Status of Pollinators in North America (2007) / Chapter Skim
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1 Role and Importance of Pollinators
1 Role and Importance of Pollinators
Pages 13-33
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From page 13... ...
Some plants self-pollinate, that is, pollen transfer occurs within the same flower or among the flowers on a single plant, usually because the anthers touch the adjacent stigma. The majority of flowering plants, however, depend on the transfer of pollen from other individuals (cross-pollination)
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From page 14... ...
It is common for plants to receive mixtures of self and outcross (nonself) pollen grains, espe cially if the male and female parts are in the same flower (Plate 1 -- a perfect or hermaphrodite flower)
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From page 15... ...
If a flower receives an inadequate number of pollen grains, some of the egg cells will not be fertilized and accordingly seeds will not develop. Economic consequences of such incomplete fertilization include
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From page 16... ...
Some plant species depend primarily on a single species or genus of pollinator, which in turn has restricted sources of pollen or nectar. An example of a closely dependent association is the relationship between plants in the genus Yucca (Agavaceae)
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From page 17... ...
. Principal pollinators of a particular species can vary spatially as well as temporally; the alpine sky pilot, Polemonium viscosum, is pollinated primarily by bumble bees at high elevations and by flies at low elevations in its native Rocky Mountain range (Galen et al., 1987)
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From page 18... ...
In North America, only a handful of pollinator species are actively managed -- that is, they are semidomesticated, produced in large quantities, and bought and sold commercially. Of these, Apis mellifera L., the western honey bee, is the premier actively managed pollinator worldwide, highly valued for its activity as a pollinator and for its production of wax and honey (Delaplane and Mayer, 2000; Free, 1993; Kearns et al., 1998; McGregor, 1976)
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From page 19... ...
. For some crops, bumble bees, megachilids, and other native bees are more efficient pollinators than are honey bees (Cane, 2002; Javorek et al., 2002; Maeta and Kitamura, 1981; Tepedino, 1997)
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From page 20... ...
, economic values can be estimated for discrete changes in supply and demand. For the case of commercial honey bee pollination services, the consum ers are the crop growers and the producers are the beekeepers.
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From page 21... ...
Such price-quantity relationships fall well outside prior experience. For pollination services provided by wild pollinators where markets do not exist, current estimates of nonmarket value are fraught with limiting assumptions.
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From page 22... ...
. The annual value of honey bee pollination to U.S.
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From page 23... ...
and by Levin (1983) include indirect benefits of the honey bee pollination required for seed production in alfalfa hay, asparagus, broccoli, carrot, cauliflower, celery, onion, and sugar beet.
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From page 24... ...
. An added complication is that insect pollinators may contribute ecosystem services other than pollination in their larval stages.
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From page 25... ...
According to this system, which takes into consideration trophic level interactions, redundancies, and competition, ecosystem services are classified into Types A through E, with Type A services at one extreme identified as those in which species losses are mostly compensated for by co-occurring species and Type E services identified as "the most brittle services; for these services, small changes in species biodiversity result in large changes in the provisioning of ecosystem services." In Type C, an intermediate response, a linear decline in ecosystem service is expected with each species loss. In this system, pollination is considered a Type C or E service for most ecosystems, with species losses having significant impacts on trophic stability.
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From page 26... ...
The agricultural community has voiced concerns over fluctuations in the health and availability of A mellifera, the principal managed pollinator in the United States, and associated impacts on crop production, whereas the ecological community has noted declines worldwide as part of a larger effort addressing biodiversity losses and associated impacts on ecosystem services.
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From page 27... ...
. The high rate of mortality is the combined result of several factors, including low levels of natural resistance to mites in the honey bee population; inadequate stock development and production facilities; widespread use of pesticides, which helps to maintain mite-susceptible genotypes in the honey bee population; and widespread pesticide resistance in the mite population.
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From page 28... ...
Wild Pollinators Concerns about pollinator status are in at least one way unique in discussions of threats to biodiversity in general, in that such concerns are often directly and explicitly linked to concerns about the status of another group of organisms -- the mutualistic flowering plant partners of pollina tors. Over the past quarter-century, declines in wild pollinator populations
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From page 29... ...
was the Schaus swallowtail, Papilio aristodemus, a flower-visiting species and a presumed pollinator. Flower-visiting Lepidoptera, many of which are actual or potential pollinators, currently dominate the list of endangered species: 17 species of butterfly and 3 species of moth constitute more than half of all insect species listed as endangered (http://ecos.fws.
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From page 30... ...
is relatively recent and quantitative studies on pollinator populations in North America are few in number. Among the possible causes suggested for declines in wild pollinator numbers are fragmentation, degradation and loss of habitat, nontarget effects of agricultural pesticides, competition from invasive species, and introduced diseases (Johansen, 1977; Kearns et al., 1998; Kevan, 1974, 1975a, 1999, 2001; Kremen and Ricketts, 2000; Morandin et al., 2005; Rathcke and Jules, 1993)
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From page 31... ...
The São Paolo proposal was ultimately presented by the Brazilian government to the SBSTTA at its fifth meeting and, at COP5 -- the fifth meeting of the Conference of the Parties -- the International Initiative for the Conservation and Sustainable Use of Pollinators was created. That initiative was to promote international cooperation with several goals: • Monitor pollinator decline, its causes, and its impact on pollination services.
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From page 32... ...
In November 1999, the USDA Agricultural Research Service (ARS) convened a workshop to obtain stakeholder input from state departments of agriculture, universities, pesticide companies, beekeepers, and extension agents on research priorities for the Bees and Pollination Component of the Crop Production National Program Writing Teams.
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From page 33... ...
The proportion of the report devoted to honey bees reflects the amount of knowledge and data available for this species. In contrast, the proportion of the report devoted to wild pollinators reflects the sparse data and our incomplete knowledge on those groups despite their critical role in ecosystem functioning.
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