Seasonal Role Reversal of Baer's Pochard in Waterbird Association Networks

Interspecific associations are fundamental to understanding community structure and stability, holding critical implications for the conservation of endangered species. However, research on the network position of species within waterbird communities remains limited, particularly regarding the Critically Endangered Baer's Pochard (Aythya baeri). To address this gap, we conducted a systematic survey of the Baiyangdian Wetland (BYD) from May 2023 to March 2024, recording Baer's Pochard and 48 sympatric waterbird species. We constructed and analyzed interspecific association networks for both breeding and wintering periods using the Phi coefficient (r _Φ ) and Lambda coefficient (L _B ), and calculated the species association diversity index (H') and community contribution rate (C _i ) to examine the network position of Baer's Pochard and its seasonal variation. Results indicated that, within the focal study year, the waterbird community in Baiyangdian exhibited a significant symmetrical positive association pattern in both seasons, consistent with community assembly influenced by environmental filtering, although additional ecological processes may also contribute. However, the network position of Baer's Pochard changed markedly between seasons: during the breeding season, it functioned as a core species, forming close associations with six other waterbird species and exhibiting higher H' and C _i values, occupying a more central position in the network; during the wintering season, it shifted to a peripheral position, with reduced connectivity and relative network centrality, while the Eurasian Coot (Fulica atra) replaced it as the central node of the wintering network. Concurrently, the number and identity of core species varied dynamically across seasons, with some species maintaining stable core status and others undergoing positional shifts. These findings suggest that the structural position of endangered species within co-occurrence networks may vary seasonally, although the interannual stability of this pattern requires further verification through long-term monitoring. This study emphasizes that conservation strategies should account for both breeding and wintering periods, maintaining overall community stability while safeguarding critical microhabitats. The study provides a scientific basis for the targeted conservation of Baer's Pochard and offers a case reference for understanding the seasonal dynamics of network position of endangered waterbirds within communities.