Which species do we put in the ark?

Species are going extinct at an alarming rate, leaving conservationists with tough choices. Which species should they try and save? 

“We call it the Noah’s Ark problem. We can’t save them all,” says Utah State University ecologist  Will Pearse. 

So far, the guiding principle has been ‘functional diversity’. 

The same idea was employed  by would-be dinosaur conservationists in the recent film Jurassic World: Fallen Kingdom. Faced with the chance to save a few species on an erupting volcanic island, they chose based on functional diversity: meat eaters, vegetarians and so on.

But in the real world, getting data on the functions a particular species performs – so-called  “ecosystem services” – can take years. “We can’t afford to fiddle while Rome burns,” says Pearse.

By contrast, the position of a species on its family tree, its “phylogeny”, is usually well-known.  

So rather than waiting years for a full CV of ecosystem services, could conservationists just go to the family tree and select species based on the greatest phylogenetic diversity?

That’s the question Pearse and colleagues from Canada, Oxford, Argentina, France and Australia, decided to ask. 

Their findings, published in Nature Communications, show that consulting the family tree is a good surrogate for functional diversity in most cases. 

Using global datasets of mammals, birds and tropical fishes, and a selection strategy dubbed “the phylogenetic gambit”, the team demonstrated that, for the most part, preserving phylogenetic diversity preserves 18 percent more functional diversity than would be expected if species for the ark were selected at random.

What this means is that conservation programs such as the EDGE of Existence who might be planning their list of species to protect on a coral reef,  for example, could use the phylogenetic gambit to decide how to spend their resources. For instance, among tropical fish, they would select species to give the widest spread on the family tree.

Importantly, Pearse and colleagues also pinpoint situations where the strategy is not likely to work.

For instance, a resource-strapped park manager in South Africa may have to make heart-breaking choices about which large carnivores to try and protect.

The phylogenetic gambit would recommend that preserving one species of large cat should be enough to preserve the ecosystem.  But if that led to selecting cheetahs over lions, that would be at odds with their ecosystem functions, since these large cats target different prey.

“In an ideal world, we’d try and save everything,” says Pearse.  “The phylogenetic gambit should help us make choices that will save our ecosystems and ourselves.”