Microorganisms are the most biodiverse life forms on our planet, yet we
know little about the spatial processes underlying their ecology and
evolution. Here, we highlight the importance of two spatial processes
that act on individual cells - spatial intermixing of different
populations and mechanical cell shoving during growth - to improve our
understanding of microbial eco-evolutionary dynamics. Using an
individual-based model, we show that the coexistence of slow- and
fast-growing populations becomes highly constrained under two
conditions: when the slow- and fast-growing populations are highly
spatially intermixed and when the ability to shove other cells (both
conspecific and heterospecific) is weak. The potential for evolution
through plasmid-mediated horizontal gene transfer between slow- and
fast- growing populations also becomes restricted in the same scenario.
Our modeling highlights that ecological constraints can dampen
evolutionary opportunities within microbial communities due to variation
in spatial intermixing and mechanical shoving at the cellular scale.