terHorst, C. P. 2010

terHorst, C. P. 2010. Evolution in response to direct and indirect effects in pitcher plant inquline communities. The American Naturalist 176: 675-685 

Abstract: Ecologists have long recognized the importance of in- direct ecological effects on species abundances, coexistence, and diversity. However, the evolutionary consequences of indirect inter- actions are rarely considered. Here I conduct selection experiments and examine the evolutionary response of Colpoda sp., a ciliated protozoan, to other members of the inquiline community of purple pitcher plants (Sarracenia purpurea). I measured the evolution of six traits in response to (1) predation by mosquito larvae, (2) compe- tition from other ciliated protozoans, and (3) simultaneous predation and competition. The latter treatment incorporated both direct ef- fects and indirect effects due to interactions between predators and competitors. Population growth rate and cell size evolved in response to direct effects of predators and competitors. However, trait values in the multispecies treatment were similar to those in the mono- culture treatment, indicating that direct effects were offset by strong indirect effects on the evolution of traits. For most of the traits measured, indirect effects were opposed to, and often stronger than, direct effects. These indirect effects occurred as a result of behavioral changes of the predator in the presence of competitors and as a result of reduced densities of competitors in the presence of predators. Incorporating indirect effects provides a more realistic description of how species evolve in complex natural communities.

Keywords: Colpoda, competition, predation, protozoa, Sarracenia purpurea, selection.

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