University of Bayreuth, Press release No.164/2021, 12 November 2021
New study on biodiversity: Functional diversity declines in ecosystems on oceanic islands
The biodiversity of ecosystems worldwide has changed greatly under the influence of humans. A research team including Prof. Dr Manuel Steinbauer from the University of Bayreuth has studied these processes using birds on ocean islands as an example. The study published in "Science Advances" shows that the number of alien species that become newly established is often higher than the number of species that have become extinct under anthropogenic influences. However, the immigrant species cannot fully replace the diverse ecological functions of extinct species. The loss of native species therefore causes a long-term unification of ecosystems and their functions.
The new study is the result of close cooperation between Prof. Dr. Manuel Steinbauer and research partners in Sweden and Great Britain. In total, the team has been able to obtain data on 1,302 bird species on nine archipelagos by studying fossils and living animals. Of these, 265 species are now extinct, at least on these islands. 143 alien species have newly established on the islands, often strongly facilitated by humans. On the Bermuda Islands, Hawaii, and St. Helena, the number of alien birds clearly exceeds that of the extinct species.
AOn the Canary Islands, Cuba, and Jamaica, as well as on New Caledonia, the situation is the opposite. The extinct species on Madagascar, the Mascarene Islands, and New Zealand only slightly outnumber the immigrant species. "But the exact number of extinct species is unknown. On almost all islands, numerous species are likely to have become extinct due to the influence of humans, of which we do not yet know," says Steinbauer.
The new study investigates the ecological functions of the bird species. These include, for example, the shape and length of the beak or the ability to fly. The new insight was that the establishment of new bird species does not compensate the loss of functions caused by previous extinctions. From a functional perspective, island bird communities become increasingly less differentiated. Numerous evolutionary adaptations to specific island conditions have been lost. New alien species are not able to replace the functional diversity of previously present species.
Steinbauer played a role in the conceptualisation of the study, which is based on extensive amounts of data. "The empirical data available worldwide on the extinction and establishment of species, as well as new possibilities in data analysis and modelling, provide fascinating insights into the dynamics of biodiversity," says the ecologist from Bayreuth, who has worked intensively on biodiversity on oceanic islands and its history over the past two decades. Together with research partners in Oxford, London, and Gothenburg, he has for the first time investigated the unresolved question of whether the global spread of non-native bird species can compensate for the ecological consequences of human-induced species loss. "The ecosystems of the oceanic islands harbour a large number of endemic bird species not present in any other region on earth. At the same time, many bird species were able to establish, often supported by humans. Islands provide a unique opportunity to study the interaction between species loss and the establishment of new" explains Steinbauer.
Ferran Sayol et al.: Loss of functional diversity through anthropogenic extinctions of island birds is not offset by biotic invasions. Science Advances (2021), DOI: https://dx.doi.org/10.1126/sciadv.abj5790