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

Filipa C Soares,Jorge M Palmeirim,Ricardo F Lima,Ana I Leal,Eva Knop

doi:10.1111/ddi.13298

Abstract

AbstractAimFew 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.LocationSeventy‐three (>100 km2) oceanic islands worldwide.MethodsWe 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.ResultsNative 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 conclusionsNiche 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.

Highlights

Across the globe, many species have been introduced outside their natural geographic range by human actions, either intentionally or accidentally
Our results provide cues on how to integrate potential competition with non-native species in conservation strategies
Protecting native ecosystems remains the best single measure to avoid extinction, but we believe that the success of this measure depends on reducing the risk of introduction of species that can inhabit native ecosystems, including those that share important components of the niche with native species

Summary

Introduction

Many species have been introduced outside their natural geographic range by human actions, either intentionally or accidentally. Despite international agreements aiming to control species introductions, globalization is expected to continue increasing the numbers of non-native species worldwide (Seebens et al, 2017). This is a major conservation problem because non-native species are one of the main direct drivers of biodiversity loss at the global scale (Bellard et al, 2016; Spatz et al, 2017). Island native species tend to have small population sizes, low reproductive rates, reduced defences against predators and restricted distributions, all of which make them susceptible to the impacts of non-native species. Islands tend to suffer more species introductions and more extensive anthropogenic land use changes (Russel & Kueffer, 2019; Spatz et al, 2017)

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