A research team led by the UAB and the universities of Southampton and Bayreuth shows that the arrival of humans 3,000 years ago triggered a process of homogenisation of island flora in the biogeographical region of Oceania, with the consequent impact on their ecosystems. The study also indicates that topographic complexity, and particularly altitude, would be protective factors against this process.
The research was led by Sandra Nogué from the Department of Animal Biology, Plant Biology and Ecology of the UAB and CREAF, Nichola Strandberg, from the University of Southampton, and Manuel Steinbauer, from the University of Bayreuth. Published in Nature Ecology and Evolution, the study also included the collaboration of researchers from Australia, New Zealand and the United States.
The researchers analysed 5,000 years of vegetation trends on 13 South Pacific islands spanning a gradient of 8,300 kilometres, using fossil pollen records from 15 sites, and compared their floristic composition before and after humans colonised them.
The results indicate that floristic uniqueness has declined over the past 3,000 years in the many island groups in the region, clearly coinciding with human migrations, and that the vegetation on most islands becomes more similar as soon as this happens, in a process called homogenisation, due to actions such as the introduction of foreign plants and animals, agriculture and the construction of settlements.
Humans of the Neolithic Lapita culture were the first to move to the South Pacific, and they did so in two stages. The most important was to the west of Polynesia, Melanesia and Samoa, between 3,500 and 2,800 years ago. Subsequently, between 1,000 and 700 years ago, humans moved eastwards to other islands such as the French Polynesia and Rapa Nui, north to Hawaii and south to Aotearoa (New Zealand). None of these islands had been previously inhabited.
The work also shows that topographically more complex areas located at higher altitudes tend to show less floristic homogenisation, because the difficulty of access would have reduced the likelihood of human impact.
"Our results show that early human settlement was the main driver of floristic homogenisation. We conducted the study in the South Pacific, but there are hundreds of thousands of other small islands around the world for which it may also be relevant. It allows us to better understand the human impact on biodiversity change and the consequences of the homogenisation process on the composition of island plant communities and on the ecological functions and services they provide," says Sandra Nogué, who leads the ERC project "Island Time-Lines to quantify biodiversity change" (TIME-LINES) at the UAB and coordinated this study.
The researchers stress that future trends in flora similarity in the region studied, as well as in other island groups, will depend on the levels of continuous modification of ecosystems by humans, the rates of introduction of non-native species and the rates of extinctions and extirpations of species.
"Long, standardised palaeoecological records that can be integrated with modern ecological observations are needed to fully understand modern island ecosystems and manage them effectively," concludes Nichola Strandberg, researcher at the University of Southampton and first author of the paper.
Article: Nichola A. Strandberg, Manuel J. Steinbauer, Anna Walentowitz, William D. Gosling, Patrícia L. Fall, Matiu Prebble, Janelle Stevenson, Janet M. Wilmshurst, David A. Sear, Peter G. Langdon, Mary E. Edwards & Sandra Nogué. Floristic homogenization of South Pacific islands commenced with human arrival. Nat Ecol Evol (2024). https://doi.org/10.1038/s41559-023-02306-3
