In general, we observe that the extinction of endemic species and the introduction of plants and animals widely distributed in other parts of the world make islands more homogeneous and increasingly similar.
Islands account for nearly 75% of global extinctions and are becoming more and more alike
The myotragus, a bovid known by the scientific name Myotragus balearicus ('Balearic rat goat', in Greek), inhabited the Balearic Islands 5,000 years ago. Today, this endemic species only remains in fossils , because the first inhabitants hunted it, new species were introduced that competed with it and it ended up disappearing. This is not an isolated case . A new study, published in Science Advances , warns that the islands concentrate nearly 75% of the global extinctions registered by the IUCN (International Union for Conservation of Nature). According to the research team, human activities have been modifying island ecosystems for thousands of years to the point that the biodiversity of the islands is increasingly homogeneous and more similar to that of the mainland . The publication was led by Dr. Thomas J. Matthews from the University of Birmingham and several Spanish entities have participated, including CREAF, the Autonomous University of Barcelona (UAB), the Granollers Natural Sciences Museum and the BETA Technology Center (UVic-UCC).
For example, the study documents extreme losses in different archipelagos, such as Christmas Island, in the Indian Ocean, which has lost nearly 80% of its endemic mammals and lizards. In the case of Rodrigues Island, also in the Indian Ocean, 100% of its native reptiles have disappeared, and in Hawaii, 70% of its land birds have become extinct.
Sandra Nogué, ERC researcher at the UAB and CREAF
Among the main causes of these extinctions are the arrival of invasive species, the cutting down of forests to open up areas for cultivation or urbanization, and the introduction of domestic animals or animals associated with human activity, such as rats, cats, goats or pigs.
Many island species evolved for millions of years without large predators, making them very trusting; therefore, they are especially vulnerable to new predators, which end up displacing them.
Natàlia Martínez-Rubio, CREAF researcher
Canary and Balearic Islands: extinctions and species on the edge
Canary and Balearic Islands: extinctions and species on the edge
According to the researchers, on the nearby islands there are also examples of unique species that have disappeared or are currently threatened. In the Balearic Islands, for example, there was an endemic species of bird, the giant barn owl (Tyto balearica ), which disappeared centuries ago. "Its disappearance is associated with the arrival of humans," explains Martínez-Rubio.
Currently, the Canary Islands' giant lizards (Gallotia ) are seeing their populations dwindle due to the expansion of the California kingsnake (Lampropeltis californiae ). The Canary Island white-tailed dove (Columba junoniae ), endemic to the laurisilva forest of the Canary Islands, is also beginning to be considered "near threatened" according to the IUCN, due to habitat loss and predators such as cats and rats. As for the Balearic Islands, the Pityuses lizard (Podarcis pityusensis ), an endemic species of Ibiza, Formentera and its islets, is at risk of extinction due to another invasive snake, the horseshoe snake (Hemorrhois hippocrepis ) .
These losses not only imply a reduction in the number of species, but also less functional ecosystems.
When an island species disappears, so do the ecological functions it performed. The Pitiusa lizard, for example, acts as a seed disperser and pollinator and controls insect pests such as isopod crustaceans.
Oriol Lapiedra, CREAF researcher
Plants also suffer the consequences of the alteration of island ecosystems, "but they tend to be the ones largely forgotten," Nogué points out. "For example, thanks to fossil pollen, it has been known that two plant species disappeared before they were even scientifically studied, such as a species of oak (Quercus ) and a hornbeam (Carpinus ) that lived on the island of Tenerife," he adds.
The task of reconstructing the past
The task of reconstructing the past
Islands have been fundamental to understanding evolutionary processes and generating new theories, such as that of natural selection formulated by Charles Darwin, and for biogeography — the discipline that studies why some species live in certain places and not in others. In this sense, the study warns that current island ecosystems are the result of thousands of years of human impact, and not only of ecological and evolutionary processes before the arrival of humans.
Natàlia Martínez and Ferran Sayol, co-authors of the study, taking steps to conduct evolutionary studies on the Nicobar Pigeon (Caloenas nicobarica) which is still alive, but is near threatened according to the IUCN. It is found on small forested islands, mangroves and jungles, from the Nicobar and Andaman Islands to Indonesia and Palau. The photos were taken at the Castell dels Tres Dragons, which is part of the Museum of Natural Sciences of Barcelona. Authorship of the photos: Cristina Claramunt.
Nicobar pigeon ( Caloenas nicobarica ) which is still alive, but is near threatened according to the IUCN. Photo credit: Cristina Claramunt.
Bird known as Spix's Macaw ( Cyanopsitta spixii ), which is extinct in the wild. Natàlia Martínez and Ferran Sayol taking steps to conduct evolutionary studies on birds. Author: Cristina Claramunt.
"Therefore, if we only study the species that have survived to this day, we have a partial and biased view of what these ecosystems really were like. In other words, scientific theories could be incomplete if historical human alterations are not incorporated ," adds Ferran Sayol, researcher at the BETA Technology Center (UVic-UCC) and another of the co-authors.
To fill these information gaps, the authors propose combining fossils, ancient pollen, ancient DNA, museum collections and historical records, in addition to improving global biodiversity databases.
"The history of islands is fundamental to understanding how species have evolved, understanding what happens when they disappear and, ultimately, contributing to preserving their future," concludes Dr. Thomas J. Matthews.
The study was led by the University of Birmingham and involved several Spanish entities, including staff from CREAF, the UAB, the BETA Technology Center (UVic-UCC), the Granollers Natural Sciences Museum, the University of La Laguna and the Biodiversity and Global Change Research Center of the Autonomous University of Madrid.
- Article Reference: Matthews, TJ, Sayol, F., Soares, FC, Heinen, JH, Chu, O., Martínez-Rubio, N., et al. Emergent patterns of island biodiversity in the Anthropocene (Science Advances).
