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By Michael Jennings
We may well lose one-half of the species on Earth before this century is out — if we do nothing.
But should all species be considered equal when we set priorities for conservation?
Lose the Aardvark…Lose a Lot
Let's begin with a quick review of how scientists classify living things: first into five kingdoms, then into progressively smaller groups, from phylum to class, order, family, genus and finally species.
As you progress from bigger to smaller classifications, the organisms within each group are more and more closely related.
Now consider the aardvark — a species that is the only one in its order. If it goes extinct, we lose an entire order of unique evolutionary traits that may have taken tens of millions of years to develop — a major limb from the evolutionary tree, if you will.
Clearly, we don’t want to lose any species. But does a species that is one of hundreds in a single genus have the same importance for conservation as a species that is the only one in its order? How can we account for evolution and genetic diversity in setting priorities for conservation?
It Depends on How You Define Biodiversity
The biodiversity of a place is most often represented by counting the number of species found there. Places with more species are assumed to contain more biodiversity.
But the "species richness" of some places can be dominated by a lot of closely related species. For example, some regions of the Andes have 60-70 frog species that are all in the same genus. These species represent relatively recent and in some cases only slight genetic changes.
We can bring evolutionary and genetic considerations into our conservation choices through the science of phylogenetics, which is the study of how organisms are related through their lineages.
The main tool for quantifying these evolutionary relationships among species is by constructing a “tree of life” or “cladogram” (see figure in the right column).
Phylogenetics allows us to quantify evolutionary diversity in a particular region — even within a single nature preserve.
To make this calculation, we add up the lengths of the branches of the tree running between every pair of species in the list. Species that are evolutionarily more distinct will contribute more to the overall measure of biodiversity.
Building Better Preserves
But how can conservationists use this approach? When we are contemplating designating a new preserve, for instance, we might have several options for where it is located, its boundaries or other aspects of its design.
Calculating the phylogenetic diversity of the various species that each option would conserve would show which option would provide the most gain in the conservation of evolutionary traits — bringing more power and efficiency to conservation designs.
The theory and mathematics for calculating phylogenetic diversity was worked out some time ago. But scientists are just now developing the tools to make quick calculations for any place in the world and then representing that diversity on a cladogram so everybody will be able to see the differences — making phylogenetic diversity ripe for a next big idea in conservation.
Fast-Forward to the Future of Conservation!
Nature picture credits (left to right, top to bottom): © Ray Packard (Frog, Chile); Courtesy Michael Jennings/TNC (Michael Jennings/TNC); © Michael Jennings/TNC (Cladogram)
