Protecting the evolutionary diversity of life

In a world in which numerous species are declining towards extinction, conservationists are forced to make the difficult choice of where to spend limited resources. The approaches for prioritizing conservation action often rest on conventional metrics of species diversity and threat.

Two new research articles, however, take a less common, but compelling, approach to prioritization by focusing on the evolutionary distinctiveness of species - i.e. the extent to which a given species is lacking in close relatives. This phylogenetic approach is based on the idea that maintaining evolutionary diversity should be an important objective.

In their article, "Rarest of the Rare...", in the journal Diversity and Distributions, researchers Marc Cadotte and Jonathan Davies explain why this is important,

"The pragmatic rationale is that by maximizing the conservation of evolutionary
diversity, we maximize genotypic, phenotypic and functional diversity, thus providing biological systems with the most options to respond to a changing world,"

"The ethical rationale argues that… maximizing the conservation of evolutionary diversity best preserves the immense history of the Earth, of which we are a small part."

Cadotte and Davies review past approaches for determining evolutionary distinctiveness. Van Wright (1991), a pioneering paper on the concept, presented a metric that "enumerates the number of splits in a species ancestral lineage, and thus a species with few preceding splits is more taxonomically distinct than one nested within a larger radiation."

Cadotte and Davies try to build on these past approaches by developing a new metric that includes the rarity of species as well. This makes sense - a species may have very few evolutionary relatives, but if the species is highly abundant, then we probably should spend fewer resources on protecting it.

Their new approach can be used to measure the evolutionary distinctiveness of individual species, or individual values can be aggregated to come up with measurements for entire regions. The hope is that this new approach will help make evolutionary distinctiveness a more commonly adopted metric by conservation practitioners.

Coincidentally, Federico Osorio-Lopez and fellow researchers from Colombia have just published a study that takes a similar concept and puts it into action. The researchers build on past approaches for measuring evolutionary distinctiveness and apply it to specific regions of the Amazon with the goal of ranking fairly large geographic areas based on their relative conservation importance.

Similar, to Cadotte and Davies, the researchers take past approaches and incorporate a second measurement to provide more information - in this case endemism - i.e. the extent to which species' ranges are restricted to the area.

The study published in Conservation Biology ended up ranking Guyana and the Brazilian states of Roraima and Amazonas as the most important areas. Interestingly they also calculated the more conventional metric of species richness and found that it gave a similar prioritization of regions. Moreover, their rankings matched up well with where conservation dollars are actually spent.

This suggests that less technical approaches to prioritizing conservation may do a pretty good job of capturing evolutionary diversity, though it would be interesting to see if similar results were found in other geographic areas or with a finer scale of analysis.

--by Rob Goldstein

Cadotte, M., & Jonathan Davies, T. (2010). Rarest of the rare: advances in combining evolutionary distinctiveness and scarcity to inform conservation at biogeographical scales Diversity and Distributions DOI: 10.1111/j.1472-4642.2010.00650.x

LÓPEZ-OSORIO, F., & MIRANDA-ESQUIVEL, D. (2010). A Phylogenetic Approach to Conserving Amazonian Biodiversity Conservation Biology DOI: 10.1111/j.1523-1739.2010.01482.x