Issues in Ecology Number 2 Spring 1997 Figure 2-Woman carrying treetrunk for boat- making in a fishing village on Chiloe Island.Chile Natural forests remain an important source of wood for construction,fuel,and other uses generating those ecosystem goods that are traded in the directly for food,drink.spices,fiber,timber,pharmaceu marketplace.As a result,this lack of awareness helps ticals,and industrial products such as waxes,rubber,and drive the conversion of natural ecosystems to oils.Even if one were highly selective,the list could amount human-dominated systems (e.g.,wheatlands or oil palm to hundreds or even thousands of species.And that would fields).whose only be a start.since one would then need to consider inpart,in standard which those usedi Dacterla. ngi,and invertebrates that help ruptions of these systems-such as introductions of ex make soil fertile and break down wastes and organic otic species,extinctions of native species,and alteration matter:the insects,bats.and birds that pollinate flow of the gaseous composition of the atmosphere through ers:and the grasses,herbs.and trees that hold soil in fossil fuel burning are difficult or impossible to reverse a hird if av The clea of this is that no nd ntinue, kno tions species ven appr will dra tically alter Earth' remain ing natural ecosys- mately how many-are required to sustain human life tems within a few decades(Daily 1997a,b). Rather than selecting species directly.one might The lack of attention to the vital role of natural try another approach:Listing the ecosystem services ecosystem services is easy to understand.Humanity came needed by a lunar colony and then guessing at the types into being after most ecosystem services had been in and numbers of species required to perform each.Yet for hundreds of millions to billion deter re critical to the functionin are so funda I to life that mining which species of a parti osystem easy to take service for gran nted,and s large in s us lake oil fertility as an example hard to imagine that human activities could irreparably crucial to the chemical conversion and physical transter disrupt them. Perhaps a thought experiment that re of essential nutrients to higher plants. But the abun moves these services from the familiar backdrop of the dance of soil organisms is absolutely staggering.Under Earth is the best way to illustrate both the importance a square-yard of pasture in Denmark,for instance.the and complexity of ecosystem services,as well as how soil is inhabited by roughly 50.000 small earthworms are to em. their relatives.50.OO nd L ngs trying to n rou And t tally is only the begi Assume for the sake of argument that the moon had ning.The number of soil animals is tiny compared to the already miraculously acquired some of the basic condi number of soil microorganisms:a pinch of fertile soil may tions for supporting human life,such as an atmosphere contain over 30.000 protozoa,50.000 algae,400,000 a climate.and a physical soil structure similar to those fungi and billions of individual bacteri on Earth.The big question facing hum an colonists wo (Overgaard-Nielsen955:Rouatt and then be.which of Earth's millic on would Cha y 1993).Which must colonists bri ng to the to be rted to the moon to make sterile sur to assure lus and plant growth.soil renewa face habitable? waste disposal,and so on?Most of these soil-dwelling One could tackle that question systematicall species have never been subjected to even cursory in by first choosing from among all the species exploited spection:no human eye has ever blinked at them through 3 Issues in Ecology Number 2 Spring 1997 Figure 2-Woman carrying treetrunk for boat￾making in a fishing village on Chiloe Island, Chile. Natural forests remain an important source of wood for construction, fuel, and other uses. Photo by Taylor Ricketts generating those ecosystem goods that are traded in the marketplace. As a result, this lack of awareness helps drive the conversion of natural ecosystems to human-dominated systems (e.g., wheatlands or oil palm fields), whose economic value can be expressed, at least in part, in standard currency. The second reason to focus on natural ecosystems is that many human-initiated dis￾ruptions of these systems -- such as introductions of ex￾otic species, extinctions of native species, and alteration of the gaseous composition of the atmosphere through fossil fuel burning -- are difficult or impossible to reverse on any time scale relevant to society. Third, if awareness is not increased and current trends continue, humanity will dramatically alter Earth’s remaining natural ecosys￾tems within a few decades (Daily 1997a, b). The lack of attention to the vital role of natural ecosystem services is easy to understand. Humanity came into being after most ecosystem services had been in operation for hundreds of millions to billions of years. These services are so fundamental to life that they are easy to take for granted, and so large in scale that it is hard to imagine that human activities could irreparably disrupt them. Perhaps a thought experiment that re￾moves these services from the familiar backdrop of the Earth is the best way to illustrate both the importance and complexity of ecosystem services, as well as how ill-equipped humans are to recreate them. Imagine, for example, human beings trying to colonize the moon. Assume for the sake of argument that the moon had already miraculously acquired some of the basic condi￾tions for supporting human life, such as an atmosphere, a climate, and a physical soil structure similar to those on Earth. The big question facing human colonists would then be, which of Earth’s millions of species would need to be transported to the moon to make that sterile sur￾face habitable? One could tackle that question systematically by first choosing from among all the species exploited directly for food, drink, spices, fiber, timber, pharmaceu￾ticals, and industrial products such as waxes, rubber, and oils. Even if one were highly selective, the list could amount to hundreds or even thousands of species. And that would only be a start, since one would then need to consider which species are crucial to supporting those used di￾rectly: the bacteria, fungi, and invertebrates that help make soil fertile and break down wastes and organic matter; the insects, bats, and birds that pollinate flow￾ers; and the grasses, herbs, and trees that hold soil in place, regulate the water cycle, and supply food for ani￾mals. The clear message of this exercise is that no one knows which combinations of species -- or even approxi￾mately how many -- are required to sustain human life. Rather than selecting species directly, one might try another approach: Listing the ecosystem services needed by a lunar colony and then guessing at the types and numbers of species required to perform each. Yet determining which species are critical to the functioning of a particular ecosystem service is no simple task. Let us take soil fertility as an example. Soil organisms are crucial to the chemical conversion and physical transfer of essential nutrients to higher plants. But the abun￾dance of soil organisms is absolutely staggering. Under a square-yard of pasture in Denmark, for instance, the soil is inhabited by roughly 50,000 small earthworms and their relatives, 50,000 insects and mites, and nearly 12 million roundworms. And that tally is only the begin￾ning. The number of soil animals is tiny compared to the number of soil microorganisms: a pinch of fertile soil may contain over 30,000 protozoa, 50,000 algae, 400,000 fungi, and billions of individual bacteria (Overgaard-Nielsen 1955; Rouatt and Katznelson 1961; Chanway 1993). Which must colonists bring to the moon to assure lush and continuing plant growth, soil renewal, waste disposal, and so on? Most of these soil-dwelling species have never been subjected to even cursory in￾spection: no human eye has ever blinked at them through