  We explore a class of hybrid (piecewise deterministic) systems characterized
by a large number of individuals inhabiting an environment whose state is
described by a set of continuous variables. We use analytical and numerical
methods from nonequilibrium statistical mechanics to study the influence that
intrinsic noise has on the qualitative behavior of the system. We discuss the
application of these concepts to the case of semiarid ecosystems. Using a
system-size expansion we calculate the power spectrum of the fluctuations in
the system. This predicts the existence of noise-induced oscillations.
