Non-native ants are breaking down biogeographic boundaries and homogenizing community assemblages

Global biogeographic realms have resulted from millions of years of evolution. Yet, it remains largely unknown to what extent these realms may change because of human-mediated dispersal of species, especially in insects, which outnumber all other known animal species.
Non-native ants are breaking down biogeographic boundaries and homogenizing community assemblages
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In the era of the Anthropocene, characterized by unprecedented human mobility and global trade, the dispersal of species across the planet has reached unprecedented levels. This phenomenon has significant implications for biodiversity, particularly in understanding the shifts in species assemblages across different regions. Historically, biogeographic patterns have been shaped by various factors including geography, environmental differences, and evolutionary history, leading to distinct boundaries between species communities. However, with the globalization of trade and transport, these boundaries are undergoing profound transformations.

Recent research has shed light on the impact of human-mediated introductions and species extinctions on biogeographic boundaries, particularly in vertebrates. Nevertheless, the extent of this phenomenon in insects, the most diverse group of animals on Earth, remains unclear. Ants, with their ubiquity, abundance, and ecological significance, serve as an excellent model system to explore these dynamics. Ants dominate terrestrial ecosystems in terms of their abundance (20 x ground-dwelling individuals) and biomass, they occupy various trophic positions and are present in nearly all terrestrial habitats in every continent. Ants are key contributors to many ecosystem functions, such as seed dispersal, soil bioturbation, resource removal, pest control, and help structure most invertebrate communities through predation or competition.  

In our recent study published in Nature Communications, we delved into the distribution patterns of ants to investigate the globalization of species assemblages. Our study focused on a comprehensive dataset comprising 13,744 ant species, including 309 non-native species. We revealed a breakdown of historical biogeographic patterns, particularly evident in the division between tropical and non-tropical regions.

Figure: Global biogeographic patterns before and after human-mediated dispersal of non-native species. Biogeographic groups of 309 non-native ant species: a before (native ranges) and b after human-mediated dispersal (native + non-native ranges). Biogeographic realms of all ant species (13,774): c before (native ranges) and d after human-mediated dispersal of non-native species (native + non-native ranges). Colors indicate biogeographic clusters identified using compositional dissimilarity (β diversity index) and clustering analysis. 

Crucially, our study demonstrated that these changes extend beyond the distribution of non-native species, fundamentally altering the biogeographic boundaries of all ant biodiversity. Despite non-native species representing a small fraction (2.2%) of total ant diversity, their introduction has had a disproportionate impact on the homogenization of ant assemblages worldwide.

The results highlight a global trend of biotic homogenization, with 52% of ant assemblages becoming more similar. This trend is particularly pronounced in tropical regions and on islands, which are home to some of the most vulnerable ecosystems. Tropical islands, in particular, have emerged as significant recipients of non-native ant species, contributing to their biotic homogenization.

The study underscores the overriding influence of anthropogenic activities on biodiversity, surpassing the biogeographic patterns shaped by millions of years of evolution. Importantly, it emphasizes the need to assess regional heterogeneity, as areas vary in their response to human-mediated species introductions. This is especially pertinent considering that many biodiversity hotspots are located in tropical regions, and islands are renowned for their high levels of endemism.

Overall, our research provides valuable insights into the complex interplay between human activities and biodiversity dynamics. By unraveling the mechanisms driving the globalization of species assemblages, our study offers crucial information for conservation efforts aimed at preserving the unique biogeographic heritage of different regions worldwide.

Illustration credit: @czbugsart

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Biogeography
Physical Sciences > Earth and Environmental Sciences > Geography > Integrated Geography > Biogeography
Community and Population Ecology
Life Sciences > Biological Sciences > Ecology > Community and Population Ecology

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