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Humans have an extremely long history of transporting and introducing mammal species outside their native geographic ranges. The characteristics of the species introduced (taxonomy, life-history, ecology, environment) can all influence which traits are available (and selected) for establishment, and subsequent invasive spread. Understanding the non-randomness in species introductions is therefore key to understanding invasions by alien species. Here, we test for selectivity in the identities and traits of mammal species introduced worldwide. We compiled and analysed a comprehensive database of introduced mammal species, including information on a broad range of life history, ecological, distributional and environmental variables that we predicted to differ between introduced and non-introduced mammal species. Certain mammal taxa are much more likely to have been introduced than expected, such as Artiodactyls in the families Bovidae and Cervidae. Rodents and bats were much less likely to have been introduced than expected. Introduced mammal species have significantly larger body masses, longer lifespans and larger litter sizes than a random sample of all mammal species. They also have much larger native geographic ranges than expected, originate from significantly further north, from cooler areas, and from areas with higher human population densities, than mammal species with no recorded introductions. The traits and distributions of species help determine which have been introduced, and reflect how the evolutionary history of mammals has resulted in certain species with certain traits being located in the way of human histories of movement and demands for goods and services. The large amount of unexplained variation is likely to relate to the intrinsically stochastic nature of this human-driven process.
The history of the green monkey Chlorocebus sabaeus, a species introduced by man, in the Cape Verde Islands is discussed. The earliest reference to the presence of monkeys on the island of Santiago dates from the late 16th century, when they were said to be abundant, suggesting that their introduction took place during the first 100 years since the first arrival of European navigators in the archipelago around 1460. Brava is the only other island in the Cape Verdes where the green monkey has been introduced. Reports of the former existence of feral monkey populations on other islands (e.g. Santo Antão and Fogo) are unsubstantiated. Today, populations of the green monkey survive on both Santiago and Brava, although – due to heavy persecution because of the damage they caused to plantations – their numbers are now probably less then they may have been in the past. In addition, the occurrence of other mammals introduced to the Cape Verde Islands is discussed. These encompass rodents (house mouse Mus musculus, brown rat Rattus norvegicus, black rat R. rattus) and the rabbit Oryctolagus cuniculus. Finally, the history of free-living ungulates, particularly goats, in the archipelago is briefly discussed.