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Food webs and trophic dynamics of coastal systems have been the focus of
intense research throughout the world, as they prove to be critical in
understanding ecosystem processes and functions. However, very few studies
have undertaken a quantitative comparison of entire food webs from a key
consumer perspective across a broad geographical area, limiting relevant
comparisons among systems with distinct biotic and abiotic components. We
investigate the structure and functioning of food webs in four tidal
ecosystems of international importance for migratory shorebirds along the
East Atlantic Flyway: Tejo estuary in Portugal, Sidi Moussa in Morocco,
Banc d'Arguin in Mauritania and Bijagós archipelago in Guinea-Bissau.
Basal food sources, shorebirds and their prey (benthic invertebrates) were
sampled in all areas, and Bayesian stable isotope mixing models and
community-wide metrics were used in a comparative analysis among areas.
Significant differences among study areas were found in the structure of
food webs, as well as in the relative importance of basal resource pools
supporting each food web. Overall, the food web of Banc d'Arguin was
characterized by lower trophic diversity and higher functional redundancy
than the other sites. This result might be explained by the low number of
trophic pathways of organic matter transfer in this seagrass-dominated
system which, as a fossil estuary, lacks inputs from both freshwater and
nutrient-rich offshore oceanic waters. Structure of shorebird communities
was consistent with the main organizational patterns found for each food
web, highlighting the less diverse character of the community of Banc
d'Arguin. At Banc d'Arguin and Bijagós archipelago, which
displayed the smallest and largest isotopic niche widths in bird
assemblage, respectively, mean niche overlap among species was low,
suggesting high interspecific partitioning in resource use. Tropical
systems typically offer comparatively lower harvestable prey biomass for
shorebirds and might thus strengthen interspecific competition, leading to
low niche overlap among species. Our study reveals relevant differences in
the structure of food webs and shorebird communities in coastal areas
along an avian flyway. While differences in trophic redundancy of food
webs point to distinct levels of ecosystem resilience, contrasts in the
organization of shorebird communities highlight the plasticity in the
foraging behaviour of species inha...
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