It has been suggested that some of these hypotheses are too broad to test, while others are truisms. However, because these ecosystem services play a role in contributing to the life-support system of human society, they are matters of vital importance. To test these broad hypotheses, it may be necessary to approach them, like other big and important issues, obliquely or piecemeal.
Bradshaw (1983) has said, ''The acid test of our understanding is not whether we can take ecosystems to bits on pieces of paper, however scientifically, but whether we can put them together in practice and make them work." Bradshaw's statement is as valid today as it was more than a decade ago when it was written. There is, however, a second test for ecology; namely, whether ecologists can document the services ecosystems provide in sufficiently explicit terms that society will not only protect and preserve those ecosystems still delivering such services but repair to whatever degree possible those ecosystems capable of delivering services at a level far beyond their present capacity.
Quantifying ecosystem services, while a formidable task, may not be as esoteric as it appears. John Harte, of the University of California, Berkeley, has carried out studies at Rocky Mountain Biological Laboratory in Colorado on the effects of global warming. During this research, he found that the soils at the laboratory itself acted as a methane sink. He estimated that, if one extrapolates from that small patch to the entire county, the amount of methane assimilated by the soils approximately equals the amount of methane produced by the cattle in the county. Not only is this information ecologically useful, but it can be easily communicated to the ranchers and other inhabitants of the area. Put in a local context, ecosystem services are no longer regarded as an esoteric issue but as one of considerable interest to area residents.
Some more specific questions related to the documentation of ecosystem services follow.
1. What is the relationship between species richness and delivery of ecosystem services?
Biotic impoverishment, or loss of species, is fairly well documented (e.g., Wilson, 1988), but the relationship between delivery of ecosystem services and the number of species present is almost certainly not linear. There is some evidence of redundancy in function, which means that, if 10 or 12 species were carrying out roughly the same function simultaneously, the loss of one or two would not cause a serious decline in delivery of services because the deficiencies would be made up by the remaining species expanding their numbers.
The decrease in species diversity, and presumably services provided by eco-