Sunday, March 19, 2006

Latent extinction risk

Latent extinction risk and the future battlegrounds of mammal extinction
M. Cardillo, G.M. Mace, J.L. Gittleman & A. Purvis. 2006 PNAS 103: 4157- 4161
This recent paper published in the Proceedings of the National Academy of Sciences makes for interesting reading. From their abstract:
Global conservation prioritisation usually emphasizes areas with highest species richness or where many species are thought to be at imminent risk of extinction. However, these strategies may overlook areas where many species have biological traits that make them particularly sensitive to future human impact but are not yet threatened because such impact is low.

The authors have carried out an analysis to identify the latent risk of extinction for different mammal species. They define latent risk as the difference between the current extinction risk for a species and the risk predicted for that species based upon models using biological traits. Their models highlighted several important factors predicting extinction risk, small geographic range, slow life histories (older age of maturity, smaller numbers of offspring), and large body mass.

Having calculated the latent risk for each species that they have used in their analysis they then identify hotspots of latent extinction risk, areas with the highest latent risk values (Figure 2 in their paper). There methods highlight areas that have the greatest potential for species losses. Latent risk comes is estimated to be low for many parts of the world, but these are areas that are already heavily modified.

Fig. 2. Hotspots of latent extinction risk in nonmarine mammals. Hotspots are defined as the 10% of grid cells with the highest mean latent risk values (from Cardillo et al., 2006)

I quite like the paper, although I think the methods section is a little too brief, but I think that is an issue with PNAS rather than with the authors. What they have presented is another tool for conservation, a prospective tool, so too speak. Conservation biology has been described as a crisis science in the past, since the point at which we step in is once the species is declining and at risk. This tool used proactively has the potential to identify potential trouble spots of the future, allowing pre-emptive measures to be taken.

An interesting point that they don’t really raise is the concept of triage, often used by medical practitioners to sort injured into groups, those that need immediate attention, those with less urgent injuries and those beyond help. In that mythical ideal world of unlimited resources this would not be a problem. However, given that resources are limited, we need to identify the best areas to concentrate those resources on.

How does this study fit in? Well if we can predict which species are likely to become endangered, it makes sense to concentrate resources before this happens. The contribution of this paper is that they identify areas that are likely to become hotspots for extinctions. So do we expend resources on species that are doomed when we could expend those resources to protect future hot spots?

Fotunately it’s not quite that bad since species will be at risk from common threats, so managing these threats for one species will benefit others. Primarily the main threats come from anthropomorphic causes, over habitat fragmentation and destruction exploitation and a smattering of introduced predators.


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