Control of invasive alien plants on an oceanic island modifies invertebrate folivory to the benefit of native biodiversity

Herbivory is one of the most important ecological interactions globally. Herbivores, among which arthropods predominate, play key roles in fundamental ecological processes, and may profoundly affect plants. Invasive alien plants (IAP) may influence herbivory in varied ways, including by supplying additional resources, yet, few comparative studies have assessed how IAP impact herbivory, particularly on heavily invaded oceanic islands. Here, we assess how IAP influences folivory, the prominent form of herbivory, to explore the ecological and conservation implications in a habitat restoration context. We studied a protected native forest on the oceanic island of Mauritius, comprising an area invaded by IAP and an adjacent area weeded of IAP used for comparison. We first quantified IAP impacts on folivory by comparing arthropod communities between invaded and weeded areas using yellow sticky traps set along 100 m transects. We then compared the incidence and severity of folivory (including chewing, galling, and mining) across habitat types on four shared native species between habitats, along with Psidium cattleyanum , the dominant IAP in invaded forest, and Harungana madagascariensis , the dominant native pioneer tree naturally regenerating in weeded forest. Finally, we compared the specific leaf area (SLA), folivory rate, and consumed leaf area on the selected species between habitats. Arthropod species richness and abundance were comparable between habitats but community structure differed. Overall, herbivory incidence on natives was higher in invaded than weeded area, with Antirhea borbonica and Labourdonnaisia calophylloides showing higher odds of folivory in invaded forest. Herbivory severity was also higher in the invaded area, with A. borbonica showing higher herbivory severity damage, although the opposite was found for Aphloia theiformis . There was no significant difference of folivory rate between habitat type, except for H. madagascariensis that sustained a significantly higher rate than P. cattleyanum . Overall, mean consumed leaf area was higher on H. madagascariensis in the weeded area, and A. borbonica in the invaded one. Finally, SLA was significantly higher on H. madagascariensis compared with P. cattleyanum , like on L. calophylloides in weeded area. Our study shows that IAP control represents limited loss for folivores. By allowing native pioneer regeneration, IAP control indirectly increases leaf resource availability, and decreases the risk of folivory damage on native species. Conservation strategies should therefore focus more strongly on in situ control of IAP, and keep native pioneer species, instead of removing them, as often done on the island. This would strengthen plant-herbivore interactions and enhance benefits for biodiversity. Ultimately, not cutting back pioneer native trees would free conservation resources, allowing the restoration of larger areas, and further improve the effectiveness of conservation measures.