Human impacts rewrite the rules of island biodiversity around the globe

A new study reveals that human activities have fundamentally reshaped biodiversity patterns on islands across the globe, providing important implications for how scientists understand ecology, evolution and conservation.

Led by the University of Birmingham, the international team of researchers examined how species extinctions and introductions have transformed island ecosystems over a millennia showing that islands have experienced a disproportionate share of global biodiversity loss.

In total, island endemic species account for around 75% of recorded anthropogenic extinctions globally, while many islands have also received large numbers of introduced species. In some cases, the number of introduced species now equals or exceeds the original native flora and fauna. For example, in the Hawaiian Islands almost all endemic species of bird have been driven extinct, with roughly the same number having been introduced from elsewhere in the world.

The study’s findings, published in Science Advances, also suggest that many biodiversity patterns observed today – such as species richness, endemism and ecological interactions – are not solely the result of natural ecological and evolutionary processes but also often reflect a long legacy of human influence.

Key findings:

• Key biodiversity patterns have been altered due to the impact of human-driven extinctions and introductions, which have changed fundamental relationships between biodiversity and different abiotic factors, such as island size and island isolation, and potentially affecting long-standing ecological and evolutionary theories.

• In several cases, human impacts commenced thousands of years ago, making it increasingly difficult to tease apart natural patterns from human influences.

• Introduced species often offset species losses numerically, but not ecologically. Many islands now have as many or more species than before human arrival due to introductions, yet they have still experienced substantial losses of native biodiversity and ecological function. 

• For certain groups – primarily birds and mammals – researchers have a reasonable idea of the biodiversity that has been lost on islands. However, for many others there is a lack of knowledge, making it difficult to identify pre-human biodiversity baselines and fully understand the extent to which island ecosystems have been altered.   

Dr Thomas J. Matthews, from the University of Birmingham and lead author of the study, said: "Islands have played a central role in the development of ecological and evolutionary theory. However, many of the biodiversity patterns we observe today have been shaped not only by natural processes but also by thousands of years of human-driven extinctions, species introductions and environmental change.

"We know that these human actions have substantially affected island environments. What we show in this study is a different kind of impact - that human actions have also substantially altered our understanding of the natural world. Many current ecological and evolutionary patterns observed on islands reflect not just natural processes but also a legacy of human-induced change spanning millennia."

Dr Sandra Nogué, ERC researcher at UAB and CREAF and co-author of the study, said: "Overall, we found that the extinction of endemic species, combined with the introduction of plants and animals that are widespread elsewhere in the world, is making islands increasingly homogeneous and more similar to one another."

Islands have long been regarded as natural laboratories for understanding biodiversity, inspiring foundational scientific ideas such as Darwin's theory of evolution and the theory of island biogeography. However, this new review highlights how extensive historical changes to island ecosystems can affect our interpretation of these systems.

The paper also highlights a range of existing and emerging approaches that can help scientists reconstruct pre-human biodiversity baselines. Approaches include fossil evidence, ancient DNA analysis, museum collections, historical records, and advanced ecological modelling. The team argues that combining these approaches will provide a more accurate understanding of how island biodiversity has changed through time.

Dr Thomas J. Matthews added: "New datasets, analytical tools and palaeoecological evidence are giving us unprecedented opportunities to better understand the natural history of island ecosystems. By integrating these different sources of information, we can develop a clearer picture of how biodiversity patterns have been transformed as well as how the ways in which they might be restored or conserved in the future."

Future biodiversity research must increasingly consider both natural and anthropogenic drivers of ecological change. As globalisation, trade and land-use change continue to influence island ecosystems, understanding the combined effects of natural and human processes will be essential for effective conservation planning.

The study was led by the University of Birmingham and involved researchers from several international institutions, including CREAF, the Universitat Autònoma de Barcelona (UAB), the BETA Technological Centre (UVic-UCC), the Granollers Museum of Natural Sciences, the University of La Laguna and the Centre for Biodiversity and Global Change Research at the Autonomous University of Madrid.