Phylogenetic niche conservatism

Linnean taxonomy system is based on classifying species into hierarchically nested groups, e.g. a genus is (and was particularly at the time of Darwin's writing) by definition a collection of similar species. In modern times this pattern has come to be referred to as phylogenetic signal, "the tendency of related species to resemble each other more than species drawn at random from the same tree ^[6]". Methods such as Abouheif’s C,^[7] Pagel's lambda,^[8] Blomberg's K,^[9] and Moran's I^[10] have been employed to test the statistical significance of the pattern. With regards to the term phylogenetic niche conservatism, many authors^{[citation needed]} have taken a significant result here—i.e. that phylogenetic information can help "predict" species traits—to be evidence of phylogenetic niche conservatism. Other authors, however, advocate that such a pattern should be expected (i.e. follow from "Descent with modification"^[5]) and, accordingly, only in instances where species resemble each other more than expected based on their phylogenetic relationships should one invoke the term phylogenetic niche conservatism.^{[citation needed]} To take a single statistical test as an example, an unconstrained Brownian motion

latitudinal diversity gradient. While support for the hypothesis that niche conservatism drives latitudinally structured variation in species richness has been found in some clades,^[11] overall, phylogenetic niche conservatism has not received strong support as the underlying cause responsible for variation in how many species occur in a given habitat.^[12][13] It has, however, found considerable support as a factor driving which species occur in a given habitat.^[13][14] That is, the study of phylogenetic niche conservatism by itself has not put an end to long-standing debate over what drives the latitudinal diversity gradient across clades, but within specific clades and across specific environmental gradients (as opposed to latitude sensu stricto), it has found support as a factor influencing which lineages are able to persist.^[15][16]