became abundantly clear in short order. More than three-quarters of angiosperm plant species rely on animals for pollination. Although most major food grains are wind-pollinated grasses that do not require services of animal pollinators, most fruits and vegetables—which add diversity to the human diet and provide nutrients—are animal pollinated. Animal-pollinated crops, including several key oilseed species, also tend to be of greater economic value than are those not pollinated by animals, and they provide relatively higher income to growers. Moreover, bee pollination is required to produce the seeds of major forage and hay crops, such as alfalfa and clover, which are used to feed animals that, in turn, supply meat and dairy products. Thus, the contribution of pollinators to the quality of the human diet makes determining their status in North America an issue of prime importance.
Estimating the ecological value of pollinators and pollination and predicting the consequences of their losses are considerably more challenging than estimating their economic value in agriculture. Such estimates are complicated by both the number of species involved and the relative paucity of information available for most of these species (particularly those in natural communities). As discussed in Chapter 1, it is reasonable to assume that a large proportion of flora in uncultivated terrestrial communities of North America rely upon pollinators to some degree. In a recent assessment of the susceptibility of ecosystem services to species losses (Chapter 1), animal-mediated pollination is considered a service for most ecosystems and losses of pollinator would affect trophic stability.
Among the first topics examined was the question of how to differentiate between pollinator shortage and pollinator decline. Shortages and declines were recognized as distinct but not necessarily related phenomena. Shortages entail insufficient supply to meet demand according to recognized norms; declines are trends toward reduction in population size or diversity over time (Chapter 2). Using these definitions, the committee evaluated the literature and consulted numerous experts to try to determine the status of major groups of animal pollinators.
Population status of most managed pollinators, such as bumble bees and alfalfa leafcutting bees, are not closely monitored in North America. Evidence for decline is compelling for the honey bee (Apis mellifera), which is among the few actively managed pollinator species. Current methods for documenting the status of managed colonies of A. mellifera, a species of enormous economic importance (Chapter 1), are surprisingly inadequate