  A principle of evolutionary adaptation is applied to the Lotka--Volterra
models, in particular to the food webs. We present a relatively simple
computational algorithm of optimization with respect to a given criterion. This
algorithm boils down to a sequence of easy to solve linear programming
problems. As a criterion for the optimization we use the total weighted
population size of the given community and an ecological fitness, which is an
analogue of the potential energy in physics. We show by computational
experiments that it is almost always possible to substantially increase the
total weighed population size for an especially simple food web -- food chain;
we also show that food chains are evolutionary unstable under the given
optimization criteria and, if allowed, evolve into more complicated structures
of food webs.
