Bird extirpations and community dynamics in an Andean cloud forest over 100 years of land-use change

Long-term studies to understand biodiversity changes remain scarce-especially so for tropical mountains. We examined changes from 1911 to 2016 in the bird community of the cloud forest of San Antonio, a mountain ridge in the Colombian Andes. We evaluated the effects of past land-use change and assessed species vulnerability to climate disruption. Forest cover decreased from 95% to 50% by 1959, and 33 forest species were extirpated. From 1959 to 1990, forest cover remained stable, and an additional 15 species were lost-a total of 29% of the forest bird community. Thereafter, forest cover increased by 26% and 17 species recolonized the area. The main cause of extirpations was the loss of connections to adjacent forests. Of the 31 (19%) extirpated birds, 25 have ranges peripheral to San Antonio, mostly in the lowlands. Most still occurred regionally, but broken forest connections limited their recolonization. Other causes of extirpation were hunting, wildlife trade, and water diversion. Bird community changes included a shift from predominantly common species to rare species; forest generalists replaced forest specialists that require old growth, and functional groups, such as large-body frugivores and nectarivores, declined disproportionally. All water-dependent birds were extirpated. Of the remaining 122 forest species, 19 are vulnerable to climate disruption, 10 have declined in abundance, and 4 are threatened. Our results show unequivocal species losses and changes in community structure and abundance at the local scale. We found species were extirpated after habitat loss and fragmentation, but forest recovery stopped extirpations and helped species repopulate. Land-use changes increased species vulnerability to climate change, and we suggest reversing landscape transformation may restore biodiversity and improve resistance to future threats.

Assessing the response of marine fish communities to climate change and fishing

Globally, marine fish communities are being altered by climate change and human disturbances. We examined data on global marine fish communities to assess changes in community-weighted mean temperature affinity (i.e., mean temperatures within geographic ranges), maximum length, and trophic levels, which, respectively, represent the physiological, morphological, and trophic characteristics of marine fish communities. Then, we explored the influence of climate change and fishing on these characteristics because of their long-term role in shaping fish communities, especially their interactive effects. We employed spatial linear mixed models to investigate their impacts on community-weighted mean trait values and on abundance of different fish lengths and trophic groups. Globally, we observed an initial increasing trend in the temperature affinity of marine fish communities, whereas the weighted mean length and trophic levels of fish communities showed a declining trend. However, these shift trends were not significant, likely due to the large variation in midlatitude communities. Fishing pressure increased fish communities' temperature affinity in regions experiencing climate warming. Furthermore, climate warming was associated with an increase in weighted mean length and trophic levels of fish communities. Low climate baseline temperature appeared to mitigate the effect of climate warming on temperature affinity and trophic levels. The effect of climate warming on the relative abundance of different trophic classes and size classes both exhibited a nonlinear pattern. The small and relatively large fish species may benefit from climate warming, whereas the medium and largest size groups may be disadvantaged. Our results highlight the urgency of establishing stepping-stone marine protected areas to facilitate the migration of fishes to habitats in a warming ocean. Moreover, reducing human disturbance is crucial to mitigate rapid tropicalization, particularly in vulnerable temperate regions.