The effects of population size and environmental composition on the utilization of an unaccustomed niche

Abstract

Population size influences various evolutionary outcomes. However, we have a very limited understanding of the effects of population sizes on niche evolution. In this study, we investigate how population sizes influence the utilization of an unaccustomed niche present alongside a habitual niche. We subjected Escherichia coli populations of two different population sizes to selection in a mixture of an unaccustomed and a habitual niche for approximately 480 generations. The selection environments consisted constant lines experiencing only one habitual niche and fluctuating lines experiencing all the habitual niches in four possible combinations in terms of predictability and speed of fluctuations, along with a constantly present unaccustomed niche. We found that all populations adapted to the unaccustomed niche with large populations adapting significantly greater than the small populations. Interestingly, the identity of the selection environment did not influence the adaptation to the unaccustomed niche. Moreover, large populations even adapted to their habitual niche better than the small populations in both the constantly selected and fluctuating lines. Also, predictability and speed of fluctuations did not affect the adaptation to the habitual niche. Therefore, our findings suggest that population size is an important parameter which must be taken into account when studying the ecological processes like niche utilization and expansion.