Friday, August 10, 2007 - 9:50 AM

COS 161-6: Convergence of ecological and evolutionary rates: Predator-driven evolution of population growth rate

Casey P. TerHorst and Thomas E. Miller. Florida State University

Evolutionary rates are generally assumed to be slow and have little influence on community structure relative to ecological processes, such as competition and predation.  Yet rapid evolutionary rates have been observed in a variety of communities and may be particularly likely to occur in natural microcosms.  In such communities, evolutionary change could significantly modify the effects of ecological processes.  We collected Colpoda sp., a ciliated protozoan, from natural pitcher plant inquiline communities and exposed replicate populations to selection by a larval mosquito predator for over 20 generations (one week).  Both selected and control populations were then grown under common conditions without a predator.  Population growth rate of the prey increased significantly when compared to control populations, likely due to evolution of the rate of cell division in the protozoa.  Genotypes with increased division rates are less susceptible to local extinction due to predation.  Selected populations also demonstrated a decrease in average cell size, a trait consistent with increased predator tolerance.  When grown under common conditions with a predator, the overall effect of predation was significantly lower in selected lines than in controls.  Due to the similarity of time scales on which ecological and evolutionary processes occur, evolution in a prey species may ameliorate ecological effects due to predation.  This demonstrates that the convergence of ecological and evolutionary rates has important effects that can influence community structure.