Phylogeny and the Hierarchical Organization of Plant Diversity

Abstract

R. H. Whittaker's idea that plant diversity can be divided into a hierarchy of spatial components from a at the within-habitat scale through b for the turnover of species between habitats to c along regional gradients implies the underlying existence of a, b, and c niches. We explore the hypothesis that the evolution of a, b, and c niches is also hierarchical, with traits that define the a niche being labile, while those defining b and c niches are conservative. At the a level we find support for the hypothesis in the lack of close significant phylogenetic relationship between meadow species that have similar a niches. In a second test, a niche overlap based on a variety of traits is compared between congeners and noncongeners in several communities; here, too, there is no evidence of a correlation between a niche and phylogeny. To test whether b and c niches evolve conservatively, we reconstructed the evolution of relevant traits on evolutionary trees for 14 different clades. Tests against null models revealed a number of instances, including some in island radiations, in which habitat (b niche) and elevational maximum (an aspect of the c niche) showed evolutionary conservatism.

Phylogenetic Clustering and Overdispersion in Bacterial Communities

“…Overdispersion of taxa across a phylogeny has been observed in natural communities (Ackerly et al 2006, Cavender-Bares et al 2006, Silvertown et al 2006 and could indicate that negative interactions (e.g., competition) are important in community assembly (Graves andGotelli 1993, Webb et al 2002). Although we did observe significant phylogenetic overdispersion in one of the freshwater bacterial communities, our observations do not suggest that competition played an overwhelming role in structuring the communities we studied at the scales examined here.…”

“…Why might this be the case? Recent work suggests that the greater the degree of environmental heterogeneity over which one samples a community, the more likely that phylogenetic clustering, rather than overdispersion, will be present (Cavender-Bares et al 2006, Silvertown et al 2006. The data sets used in our study consisted of samples that were extremely large relative to the size of the target organisms and the scales over which individuals interact (as is the case in most studies of microbial diversity) and thus likely included substantial environmental heterogeneity.…”

“…Recent studies have also suggested that phylogenetic scale should affect the prevalence of clustering; increasing phylogenetic scale (i.e., an increase in taxonomic lumping) might result in an increased prevalence of clustering (Silvertown et al 2006). Substantial ecological diversity has been shown to be present within microbial taxa defined using molecular markers, especially ribosomal markers (e.g., Ward et al 1998, Rocap et al 2002.…”

Phylogenetic Structure of Floridian Plant Communities Depends on Taxonomic and Spatial Scale

“…However, in a study of almost 13 000 seed plants, Moles et al (2005) showed that higher divergences sometimes occurred within a family than between families. A number of genera, particularly speciose genera in which many members co-occur, have also been shown to have divergences within them equal to or greater than those between co-occurring species that are distantly related (Silvertown et al 2006). Therefore, the shift toward trait conservatism at the broader phylogenetic scale can also be explained as a result of swamping out the signal of high trait lability within the oaks by the addition of many more taxa that have conserved traits.…”

Genetic distance predicts trait differentiation at the subpopulation but not the individual level in eelgrass, Zostera marina

“…However, the underlying assumption that phylogenetic diversity serves as a proxy for trait differentiation is not always supported; in some cases, phylogenetic diversity influences ecosystem structure and functioning even when phylogenetic distance is not correlated with trait differences (Flynn et al., 2011; Tan, Pu, Ryberg & Jiang, 2012). Furthermore, not all traits relevant to the outcome of interactions are evolutionarily conserved (Best, Caulk & Stachowicz, 2013; Best & Stachowicz, 2013; Cavender‐Bares, Ackerly, Baum & Bazzaz, 2004; Cavender‐Bares, Keen & Miles, 2006; Moles et al., 2005; Silvertown, Dodd, Gowing, Lawson & McConway, 2006) and phylogenetic distance does not always influence ecological processes in the expected direction (Burns & Strauss, 2011; Cadotte, Davies & Peres‐Neto, 2017; Godoy, Kraft & Levine, 2014; Narwani, Alexandrou, Oakley, Carroll & Cardinale, 2013). …”