Trait‐habitat associations explain novel bird assemblages mixing native and alien species across New Zealand landscapes

Luc Barbaro,Jean‐Yves Barnagaud,Eckehard G. Brockerhoff,Marc Deconchat,Raphaël Mossion,Sandrine Pavoine,Paul Dufour

doi:10.1111/ddi.13432

Abstract

AbstractAimSpecies introductions have reshaped island faunas for the last 200 years, often threatening native biodiversity. Approximately equal numbers of native and alien species currently co‐occur in the New Zealand avifauna, but they show distinct habitat use. Antagonistic interactions, habitat affinities and legacies of introduction history may concur to explain their segregation along habitat gradients. To investigate these processes, we explored how habitat, ecological traits and introduction history relate with the current composition of bird assemblages.LocationNew ZealandTaxonBirdsMethodsWe analysed 917 bird point counts spread along habitat and elevation gradients in the Canterbury region, South Island and related 10 ecological traits to landscape composition using a three‐table ordination method known as “RLQ analysis”, accounting for spatial autocorrelation and phylogeny. We tested whether alien species’ positions in the RLQ were related to proxies of introduction history.ResultsEighteen endemic, 11 native and 19 alien species were distributed along a gradient from forest to open‐habitat assemblages, in relation to foraging mode, nesting site and body size. A second gradient segregated species between native and exotic forests according to territoriality, sedentarity and diet. Traits accounted for the separation of native and alien bird species in forests, but not in open habitats. Phylogenetic signals emerged from the separation of native and alien species by forest type, and spatial structures suggested a landscape‐level, rather than regional or local determinism. These correlations were independent of introduction history, although open‐habitat assemblages tended to host alien species introduced later in time.Main conclusionsHabitat type and resource availability explain the spatial partitioning of New Zealand bird assemblages between native and alien species more consistently than competitive exclusion. We conclude that trait‐mediated ecological differences among species have likely played a predominant role in species’ segregation among landscapes, while maintaining endemic bird assemblages in native forests.

Highlights

Avifaunas of oceanic islands are amongst the most distinctive in the world, with disproportionate rates of endemism and narrow distributions (Newbold et al, 2018)
Previous studies on New Zealand bird assemblages showed that native and alien species are segregated along gradients of anthropogenic land use
Others used functional diversity metrics based on occurrence-only data from the New Zealand breeding bird atlas (Méndez et al, 2018; Robertson et al, 2007). We showed that such niche partitioning within bird communities is stronger in forests than in open habitats and is related to distinct trait syndromes, consistent with those found at broader spatial scales (Soares et al, 2021)

Summary

| INTRODUCTION

Avifaunas of oceanic islands are amongst the most distinctive in the world, with disproportionate rates of endemism and narrow distributions (Newbold et al, 2018). The composition of island bird assemblages could result from species’ idiosyncratic responses to habitat, land use and abiotic features, but may arise from niche-based exclusion between native and alien species Because these processes can hardly be tested experimentally, a comprehensive way to explain patterns of native and alien species’ co-occurrence within assemblages relies on correlative methods to analyse the spatial distribution of ecological traits and compare their influence with that of other possible drivers (Allen et al, 2013; Kennedy et al, 2010; Vandewalle et al, 2010). Some grassland areas are interspersed with more or less substantial areas of regenerating native, exotic or mixed shrubland

| MATERIALS AND METHODS

Findings

| DISCUSSION