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pay for these services in many ways (paying for park entry fees, rooms at hotels, vehicle repairs at the local mechanic, etc.).

But ecotourism is exceptional in these respects. The biosphere provides a steady stream of other direct and indirect benefits to humanity for which nobody pays. The last decade has seen “ecosystem services” transformed from an abstract academic concept (Ehrlich and Mooney, 1983) into an applied research program and a powerful policy tool (Daily, 1997; Millennium Ecosystem Assessment, 2005a). These services include, but are not limited to, providing raw materials, natural water filtration, carbon sequestration and storage in forests, flood and erosion mitigation by plant communities, and pollination of crops by wild animals (Daily, 1997). Ecosystems, in addition to being reservoirs of biological diversity and an integral part of our planetary and cultural heritage, are capital assets.

The global economy does not in any serious way account for the value of ecosystem services. The perversity of this situation is obvious. The costs, both in the traditional economic sense and in terms of human health and well-being, of losing these services would be immense: many economic institutions would either collapse outright or require technological surrogates vastly more expensive than simply conserving the relevant ecosystems. The archetypal example of an ecosystem service in action is the conservation of the Catskill watershed, which has (thus far) spared the city of New York the $8 billion cost of building a water-filtration plant. Elsewhere, there are indications that mangroves and other coastal vegetation might have protected some coastal villages from the devastating Asian tsunami of 2004 (Danielsen et al., 2005). Recent population crashes of honey bees (Apis mellifera) have threatened an approximately $15 billion crop-pollinating industry in the United States, highlighting the importance of conserving diverse native-bee communities (Kremen et al., 2002; Winfree et al., 2007). These case studies are small components of a total-biosphere value that is, effectively, infinite (Dasgupta et al., 2000).

The idea that economic growth is independent of environmental health, and that humanity can therefore indefinitely expand its physical economy, is a dangerous delusion. The problem is that although we know that individual ecosystem services are valuable, we rarely know precisely how valuable. And although quantitatively estimating the dollar value of individual services can be an eye-opening exercise, the effort required makes doing so prohibitive for every ecosystem (to say nothing of the futility of trying to add up to infinity). The challenges, then, are to provoke society to acknowledge ecosystem-service values (even though approximate or only qualitative) and to maintain service provision by protecting service sources.

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