The following sections briefly describe these four recommended research investments and some of the key issues for each, including data needs, coordination with other environmental science research, and other key issues that must be addressed in undertaking the research. The key issues raised in this chapter are specific to or especially critical for particular research areas. Some additional issues apply to all the grand challenges and therefore arise with all four recommended research investments; these cross-cutting issues are discussed in Chapter 4 .
The committee is enthusiastic about its recommendations for immediate action, but we recognize that the relative importance of scientific challenges and recommended actions in light of the above criteria will evolve over time. As new challenges emerge or significant progress is made in addressing existing ones, the priorities for action will require reevaluation. The same is likely to be true if a non-U.S, perspective is taken, since groups from other areas of the world might view the priorities differently. Therefore, we recommend that an evaluation similar to the present one be repeated at approximately 5-year intervals, perhaps in collaboration with international organizations.
Recommendation: Develop a comprehensive understanding of the relationship between ecosystem structure and functioning and biological diversity. This initiative would include experiments, obser vations, and theory, and should have two interrelated foci: (a) de veloping the scientific knowledge needed to enable the design and management of habitats that can support both human uses and native biota; and (b) developing a detailed understanding of the effects of habitat alteration and loss on biological diversity, espe cially those species and ecosystems whose disappearance would like ly do disproportionate harm to the ability of ecosystems to meet human needs or set in motion the extinction of many other species.
This initiative is compelling because (a) understanding the relationship between species diversity and ecosystem functioning poses a great intellectual challenge, and would lead to both scientific and practical breakthroughs; (b) humans use a large proportion of the nonglaciated land surface of the Earth, as well as its marine resources, creating the likelihood that biotic reserves—even combined with environmental restoration—will not by themselves be sufficient to prevent the extinction of many species; (c) increasing human demand for ecosystem goods and services threatens to outpace ecosystems' capacity to sustain those supplies and to maintain natural diversity; (d) given recent advances in the science of biological diversity, we are poised to make breakthroughs in understanding how diversity has been generated and maintained in nature, as well as how