The number of endangered bird species is rising and even with our best intentions, there isn’t enough money to save them all – so how do we decide which species we should let go?
A new approach has been pioneered by a collaboration of universities that could provide a method to decide how limited conservation funds should be spent. The technique uses genetics to ascertain how many relatives a bird species has, evolutionarily speaking, with the aim of identifying and prioritising species that demonstrate the most genetic uniqueness for conservation efforts, rather than simply those that are few in number.
It could be argued that we shouldn’t have to do this at all. We could petition governments and funding organisations to spend more money to stop the ongoing loss of biodiversity right now. But conservation will always be less important than societal needs such as health care, and this means we have to conserve species efficiently.
So we have to assign species some value, to help us decide which ones to save. We might value species by their benefit to humans as ecosystem services providers (for example bees and pollination), their charismatic value (pandas and tigers) or their importance for ecological processes (elephants felling trees). The problem is that we don’t really know in a directly measurable way the value of a species ecologically or economically.
It has long been argued that we can use the evolutionary history, or phylogeny, of a species to capture their uniqueness and value. Phylogenies show how species are related to one another – they are the evolutionary equivalent of family trees. By examining phylogenetic trees we can see whether a species has many or few close relatives.
Most species have lots of close relatives and are not very distinct. For example, the greenfinch (Carduelis chloris), a familiar garden bird, has many close relatives and is ranked at 7909 on the list of evolutionary distinct birds. But any phylogenetic tree will usually have a small number of species whose closest relatives diverged many hundreds of thousands or millions of years ago and who now have very few recent relatives. These are the species that are termed the most evolutionarily distinct.
Keeping this concept in mind, we looked at every bird species – 10,000, in total – and found out how genetically isolated they were from each other. We used a measure called evolutionary distinctness (ED). A species that is highly distinct has few evolutionary relatives and is genetically distinct. A species that scores low on the distinctness scale will have many relatives and will have a common genetic make-up. Less genetic biodiversity will be lost if these species go extinct.
In fact, if highly distinct species become extinct we risk losing entire branches from the phylogenetic tree of birds, and with that we lose important ecological functions (such as pollination by nectar-feeding hummingbirds or seed dispersal by fruit-eating waxwings) and large amounts of our evolutionary heritage. For instance, our most evolutionary distinct bird is the Oilbird (Steatornis caripensis) of northern South America, which has almost 80 million years of unique evolutionary history. There is simply nothing quite like it.
But identifying those most distinct species is just a first step. A challenge for conservationists is not just to identify which species to save, but where and how to save them. In our study we show that the measure “evolutionary distinctness” can be combined with information about the size and placement of species' ranges to generate a means to efficiently protect them, and the evolutionary history that lies within their genes. If we can identify those areas containing species that are both highly distinct and are restricted to occurring only in those regions, then it makes sense to target conservation efforts there.
Change has begun
Despite being a goal of conservation biologists for more than 20 years, the technique of identifying the most evolutionarily distinct species has only slowly been incorporated into real world conservation. But things are beginning to change – the Zoological Society of London’s Edge of Existence programme now ranks species by combining their evolutionary distinctness with the level of threat to their survival. And this concept is not just limited to birds; with the amount of genetic data available – and initiatives such as the Map of Life project making geographical data accessible – we can expand the scope to many other groups of organisms.
Using evolutionary information is just one way to value species for conservation, but there are many practical challenges that lie between the recommendations the technique suggests and conservation decisions made on the ground. Our work can be seen as one step along the road of making better decisions that fully encapsulate species’ ecological, evolutionary and social value, alongside practical aspects such as financial cost and future environmental threats. This way we can ensure the future survival of the species we cannot afford to lose.