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Luis Herrera Mesa, Full Professor of Zoology, University of Navarra, Spain
Invasive species and Canary Island fauna
The effects of invasive alien species on the natural environment are very significant, especially in isolated ecosystems such as islands. McArthur and Wilson developed a theory about the effects of invasive species on ecosystems in terms of biogeography and species distribution on islands according to which, the introduction of a species can trigger different situations: disappearance of one or several species, with or without effect on the niche of native species; disappearance of one or several species by altering the ecosystem or the food chain, and finally, failure in the establishment of the invasive species. In theoretical terms, the probability of each species would be determined by the status of the ecosystem. The higher the issue of species in the community, the lower the number of available ecological niches; thus, a well-structured and species-rich community is less vulnerable to invasion than an ecosystem with low diversity. A recent publication by CSIC scientists has found that feral cats have contributed to the extinction of at least 33 endemic vertebrate species on various islands around the world, all of which are small and sparsely populated. They diagnose the likelihood of future extinctions due to the presence of invasive cats and propose that 13 species are critically endangered. Specifically, two reptiles, nine birds and two mammals, from agreement with the catalog of the International Union for Conservation of Nature (IUCN). Seven of the twelve islands that harbor critically endangered vertebrate species are in the Pacific Ocean, three in the Caribbean, one in the Indian Ocean, and one in the Mediterranean. All of them have an area of less than 290 square kilometers and their population does not exceed 900 inhabitants.
The study took into account data feeding, impacts on the conservation of endangered species and the experience of eradication campaigns already carried out. According to this study, the introduction of invasive species -particularly predatory mammals- is one of the main factors contributing to the extinction of species on the islands. Since the domestication of the African wild cat some 9,000 years ago, man has widely dispersed the domestic cat, and feral populations have become established on islands all over the world, even in remote archipelagos, leading to the reduction of the islands' faunal biodiversity.