Thursday, 19 May 2011

May review for F1000

At last, a paper about cane toads!  Well, not quite, but this study on amphibians is an interesting one, as the literature on establishment success is somewhat swamped by plant studies.  Therefore, this study, which uses a meta-analysis of amphibian populations across the globe to examine Darwin's Naturalization hypothesis, is interesting and refreshing.

R Tingley, BL Phillips, R Shine Am Nat 2011 Mar 177 3:382-8 DOI 10.1086/658342

When it comes to testing ecological theories of invasion processes, plants have often been the organism of choice. So, to see amphibians being used to test Darwin’s naturalization hypothesis, as in this paper, is exciting. 

Darwin's naturalization hypothesis predicts that when species are introduced to a new range, those with fewer close relatives in the region would tend to have greater success. The results of the meta-analysis presented here contradict this. They indicate that the probability of successful amphibian establishment increases when congeneric species are present at the introduced location. It is argued that the underlying reason for this is the consequent pre-adaption of introduced species to climatic and other abiotic factors.

This neat little paper presents the results in a concise manner, incorporating important details of the key factors to account for in such an analysis, such as including a measure of ‘propagule pressure’ and identifying confounding species, event and location characteristics, which serves as a guide for similar analyses in the future.

It should be noted that another recent paper, based on laboratory experiments with bacteria, supports Darwin's hypothesis {1}. Likewise, there have long-been opposing conclusions reached when testing this hypothesis on flora: a recent study also supports Darwin’s hypothesis {2} whereas another refutes it {3}. In some other cases, contradictions between studies result from a focus on different stages in the invasion process: the ability of a species to invade a region versus the ability of a species to naturalize {2}.
{1} Jiang et al. Am Nat 2010, 175:415-23
{2} Schaefer et al. Ecol Lett 2011, 14:389-96
{3} Duncan and Williams, Nature 2002, 417:608-9

I also came across an article about this paper on the web, which can be viewed here: American Society of Naturalists.  An intriguing comment at the bottom - someone has tried to find what Darwin actually says in the Origin of Species that can be termed his 'Naturalization hypothesis'.  I haven't read this book myself - perhaps I should as an ecologist! - but it is an interesting question, where and how does Darwin state this hypothesis?  Sometimes ideas can gain a life of their own in the academic literature, it would certainly be interesting to know the precise source and statement of this hypothesis.   

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