Environmental predictors of global parrot (Aves: Psittaciformes) species richness and phylogenetic diversity

Abstract

Aim Spatial patterns of phylogenetic diversity (PD) aid our ability to discern diversification rate mechanisms underlying hypotheses for the large-scale distribution of biodiversity. We develop a predictive framework for the way in which spatial patterns of PD vary with those of species richness, depending on the balance between speciation and extinction rates. Within this framework, diversification processes thought to underlie the productive energy, ambient energy, topographic variability and habitat variety hypotheses predict that gradients of increase in species richness will be associated with: (1) decreasing extinction rates where driven by productive energy, hence increasing relative PD (i.e. PD controlling for species richness, or PD rel ); (2) a similar positive relationship between ambient energy and PD rel ; (3) increasing speciation rates where driven by topographic variability, hence decreasing PD rel ; and (4) no consistent relationship between PD rel and habitat variety when driven by the latter. We test these predictions using distributional data on parrots.Location Neotropical, Afrotropical, Indo-Malayan and Australasian realms.Methods Spatial models were used to test the predictions. ResultsGlobally, a positive association between productive energy and PD rel confirms prediction (1). However, within realms, hump-shaped relationships suggest the importance of decreasing extinction rates up to a threshold level of productive energy, and the increasing importance of speciation rates thereafter. Ambient energy is positively associated with PD rel in Australasia, Indo-Malaya, and globally, supporting prediction (2). However, this is driven by the coincidence of highest PD rel in areas of high ambient energy and intermediate productive energy (i.e. in seasonal tropical environments), which may be characterized by relatively low speciation and extinction rates. In the Neotropics, increasing topographic variability is associated with decreasing PD rel and increasing species richness, suggesting an increasing gradient of speciation, supporting prediction (3). Elsewhere, the signal of this mechanism may be obscured by collinearities with energy gradients. The lack of an overall relationship between habitat diversity and PD rel confirms prediction (4).Main conclusions Spatial patterns of PD rel in relation to environmental gradients may be sensitive to collinearities among those gradients. Nevertheless, patterns emerge which have implications for the relative importance of speciation and extinction processes in generating latitudinal diversity gradients.

Phylogenetic measures of biodiversity and neo- and paleo-endemism in Australian Acacia

“…One tree that can be used is the actual tree, and indeed the basic hypothesis test of PD and PE we applied (shown in Fig. 2a,c) simply compares the observed value with what one would expect if the same number of taxa were randomly drawn from the actual tree, similar to the relative phylogenetic diversity (PD rel ) measure of Davies et al 27 This allows one to infer whether the measure is significantly high or low for a given number of terminal taxa drawn from that tree, but this test is entirely dependent on the particular tree at hand, and not comparable to other studies underlain by a different tree. One could attempt to generalize solely based on the number of terminal taxa present, but that would not be a sound reasoning without basing the expectation for PD and PE on a generalizable comparison tree giving relationships among the terminal taxa.…”

“…For example, the magnitude of PD and PE are clearly affected by the number of terminal taxa present. Therefore, the significance of PD and PE can be tested in one way by comparing the actual value for a grid cell with the value for many random selections of the same number of terminal taxa from the same tree 27 , and this was done in the present study.…”

Altitudinal biodiversity patterns of seed plants along Gongga Mountain in the southeastern Qinghai–Tibetan Plateau

“…Phylogenetic diversity quantifies the combined phenotypic or genetic diversity across species, reflecting the evolutionary history of a set of taxa (Cadotte & Davies, 2016;Davies et al, 2007). A most commonly used measure of phylogenetic diversity is evaluated as the total branch lengths of the phylogeny linking species in an area (Faith, 1992).…”

The Rarefaction of Phylogenetic Diversity: Formulation, Extension and Application

“…This can easily be done by either rarefying all locations to a given number of species (Nipperess and Matsen 2013) or via ∆PD as demonstrated here. This kind of correction has previously been done by including species richness as an explanatory variable in a statistical model and taking the residuals (Davies et al 2008) or by comparison to a null model derived by repeated subsampling (Davies et al 2007). The latter method is often used as a statistical test of phylogenetic dispersion (also known as phylogenetic structure) where random draws are taken from a species pool, representing a null community assembly process (Webb 2000).…”

“…We can then use the standardised PD values (called relative PD by Davies et al 2007) to explore the environmental, ecological and historical processes that lead to the observed patterns of high or low phylogenetic dispersion (Kooyman et al 2013). Ultimately, we may be able to develop the theory to predict these patterns (Davies et al 2007), in a similar vein to what has been done for species richness (Arrhenius 1921;MacArthur and Wilson 1963;Rosindell et al 2011). For example, the relationship of species richness with area is well known but the phylogeny-area relationship has only recently begun to be explored (Morlon et al 2011).…”