What is the magic number? New debates about the old question on minimum viable population size

The word “new” is a funny term in this context, as one might think that most of what could be said about minimum viable populations (MVP) has been said already. Nevertheless, it seems the subject is still always good for a debate, a point proven by a two recent reviews and responses in TREE.

In a review paper from 2011, “Minimum viable populations: is there a ‘magic number’ for conservation practitioners?”, Curtis Flather et al.. 2011 conclude regarding the MVP:

… recent studies have revived the concept of the minimum viable population (MVP), the population size required to provide some specified probability of persistence for a given period of time. These studies conclude that long-term persistence requires ≥5000 adult individuals, an MVP threshold that is unaffected by taxonomy, life history or environmental conditions. Here, we re-evaluate this suggestion. We find that neither data nor theory supports its general applicability, raising questions about the utility of MVPs for conservation planning.

This conclusion, however, is contested by a reply by Brook et al., who, with reference to an earlier review of theirs, express their opinion quite clearly in their title: “Minimum viable population size: not magic, but necessary”.

A more recent exchange on the genetic mechanisms contributing to MVP, which actually triggered this post, is the review paper “How does the 50/500 rule apply to MVPs?” by Jamieson and Allendorf in TREE. This paper invoked a strong reply “50/500 rule and minimum viable populations: response to Jamieson and Allendorf” by Richard Frankham et al. that just went into press at TREE. They end with the conclusion

The many assertions made by JA2012 (detailed above) about the lack of evidence for causal connections between genetic factors, population demography, and extinction risk contradict their statement that ‘Early doubt and controversy about whether genetic factors had any part to play in extinction risks of threatened organisms…have now mostly disappeared…’, because establishing the causal links between genetic factors and extinction risk were critical to resolving the controversy.

We are preparing an extended critique of JA2012 for another journal.

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