Describing resources and their relationships with organisms seems to be a useful approach to a ‘unified ecology’, contributing to fill the gap between natural and human oriented processes, and opening new perspectives in dealing with biological complexity. This Resource Criterion defines the main properties of resources, describes the mechanisms that link them to individual species, and gives a particular emphasis to the biosemiotic approach that allows resources to be identified inside a heterogeneous ecological medium adopting the eco-field model. In particular, (...) this Criterion allows to couple matter, structured energy and information composing the ecological systems to the biosemiotic and cognitive mechanisms adopted by individual species to track resources, transforming neutral surroundings into meaningful species-specific Umwelten. The expansion of the human semiotic niche that is a relevant evolutionary process of the present time, assigns the role of powerful and efficient agency to the Resources Criterion to evaluate the effect of human intrusion into the natural systems with habits of key stone species, under the challenge of a growing use of alloctonous, immaterial and symbolic resources of the actual globalized societal models. The Resource Criterion interprets the ecological dynamics contributing to complete the epistemology of the ecology, to open a bridge toward economy and other societal sciences, and to contribute to formulate a General Theory of Resources. (shrink)