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Pollinator decline – an ecological calamity in the making?

Posted on 6. August, 2018.

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Pollination is an ecosystem function that is fundamental to plant reproduction, agricultural production and the perpetuation of terrestrial biodiversity. An estimated 87.5% (approximately 308,000 species) of the world’s flowering plants are pollinated by insects and other animals, and more than three quarters of the major types of global food crops derive at least some benefit from animal pollination. 

The process is estimated to advantage one third of the volume of food produced globally. The act of pollination1,2 involves the transfer of pollen from the anther (male) of a flower to the stigma (female) of a flower, which allows fertilisation to occur of a flower’s ovules (female) by the gamates (male) from the pollen grains, and leads to the production of fruit and seed. Self-pollination refers to the transfer of pollen either within a single flower (autogamy), or between different flowers on the same plant (geitonogamy); cross-pollination is when pollen is transferred between flowers of different plants of the same species (xenogamy). Some plants have mixed pollination systems. It is probable that plants adapted for self-pollination evolved during times when the presence of pollinators (mainly insects) was intermittent, while cross-pollinating plants have a number of barriermechanisms to deter self-pollination, e.g. the physical features of the reproductive organs may be such that in situ pollen transfer is improbable, or the carpels and stamens may not mature at the same time. A striking example of a strategy to avoid self-fertilisation is to have male and female flowers on different individual plants. Although pollination can occur abiotically (mainly where the pollen grains are carried by wind), more frequently, the process is biotic, where organisms known as pollinators are necessary, which carry or move the pollen from the anther of one flower to the stigma of another. 

According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES): ‘The complexities of plant–pollinator interactions, even in modern agricultural ecosystems, are poorly understood because usually more than one pollinator species is involved and they vary between seasons and locality (established but incomplete). There are over 20,000 species of bees worldwide; they are the dominant pollinators in most ecosystems and nearly all bees are pollinators (established but incomplete). Flies are the second most frequent visitors to the majority of flowers with approximately 120,000 species. In  addition, some butterflies, moths, wasps, beetles, thrips, birds and bats and vertebrates also pollinate plants, including crops (established but incomplete).’ Although the most common pollinators are insects, this is not exclusively so, since around 1,500 species of mammals and birds have been reported to transfer pollen between flowers. The  total number of different pollinator species may number as many as 200,000, which serve to fertilise around 308,000 species of flowering plants.

Read the full article in Science Progress.

DOI: https://doi.org/10.3184/003685018X15202512854527

Author: Christopher J. Rhodes
Director, Fresh-lands Environmental Actions, UK
E-mail: cjrhodes@fresh-lands.com

Keywords:  honey bee, bumble bee, pollinator, pollination, pollinator decline, neonicotinoids, pesticides, soil, biodiversity, climate change, colony collapse disorder, CCD, mad honey, ecological Armageddon, global food production, flying pollinators, insects, flying insects, habitat loss, fragmentation, degradation, vermicompost, plant–pollinator network

Image: A European Honey Bee (Apis mellifera) extracts nectar from an Aster flower using its proboscis. Tiny hairs covering the bee’s body maintain a slight electrostatic charge, causing pollen from the flower’s anthers to stick to the bee, allowing for pollination when it moves on to another flower. Credit: John Severns, https://upload.wikimedia.org/
wikipedia/commons/1/1d/European_honey_bee_extracts_nectar.jpg.