Seasonality governs species composition at a given place and time. However, the effects of climate and land-use change can vary by season, altering species composition. These changes can lead to a loss of distinct seasonal community composition, representing a novel form of biotic homogenisation. We ask if breeding and winter bird communities are becoming more similar over time. If so, is homogenisation occurring more rapidly in winter than in the breeding season, and has the presence of individual species changed between seasons?
Northeastern United States.
1989–2019.
Two hundred thirty-eight bird species.
We use data from The National Audubon Society's Christmas Bird Count and the North American Breeding Bird Survey to test if winter and breeding bird communities have become more similar (homogenised). We evaluate this change using the Sørensen dissimilarity index, and its components of turnover (species replacement) and nestedness (a subset of a more species rich community) and describe the mechanism in which the seasonal winter and breeding bird communities are changing.
We found that winter and breeding bird communities are homogenising, driven by significant decrease in turnover and a marginal decrease nestedness. When viewing breeding and wintering communities separately, we observe different trends. Breeding communities are becoming more unique with decreasing turnover and nestedness. Winter communities are becoming more similar to each other, with decreasing turnover and nestedness. More breeding species are declining and species that are typically found in the winter and year-round residents are the main contributors to the homogenisation between seasons.
We show for the first time homogenisation between winter and breeding bird communities over time across the northeastern United States. This insight into how individual species are faring between seasons, and how they impact community structure, can be used when implementing conservation measures for maintaining ecological functioning and integrity.
Biogenic structural complexity increases mobile animal richness and abundance at local, regional and global scales, yet animal taxa vary in their response to complexity. When these taxa also vary functionally, habitat structures favouring certain taxa may have consequences for ecosystem function. We characterised global patterns of epifaunal invertebrates in eelgrass (Zostera marina) beds that varied in structural and genetic composition.
North America, Europe and Asia.
2014.
Peracarid crustaceans and gastropod molluscs.
We sampled epifaunal invertebrate communities in 49 eelgrass beds across 37° latitude in two ocean basins concurrently with measurements of eelgrass genetic diversity, structural complexity and other abiotic and biotic environmental variables. We examined how species richness, abundance and community composition varied with latitude and environmental predictors using a random forest approach. We also examined how functional trait composition varied along with community structure.
Total species richness decreased with latitude, but this was accompanied by a taxonomic shift in dominance from peracarid crustaceans to gastropods, which exhibited different sets of functional traits. Greater eelgrass genetic diversity was strongly correlated with both richness and abundance of peracarids, but less so for gastropods.
Our results add to a growing body of literature that suggests genetic variation in plant traits influences their associated faunal assemblages via habitat structure. Because peracarids and gastropods exhibited distinct functional traits, our results suggest a tentative indirect link between broad-scale variation in plant genetic diversity and ecosystem function.
Habitat loss is the dominant cause of biodiversity decline around the world, yet the complexity and stability of terrestrial assemblages related to suitable habitats have been almost unknown on a global scale.
Global.
Contemporary.
Mammalia, Aves, Reptilia, Amphibia.
We constructed gridded maps of species–habitat networks of terrestrial vertebrates based on global species distributions and a recently developed habitat type dataset. Then, we investigated the biogeographic patterns of emergent network structures and analysed network robustness to habitat loss by simulating habitat removals on a global scale.
We found that, compared with reptiles and amphibians, the species–habitat networks of mammals and birds were characterised by higher habitat diversity, connectance and modularity. All four taxonomical groups have high robustness globally, but after adjusting for species and habitat diversity, we found a variation of surplus and deficiency of network structures and robustness. Temperature and precipitation contributed most to relative network robustness globally, whereas geographical and human population factors played important roles in scattered regions on all continents.
Overall, we provide novel insights into the biogeographic patterns of species–habitat connections through a network approach, which can help to identify gaps for reestablishing species–habitat links to improve conservation outcomes.
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