Phylogenetic diversity is a measure of biodiversity which incorporates phylogenetic difference between species. It is defined and calculated as "the sum of the lengths of all those branches that are members of the corresponding minimum spanning path", [1] in which 'branch' is a segment of a cladogram, and the minimum spanning path is the minimum distance between the two nodes.
In biology, phylogenetics is the study of the evolutionary history and relationships among individuals or groups of organisms. These relationships are discovered through phylogenetic inference methods that evaluate observed heritable traits, such as DNA sequences or morphology under a model of evolution of these traits. The result of these analyses is a phylogeny – a diagrammatic hypothesis about the history of the evolutionary relationships of a group of organisms. The tips of a phylogenetic tree can be living organisms or fossils, and represent the "end", or the present, in an evolutionary lineage. A phylogenetic tree can be rooted or unrooted. A rooted tree indicates the common ancestor, or ancestral lineage, of the tree. An unrooted tree makes no assumption about the ancestral line, and does not show the origin or "root" of the gene or organism in question. Phylogenetic analyses have become central to understanding biodiversity, evolution, ecology, and genomes.
A cladogram is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to descendants, nor does it show how much they have changed; nevertheless, many evolutionary trees can be inferred from a single cladogram. A cladogram uses lines that branch off in different directions ending at a clade, a group of organisms with a last common ancestor. There are many shapes of cladograms but they all have lines that branch off from other lines. The lines can be traced back to where they branch off. These branching off points represent a hypothetical ancestor which can be inferred to exhibit the traits shared among the terminal taxa above it. This hypothetical ancestor might then provide clues about the order of evolution of various features, adaptation, and other evolutionary narratives about ancestors. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational phylogenetics are now very commonly used in the generation of cladograms, either on their own or in combination with morphology.
This definition is distinct from earlier measures which attempted to incorporate phylogenetic diversity into conservation planning, such as the measure of 'taxic diversity' introduced by Vane-Wright, Humphries, and William. [2]
The concept of phylogenetic diversity has been rapidly adopted in conservation planning, with programs such as the Zoological Society of London's EDGE of Existence programme focused on evolutionary distinct species. Similarly, the WWF's Global 200 also includes unusual evolutionary phenomena in their criteria for selecting target ecoregions.
The Zoological Society of London (ZSL) is a charity devoted to the worldwide conservation of animals and their habitats. It was founded in 1826.
The EDGE of Existence programme is a research and conservation initiative that focuses on species deemed to be the world’s most Evolutionarily Distinct and Globally Endangered (EDGE). Developed by the Zoological Society of London (ZSL), the programme aims to raise awareness of the world’s EDGE species, implement targeted research and conservation actions to halt their decline, and to train in-country conservationists to protect them now and in the future.
The World Wide Fund for Nature (WWF) is an international non-governmental organization founded in 1961, working in the field of the wilderness preservation, and the reduction of human impact on the environment. It was formerly named the World Wildlife Fund, which remains its official name in Canada and the United States.
Some studies have indicated that alpha diversity is a good proxy for phylogenetic diversity, so suggesting that term has little use, [3] but a study in the Cape Floristic Region showed that while phylogenetic and species/genus diversity are very strongly correlated (R2 = 0.77 and 0.96, respectively), using phylogenetic diversity led to selection of different conservation priorities than using species richness. It also demonstrated that PD led to greater preservation of 'feature diversity' than species richness alone. [4]
In ecology, alpha diversity (α-diversity) is the mean species diversity in sites or habitats at a local scale. The term was introduced by R. H. Whittaker together with the terms beta diversity (β-diversity) and gamma diversity (γ-diversity). Whittaker's idea was that the total species diversity in a landscape is determined by two different things, the mean species diversity in sites or habitats at a more local scale and the differentiation among those habitats.
The Cape Floristic Region is a floristic region located near the southern tip of South Africa. It is the only floristic region of the Cape Floristic Kingdom, and includes only one floristic province, known as the Cape Floristic Province.
