Pollinators are a fascinating group of animals, though often misunderstood! What happens when you try to picture a quintessential pollinator species in your head? For many, it's the bee.
The honeybee Apis mellifera represents a fraction of the pollinator population. Most of the bee species in the U.K. are solitary, meaning they do not live together in hives, unlike honeybees. As such, over half of pollination, in both nature and crops, occurs through wild species.
Wild bee species in the U.K. that contribute to the pollination of many flower species such as clover (Trifolium) and knapweed (Centaurea) include:
- The Buff-tailed bumblebee Bombus terrestris.
- Common carder bee Bombus pascorum.
- Tawny mining bee Andrena fulva.
Pollinator conservation is pivotal to enhancing ecosystem resilience naturally and at a lower cost than any other currently existing alternative.
Definition of Pollinators
Pollinators are animals that transfer pollen from the male organs, or stamens, of a flower to the female organ, or pistil, of another flower of the same species.
The pollination process begins when a pollinator brushes against the stamens of a flower, picking up pollen. The pollinator then transfers the pollen to the pistil of another flower, fertilizing the ovules and allowing the plant to produce seeds. In return for their services, pollinators are rewarded with nectar, which is a sweet liquid produced by flowers. Nectar provides pollinators with energy, and it also contains essential nutrients that help pollinators to survive.
Some common pollinators include
- Bees
- Butterflies
- Moths
- Birds
- Bats
- Beetles
Pollination happens because the plant attracts a pollinator through colour, scent, shape and nectar to use as a gene vector. Flowers and their pollinators evolved together with the intention to maximize benefits on both sides.
It is a mutualistic interaction! This means that both species involved in the exchange benefit from it.
Palyniores are attracted by pollen; nectarivores, by nectar.
Pollinators Examples
A non-exhaustive list of pollinators includes:
Bees: Ruderal bumblebee Bombus ruderatus, the largest bumblebee species in Britain, supports flower-rich meadows.
Flies: Delhi Sands flower-loving fly Rhaphiomidas terminatus abdominalis visits buckwheat flowers. It was the first fly species to be put on the Endangered Species List in the U.S.
Butterflies: Dingy skippers feed on Common Bird's-foot Trefoil.
Moths: Sphinx moths like Honeysuckle flowers that remain open at night.
Wasps: Wasps of the family Agaonidae are the sole pollinators of fig trees.
Birds: Sunbirds and sugarbirds, specialist nectarivores from South Africa, especially like Protea flowers.
Lemurs: Black and white ruffed lemurs feed on Traveller's palm tree Ravenala madagascariensis.
Lizards: Gold dust day geckos P. laticauda can be seen sipping on Trochetia blackburniana or banana flowers.
The Global Situation
There are around 200,000 pollinators across the globe and approximately 6.5 million terrestrial species1. Our resources indicate that all these terrestrial species have sported an overall decline of 60% since 19402.
Less than 3% of all known terrestrial animal species provide pollination services. Yet, an estimated 87.5% of all flowering plants depend on pollinators, interacting with them to ensure the spreading of their flowers' genes3.
More precisely, animal-mediated pollination contributes to the sexual reproduction of over 90% of approximately 250,000 species of modern angiosperms4. This unique co-evolution has given birth to multiple plant-host preferences and specialized pollen and nectar selection by species.
Angiosperm: plants that have evolved to produce flowers, seeds or fruits. The fern Athyrium filix-femina isn't an angiosperm, for instance.
Pollinators are essential in environments where wind pollination is difficult, such as forests.
The yield of most crop species used for human food production is enhanced by pollinator activity. These include:
The oldest records of insect pollination that we have are of beetles! One such fossil dates back to 99 million years ago. They have been and still are important pollinators for plants like Magnolias, which evolved with beetles "in mind".
Endangered Pollinators
A host of stressors causes losses in pollinator numbers worldwide. Examples of stressors include:
- Land-use changes for agriculture
- Forestry practices
- Urbanization
The role of wasps in pollination is less researched and analysed than that of bees, moths, and butterflies. However, this doesn't mean that their pollination role is unimportant!
Additional reasons for which pollinators can become threatened or endangered include:
Insufficient research: Sometimes, we do not know when a species is endangered because we don't have enough data on it. Lack of research and knowledge in the first place can be a reason why we unintentionally threaten a species with our activities.
Diseases: Unsteady practices in agriculture and specifically in bee rearing can lead to direct losses and enhanced costs caused by bee parasites developing resistance to treatments, with these parasites possibly migrating to their wild counterparts.
Examples of threatened pollinators:
- all pollinator lemur species e.g. red-ruffed lemurs Varecia rubra
- beetles: valley elderberry longhorn beetle Desmocerus californicus dimorphus
- moths: Brighton wainscot moth Oria musculosa
Pollinators being endangered, in turn, affects:
- World-wide crop production: e.g. strawberry
- Their spatial and temporal distribution
- Animals using them as a food source: e.g. European bee-eater M. apiaster
- The flowering times and reproduction of pollinator-dependent plants: e.g. the Penstemon haydenii flower, protected under the U.S. Endangered Species Act.
Climate Change and Pollinators
From a current anthropogenic perspective, important knowledge of pollinators’ vital ecosystem services enables people worldwide to, at least:
- Hit food production targets
- Avoid rises in costs associated with practising agriculture in fragile or disrupted ecosystems
- Prevent trophic extinctions and species loss related to dwindling pollinator diversity
An anthropogenic perspective refers to the human perspective, something that works or looks in a certain way primarily to humans.
Some of the biggest pollinator population shifts attributed to climate change have been reported in butterflies. In the UK, 36 species of butterflies out of 57 monitored have been characterized by a constant population decline since 19765. The number of pollinating insects has declined by 30% since 19806.
Attracting Pollinators and Beneficial Insects
Through the cascade effect, changing insect pollinator numbers also determine changes in natural predators specialized in hunting them, specifically bird, spider and bat species. Sudden pollinator collapse can also generate unexpected changes in the trophic structure. It is important to ensure that the right species can be allowed to survive in our current climate.
The trophic structure of an ecosystem is the feeding relationships between trophic levels within that ecosystem. Trophic means "pertaining to nutrition" and trophos means "nourishment". In a food web, trophic levels can be thought of as steps in an energy transfer pathway. When one organism consumes another, some of the sun's energy that was used by the producer to create organic matter is passed on to the consumer and then to the next consumer, and so on. A cascade or ripple effect is when changes occur, such as a decline in the population of top predators (e.g. a secondary consumer) which usually lead to an increase in the population of their prey (e.g. a primary consumer).
Pollinators are usually attracted by:
- Trees: common whitebeam Sorbus aria, common alder Alnus glutinosa, oak gen. Quercus, etc.
- Flowers: Crocus, Snowdrop, Foxglove, etc.
Pollinators also feed off honeydew - a sweet liquid excreted by insects like aphids.
Lepidoptera
Insects from the order Lepidoptera are the most prevalent agricultural pests and consume all species of plant, with the ability to thrive in agricultural environments because of their short life spans and dispersive natures.
Despite directly having a negative impact on farmlands, Lepidoptera indirectly influences the prosperity and output of agricultural ecosystems. Neighbouring species of Lepidoptera will maintain healthy agricultural ecosystems through their role as pollinators (mostly done by moths) and their importance in surrounding food webs. Many Lepidoptera, especially butterflies, act as valuable bioindicators. The presence of butterflies can signify healthy ecosystems and various environmental factors. Certain Lepidoptera species have proved to be useful as biological control agents for invasive weeds.
Moths
Most of the global moth pollination can be attributed to the families Noctuidae and Sphingidae. In agricultural ecosystems, it is not the farmed crops which are reliant on pollination from moths, but the surrounding plants in hedgerows, field margins and other habitats. Therefore, moth pollination offers an ecosystem service.
They do not only sustain biodiversity by pollinating wild crops in farmland areas, but also by being an essential part of local food webs, upholding cyclical predator-prey relationships. Moths are predated by bats, so a sufficient moth population is required for bat survival.
Butterflies
The presence of butterflies in agricultural ecosystems is a reliable bioindicator for many factors such as biodiversity and environmental stability, as well as recent anthropogenic habitat fragmentation and urbanization.
Additionally, because of butterflies’ high sensitivity to variations in environmental factors like sunlight, humidity, temperature and even air pollution, we can analyse their migration and distribution to quantify the impact of habitat disturbance from agricultural methods.
Hymenoptera
Hymenoptera is one of the larger orders of insects. Hymenoptera species also act as excellent bioindicators of agricultural land ecological health, much like Lepidoptera. More on that below:
Honeybees
The western honey bee, Apis mellifera, is presently considered the most economically valuable bee pollinator species globally. It has also sported the most significant evidence of specific pollinator decline.
Ten species of more or less managed melliferous honeybees have been reported in 104 different countries. This includes:
- A. m. carnica
- A. m. ligustica
Honeybees display preferences for a wide range of nectar and pollen sources, from dandelions to pine tree sap and honeydew.
Different species and subspecies within the bee and other pollinator families may specialize in foraging from specific plants and even develop morphological adaptations and traits.
Morphological adaptations: structural changes of the body to increase survival chances.
Wild bees
Bumblebees of the species Bombus terrestris, a wild member of the bee family, are a heavily economically valuable bee pollinator species. Part of the reason is that many species can usually survive harsher conditions than honeybees, such as low light, high elevations and cold temperatures. This makes them excellent pollinators for such areas. They also employ buzz pollination.
Buzz pollination: buzzing technique specific to wild bees, which helps release firmly attached pollen from the flower anthers.
Others
In the UK, birds and bats also provide pollinating services, but insect pollination is the most important.
After honeybees and wild bees, butterflies, flies, as well as wasps, birds, beetles, moths, ants, bats and other vertebrates account for the remaining percentages of flower pollination.
Bees and Other Pollinators Protection
Conservation of wild population is as important as honeybees’, as the latter are not efficient pollinators of all flowering species.
Laws that protect pollinators include:
- The Environment Act 2021 - UK
- Neonicotinoid ban 2013 - EU
- The Habitats Directive 1992
Since honeybees are considered a ‘domesticated’ species, introduced in most places where humans exist and the weather allows for honey production, they can sometimes become a problem. As such, it is not indicated to over-saturate environments with honeybees. Imported or introduced bees and their pathogens may also raise ecological concerns.
Conservation of pollinators sometimes includes:
- Avoiding the practice of bee-rearing (apiculture) in protected areas.
Pollinators' value is not derived solely from direct ecosystem services. As with many other elements of nature, pollinators have been integrated into the human culture and at times sacralized. They are important symbols across several cultures.
Cultural value protection
Pollinator symbols such as bees and butterflies can be found in painting, architecture, pottery, musical compositions, literature, spirituality, oral traditions and legends. Therefore, ensuring their survival means keeping alive an integral part of our cultural heritage, no matter the fact that such benefits might be harder to quantify numerically.
In a low-intensity farm from Virginia, USA, enhancing wild bee pollination was estimated to improve blueberry crop revenue by up to 36%, or the equivalent of £110,000/year7.
Pollinators - Key takeaways
- Both wild and domestic pollinators are essential to ecosystem functioning and the human economy.
- Pollinators come in surprising forms: lizards and mammals also help spread pollen in exchange for nectar!
- The most economically valuable pollinator species is the honeybee, seconded by the bumblebee.
- The loss, degradation and fragmentation of habitats is the leading cause of pollinator decline across most continents.
- Pollination is a mutualistic interaction between the plant and its vector, such as the bee.
References
- Camilo Mora et al., How Many Species Are There on Earth and in the Ocean?, 2011
- WWF, Living Planet Index, 2018.
- University of Leeds, Consequences of pollinator declines, 2022.
- IPBES, The assessment report on pollinators, pollination and food production, IPBES, 2016.
- UKBMS, Official Statistics, 2019.
- JNCC, Status of pollinating insects, 2021.
- Nicholson, C. Charles & Ricketts, T. H., Wild pollinators improve production, uniformity, and timing of blueberry crops, 2019.
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