Can waterbirds with different movement, dietary and foraging functional traits occupy similar ecological niches?

Abstract

Context: Competitive interactions potentially play an important role in structuring bird communities. It is unclear how differences in functional traits influence the niche dimensions of highly mobile waterbird species, particularly when they co-exist in spatiotemporally heterogeneous communities. Objectives: We investigated the inter-relationships between waterbird trait groupings (movement, dietary and foraging habitat) and environmental variable groupings (rainfall, land cover, vegetation structure and water quality). Specifically, we tested whether the scale of environmental variables filtered movement traits and whether these traits operated in conjunction with dietary and foraging habitat traits to form distinct ecological niches in waterbirds. Methods: We conducted waterbird and environmental variable surveys in 60 sites, sampled seven times each at bimonthly intervals, in KwaZulu-Natal, South Africa. Trait-environment relationships were tested using a combination of RLQ and fourth-corner analyses. Results: Several significant trait-environment relationships emerged in bivariate correlations and multivariate ordination space. Movement traits correlated with the scale of environmental variables; migrant and nomadic species responded to broad scale environmental variables. Vegetation structure and land cover were particularly important in explaining the abundance of species foraging in emergent vegetation. Three groups emerged along a gradient in multivariate ordination space providing evidence for ecological niche separation of waterbirds with different movement traits. Conclusions: Our findings suggest that the scale of landscape resources can act as a filter of movement traits, and that in conjunction with dietary and foraging traits, waterbirds with different movement traits occupy distinct ecological niches.