More closely related species are more ecologically similar in an experimental test

Abstract

The relationship between phylogenetic distance and ecological similarity is key to understanding mechanisms of community assembly, a central goal of ecology. The field of community phylogenetics uses phylogenetic information to infer mechanisms of community assembly; we explore, the underlying relationship between phylogenetic similarity and the niche. We combined a field experiment using 32 native plant species with a molecular phylogeny and found that closely related plant species shared similar germination and early survival niches. Species also competed more with close relatives than with distant relatives in field soils; however, in potting soil this pattern reversed, and close relatives might even have more mutalistic relationships than distant relatives in these soils. Our results suggest that niche conservatism (habitat filtering) and species interactions (competition or facilitation) structure community composition, that phylogenetic relationships influence the strength of species' interactions, and that conserved aspects of plant niches include soil attributes.

Fig. 1.

(A) The germination niche was phylogenetically conserved. There was a negative relationship between total germination and phylogenetic distance in the mixed model with species and the interaction between species and phylogenetic distance as random effects (Table 1). (B) Germination and early survival were also phylogenetically conserved for the majority of species (last census) (Table 1). Significant slopes in black (Table S4); conditional prediction lines are from the mixed model.

Fig. 2.

Species performed better when grown with more distant relatives than when grown with close relatives in field soils but not in potting soil. Here, for visual clarity, we present mean relative interaction intensity (RII) across interactor type (conspecific, congener, and confamilial) and by soil type; however, our analyses were all conducted on a continuous measure of phylogenetic distance to the interacting species (Table 2). Values of RII of +1 indicate obligate facilitation, values of −1 indicate competitive exclusion, and values of 0 indicate no effect of the interacting species. Squares are interactions in conspecific soil, triangles are interactions in congener soil, diamonds are interactions in confamilial soil, and circles are interactions in potting soil (means ± SE). Plants performed best in conspecific soil (Fig. S4; SI Results and Discussion).