Organisms are perpetually buffetted by the external environment,
yet of course somehow manage its effects. In ectothermic
species in particular the external environment impinges directly
upon cellular and subcellular functions; i.e., directly upon cell
chemistry and cell metabolic machinery. Adaptive adjustments
in response to environmental change activated in one tissue therefoie
must be balanced with adjustments at other sites so as not too
seriously (i) to disrupt functions at other sites or (ii) to disrupt cooperative
metabolic interactions between tissues and organs in the
integrated physiology of the whole organism. Making problems
worse are simultaneous changes in more than one parameter of the
environment. Not only must organisms then cope with differential
effects of each parameter on specific metabolic processes or
upon specific tissues and organs; they must also successfully adjust
to interacting effects of the external environmental parameters
which may drive the same processes or pathways in the same or in
opposite directions
