Hydrological Conditions and Climatic Factors Shape Waterbird Functional Diversity in a Ramsar Site of Argentina

Abstract

With global biodiversity in decline, functional biodiversity metrics help link biodiversity changes to ecosystem functioning. In wetlands, extreme events like droughts and floods challenge waterbirds, affecting survival and reproduction. At Pampean lakes in Argentina, hydrological fluctuations are significant. We examined how waterbird functional diversity responds to these changes at the Melincué Ramsar Site, considering seasonality and whether environmental filtering or competition shapes community structure. Using waterbird counts from 1992 to 2019, we calculated functional richness, evenness, divergence and dispersion based on species traits. We employed general linear models and beta distance to assess relationships between functional diversity indices and hydrological variables, and explore assembly patterns. We recorded 71 waterbird species. Functional richness decreased by nearly 26% in drier years, indicating a loss of trait diversity under reduced hydrological conditions. Evenness correlated positively with precipitation and negatively with lake area, peaking at intermediate Standardized Precipitation-Evapotranspiration Index over a 12-month period (SPEI 12) values. Divergence increased with precipitation but was lowest at intermediate SPEI 12 values and highest in summer. Dispersion peaked at intermediate lake areas, increasing with summer precipitation but decreasing with winter precipitation. Trait-convergence assembly patterns (TCAP) analysis showed community structure significantly changed with lake area, was marginally significant for SPEI 12 and not significant for precipitation. Maximum functional diversity occurred when the lake was neither too high nor too low and seasonality influenced functional diversity responses. These results highlight environmental filtering as the primary driver of waterbird assembly over time and underscore the need to incorporate hydrological dynamics into wetland conservation planning.