et al., 2004). Dispersing small fragments extensively throughout an area seems logical but leaves open the question of how to configure large parcels to allow pollinator populations to persist. Both metapopulation theory (reviewed in Hanski and Ovaskainen, 2000; Harrison and Fahrig, 1995) and empirical data (Harrison et al., 1988) suggest that some larger patches are needed to support larger sized populations that are more resistant to extinction (see also Berger, 1990; Zayed and Packer, 2005). Larger areas also will, in theory, contain more diverse assemblages of pollinators (MacArthur and Wilson, 1967; Simberloff and Wilson, 1969) that might provide more services, more consistently, and contribute to pollination of a wider variety of crops (Kremen and Chaplin, in press) and other plants (Memmott, 1999; Memmott et al., 2004). More research is needed to determine the optimal configuration of landscape fragments and their connectedness to maintain pollinator populations, communities, and functions.

PUBLIC POLICY AND POLLINATOR POPULATIONS

U.S. Endangered Species Act

The Endangered Species Act (ESA) of 1973 is the broadest and most powerful U.S. law for the protection of endangered species and their habitats (NRC, 1995). The act lists species of plants and animals (vertebrate and invertebrate) as endangered or threatened according to assessments of their risk of extinction (Congressional Research Service [CRS], 2006). Once a species is listed, ESA’s strict substantive provisions become legal tools to assist in the species’ recovery and the protection of its habitat. Endangered species and their critical habitats are entitled to strong protections. It is illegal, for example, to take any endangered species in the United States or its territorial waters, and any federal action that will jeopardize the future of an endangered species is prohibited, including any action that threatens to destroy or damage critical habitat. At press time for this volume, in the fall of 2006, 1879 U.S. and foreign animals and plants were listed as endangered or threatened (U.S. Fish and Wildlife Service [USFWS], 2006).

ESA’s major goals include the recovery of endangered and threatened species to the point at which protection is no longer needed. As this volume went to press, USFWS (2006) had cataloged 17 U.S. and foreign species that had been recovered and removed from the list. The populations of other listed species have increased, and some appear to have stabilized even though they remain on the list.

A species is placed on the Endangered Species List on the initiative of the secretary of the interior or of the secretary of commerce. The decision is based on the best available scientific and commercial information and a



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