Disentangling the effects of natural and anthropogenic factors in species invasions

Pysek et al. 2010. Disentangling the role of environmental and human pressures on biological invasions across Europe. PNAS. vol. 107. no. 27. pp. 12157–12162.

This paper utilizes a massive dataset to explore the effects of climatic, geographic, and anthropogenic (economic and demographic) factors on levels of species invasion across Europe. Analyses were conducted for all taxa pooled, as well as individually for vascular plants, bryophytes, fungi, terrestrial insects, aquatic invertebrates, fish, amphibians, reptiles, birds, and mammals. In general, the authors found that anthropogenic variables (population density and wealth) were more predictive of current patterns than climatic or geographic variables, but that all three classes (alone and in interactions) were influential.
The paper does a nice job of concisely demonstrating and quantifying the role of human factors, relative to natural constraints, in the invasion process. Similarly, the authors successfully argue that attempts to understand invasion patterns without explicitly considering anthropogenic influences are likely to be flawed. However, they also stress that the relationships they have identified are strictly correlative and thus they cannot determine which specific human activities are most important. Nonetheless, they do offer a few suggestions aimed at minimizing invasion. For instance, “Where commodities themselves pose a risk either as deliberate releases or escapes e.g., pets, ornamental plants, new crops, etc., a possible solution would be to ensure the market price also reflects the likelihood and subsequent cost should the species prove to be invasive”. Perhaps I’m a pessimist, but I have a hard time imagining that such a policy has any real chance of implementation. In summary, this paper reports some illuminating patterns, but fails to offer any feasible solutions (however, in fairness to the authors, it should be pointed out they are tackling a problem that may well be insurmountable).

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