ing the use of radio bandwidth may thus be quite different from those needed to regulate the use of a biological species.
Major international problems, such as river and lake pollution, transmission of air pollutants across long distances, global climate change, threats to biodiversity, declines of ocean fisheries, and control of the use of outer space and the North and South Poles, have called attention to the attribute of scale among common-pool resources (Benedick, 1991; Buck, 1998; Gibson et al., 2000b; Haas et al., 1993; Young, 1989). Many important similarities exist between local and global common-pool resources even though there are obvious differences. Research has moved beyond studying resources at a single level (local or international) to comparing common-pool resources across levels and drawing lessons from one level to another (Keohane and Ostrom, 1995; Ostrom et al., 1999). One obvious difference between local and global resources is the sheer extent of the resource and thus the cost of monitoring use patterns at widely diverse locations. Global and local resources differ in two additional ways. The number of actors using, or having a say in decisions about, a global resource is usually larger than is the case for local resources, and these actors are usually much more heterogeneous. Both of these factors can affect the level of cooperation likely to be achieved in designing and complying with rules.
The literature on local common-pool resources suggests that a greater number of resource users does not necessarily impede cooperation (Ostrom, 1990), even though this may increase costs of devising, monitoring, and enforcing the rules. It also may make it necessary to design nested sets of institutions rather than a single layer. The literature on cooperation in international arenas, however, suggests that cooperation is less likely with a larger number of actors. These actors often include not only countries that are sovereign decision makers, but also a large number of nonstate actors that play important roles (Benedick, 1991; Mitchell, 1995; Vogel, 1986). The institutions granting these nonstate actors access to the political decision-making process also may play an important role in determining the potential for cooperation (Dolšsak, 2001; International Human Dimensions Program, 1999; Weaver and Rockman, 1993; Young, 1997).
Heterogeneity of resource users may not have the same effects on local common-pool resources and on international resources. The literature on local common-pool resources suggests different, even opposing effects of heterogeneity among actors on cooperation. It has been argued that heterogeneity will induce cooperation (Olson, 1965) and that it will impede cooperation (Libecap, 1995). In empirical research, heterogeneity has been found to be a difficulty that users frequently are able to overcome so as to manage a common-pool resource (Lam, 1998; Varughese and Ostrom, 2001). This issue is discussed further by Bardhan