Setting conservation priorities can be difficult — we want to save it all, but inevitably, must make decisions and sacrifices. Therefore it helps to have a standardized, objective method for determining which areas or ecosystems deserve conservation.

One method is to come up with a measure of the biodiversity present in an area — you can think of this measure as the ecosystem’s currency, or conservation value. In the best cases this measure will take into account genetic diversity, species diversity, as well as ecosystem diversity. It can be a powerful tool when taken in concert with less quantifiable or comparable factors, such as the identity of the species that are present in the ecosystems. Although conservation decisions are not based solely on the numbers provided by the currency system, the system can provide a more objective criterion for decisions.

How is currency calculated?

Step 1. Start with a phylogeny. The phylogenetic relationships that exist among an ecosystem’s species provide the basic framework for calculating the system’s currency value:

Step 2. Figure out how much change has happened on each branch. To determine the “length” of a branch on the phylogeny (i.e., the amount of change that has occurred), scientists decide how quickly and consistently the genes and morphology of the species have evolved. The numbers on the phylogeny to the right correspond to the amount of evolutionary change. Longer branches (higher numbers) represent more evolutionary change.

Step 3. Measure gene/character richness. To calculate the total currency value for a set of species, sum up the branch lengths associated with each species. Since only A, B and D are present in the ecosystem, we add the branch lengths of only those three species to get a “currency value” of 9.