Since animals do not put explicit prices on ecosystems they use , but do behave as if they are valuable , e.g. by defending turf or access to water , it is mostly a matter of definition whether ecology should include valuation as an issue . Since animals do not put explicit prices on ecosystems they use , but do behave as if they are valuable , e.g. by selecting one territory vs. another , defending their territories , etc , it is mostly a matter of definition whether ecology should include valuation as an issue .