Conservation on the EDGE

About a week or so back I actually checked my MySpace account to find an invite from a new conservation organization called EDGE: Evolutionarily Distinct and Globally Endangered, sponsored by the Zoological Society of London. NGOs nowadays are a dime a dozen, valuable but virtually identical. EDGE, however, seems to have, well, an edge.

They published a paper describing the application of their plan in PLoS One, my new favorite publication (a ton of ecology stuff, free and open access). EDGE is based on a relatively simple idea; they seek to prioritize mammalian conservation practice with phylogeny in mind. That's where the Evolutionary Distinctiveness (ED) comes in. Basically, individual species represent a trove of sorts of evolutionary history. In the author's words,

Species represent different amounts of evolutionary history, reflecting the tempo and mode of divergence across the Tree of Life. The extinction of a species in an old, monotypic or species-poor clade would therefore result in a greater loss of biodiversity than that of a young species with many close relatives.

They're using this idea to combat the "agony of choice" often referred to as the Noah's Ark Problem; with so many organisms in danger, and relatively little funding and manpower, how do we choose which should receive the most attention?

Early on they address potential problems with the plan. One is obvious: Just how intact (and accurate) are most of our species-level phylogenies (about 300 mammal species were deemed "Data Deficient" and not included by the researchers)? Which history do you choose? Also, this type of conservation effort requires implementers to step back from the idea of charismatic megafauna - many of the top 100 mammals listed as high priority by EDGE are not well known by the public, and EDGE concentrates funding on 10 per year at this point. But, at the same time, both the red panda and the giant panda are on that top 100 list, and they are certainly cute enough and well known enough to be publicized as evolutionarily distinct.

So how do they determine who's in and who's out? It's calculated with a fairly simple equation, and it fleshes out the group's acronym a little more.

First, you calculate the ED by taking a look at a cladogram like the sample below.

The basic procedure for calculating ED scores is illustrated in figure 1, which describes a clade of seven species (A-G). The ED score of species A is given by the sum of the ED scores for each of the four branches between A and the root. The terminal branch contains just one species (A) and is 1 million years (MY) long, so receives a score of 1 MY. The next two branches are both 1 MY long and contain two and three species, so each daughter species (A, B and C) receives 1/2 and 1/3 MY respectively. The deepest branch that is ancestral to species A is 2 MY long and is shared among five species (A to E), so the total ED score for species A is given by (1/1+1/2+1/3+2/5) = 2.23 MY. Species B is the sister taxon of A, so receives the same score. By the same arithmetic, C has a score of (2/1+1/3+2/5) = 2.73 MY, both D and E receive (1/1+2/2+2/5) = 2.4 MY, and both F and G receive (0.5/1+4.5/2) = 2.75 MY.

Species F and G are prioritized because of their high ED scores, which represent an older, more unique and more precarious lineage. The ED score is then inserted into the following equation, which incorporates World Conservation Union (IUCN) Red List values (Least Concern = 0, Near Threatened and Conservation Dependent = 1, Vulnerable = 2, Endangered = 3, Critically Endangered = 4) for the variable GE (Globally Endangered):

EDGE = ln(1 + ED) + GE x ln(2)

ED scores topped out with (what else) the duck-billed platypus as the most distinct mammal, but when GE was factored in, the Yangtze River dolphin was clearly EDGE's highest priority.

The 100 highest priority (EDGE) species includes several large-bodied and charismatic mammals, including the giant and lesser pandas, the orang-utan, African and Asian elephants, four rhinoceroses, two tapirs, two baleen whales, a dugong and a manatee. However, many smaller and less appreciated species also receive high priority, including sixteen rodents, thirteen eulipotyphlans, twelve bats, four lagomorphs and an elephant shrew.

Histogram of EDGE scores for 4182 mammal species (.xls file), by threat category. Colours indicate the Red List category: Least Concern (green), Near Threatened and Conservation Dependent (brown), Vulnerable (yellow), Endangered (orange) and Critically Endangered (red).

EDGE even has a blog, which it lends to scientists that are working on the top 100 species, giving updates from the field. If you know anyone who is doing research on any of these mammals, get them to e-mail EDGE and participate. They also have plans for EDGE Amphibians and Birds in the near future.

All images and quotes from: doi:10.1371/journal.pone.0000296.g003