Patterns of selectivity in introductions of mammal species worldwide

Abstract

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. Blackburn et al. / NeoBiota 33: 33-51 (2017) 34

Advances in population ecology and species interactions in mammals

“…The observation that successful invasive species are hyperproductive is consistent with the suggestion that human preferences for game species or those easy to find, transport, and breed, has strongly influenced the choice of species for introduction (Capellini et al 2015). Finally, Blackburn et al (2017) showed that introduced mammal species have much larger native geographic ranges than those of randomly selected mammals, and that they originate from significantly further north in the Northern Hemisphere and from areas with higher human population densities compared to mammal species with no recorded introductions. Hence, species with human affiliations in northern latitudes of Europe were transported to North America, Australia, New Zealand, and South Africa, and generally at temperate latitudes.…”

“…Estimates of the number of mammalian species that have been introduced have been refined in recent years, building on Long's (2003) original compilation. Capellini et al (2015) and Blackburn et al (2017) identified 232 and 306 mammal species, respectively, as having been introduced to areas outside their native distributions (representing 2.6% and 4.7% of mammal species, respectively). Using the same data, Clout and Russell (2008) estimated that 124 mammal species had established self-sustaining wild populations in at least one location outside their natural range, thereby qualifying as successful invaders.…”

“…Hence, species with human affiliations in northern latitudes of Europe were transported to North America, Australia, New Zealand, and South Africa, and generally at temperate latitudes. In short, humans from northern latitudes moved the species that were available and useful to them, and these were generally larger than species that were not selected for transport (Blackburn et al 2017).…”

Bergmann's rule in alien birds

“…The tendency for introduced species to be larger-bodied than expected by chance is also found for amphibians (Tingley et al 2010) and mammals (Capellini et al 2015, Blackburn et al 2017), although we currently await analyses of spatial variation in alien body mass for these taxa. As far as we are aware, the only other study to explore Bergmann's rule in the context of alien species is by Blanchet et al (2010) for fish assemblages worldwide.…”

Colonization pressure: a second null model for invasion biology

“…This will not just be true for birds, given that we know that introduced species are a non-random selection of other taxa as well (e.g. Tingley et al 2010;Capellini et al 2015;Allen et al 2017;Blackburn et al 2017;Pyšek et al 2017). Alien macroecology is unlikely to provide many insights into species responses to the environment without this information.…”