Reserves for nature /

Abstract

tion ensures that we will reap such benefits in the future. Examples abound (Oldfield 1984). The value of plants for medicinal purposes is one example of the economic benefit of preserving species. Hie International Union for the Conservation of Nature and Natural Resources recently estimated the worldwide retail value of tropical plants for medicinal uses at $20 billion (WWF 1986). The third argument, and perhaps the most critical one, is that ecosystems and the organisms they comprise provide us with services upon which we humans depend for survival, for example, production of oxygen, nitrogen fixation, and breakdown of organic wastes and chemical pollutants, among many others (Pimentel et al. 1980). Aside from survival value, the services provided by ecosystems are of great economic benefit to society. Hie benefit, however, tends to be underestimated because the interconnectedness of components of the biosphere is not always recognized. Consider, for example, the ability of soil micro-organisms to fix nitrogen from the atmosphere. Assigning a dollar value to the nitrogen in the soil inadequately accounts for the benefits provided by nitrogen because other, related services, such as better soil erosion control and support of larger or more diverse plant and animal populations, are also provided Trophic Level: aganisms that obtain food (Westman 1977). from plants by the same number of steps The problem belong to the same trophic level. Plants ocwith the ecosystem-'^^Py^®^' ''st trophic level and plant-eaters service argument is^® second. An organism may occupy more that while scien-humans eat plants, they occupy the second trophic level; tists are sure of the when we eat beef, we occupy the third level. disastrous ecological consequences of causing the dysfunction of a whole trophic level, for example, the producer (plant) level, or the decomposer level, they effectively do not know what the consequen-Readers wanting more detailed coverage of the subject may consult The Theory of Island Biogeography by RH. MacArthur and E.O. Wilson, or Geographical Ecology by RH. MacArthur.