Functional diversity (FD), species richness and community composition

TLDR

Functional diversity is a key biodiversity component, but its quantification methods lag behind taxonomic diversity. The study proposes a new method to quantify functional diversity to assess its relationship with ecosystem functioning. FD is defined as the total branch length of a functional dendrogram, and simulations of species trait values show that its dependence on richness and composition varies with the dimensionality of trait space. FD outperforms other functional diversity metrics, and its relative importance of richness versus composition shifts with trait dimensionality—fewer dimensions heighten composition and redundancy, while more dimensions favor richness and reduce redundancy—and clumping of species amplifies composition effects, with five natural communities exhibiting consistent FD–species richness relationships.

Abstract

Abstract Functional diversity is an important component of biodiversity, yet in comparison to taxonomic diversity, methods of quantifying functional diversity are less well developed. Here, we propose a means for quantifying functional diversity that may be particularly useful for determining how functional diversity is related to ecosystem functioning. This measure of functional diversity “FD” is defined as the total branch length of a functional dendrogram. Various characteristics of FD make it preferable to other measures of functional diversity, such as the number of functional groups in a community. Simulating species' trait values illustrates how the relative importance of richness and composition for FD depends on the effective dimensionality of the trait space in which species separate. Fewer dimensions increase the importance of community composition and functional redundancy. More dimensions increase the importance of species richness and decreases functional redundancy. Clumping of species in trait space increases the relative importance of community composition. Five natural communities show remarkably similar relationships between FD and species richness.