Interspecific competition suppresses adaptive radiation

Background/Question/Methods

Understanding ecological mechanisms that influence the evolution of biodiversity is a major component of modern ecological and evolutionary research.  Adaptive radiation, a process in which a lineage diversifies to occupy available niches within a habitat, constitutes an important mechanism by which biodiversity can be generated.  Interspecific competition may inhibit adaptive radiation if the competing lineages occupy niches that otherwise could be utilized by the emerging lineages.  Alternatively, interspecific competitors may promote adaptive radiation if they generate novel niches for the radiating lineages.  Furthermore, other ecological factors, such as the history of community assembly and species phylogenetic relatedness, may affect the strength of interspecific competition, and in turn adaptive radiation.  We tested these hypotheses with a laboratory microcosm experiment in which the rapidly evolving bacterium Pseudomonas fluorescens interacted with different competing bacterial species that were introduced either before or after P. fluorescens.

Results/Conclusions

Our experiment produced three main findings.  First, whereas P. fluorescens diversified quickly in its monocultures, the presence of competing species significantly reduced the extent of diversification.  Second, community assembly history influenced adaptive radiation, such that competitors exerted a stronger inhibitive effect on diversification when they were introduced earlier than P. fluorescens.  Third, species phylogenetic relatedness affected adaptive radiation, with competitors more closely related to P. fluorescens more strongly suppressing its diversification.  These results demonstrate the important, yet variable, role of interspecific competition in modulating adaptive radiation.