Tuesday, 13 April 2010

April Review for F1000

An Experimental Test of Darwin’s Naturalization Hypothesis in Jiang, Jiaqi Tan, and Zhichao The American Naturalist, vol. 175, no. 4 (April 2010) pp. 415–423 DOI: 10.1086/650720

We decided to review the above paper as our April review for F1000.  This article is interesting because it is an elegant experimental test of Darwin's ‘Naturalization hypothesis’: a theory about the role of interspecific competition in invasion success.

Our Review 
Mark Lonsdale: Faculty of 1000 Biology, 19 Apr 2010 http://f1000biology.com/article/id/2902956/evaluation
Copyright F1000

This article is interesting because it is an elegant experimental test of Darwin's 'naturalization hypothesis' -- a theory about the role of interspecific competition in invasion success. Darwin theorised that introduced species would be more successful in colonising communities from which their close relatives are absent. These authors set up experimental communities of bacteria and then introduced an 'invading' bacterium. They found that invaders that were more closely related to the experimental community were less likely to establish. They also found that this effect was more pronounced when the invaded community also included a 'predator' (this was a protist bacterivore).

Darwin's justification for his theory was that competition would be more intense between more closely related species and these results are certainly consistent with that idea. However, a further reason would be that natural enemies (predators and pathogens) pre-adapted to the invader would be more likely to be present in the community of closely related species. Although the authors test the hypothesis with the introduction of a predator, this experimental set-up does not really get at this alternative explanation, focusing more on competition as the driving mechanism. A similar study {1} concluded that, in an experimental plant community, an exotic plant closely related to natives in the invaded community may experience more damage from herbivores than a phylogenetic outlier. Darwin's naturalization hypothesis is a hot topic in the literature at the moment, and a review paper just published outlines the key debates and studies {2}. This review also provides some important guidelines for future studies in this field. Now that the authors have developed a functioning experimental system, it will be interesting to see them explore the relationship between invasibility and functional diversity, which has been a major focus of research over the last 10 years. As the authors point out, the range of diversity used in their microcosms is rather small in this experiment; they will need to create a larger gradient of species diversity. Phylogenetic similarity is unlikely to be present where an invasive species arrives into a community from some distance (e.g. another continent). Ecological niches and functional similarity are likely to play a more important role in this case. Overall, the current paper is an exciting piece of work that provides a valuable experimental system for future studies to delve yet deeper into this intriguing topic.
[1] Hill, S.B. and Kotanen, P.M. (2009) Evidence that phylogenetically novel non-indigenous plants experience less herbivory Oecologia 161:3 pp 581-590

[2] Thuiller, W., Gallien, L., Boulangeat, I., de Bello, F., Münkemüller, T., Roquet, C. and Lavergne, S. (2010) Resolving Darwin's naturalization conundrum: a quest for evidence Diversity and Distributions Early View online DOI: 10.1111/j.1472-4642.2010.00645.x

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