-nutritional composition more similar to the rats’ nutrient intake targets. In the second part of the project, the effects of invasive rat predation on the taxonomic diversity of insular invertebrate communities will be investigated. Thereby, it will be tested explicitly whether there exists a directional selection on the invertebrate community driven by selective predation of rats based on their nutritional requirements. If invasive rats select their prey primarily based on its nutritional composition, it would be expected that those species of the insular invertebrate community become more strongly suppressed that have a nutritional composition that matches the intake targets of the invasive rats. As invertebrates fulfil various critical ecological functions, the third part of the project will then investigate the consequences of selective rat predation for the functional diversity of the insular invertebrate community. In its entirety, this project aims to examine the impact of invasive rats on insular invertebrate communities. Based on a nutritional perspective, the goal is to identify the selective mechanism behind invasive rat predation and link it to directional shifts in the taxonomic and functional diversity of invertebrate communities on invaded insular ecosystems.

• DFG Programme: WBP Fellowship
• International Connection: New Zealand
• Host: Professor Dr. James Russell