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Status of Pollinators in North America
number of plant species that might be lost as a result of reproductive failure that is caused by a loss of pollinators is likely to be small. Finally, some economically important wild species (for example, ginseng) that suffer from pollinator limitation also are severely threatened by other stressors, such as overharvesting and deer grazing (McGraw and Furedi, 2005). In such cases, species demise is only partially attributable to pollinator limitation.
Severe shortages of pollinators could cause many common food crops to become more expensive and perhaps less available, but there is no strong evidence for a current pollination crisis in agricultural production in North America. Most animal-pollinated crops can be serviced by honey bees, and farmers are accustomed to paying more for these services when necessary. Chronic pollinator shortages should lead to market adjustments and other innovations, although the demand for supplemental pollination has been strong recently, especially among California’s almond growers. Importing managed pollinators from other countries or regions can lead to the introduction and spread of pathogens and unwanted bee species (Chapter 3). Therefore, it is prudent to sustain wild-pollinator populations as a means of buffering current and future shortages of managed pollinators of agricultural crops. In some cases, farmers could find that promoting wild pollinators that can supplement or substitute for managed pollinators could provide greater yields than will complete dependence on rented honey bee colonies (for example, Greenleaf, 2005). Intensive agricultural practices and pesticide use can reduce wild-pollinator diversity and abundance (for example, Kevan, 1975b; Kremen et al., 2002b; Larsen et al., 2005). Strategies for promoting abundance of wild pollinators are presented in Chapter 6.
In natural areas, the consequences of pollinator shifts on ecosystem services and possible solutions to these problems are varied and complex. Relatively few plant species rely on a single pollinator species or even on a single category of pollinators for reproduction. Because of the redundancy of most plant-pollinator communities, the ecological consequences of losing a small number of pollinator species could be limited. However, the loss of pollinator species reduces the redundancy of pollinator services in the ecosystem, and thus its resiliency, so that further losses of pollinator species would likely have more severe consequences for the ecosystem.
Plant communities in which massive pollinator declines are reported, for example because of persistent pesticide use or extensive habitat degradation, merit careful study of ramifying consequences for biodiversity. The ecological consequences of widespread pollinator declines could be substantial, but they could be difficult to detect because seed production varies dramatically in response to many biotic and abiotic factors (Figure 4-4). Moreover, the