Revealed: The long legacy of human-driven ant decline in Fiji
Summary author: Walter Beckwith
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.”
Journal
Science
Article Title
Genomic signatures indicate massive declines of endemic island insects
Article Publication Date
11-Sep-2025
Island ant communities show signs of ‘insect apocalypse’
79% of endemic species show signs of decline, highlighting the vulnerability of island biodiversity to ecosystem changes.
Okinawa Institute of Science and Technology (OIST) Graduate University
image:
Museum collection of pinned ants from Fiji. This study involved extensive genome sampling from thousands of Fijian ant specimens, highlighting the vital importance of these museum collections as resources for biodiversity monitoring and conservation.
view moreCredit: Peter Ginter
From pollinating flowers to enabling decomposition and supporting nutrient cycles, insects’ abundance and biodiversity are critical for maintaining healthy ecosystems. However, recent studies showing population declines have raised alarm about how insects are coping with the modern world. Understanding whether recent observations are part of longer timescale trends can help inform global conservation efforts, and identify the reasons behind the so-called “Insect Apocalypse”.
Published in Science, researchers from the Okinawa Institute of Science and Technology (OIST) used a community genomics approach to explore ant populations in the Fijian archipelago as a model system to understand insect biodiversity trends. By studying the genomics of museum collections, they were able to trace the ants’ evolutionary relationships to explore their arrival to the islands and reconstruct the population history of the species.
Global conservation efforts rely on biodiversity monitoring, but often focus on larger photogenic animals, and on easier to monitor areas, like temperate habitats. However, it’s widely suspected that many insect species are experiencing rapid population decline. We know that island systems are hotspots of biodiversity, so they are critical to study. Dr. Evan Economo, a Professor at OIST and the University of Maryland, and one of the senior authors on the paper, explains, “It can be difficult to estimate historical changes to insect populations, because with few exceptions, we haven’t been directly monitoring populations over time. We take a novel approach to this problem by analyzing the genomes of many species in parallel from museum specimens collected recently. The genomes hold evidence of whether populations are growing or shrinking, allowing us to reconstruct community-wide changes.”
What the researchers found is alarming; 79% of the endemic species (species found only in Fiji) are in decline, over a timescale which correlates with the arrival of humans to the islands. Meanwhile, ant species recently brought by humans are exploding in population. The largest proportion of declines are seemingly within the most recent few hundred years, coinciding with European contact, colonization, global trade and the introduction of modern agricultural techniques.
A community-wide approach
By focusing on the Fijian archipelago, a region of long-term interest to the researchers, they were able to get a broad, comprehensive overview of the population changes and colonization history of almost all the different ant species in the region. "Being closed, isolated ecosystems, islands are expected to feel the effects of human impact faster, so they are kind of a canary in the coal mine,” notes Dr. Cong Liu, first author on this paper.
However, studying the populations of tropical islands is not without challenges. Often fieldwork can be extremely difficult, and it isn’t easy to do continuous surveys. Therefore, instead of relying on real-time field monitoring, here the team used museum collections built across decades of fieldwork, including both the team’s previous collection efforts and those by other entomologists.
Museumomics: reconstructing ant colonization
One challenge of using museum collections is that DNA degrades over time. Therefore, the researchers had to use special sequencing methods (museumomics) to compare small fragments of DNA. In this study, they sequenced samples of genomes from thousands of ants from over one hundred different confirmed ant species. Using these data, they identified 65 separate instances (colonization events) where new ant species came to the island. These ranged from natural colonization (i.e. arrival of the ants with no human involvement) millions of years ago, to recent human introduction after Fiji became part of global trade networks.
Building on this history, the researchers were able to use their population genetics models to identify the rise or decline in population of different ant groups throughout the Fijian archipelago, noting the decline of endemic species, as well as dramatic increases in population of non-native species in more recent years.
Island endemic species have often evolved traits that make them sensitive to environmental changes, including the arrival of new damaging species. “Most recorded extinctions have historically been from island systems,” adds Dr. Liu.
Going beyond the archipelago
The team hopes that this work can act as inspiration for future work to continue building scientific understanding of insect populations, and to inform conservation efforts. “This study also highlights the importance of biodiversity and museum collections,” explains Professor Alexander Mikheyev of the Australian National University, a senior author on this study. “As our scientific toolbox expands, there is more and more information that we are able to capture from biodiversity collections, so it’s essential that we continue investing in and maintaining these vital resources.”
The team are looking into this locally as well, to measure the biodiversity of Okinawan insect populations in real-time through acoustic monitoring and trapping as part of the Okinawa Environmental Observation Network (OKEON).
“Insects are essential for the environment,” emphasizes Prof. Economo. “As scientists, we need to play our part in their protection, and provide and analyze the relevant data to ensure the long-term integrity of our ecosystems”.
A small selection of the species encountered by the team in Fiji. A) Acropyga sp. FJ02 (endemic) carrying mealybug. B) Hypoponera eutrepta (endemic) carrying larva. C) Tetramorium lanuginosum (introduced). D) Colobopsis dentata (endemic). E) Odontomachus simillimus (Pacific native). F) Colobopsis polynesica (endemic).
Credit
Eli Sarnat
During their fieldwork, the researchers sampled ants in Fiji by using bags to extract them from leaf litter, among other methods.
Credit
Evan Economo
Journal
Science
Method of Research
Data/statistical analysis
Article Title
Genomic signatures indicate biodiversity loss in an endemic island ant fauna
Article Publication Date
11-Sep-2025
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