Tue, Aug 16, 2022: 3:30 PM-3:45 PM
513F
Background/Question/MethodsBiotic homogenization is an ecological process where community composition converges over space and time. Observed patterns of biotic homogenization are amplified by anthropogenic factors such as climate change, species introductions/biological invasions, urbanization, and land-use change. For birds, there is a growing body of literature suggesting species distributions are changing at disproportionate rates between winter and breeding seasons, and between different migratory guilds. Differential, long-term shifts will impact community structure and how winter and breeding communities are changing relative to each other. In this study we test if taxonomic biotic homogenization is occurring between winter and breeding season of avian communities in the northeastern United States. We use two community science datasets, National Audubon’s Christmas Bird Count (CBC), which takes place within the months of December and January and USGS Breeding Bird Survey (BBS) which takes place in the months of May and June from 1989–2019. We conduct simulation analyses using CBC circles (n = 658) and BBS routes (n = 515) to model trends in Sørensen dissimilarity between winter and breeding communities over a regional space and by habitat type. We also simulate temporal dissimilarity trends of winter and breeding communities separately.
Results/ConclusionsOur analyses show that inter-seasonal taxonomic biotic homogenization is occurring in avian communities. Temperate deciduous forests, Mixed Forests, Cropland and Urban habitats show negative temporal trends in Sørensen dissimilarity. Coastal habitat does not exhibit a significant trend. Taxonomic homogenization is driven by decreasing species turnover in winter communities, which are converging in composition more rapidly relative to breeding communities. The proportion of species shared between winter and breeding communities has increased, as has the proportion of species only found in winter. The proportion of species only found in the breeding season has decreased. Our results show that differential, long-term shifts between seasons and migratory guilds are contributing to the pattern of taxonomic homogenization. Arctic and subarctic waterfowl migrants that travel southward to the coastal Atlantic states in winter, compounded by more rapid shifts in short-distance and year-round resident species in winter are potentially a mechanism driving this pattern. Breeding communities are changing less slowly, potentially buffered by rigid migratory behaviors of neotropical migrants. Identifying patterns of biotic homogenization throughout the year is important to establish conservation practices aimed to mitigate the accelerating effects of anthropogenic climate change.
Results/ConclusionsOur analyses show that inter-seasonal taxonomic biotic homogenization is occurring in avian communities. Temperate deciduous forests, Mixed Forests, Cropland and Urban habitats show negative temporal trends in Sørensen dissimilarity. Coastal habitat does not exhibit a significant trend. Taxonomic homogenization is driven by decreasing species turnover in winter communities, which are converging in composition more rapidly relative to breeding communities. The proportion of species shared between winter and breeding communities has increased, as has the proportion of species only found in winter. The proportion of species only found in the breeding season has decreased. Our results show that differential, long-term shifts between seasons and migratory guilds are contributing to the pattern of taxonomic homogenization. Arctic and subarctic waterfowl migrants that travel southward to the coastal Atlantic states in winter, compounded by more rapid shifts in short-distance and year-round resident species in winter are potentially a mechanism driving this pattern. Breeding communities are changing less slowly, potentially buffered by rigid migratory behaviors of neotropical migrants. Identifying patterns of biotic homogenization throughout the year is important to establish conservation practices aimed to mitigate the accelerating effects of anthropogenic climate change.