The Pollinator Crisis
The importance of bees for pollination
No other group of insects are of more benefit to humans than bees. More than one-third of the world’s crops require pollination to set seeds and fruits, and most meat and dairy industries rely on bees for pollination of clover and Lucerne (Dias et al 1999).
Crops relying on bee pollination include apple, citrus, tomato, melon, strawberry, apricot, peach, cherry, mango, grape, olive, carrot, potato, onion, pumpkin, bean, cucumber, sunflower, various nuts, a range of herbs, cotton, alfalfa and lavender. The annual value of this service is estimated at US$112 billion worldwide (Southwick & Southwick, 1992). Even crops that do not require pollination for harvesting, such as those producing fibre or timber, still require pollination to produce further generations, and crops such as cotton that do not require pollination to produce seeds, provide greater yields when pollinators are available (Allen-Wardell et al 1998).
The European honeybee (Apis mellifera) dominates crop pollination worldwide, but local native bee species also play their part. Studies in northern California showed that, where agricultural systems were interspersed with a range of native habitats, crops on organic farms were visited by 21 species of local bees (Kremen & Ricketts 2000).
The decline of European honeybees
Despite much of the world’s agriculture relying on pollination by European Honeybees, their numbers worldwide have declined due to a range of natural and human mediated causes (see below). In the USA, Mexico and Canada, both feral and managed honeybees declined by 25% between 1990 and 1998 (Allen-Wardell et al 1998, Loper 1995). In Europe, particularly France and Germany, the same species (which is native to the continent) declined by about 10% between 1992 and 2002 (unpublished data from the European Pollinator Initiative). Honeybee “specialists consider all countries will become seriously affected” by this decline, which is expected to continue for at least the next few years (Dias et al 1999).
The decline of other bee species
In natural systems, particularly biodiversity hotspots such as tropical rainforests, the decline in pollinator numbers has a more significant effect because their services are essential to maintain that diversity. The more plant species that are present in a habitat, the less is the access for each species to the pool of pollinators. As each pollinator declines and the ‘pollination limitation’ increases, the risk of extinction for any plant species also increases (Vamosi et al 2006). Pollination limitation, involving reproductive shortfall or failure of seed set, is thought to be in the range of 50-60% in rare plant species or plants found in fragmented habitats (Allen-Wardell et al 1998), and some research suggests more than 60% of plant species studied are pollination limited (Burd 1994). Tropical forests in South America have the added burden of habitat loss due to agricultural encroachment, habitat fragmentation, and the invasion of Africanised bees (Roubik 2000).
Aside from biodiversity hotspots, there are a number of other natural ecosystems particularly susceptible to the effects of pollinator decline. In tropical communities dominated by large tree species, such as figs, where each fig species is dependent on one or two species of fig wasps for pollination, and where 80% of the vertebrate species rely on the fruit as the basis of their diet, loss of a few pollinator species can be catastrophic to the entire ecosystem. This is also the case on islands, where pollinator guilds are often depauperate even without human interference, and a number of plant species may rely on a single pollinator (Allen-Wardell et al 1998).
One particularly important area for pollinators is the interface between agricultural lands and natural ecosystems. When managed pollinators such as European honeybees are not capable of pollinating a crop to full capacity, other bee species from surrounding areas may be able to complete the task (Kremen & Ricketts 2000). However, the impact of pesticides and other human-generated activities may extend for some distance into natural ecosystems, affecting both the crops and native plant species.
Reasons for pollinator decline
Pollinator decline has been a global issue for many decades as natural ecosystems were cleared to make way for agricultural systems, particularly monocultures. This decline has accelerated dramatically in recent years because, in addition, a number of factors such as climate change, the spread of bee parasites and diseases, the overuse of pesticides, the spread of Africanised bees and other invasive species, and the introduction of GMOs appear to have compounded the situation.
Parasites and diseases on
European honeybees
Global populations of European honeybees
have suffered for many years from a range of diseases such as European
and American Foulbroods, with parasites causing additional problems in
recent years. The Honeybee Tracheal Mite (Acarapis woodi) was
discovered in the 1920s and slowly spread throughout the world, reaching
the USA in the 1980s. Today it is found in all countries except
Australia, New Zealand, Scandinavia and Canada. The mites infect the
tracheal walls of young adult bees and shorten their lives, reducing
honey production and pollination efficacy (Morse 1978).
The Varroa Mite (Varroa jacobsoni), a more serious pest of honeybees, is cosmopolitan throughout the world except a few isolated countries such as Australia. In 1987 it was detected in Florida and within a short period had spread across most of the USA. The mite feeds externally on bee larvae, pupae and adults and, if left unchecked, will kill most bee colonies in seven months to three years (Ritter 1981).
Habitat changes
One of the major causes of native
pollinator decline around the world is changes to habitat. This may
include habitat loss and reduction, particularly in areas where natural
ecosystems are replaced with agricultural systems; habitat
fragmentation, where natural ecosystems survive but in patches too small
to support sustainable pollinator populations; and habitat disturbances,
where human activities disrupt pollination systems even when the habitat
itself remains intact (Kremen & Ricketts 2000).
An additional complication is the replacement of natural habitat with monocultures. Even for bee species that will feed on the crop and effectively pollinate it, the bees may be unable to find suitable nesting sites or alternative flowers when the monoculture is not in flower (Dias et al 1999).
Pesticides
In many parts of the world, pesticides
are used to control insect pests on a large scale, but pollinators (as
well as the natural predators of the pests) are usually more susceptible
to the pesticide than the target insects. Widespread use of pesticides
in many parts of the world has reduced the overall numbers of
pollinators (Pimentel et al 1992) and this, particularly in the case of
rare insect pollinators and/or rare plants, can have a devastating
impact on pollination systems (Nabhan & Buchmann, 1996). There is also
concern that sublethal doses of pesticides may disrupt the pollinating
behaviour of all types of bees and render them more susceptible to
diseases and parasites (Allen-Wardell et al 1998).
Invasive species
Invasive plant species, often not requiring pollination to reproduce,
are able to move in and displace native plant species, disrupting the
ecology of both local plants and their pollinators. This is particularly
destructive on small islands. Invasive animal species may impact the
pollinators through competition with or predation on local pollinators (Kremen
& Ricketts 2000).
Other factors
Two other factors whose impact on pollinators is not so clear are
Africanised bees and the role of genetically engineered crops. Long term
studies in South America have shown that the invasion of the aggressive
and adaptable Africanised bees into native ecosystems has undoubtedly
caused the loss of some native species of bees, but their impact on
overall pollination systems is still under review (Roubik 2000), given
that they have negative effects in some regions but neutral and
occasionally positive effects in others.
Genetic engineering and “the rapid development of transgenic crops raises additional causes for concern among specialists on bees” (Dias et al 1999). The practice of incorporating the insecticidal Bacillus thuringiensis (Bt) gene into crops has raised concerns about the effect of pollen from these plants on pollinators, but so far the evidence is scant. Some studies have suggested GM pollen from a number of crops reduces the survival rate of caterpillars such as the Monarch or Wanderer Butterfly (Danaus plexippus), as well as European Honeybees (Conner et al 2003).
The pollination crisis
The risk of relying on a single pollinator is becoming clear, and global organisations are recognising the need for a diversity of pollinators, particularly native species. Many of these species need to be managed if they are to fulfill their potential as pollinators of agricultural and horticultural crops, because “although the most important causes of pollination disruption are shared among regions of the world, their consequences vary widely in complex, idiosyncratic ways” (Kremen & Ricketts 2000). As much as anything, the pollination crisis may be an economic crisis; Southwick & Southwick (1992) estimated the then economic loss due to declines in European honeybee populations to be US$5.7 billion per year worldwide.
The potential loss of pollinators, particularly specialist pollinators such as orchid wasps, has serious consequences for not only individual plant species but, potentially, entire plant guilds and ecosystems; “the loss of specialised pollinators will strongly select for self-compatibility, self pollination, and reduced genetic variability in plants, resulting in a possible reduction in their evolutionary adaptability to environmental change” (Allen-Wardell et al 1998). These effects may then cause further ripples through natural and managed ecosystems; in Canadian blueberry fields, a reduction in available pollinators due to the overuse of pesticides affected a great range of organisms including invertebrates, birds, bears and even humans (Kevan 1977).
In the last two decades there have been a number of examples of local or widespread failure of crops directly attributable to the pollinator decline, including failure of pumpkins, cherries, alfalfa, blueberries, cashews and Brazil nuts (Allen-Wardell et al 1998). There may also be a reduction in crop quality due to lack of pollinators (eg fewer seeds fertilized in fruit and therefore smaller fruit) and, additionally, crop failures attributed to other factors, such as poor weather, may be exacerbated by lack of pollinators.
Perhaps
belatedly, efforts are underway to redress this problem. The
International Convention on Biological Biodiversity, a United Nations
Environment Programme, has developed the International Pollinator
Initiative, working in conjunction with a number of national and
international programs including:
·
European Pollinator Initiative;
·
North American Pollinator Protection Campaign;
·
African Pollinator Initiative;
·
Brazilian Pollinator Initiative;
·
Pollination Working Group of the International Commission of Plant-Bee
Relationships;
·
Task Force on Declining Pollinator Services of the Species Survival
Commission, World Conservation Union (IUCN).
The International Convention on Biological Diversity specifically cites pollination as a key ecosystem function that is threatened globally. Its aims are to address the lack of taxonomic information on pollinators, and promote the conservation and the restoration and sustainable use of pollinator diversity in agricultural and related ecosystems.
The Sao Paulo Declaration on Pollinators (1999), based on the available global evidence at the time, reported that “the numbers of native bees are dwindling, some species seriously so” (Dias et al 1999). One practical way to redress the problem is to begin the search for alternative pollinators now. “For some years several species of wild bees have been managed for the pollination of crops, and the management of additional species for glasshouse crops has developed rapidly during the past few years” (Dias et al 1999).
What should be done now?
Educate the public on the importance of
pollinators
As stated previously, humans rely totally on pollination for survival
and “the management and protection of wild pollinators is an issue of
paramount importance to our food supply system” (Allen-Wardell et al
1998).
The European Pollinator Initiative and the Sao Paulo Declaration on Pollinator Decline both raise the need for increased public awareness of the importance of pollinators, particularly bees, and both emphasise the value in targeting the world’s education systems (Dias et al 1999). The landmark paper on the global pollination crisis, co-authored by 22 pollination ecologists, scientists and resource managers, and endorsed by 13 universities and international organisations, “identified the need for…a better focus at primary, secondary and higher education levels on how pollination services benefit society” (Allen-Wardell et al 1998).
Raise awareness of the pollination crisis
Pollination ecologists and environmental scientists around the world are
well aware of the pollination crisis and “an increasing number of
organisations are beginning to promote the restoration of ecological
functions such as pollination” (Kremen & Ricketts 2000) to the rest of
the community. Time is short, as “populations of many native plants and
their pollinators are being diminished and lost due to habitat
fragmentation, degradation and loss” (Allen-Wardell et al 1998) at an
increasingly rapid rate, and “loss of pollinators from a biotic
community may not be easily reversible. We do not know…how to remedy the
loss of native pollinators, or even if such remedies are possible.”
(Allen-Wardell et al 1998)
The global organisations currently tackling the
pollination crisis emphasise the need to raise awareness, and the
European Pollinator Initiative plan of action aims to:
·
educate land managers, farmers and conservationists;
·
train the next generation of researchers and taxonomists; and
·
support national plans for the conservation of bees and increase the
awareness of governments, industry and the public.
There are a range of options to remediate the pollination crisis but, “as with many conservation issues, the final challenge will be to gather sufficient public support to implement [pollination crisis] solutions” (Kremen & Ricketts 2000).
Undertake research on alternative pollinators
One of the biggest hurdles in overcoming the pollination crisis is lack
of knowledge, as “there have been few comprehensive studies of
pollination webs” (Corbet 2000) and “a serious threat to conserving
pollination systems is the paucity of verifiable scientific data on
pollinator abundance or effect” (Roubik 2000). The European Pollinator
Initiative identifies the need to “develop alternate species of
pollinator for management” as a key element, and the International
Pollinator Initiative highlights the need to “assess breeding techniques
of native pollinators” before serious work can begin (Dias et al 1999).
Management of a range of bee species is required to
maintain the world’s pollination systems, particularly in agricultural
areas, but management is unlikely until more is known about their
taxonomy, ecology and biology. Over most of the
world, even in managed agricultural areas, the pollination ecology (ie
which species are undertaking what proportion of the pollination) is
very poorly known. In natural ecosystems our knowledge is significantly
poorer still. Without properly understanding the current situation it is
difficult to determine remedies. Other important questions which require
answers to assess and rectify the situation include:
·
which local bee species are suitable as pollinators in each region of
the globe?
·
how
effective are they as pollinators and how do they compare with
pollination services provided by European honeybees?
·
can
their services be improved through management and what management
techniques are necessary?
·
can
local species be translocated to other areas and still have the same
pollination efficacy without further disrupting the local ecosystems?
·
over what area do the bees forage and therefore what is their
pollination radius?
·
do
the bees require roosting and/or nesting sites and can these be provided
by the agriculturalist, or do they require natural areas to be set
aside?
·
if
supplemental feeding of colonies is required, over what area do they
need to forage and how is this affected by habitat fragmentation?
·
what impact will local predators and parasites have on the bees and what
impact will an artificially elevated bee population have on local food
webs?
The most basic requirement to answer these questions is information on the biology of each species. Social bees require different management strategies to solitary bees; nesting and foraging sites differ markedly between species; their survival rate and longevity is in part dependent on the habitat, including agricultural habitats; and the way each species harvests nectar and the efficacy of pollen transfer is also dependent on their biology and social system (Klein et al 2002). Research is required at all levels and efforts must be made wherever possible to “invest in the development or domestication of (non-Apis) alternative pollinators that can be employed when the services provided by managed honey bees are inadequate to ensure high fruit set” (Allen-Wardell et al 1998).
Wherever preliminary studies have been undertaken around the world, the situation has been found to be more complex than at first glance (Klein et al 2002), and the situation is particularly important in Australia, where “groups of native bees that have special importance for pollination systems need to be identified and cross-checks with possible conservation threats need to be made” (Schwarz & Hogendoorn 1999).
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