In this note we present two types of biological models which have interesting ergodic and chaotic properties. The first type are one-dimensional transformations, like a logistic map, which are used to describe the change in population size in successive generations. We study ergodic properties of such transformations using Frobenius–Perron operators. The second type are some structured populations models, for example a space-structured model, or a model of maturity-distribution of precursors of blood cells. These models are described by partial differential equations, which generate semiflows on the space of functions. We construct strong mixing invariant measures for these semiflows using stochastic precesses. From properties of invariant measures we deduce some chaotic properties of semiflows such as the existence of dense trajectories and strong instability of all trajectories.