Abstract:

Aims: Urban development influences local aquatic ecosystems. As one of the world’s megacities, urbanization process in Beijing are more rapid compared to other cities. Beijing’s local aquatic ecosystem is more affected by its urbanization projects, particularly the fish fauna, which is one of the most sensitive groups in the aquatic ecosystem. This study focuses on fish to better understand the impact of urbanization on Beijing’s aquatic ecosystem over the past decades. We apply functional diversity (FD), a crucial component of biodiversity, to assess ecosystem function, and to reflect the extent of resource allocation and complementarity among species within fish communities.

Methods: Using field survey data, historical specimens, and relevant literature, this study screened functional indicators that relate to fish habitat, feeding, movement, and reproduction. This enabled us to calculate and compare the functional richness index (FRic), functional evenness index (FEve), functional divergence index (FDiv), and functional dispersion index (FDis) of fish in Beijing across four periods (1920-1960, 1960-1984, 1984-2013, and 2013-2024). This study then compares these indices from developed/ developing areas in Beijing, and its ecological conservation area.

Results: We found that decreasing numbers of indigenous fish were recorded in Beijing as urban development was progressing, with 81, 66, 48 and 55 species detected in 1920-1960, 1960-1984, 1984-2013 and 2013-2024, respectively. The fish FRic in Beijing initially decreased and then increased over the four periods, from 28.889 to 17.693, then to 11.358, and finally to 19.888, which was synchronized with the change in species diversity. The FEve, FDiv, and FDis showed no significant changes. There was a positive correlation between the FRic and species diversity in both the built-up area and the ecological conservation area of Beijing. The FRic in the built-up area (1.639) was significantly lower than in the ecological conservation area (14.156), while the other three indices showed little variation between the two areas. Additionally, the introduction of non-native fish species had some impact on FRicbut had minimal impact on the other three indices.

Conclusions: Overall, FRic responds more clearly to the changes caused by urban development. Fish FRicin Beijing continuously declined before 2013 and slightly rebounded after 2013 due to the restoration of native fish resources, however it has yet to rebound to the level of the pre-urbanization 1960s. The functional diversity in built-up areas is significantly lower than in the ecological conservation area, clearly due to the impact of urban development. Moreover, non-native fish species can occupy the niches of native fish, making it challenging for native fish species to recover. Although the non-native fish can increase functional diversity to some extent, they introduced threats to the survival of native fish. Therefore, it is necessary to control the non-native fish species in Beijing.

Key words: biodiversity conservation, urbanization, urban fish, non-native fish, aquatic ecosystem