The term pollinator decline refers to the reduction in abundance of insect and other animal pollinators in many ecosystems worldwide beginning at the end of the 20th century, and continuing into the present.
Pollinators participate in sexual reproduction of many plants, by ensuring cross-pollination, essential for some species, or a major factor in ensuring genetic diversity for others. Since plants are the primary food source for animals, the reduction of one of the primary pollination agents, or even their possible disappearance, has raised concern, and the conservation of pollinators has become part of biodiversity conservation efforts.
Pollinators, which are necessary for 75% of food crops, are declining globally in both abundance and diversity. Bees, in particular, are thought to be necessary for the fertilization of up to 90% of the world's 107 most important human food crops.
The decline in bee numbers has attracted much public attention. Members of the British Beekeepers' Association have issued numerous warnings in the 21st century that the country's bees are in rapid decline. Writing in 2013, Elizabeth Grossman noted that the winter losses of beehives had increased in recent years in Europe and the United States, with a hive failure rate up to 50%. In France, the honey harvest for 2017 has been estimated at around 10,000 tons, representing a decline of two-thirds against the average annual harvest during the 1990s.
A 2017 study led by Radboud University's Hans de Kroon, using 1,500 samples from 63 sites, indicated that the biomass of insect life in Germany had declined by three-quarters in the previous 25 years. Participating researcher Dave Goulson of Sussex University stated that their study suggested that humans are making large parts of the planet uninhabitable for wildlife. Goulson characterized the situation as an approaching "ecological Armageddon", adding that "if we lose the insects then everything is going to collapse". Lynn Dicks at the University of East Anglia in 2017 estimated the rate of decline in flying insect biomass at roughly 6% a year. The decline has been termed by entomologists as the windshield phenomenon, since it is associated with anecdotal reports that far fewer insects end up on car windshields now than a few decades ago.
An estimated 87.5% of the world's flowering plant species are animal-pollinated, and 35% of crop production and 60% of crop plant species depend on animal pollinators. This includes the majority of fruits, many vegetables (or their seed crop), and secondary effects from legumes such as alfalfa and clover fed to livestock.
In 2000, Drs. Roger Morse and Nicholas Calderone of Cornell University attempted to quantify the effects of just one pollinator, the western honey bee, on only US food crops. Their calculations came up with a figure of US$14.6 billion in food crop value. In 2009, another study calculated the worldwide value of pollination to agriculture. They calculated the costs using the proportion of each of 100 crops that need pollinators that would not be produced in case insect pollinators disappeared completely. The economic value of insect pollination was then of €153 billion.
Several large-scale studies have looked at the nutritional consequences of pollinator decline. Since pollinators are responsible for propagating certain plants and crops, populations that are heavily reliant on those crops are at risk for malnutrition. As such, the size of the effect that pollinator decline has on an area depends on the local diet. According to a 2015 study published in the Public Library of Science, pollinator decline is most likely to have negative impacts on the nutritional health of an area when the people living there get the majority of their nutrients from crops that are heavily dependent on pollinators, the affected people are not already severely deficient in a nutrient or consuming significantly higher amounts of the nutrient than is recommended, they do not have access to other foods that could substitute the nutrients from the crops they are losing, and they do not have access to supplements, fortified foods, or targeted nutrition programs that could help ensure they are still getting adequate nutrients. In contrast, populations whose diets are not heavily based on pollinator-dependent crops likely will not be affected by pollinator decline to the same extent.
A 2015 study done by the Harvard School of Public Health modeled what would happen should 100% of pollinators die off. In that scenario, 71 million people in low-income countries would become deficient in vitamin A, and the vitamin A intake of 2.2 billion people who are already consuming less than the recommended amount would further decline. Similarly, 173 million people would become deficient in folate, and 1.23 million people would further lessen their intake. Additionally, the global fruit supply would decrease by 22.9%, the global vegetable supply would decrease by 16.3%, and the global supply of nuts and seeds would decrease by 22.1%. This would lead to 1.42 million additional deaths each year from noncommunicable and malnutrition-related diseases, as well as 27 million disability-adjusted life years. In a less extreme scenario wherein only 50% of pollinators die off, 700,000 additional deaths would occur each year, as well as 13.2 million disability-adjusted years.
In a 2014 study done in the United Kingdom, vitamin A was identified as the most pollinator-dependent nutrient. Vitamin A deficiency is one of the biggest malnutrition concerns when it comes to pollinator decline, as it is one of the leading causes of blindness, accounting for 500,000 cases annually. Vitamin A deficiency is also responsible for the deaths of about 800,000 women and children worldwide, as well as between 20% and 24% of deaths from measles, diarrhea, and malaria. An estimated 70% of dietary vitamin A worldwide is found in crops that are animal pollinated.
Folate deficiency, a type of vitamin B, is also of concern. An estimated 55% of folate is found in animal-pollinated crops such as beans and dark, leafy, green vegetables. Folate is highly recommended for pregnant women, as it helps to prevent neural tube defects in fetuses.
Calcium, fluoride, and iron deficiencies are also likely consequences of pollinator decline. Animal pollinators are responsible for 9%, 20%, and 29% of fruits and nuts that contain calcium, fluoride, and iron, respectively. While those percentages are not high compared to how much of those nutrients come from meat and dairy, fruits and nuts are more bioavailable. More so, meat and dairy production is expensive, inefficient, and not feasible in certain areas. Iron deficiency is the most common micronutrient deficiency worldwide, leading to preventable cognitive impairment and infection.
Additionally, 74% of all globally produced lipids are found in oils from plants that are animal pollinated, as well as 98% of vitamin C.
Increasing public awarenessEdit
Some international initiatives (e.g. the International Pollinator Initiative (IPI)) highlight the need for public participation and awareness of pollinator, such as bees, conservation.
Pollinators and their health have become growing concerns, resulting in an increase in public awareness. Around 18 states within America have responded to these concerns by creating legislation to address the issue. According to the National Conference of State Legislatures, the enacted legislation in those states addresses five specific areas relating to pollinator decline: "awareness; research; pesticides; habitat protection; and beekeeping".
Probable explanations for the decline in pollinators can be attributed to the use of pesticides, pests and diseases, habitat destruction, air pollution, pollinators' reaction to climate change, the effects of monoculture (especially in regards to bees), and the intraspecific competition and interspecific competition between "native and introduced or invasive species".
Studies have linked neonicotinoid pesticide exposure to bee health decline. These studies add to a growing body of scientific literature and strengthen the case for removing pesticides toxic to bees from the market. Pesticides interfere with honey bee brains, affecting their ability to navigate. Pesticides prevent bumble bees from collecting enough food to produce new queens.
Neonicotinoids are highly toxic to a range of insects, including honey bees and other pollinators. They are taken up by a plant's vascular system and expressed through pollen, nectar, and guttation droplets from which bees forage and drink. They are particularly dangerous because, in addition to being acutely toxic in high doses, they also result in serious sublethal effects when insects are exposed to chronic low doses, as they are through pollen and water droplets laced with the chemical, as well as dust that is released into the air when coated seeds are planted. These effects cause significant problems for the health of individual honey bees, as well as the overall health of honey bee colonies, and they include disruptions in mobility, navigation, feeding behavior, foraging activity, memory and learning, and overall hive activity.
A French 2012 study of Apis mellifera (western honey bee or European honey bee) that focused on the neonicotinoid pesticide thiamethoxam, which is metabolized by bees into clothianidin, a pesticide cited in legal action, tested the hypothesis that a sublethal exposure to a neonicotinoid indirectly increases hive death rate through homing failure in foraging honey bees. When exposed to sublethal doses of thiamethoxam, at levels present in the environment, honey bees were less likely to return to the hive after foraging than control bees that were tracked with radio-frequency identification (RFID) tagging technology, but not intentionally dosed with pesticides. Higher risks are observed when the homing task is more challenging. The survival rate is even lower when exposed bees are placed in foraging areas with which they are less familiar.
In their 2014 study of Bombus terrestris (buff-tailed bumblebee or large earth bumblebee), researchers tracked bees using RFID tagging technology, and found that a sublethal exposure to either imidacloprid (a neonicotinoid) and/or a pyrethroid (?-cyhalothrin) over a four-week period caused impairment of the bumblebee's ability to forage.
Imidacloprid effects on bees were examined by researchers exposing colonies of bumblebees to levels of imidacloprid that are realistic in the natural environment, then allowed them to develop under field conditions. Treated colonies had a significantly reduced growth rate and suffered an 85% reduction in production of new queens compared to unexposed control colonies. The study shows that bumblebees, which are wild pollinators, are suffering similar impacts of pesticide exposure to "managed" honey bees. Wild pollinators provide ecosystem services both in agriculture and to a wide range of wild plants that could not survive without insect pollination.
In March, 2012, commercial beekeepers and environmental organizations filed an emergency legal petition with the U.S. Environmental Protection Agency (EPA) to suspend use of clothianidin, urging the agency to adopt safeguards. The legal petition, supported by over one million citizen petition signatures, targets the pesticide for its harmful impacts on honey bees. The petition points to the fact that the EPA failed to follow its own regulations. EPA granted a conditional, or temporary, registration of clothianidin in 2003 without a field study establishing that the pesticide would have no "unreasonable adverse effects" on pollinators. The conditional registration was contingent upon the submission of an acceptable field study, but this requirement has not been met. EPA continues to allow the use of clothianidin 9 years after acknowledging that it had an insufficient legal basis for initially allowing its use. Additionally, the product labels on pesticides containing clothianidin are inadequate to prevent excessive damage to nontarget organisms, which is a violation of the requirements for using a pesticide and further warrants removing all such mislabeled pesticides from use.
Rapid transfer of parasites and diseases of pollinator species around the worldEdit
Increased international commerce has moved diseases of the honey bee such as American foulbrood and chalkbrood, and parasites such as varroa mites, acarina mites, and the small African hive beetle to new areas of the world, causing much loss of bees in the areas where they do not have much resistance to these pests. Imported fire ants have decimated ground-nesting bees in wide areas of the southern US.
Loss of habitat and forageEdit
Bees and other pollinators face a higher risk of extinction due to loss of habitat and access to natural food sources. The global dependency on livestock and agriculture has rendered no less than 50% of the earth's landmass uninhabitable for bees. The agricultural practice of planting one crop (monoculture) in a given area year after year leads to extreme malnourishment. Regardless if the planted crop does flower and provide food for the bee, the bee will still be malnourished because a single plant cannot meet its nutrient requirements. Furthermore, the crops needed to support livestock (primarily cattle) tend to be grains which do not provide nectar. Artificial water bodies, open urban areas, large industrial facilities including heavy industry, railways and associated installations, buildings and installations with sociocultural purpose, camping, sports, playgrounds, golf courts, oilseed crops other than oilseed rape such as sunflower or linseed, some spring cereals and former forest clearcuts or windthrows were frequently associated with high honey bee colony losses.
Researchers at UC Berkeley and UC Davis have found that if farms were to plant and maintain wildflower borders around their crop fields, they would see an eight-fold increase in bee abundance compared to farms without wildflower habitat. While most farms use managed bees, from either their own hives or rented, to pollinate their crops, wild bees can meet 100% of their pollination needs so long as they are plentiful. By maintaining wildflowers near their crops, farms would be able to resource natural pollination. The act of providing pollinators with more nutrient rich habitats, while having the benefit of "free" crop pollination, is a simple way to aid in the reduction of pollinator decline.
Researchers at the University of Virginia have discovered that air pollution from automobiles and power plants has been inhibiting the ability of pollinators such as bees and butterflies to find the fragrances of flowers. Pollutants such as ozone, hydroxyl, and nitrate radicals bond quickly with volatile scent molecules of flowers, which consequently travel shorter distances intact. There results a vicious cycle in which pollinators travel increasingly longer distances to find flowers providing them nectar, and flowers receive inadequate pollination to reproduce and diversify.
Changes in seasonal behaviour due to global warmingEdit
In 2014, the Intergovernmental Panel on Climate Change reported that bees, butterflies, and other pollinators faced increased risk of extinction because of global warming due to alterations in the seasonal behaviour of species. Climate change was causing bees to emerge at different times in the year when flowering plants were not available.
Artificial lighting at nightEdit
In June 2018, the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (de) released an article that discusses a possible link between the sharp decline in flying insects and also high levels of light pollution. Many studies would suggest that artificial light at night has negative impacts on insects, and scientists should therefore pay greater attention to this factor when exploring the causes of insect population decline.
The structure of plant-pollinator networksEdit
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Wild pollinators often visit a large number of plant species and plants are visited by a large number of pollinator species. All these relations together form a network of interactions between plants and pollinators. Surprising similarities were found in the structure of networks consisting of the interactions between plants and pollinators. This structure was found to be similar in very different ecosystems on different continents, consisting of entirely different species.
The structure of plant-pollinator networks may have large consequences for the way in which pollinator communities respond to increasingly harsh conditions. Mathematical models, examining the consequences of this network structure for the stability of pollinator communities suggest that the specific way in which plant-pollinator networks are organized minimizes competition between pollinators and may even lead to strong indirect facilitation between pollinators when conditions are harsh. This makes that pollinator species together can survive under harsh conditions. But it also means that pollinator species collapse simultaneously when conditions pass a critical point. This simultaneous collapse occurs, because pollinator species depend on each other when surviving under difficult conditions.
Such a community-wide collapse, involving many pollinator species, can occur suddenly when increasingly harsh conditions pass a critical point and recovery from such a collapse might not be easy. The improvement in conditions needed for pollinators to recover, could be substantially larger than the improvement needed to return to conditions at which the pollinator community collapsed.
Conservation and restorationEdit
Efforts are being made to sustain pollinator diversity in agricultural and natural ecosystems by some environmental groups. Prairie restoration, establishment of wildlife preserves, and encouragement of diverse wildlife landscaping rather than mono culture lawns, are examples of ways to help pollinators.
In June 2014, the Obama administration published a fact sheet, "The Economic Challenge Posed by Declining Pollinator Populations", which stated that the "President's 2015 budget recommends approximately $50 million across multiple agencies within USDA to ... strengthen pollinator habitat in core areas, double the number of acres in the Conservation Reserve Program that are dedicated to pollinator health".
The Obama administration's 2015 budget also recommended to "enhance research at USDA and through public-private grants, ... and increase funding for surveys to determine the impacts on pollinator losses".
SmartBees is a European research project of 16 entities (universities, research institutions and companies) funded by the EU, headquartered in Berlin. Its goal is to elicit causes of resistance to CCD, develop breeding to increase CCD resistance and to counteract the replacement of many native European bees with only two specific races.
CoLOSS (Prevention of honey bee COlony LOSSes) is an international, nonprofit association headquartered in Bern, Switzerland, to "improve the well-being of bees at a global level", composed of researchers, veterinarians, agriculture extension specialists, and students from 69 countries. Their three core projects are standardization of methods for studying the honey bee, colony loss monitoring, and bridging research and practice.
The decline of pollinators is compensated to some extent by beekeepers becoming migratory, following the bloom northward in the spring from southern wintering locations. Migration may be for traditional honey crops, but increasingly is for contract pollination to supply the needs for growers of crops that require it.
In 2014, Honey Nut Cheerios and Burt's Bees joined forces to support the Bring Back the Bees campaign, which aims to inform people about the potentially catastrophic decline in the bee population. As of 2017, Honey Nut Cheerios has sold over 1.5 billion wildflower seeds, greatly surpassing their goal of 100 million.
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