  Organisms often grow, migrate and compete in liquid environments, as well as
on solid surfaces. However, relatively little is known about what happens when
competing species are mixed and compressed by fluid turbulence. In these
lectures we review our recent work on population dynamics and population
genetics in compressible velocity fields of one and two dimensions. We discuss
why compressible turbulence is relevant for population dynamics in the ocean
and we consider cases both where the velocity field is turbulent and when it is
static. Furthermore, we investigate populations in terms of a continuos density
field and when the populations are treated via discrete particles. In the last
case we focus on the competition and fixation of one species compared to
another
