Isotopic and conventional dietary approaches uncover niche partitioning
among resident and migratory species in a shorebird assemblage
Abstract
Niche partitioning is a strategy whereby specialization allows species
with similar ecological requirements to coexist. This is particularly
important for organisms exploiting specific food resources, such as
migratory birds at stopover and nonbreeding sites. However, the relative
interplay between niche sharing and segregation among resident and
migratory species at the same site has been challenging to quantify. We
carried out conventional dietary (i.e. feces), as well as δ13C and δ15N
stable isotope analyses of blood samples, on eight migratory and
resident shorebirds (Charadriidae and Scolopacidae) in a Ramsar site of
international importance for shorebirds in southern Brazil during the
Nearctic winter. We assessed interspecific trophic niche variation and
overlap to uncover the potential relationships between dietary and/or
isotopic composition and species’ functional traits. We hypothesized
that shorebird species should differ in they prey consume and segregate
along at least one dimension, and predicted that migratory species would
exhibit broader trophic niches. Limited trophic niche overlap was
observed between most species: most migrants had diets comprised of
intertidal prey, while most residents had diets composed by freshwater,
grassland, or supralittoral prey. Niche overlap was, in general, higher
and isotopically more variable between residents than migrants. Finally,
diet dissimilarities were negatively correlated with the degree of
isotopic similarity between species. Our results reveal distinct degrees
of trophic and isotopic partitioning among migratory and resident
shorebirds. There was no evidence that similarity of morphological
traits or migratory status was related to similarity of diet or the
isotopic niche of species. Resource partitioning and dietary variability
and morphological differences seems to allow coexistence of resident and
migratory shorebirds. In this scenario, high prey availability combined
with recent declines in shorebird abundance can relax potential
competition, facilitating species coexistence via niche overlap in a
dynamic, yet critical, site for shorebirds in the Western Hemisphere.