Faith's Phylogenetic Diversity
Also known as: phylogenetic diversity, PD, evolutionary distinctiveness, branch length
Faith's Phylogenetic Diversity (PD), introduced by David Faith (1992), measures the evolutionary diversity within a community by summing the branch lengths of a phylogenetic tree connecting all species. Unlike species richness, which counts species equally regardless of evolutionary relationships, PD weights species by their evolutionary distinctiveness: a community with evolutionarily distant species has higher PD than one dominated by recently diverged species. PD is widely used in conservation to prioritize protection of species and habitats that preserve evolutionary history.
Key highlights
- Intuitive measure that incorporates evolutionary relationships, aligning conservation with evolutionary heritage
- Computationally simple: just sum branch lengths
- Enables phylogenetically informed conservation: identifies species whose loss would disproportionately reduce evolutionary diversity
- Works with molecular data to infer evolutionary relationships for data-poor organisms
Intuition
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How it works
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When to use it
Use Faith's PD when conservation goals include preserving evolutionary heritage, prioritizing species, or comparing communities. Requires a phylogenetic tree of adequate resolution. Most useful when phylogenetic tree is well-supported and reliable.
Strengths & limitations
- Intuitive measure that incorporates evolutionary relationships, aligning conservation with evolutionary heritage
- Computationally simple: just sum branch lengths
- Enables phylogenetically informed conservation: identifies species whose loss would disproportionately reduce evolutionary diversity
- Works with molecular data to infer evolutionary relationships for data-poor organisms
- Heavily dependent on tree topology and branch length accuracy; phylogenetic uncertainty propagates to PD estimates
- Cannot be directly compared across different parts of the tree; loses absolute scale
- Sensitive to unresolved nodes and polytomies (multiple species diverging simultaneously); PD is ill-defined if tree has many polytomies
- Does not account for functional or ecological diversity; evolutionarily distinct species may have similar ecological roles
Common pitfalls
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Applications
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Frequently asked
How does Faith's PD differ from species richness?
Species richness counts species equally regardless of evolutionary distance. A community of five congeners (closely related) has the same species richness as a community with representatives from five families. But the family-rich community has much higher PD because it spans more evolutionary time. PD aligns conservation with preserving evolutionary history.
What if my phylogenetic tree is uncertain?
Use trees from multiple analyses, Bayesian posterior distributions, or bootstrap trees to assess PD sensitivity. Compute PD for each tree and report the range. If PD estimates vary widely across trees, phylogenetic uncertainty is large and conservation decisions should be robust to that uncertainty.
How do I prioritize species for conservation using PD?
Use evolutionary distinctiveness (ED): the contribution of each species to total community PD. Species with high ED (long isolated branches) contribute more to PD than do related species. Prioritize protection of species with high ED relative to their extinction risk (the ED/risk ratio identifies most-important conservation targets).
Sources
- 1.Faith, D. P. (1992). Conservation evaluation and phylogenetic diversity. Biological Conservation, 61(1), 1-10.
- 2.Steel, M., & Mooers, A. O. (2010). The expected value of shed phylogenetic diversity. PLoS Biology, 8(9), e1000475.
- 3.Redding, D. W., & Mooers, A. O. (2006). Incorporating evolutionary measures into conservation prioritization. Conservation Biology, 20(6), 1670-1678.
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Cite this page
ScholarGate. (2026, June 3). Faith's Phylogenetic Diversity. ScholarGate. https://scholargate.app/ecology/faiths-phylogenetic-diversity