Easy math: Less habitat = less diversity

U. OREGON (US) — Evolutionary diversity is more sensitive to extinction or loss of habitat than previously thought, making it all the more important that conservation efforts take into consideration how species are related.

“We are all interested in preserving biodiversity,” says Hélène Morlon, formerly with the University of Oregon and now at the University of California, Berkeley.

“This means trying to preserve the most species we can, but remembering that all species are not equal,” she says. “None of us want to make choices on which species to preserve, but if we have to, we might be interested in preserving the species that are the most unique in evolutionary history.

“There are also other characteristics of species to consider, of course. Biodiversity is simply too complex to be summarized by a single number—be it species richness or phylogenetic diversity.”

The study, one of the first to mathematically compute spatial diversity patterns involving phylogenetic relationships, is reported online in the journal Ecology Letters.

Since conservation efforts take place within specific geographical or geopolitical areas, Morlon says it is important to understand how biodiversity is distributed spatially.

South Africa-plant_2

“None of us want to make choices on which species to preserve, but if we have to, we might be interested in preserving the species that are the most unique in evolutionary history,” says Hélène Morlon. (Credit: Hélène Morlon)

In consideration of that, for the current study, researchers focused on plant species living within defined areas in Mediterranean-type regions around the world—Australia, California, Chile, and South Africa.

For 538 plant species, which covered 254 genera and 71 families, researchers built an evolutionary tree tracing them back to their common ancestor.

They then applied mathematical approaches that considered the increase of evolutionary diversity with the size of geographic areas, as well as the decay of evolutionary similarity with the geographic separation between various communities.

The approach is based on realistic ancestry trees.

A general belief says that only a small amount of evolutionary diversity is being lost when extinction occurs. This would be true if the terminal branches of phylogenetic trees were short, Morlon says, but because phylogenetic trees typically have long terminal branches,  the impact of extinction on phylogenetic diversity is huge.

“When you think about species, you usually think of, say, those in the Northwest, and they are not present in South Africa,” she says.

“When people have thought about preserving the tree of life, not preserving only species but also all this evolutionary history, they have tended to think at a global scale.

“If you consider a branch of the tree of life that is present in the Northwest and also in South Africa, you can lose one while the other remains to preserve diversity on the planet. These connections are important to make, but it is important to preserve phylogenetic diversity at regional scales, not only the global scale.

“The tools that conservationists use to preserve species at regional scales are not well adapted for preserving phylogenetic diversity,” says Morlon, who is also on the faculty of Ecole Polytechnique in France. “This paper gives some clues on how to preserve that diversity.”

Researchers from Texas Tech University, Massachusetts Institute of Technology, Pontifical Catholic University of Chile, the Institute of Ecology and Biodiversity in Santiago, Chile, the South African National Biodiversity Institute, and the University of Western Australia contributed to the study, which was supported by the National Science Foundation.

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