Introduced Species Give a False Impression of Biodiversity

On July 23, 2026, an international team led by researcher Thomas J. Matthews of the University of Birmingham published in Science Advances (1) a synthesis that revisits decades of knowledge about island species. The authors demonstrate that human activities have profoundly reshaped the nature of islands for millennia. Consequently, many ecological models used today describe ecosystems already transformed by introductions and extinctions of species, rather than a truly natural state.

Introduced species obscure a deep upheaval in island biodiversity

Since Charles Darwin, islands have been regarded as natural laboratories of evolution. Yet this vision rests on landscapes where native species have often already disappeared. According to the researchers, endemic island species account for about 75% of anthropogenic extinctions recorded worldwide, a figure illustrating the exceptional vulnerability of these territories. At the same time, trade, transportation, and human activities have introduced a substantial number of new species, sometimes giving the impression that biological richness remains intact even as local biodiversity has become profoundly impoverished.

The Hawaii example epitomizes this transformation. Almost all of the archipelago’s endemic birds have vanished, while a comparable number of bird species from other parts of the world now occupy the same ecological niches. Numerically, diversity appears preserved. Yet ecologically, the replacement is far from equivalent. As Thomas J. Matthews notes, “the ecological and evolutionary models observed today reflect not only natural processes but also a legacy of changes caused by humans over millennia,” according to the official Birmingham University press release published July 23, 2026. This observation shows that the current nature no longer serves as a reliable benchmark for measuring biodiversity losses.

Introduced species challenge the grand theories of ecology

The study is not limited to documenting extinct species. It also shows that massive introductions of species have altered the fundamental relationships between island size, geographic isolation, and biodiversity richness. These relationships form the backbone of island biogeography theory, developed in the 20th century and largely inspired by observations on islands. The researchers estimate that some ecological laws describe today a world already deeply transformed by human activities rather than a strictly natural functioning.

Sandra Nogué, coauthor of the study, stresses another major phenomenon. “We found that the extinction of endemic species, combined with the introduction of plants and animals widely spread elsewhere in the world, makes islands increasingly homogeneous and more alike to each other,” she explains in the Birmingham University press release. This homogenization gradually reduces the ecological peculiarities that gave each island its uniqueness. Consequently, nature loses part of its functional diversity, even when the total number of species seems to stay stable.

Understanding extinct species to restore biodiversity for tomorrow

Restoring the pre-human state of islands has become a major scientific challenge. The authors remind us that the earliest human activities date back thousands of years on some territories. It therefore becomes extremely difficult to distinguish what stems from natural processes and what results from introductions or extinctions of species. The knowledge remains relatively robust for birds and mammals. By contrast, data for insects, mollusks, or many plants remain very fragmentary, limiting precise reconstruction of past biodiversity.

To move beyond these limits, scientists propose combining several complementary approaches. Fossils, ancient DNA, museum collections, historical archives, as well as new ecological modeling techniques are gradually enabling the reconstruction of the communities of species present before major human transformations. Thomas J. Matthews also emphasizes that “the new databases, analytical tools, and paleoecological evidence offer unprecedented possibilities to better understand the natural history of island ecosystems.” According to the researchers, this knowledge is essential to define realistic restoration and biodiversity conservation goals.

The Mauritius example perfectly illustrates this difficulty. The large-beaked parrot (Lophopsittacus mauritianus), extinct in the 17th century due to hunting, habitat destruction, and animals introduced by ships, was never ecologically replaced. Other bird species have indeed colonized the island since, but none fill the ecological functions of this emblematic species. The authors also remind us that globalization continues to accelerate unintentional introductions of species through maritime trade. Each shipment can carry an insect, a rodent, or a seed capable of permanently altering ecological balances. This dynamic underscores the urgency of better understanding the transformations already undergone by island nature to guide future biodiversity protection policies.