More complex arguments in ecosystem valuation regard environmental ethics and deep ecology. Economists and some ecologists concentrate upon nature's services and the assignment of values in a service economy to all that Nature does "for humans". Studies compiled by ecologist Robert Costanza in the 1990s argued strongly that even just considering the most basic seventeen of these services, the combined value of the ecosystems of the earth was worth more (US$33T) each year than the whole human exchange economy (US$25T) at that time (1995). Other studies have focused on the marginal value of ecosystem changes, which can be used in cost-benefit analysis of environmental policies.
In Natural Capitalism, 1999, Paul Hawken, Amory Lovins and Hunter Lovins advanced an argument to assign the value of Earth in current currency. See value of Earth article for that and other examples of this extreme case of ecosystem valuation - biosphere valuation.
Economists assign several types of values to ecosystems:
Methods to place a monetary value on ecosystem services where there are no market prices include "stated preference" methods and "revealed preference" methods. Stated preference methods, such as the contingent valuation method ask people for their willingness to pay for a certain ecosystem (service). Revealed preference methods, such as hedonic pricing and the travel cost method, use a relation with a market good or service to estimate the willingness-to-pay for the service.
Considering "valuation" as an "economic not ecological issue" reflects the way these fields divide of the activities of humans versus non-humans in "making a living". When humans go out to get food or homes, that is studied in "economics", but when non-humans do it, that is "ecology", though it is clear that there are motivations, methods and certainly bodily needs in common.
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. It may be anthropocentric to do so, since "valuation" more clearly refers to a human perception rather than being an "objective" attribute of the system perceived. Ecology itself is also human perception, and such related concepts as a food chain are constructed by humans to help them understand ecosystems. In many cases by those who hold that markets and pricing exist independently of any individual human observers and "users", and especially those who deem markets to be "out of control", ecosystem valuation is considered a (marginal, ignored) part of economics. Others argue that natural capital is an economic concept that is at least as viable as financial capital, which itself is determined on subjective valuation. Some even suggest that valuation of ecosystem services is more cogent than financial valuation, as the ecosystem would continue after the collapse of the economy, while the inverse is not valid.
Some versions of conflict theory focus on the role of resource scarcity in sparking or propagating human conflicts - in effect holding that the resources or ecosystems they fight over are being held so valuable that they are worth considerable risk of harm to control. This is at least a relative notion of value and value at risk applied to ecosystem.