Global Change Biogeography: Global Invasion

Thursday, 29 December 2011

Global Invasion - blurring the boundaries

Global economy, ease of travel and transportation, pet trade. What do these things have in common? Well, they all contribute towards a new component of human induced global environmental change: biological invasion. Throughout Earth's history species colonized new geographic areas and established successfully, so arguably to some extent biological invasion is a natural phenomenon. However the process we witness today is quite different from that of historical times regarding both spatial and temporal scales.

Biological invasion is problematic for several reasons: Firstly, many invasive species act as disease vectors or are pathogens themselves. As a result they not only pose a threat to domestic livestock and other animals (see white nose syndrome in news section), but they also pose serious threat to humans. Secondly, despite some 'invasive' species are economically highly valuable (potato in Europe or wheat in the USA), many invasies become pests and have devastating effect on agriculture, or harm economy otherwise. A famou example is that of the zebra mussel, a marine bivalve brought to the USA in the ballast water of cargo ships ( see video). It spread rapidly, and grew so densely on the substratum that it often blocked pipe systems and canals. Lastly and most importantly, invasive species interact with local species and ecosystems, and often cause several disturbance. They often outcompete or predate on local and endemic species and later food chains, causing sever biodiversity loss. The most dramatic example is that of the introduction of Nile Perch to Lake Victoria in Africa. Since its introduction in the 1950 it predated on and eradicated hundreds of species from the highly diverse and endemic cichlid fishes. Invasive species may also interact with other components of global change. For example altered land use may aid the spread of invasive grass species, which in turn is change local species composition through altering fire dynamics.
In summary the consequences of biological invasion on global biogeographical patterns are twofold: Firstly, as Vitousek and colleagues put it, 'biological invasion breaks down global biogeographic barriers and blurs the regional distinctiveness of local biota'. The number of local, endemic species will decrease and there will be an increasing number of species which are found all around the world. Secondly, invasive species eradicate local species and decrease global biodiversity.

Vitousek, PM., Antonio, CM., Loope, LL., Rejmanek, M., Westbrooks, R. (1997). New Zeland Journal of Ecology. Introduced species: A significant component of human-caused global change. (21) 1-16.

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