Phylogenetics: predicting rarity and endangerment
Davies, T. Jonathan National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, California.
- The extinction crisis
- Taxonomic selectivity
- Correlates of extinction risk
- Future goals
- Links to Primary Literature
- Additional Readings
Phylogeny is the evolutionary or ancestral history of organisms. Phylogenetic trees (branching diagrams used to indicate phylogenetic relationships) depict the shared evolutionary histories of species. For well-studied groups, for example, mammals, we can estimate the Tree of Life that connects all species. In cases where there is a well-sampled fossil record, it is also possible to place species that are now extinct along these evolutionary branches. Although we are most often restricted to information on relationships among living species, such phylogenetic trees may still allow us to infer the evolutionary processes that have determined the distribution of species among the major limbs of the tree. Frequently, we find that closely related taxa of similar ages differ greatly in species richness, indicating variation in rates of diversification (speciation minus extinction) over the evolutionary history of the clade (a taxonomic group defined by a common ancestor). Of more pressing concern is the increasing rate of extinction observed within recent time periods, perhaps several orders of magnitude greater than background rates, depending on the taxa of study. Identifying the drivers of extinction is complicated by the nonindependence of species, which is a product of their shared evolutionary history. Phylogenetic methods can correct for evolutionary nonindependence and offer a powerful tool for discriminating among variables that covary with phylogeny, as is the case for many species' traits associated with elevated extinction risk.
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