Phylogenetic nich conservatism in plant functional traits

Background/Question/Methods

The ready availability of phylogenetic information has increasingly motivated community ecologists to employ tools from evolutionary biology. However, a major challenge is the assumption that there is substantial phylogenetic niche conservatism in functional traits relevant for community interactions; instead closely related species may be more or less similar in traits than expected based on phylogeny. We take advantage of uniquely detailed plant functional trait and molecular phylogeny datasets for 60 grassland species in Jena, Germany, with multiple trait measurements made both within species and over time. Here we test 1) whether plant functional traits demonstrate significant phylogenetic niche conservatism; 2) whether traits for resource acquisition, competitive ability, or life history differ in the amount of phylogenetic niche conservatism; 3) whether such conservatism extends to both mean trait values and the intraspecific variability in traits; and 4) how such conservatism or lack thereof would alter conclusions drawn from studies of phylogenetic patterns for community assembly or biodiversity–ecosystem functioning relationships. We use measures of phylogenetic signal such as Blomberg's K statistic, with extensions to assess not just mean trait values per species, but also the intraspecific and temporal variation.

Results/Conclusions

The strength of phylogenetic signal assessed for 52 plant trait means varied widely. Trait mean values related to plant size and nutrient acquisition and use consistently exhibited significant, but not large, phylogenetic signal. Means of flowering phenology, specific leaf area, and allometric ratios exhibited no significant phylogenetic signal. Trait variances, i.e. the degree of intraspecific variability, a measure of either phenotypic plasticity or genotypic variation, were not conserved for any trait except individual height. These results show that the use of phylogenetic relatedness in community ecology cannot easily be directly linked to commonly-measured morphological and physiological traits. Both mean values for species and the variability of such values within populations for traits that drive community interactions may be the product of forces other than phylogenetic history, for example shorter-term evolutionary adaptations or plastic responses within species.