Simon P. Hart, Martin M. Turcotte, and Jonathan M. Levine

PNAS February 5, 2019 116 (6) 2112-2117

ECOLOGY

Significance

Understanding the dynamics of competing species is essential for explaining the origin and maintenance of species diversity. However, ecologists have typically ignored the potential for rapid evolution to alter the contemporary population dynamics of competing species. By disrupting the ability of aquatic plants to evolve in response to interspecific competition, we show that competition drives evolutionary change and this evolutionary change simultaneously feeds back to alter the abundance of competing species over just a few generations. Rather than increasing niche differences as classic theory predicts, evolution causes population trajectories to converge by changing the competitive hierarchy. Our results suggest that understanding how species diversity is maintained requires explicitly accounting for the effects of rapid evolution on competitive population dynamics.

Abstract

Increasing evidence for rapid evolution suggests that the maintenance of species diversity in ecological communities may be influenced by more than purely ecological processes. Classic theory shows that interspecific competition may select for traits that increase niche differentiation, weakening competition and thus promoting species coexistence. While empirical work has demonstrated trait evolution in response to competition, if and how evolution affects the dynamics of the competing species—the key step for completing the required eco-evolutionary feedback—has been difficult to resolve. Here, we show that evolution in response to interspecific competition feeds back to change the course of competitive population dynamics of aquatic plant species over 10–15 generations in the field. By manipulating selection imposed by heterospecific competitors in experimental ponds, we demonstrate that (i) interspecific competition drives rapid genotypic change, and (ii) this evolutionary change in one competitor, while not changing the coexistence outcome, causes the population trajectories of the two competing species to converge. In contrast to the common expectation that interspecific competition should drive the evolution of niche differentiation, our results suggest that genotypic evolution resulted in phenotypic changes that altered population dynamics by affecting the competitive hierarchy. This result is consistent with theory suggesting that competition for essential resources can limit opportunities for the evolution of niche differentiation. Our finding that rapid evolution regulates the dynamics of competing species suggests that ecosystems may rely on continuous feedbacks between ecology and evolution to maintain species diversity.

See: https://www.pnas.org/content/116/6/2112

Figure 1: Competition between species drives evolutionary change. Bars show the mean change in frequency of each genotype of (A) L. minor and (B) S. polyrhiza in the conspecific and heterospecific selection treatments. The change in genotype frequency is the change from the beginning of the experiment in June until the sampling date in August. Each color and number represents a different genotype. Errors are SEMs.