In natural ecosystems resistance is apparently associated
with diversity (species richness); this suggests
that ecosystem response to perturbation primarily
depends on the adaptive characteristics of the populations
in the system. These characteristics reflect historical
perturbations and the continual evolution of
associated species. Selection acts to maximize fitness
of populations in the system and not directly on stability
properties of the system as a whole. Ecosystem
response to environmental variability is consequently
a complex product of coevolution. Coevolution may.
depending upon the magnitude of perturbations and
their distribution in time and space, therefore be of
outstanding importance for stability of ecological systems.