Niche differences may reduce susceptibility to competition between native and non-native birds in oceanic islands

• Published in: Diversity & distributions 2021-08, Vol.27 (8), p.1507-1518
• Main Authors: Soares, Filipa C., Leal, Ana I., Palmeirim, Jorge M., de Lima, Ricardo F.
• Format: Article
• Language: English
• Subjects: Analysis; Animal behavior; Anthropogenic factors; Biodiversity; Biodiversity loss; Birds; Competition; Ecosystems; Endangered & extinct species; extinction; Foraging habitats; Functional Nearest Neighbour Index; Indigenous species; Insectivores; Introduced species; island biogeography; Islands; Niche (Ecology); Niches; Oceanic islands; Predation; recently established species; Regression analysis; Regression models; RESEARCH ARTICLE; species interactions; species traits
• ISSN: 1366-9516; 1472-4642
• DOI: 10.1111/ddi.13298

Aim Few bird extinctions on oceanic island have been attributed to competition with non‐native species, even though it might be an overlooked driver of biodiversity loss. We evaluate the potential competition between native and non‐native island bird species, identifying species and island characteristics that enhance it and may promote future extinctions. Location Seventy‐three (>100 km2) oceanic islands worldwide. Methods We compiled a species list for each island and used single‐trait meta‐analyses to assess differences between native and non‐native species. Then, we used single‐trait beta regression models to identify species traits linked to potential competition. Finally, we used a trait‐based approach to calculate the potential competition between native and non‐native species on each island and identify island characteristics linked to potential competition. Results Native bird species tended to be smaller forest dwellers, that were either carnivore, frugivore or insectivore, and that foraged in flight, in the canopy or at mid‐height. In contrast, non‐native birds tended to be open habitat granivores, that were either ground or unspecialized foragers. Potential competition tended to be higher for native species with typical non‐native traits and forest‐dwelling unspecialized non‐native species. Potential competition between native and non‐native birds was consistently higher in islands that were larger, had more non‐native birds or were drier. Main conclusions Niche differentiation of native and non‐native species may explain the scarcity of reported competition‐driven extinctions since non‐natives clearly tend to favour and are better adapted to anthropogenic environments. However, the few non‐native birds that occur in native ecosystems may be problematic. The loss of native ecosystems coupled with the introduction of species that might outcompete native species may enhance the relevance of competition in future island extinctions.