Quo vadis ecosystem?

In order to answer this question the characteristics of a suitable indicator are discussed and two state indicators are proposed, based on the assumption that costs and benefits of the ecosystem growth have to be in balance. The first one, the benefit/cost indicator (BC), is a function of well known state indicators, that fully satisfies the properties required although is difficult to compute and complex to understand. Nevertheless, from the researcher point of view, this indicator gives interesting insights into system behavior. The second, the supply demand balance (SDB), is an indicator based on two main assumptions, the first one being that an ecosystem can be represented by a network of compartments and flows, the second that the metabolic rates scale across species approximately as the (3/4) power of mass. The SDB indicator summarizes the distance of an ecosystem from an optimal state in a single number. Under these assumptions the SDB indicator can be regarded as a measure of ecosystem state. It is easy to compute and simple to understand. SDB looks like a good indicator both for scientific and practical uses to understand where the ecosystem is going. Finally the applicability of SDB is investigated by computing its values for 33 trophic networks describing the food webs of different aquatic ecosystems.