Revealed: The long legacy of human-driven ant decline in Fiji

A new study of ants in Fiji – involving genomic sequencing of over 4,000 ant specimens from museum collections – shows that most native species have been in decline since humans first arrived in the archipelago 3,000 years ago. Meanwhile, recently introduced ant species have expanded. The findings underscore how human activity has and continues to reshape fragile island ecosystems. Insects, which make up much of Earth’s biodiversity, provide crucial ecosystem services, including pollination, soil health, and natural pest control. Recent reports of dramatic declines in insect abundance and diversity – sometimes referred to as the “insect apocalypse” – have raised global concern. Although factors such as habitat destruction, agricultural intensification, climate change, pesticide use, and light pollution are frequently implicated, the scale and universality of these declines remain debated because most studies rely on relatively short-term data or historical collections spanning only decades to centuries, leaving long-term trends largely unexplored. Advances in genomic techniques now allow scientists to reconstruct historical population trends over thousands of years, however, providing insight into how both recent and ancient human activities have shaped insect communities.

Here, Cong Liu and colleagues examined long-term trends in abundance, diversity, and ecological roles of ants in the Fijian archipelago. Ants – abundant and functionally important – serve as indicators of broader biodiversity patterns, making them ideal for such studies. And islands like Fiji, with high numbers of endemic species, are especially vulnerable to human impacts. Liu et al., applied a community genomics approach, which used high-throughput genomic sequencing on over 4,000 ant specimens from Fijian museum collections, to estimate long-term community assembly and demographic trends of ants on the islands. Fiji’s ant fauna was shaped by at least 65 colonization events, they say. Some arrived millions of years ago, which led to endemic Fijian species. Regional Pacific colonizations also impacted Fiji’s ant fauna, as did more modern introductions of ant species by humans through global trade. Notably, population modeling revealed stark differences between endemic and non-endemic species. About 79% of endemic ants – mostly confined to high-elevation, intact forests – have declined, with reductions beginning after humans first settled Fiji ~3,000 years ago and accelerating in the past 300 years alongside European contact, industrial agriculture, and species introductions. In contrast, widespread Pacific species and recent human-introduced invasive ants, which are more tolerant or adapted to human-dominant habitats, have generally expanded their populations, particularly in disturbed lowland habitats. These divergent trajectories reflect how ecological traits, habitat preference, and biogeographic context determine which species “win or lose” in the Anthropocene, Liu et al. say.

For reporters interested in the novelty of the methods and collections used in this study, study coauthor Evan Economo notes; “Community genomics refers to approaches that infer patterns and processes from genomic data across many species living together (i.e. an ecological community), rather than one or a few species at a time.  In this case, by analyzing many species in parallel, we were able to infer patterns of population change across the community to recover general trends. In principle, approaches like this have a lot of potential to analyze communities of any taxon, whether it is to look for evidence for declines or other ecological dynamics of interest. In this project, we recovered genomic data from museum collections, and this is an example of how such specimens are a continual source of insight as new technologies come online.  Collections are not just some old stuff we store in the attic, they become more valuable over time as the information they contain is unlocked in ways that may have been unimaginable to the people who originally collected the specimens decades or centuries ago.  Furthermore, we cannot fully anticipate how biodiversity collections can be used by humanity in the future, and this is why it is critical to invest in stewarding and growing collections for future generations.”