  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.
