ABSTRACT
The term ecological system or ecosystem is commonly understood as describing a group of organisms that interact among themselves and with their physical or abiotic environment [242]. There are many definitions of this subtle concept and most of them suffer from some degree of vagueness [234]. We will not attempt here an exact definition, but rather emphasize an aspect of this concept which becomes important in modeling complex ecosystems, namely, the distinction between what constitutes the ecosystem and what can be considered as its environment.
