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Pollination

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Pollination is the process by which pollen grains from one flower reach the stigma of a flower, so that fertilisation can take place.[1] Plants cannot move, so they rely on wind, water or, more often, animals to carry their pollen.[2] About 90 per cent of all flowering plants are pollinated by animals.[3]

Cross-pollination and self-pollination

Cross-pollination happens when pollen is carried to a flower on a separate, genetically different plant. Self-pollination happens when pollen lands in the same flower that produced it, or on another flower on the same plant.[1][1] Self-pollination can be a useful back-up for plants when cross-pollination fails.[4]

Pollination by animals

Pollination by animals is a mutualism, a relationship that benefits both partners. The plant has its pollen moved, and the animal gets food.[5][6] Many plants offer nectar to visiting insects, and most animal-pollinated flowers reward their visitors with nectar, pollen or both.[6][7] As the insect feeds, the flower's parts are arranged so that pollen is picked up and then rubbed onto the stigma of the next flower it visits.[8]

At least 130,000 species of animal regularly visit flowers and may pollinate them.[9] According to one ecology textbook, "The pollinators par excellence are, without doubt, the insects."[7] Bees are especially important, because they feed on both nectar and pollen. There may be more than 40,000 species of bee.[10][11] Other pollinators include flies such as hoverflies, butterflies and moths, hummingbirds, bats, small rodents and marsupials.[12][13][7]

Flowers and their pollinators

Different flowers suit different pollinators. Some flowers are open, flat cups that many kinds of insect can visit. Bee flowers are often tubular, and many orchids are bee flowers.[14] Flowers with exposed nectar attract many kinds of visitor, while flowers with nectar hidden in long tubes, such as those of Aquilegia, rely on specialist pollinators.[7] Some insects, called nectar robbers, take the reward without pollinating the flower, for example by chewing a hole at the base of the flower.[15]

A few plants have very close partnerships with one pollinator. Each of the roughly 750 species of fig tree, for example, is pollinated by its own species of wasp. However, such tight pairings are rare.[16] Tomato flowers need buzz pollination. Bumblebees can buzz at the right frequency to pollinate them, but honeybees cannot.[17][18]

Pollination by wind and water

Some plants are pollinated without animals, by pollen carried in air or water. Wind pollination is much the commoner of the two.[19][19] Wind is much less accurate than a flying insect at hitting the stigma, so wind-pollinated plants produce far more pollen than insect-pollinated ones.[14][7] Wind-pollinated plants tend to grow close together in large groups of the same species, and wind pollination is rare in tropical rainforests.[14][20] Cereal crops such as wheat, rice, maize and barley are wind-pollinated.[21]

Importance

About one-third of the food people eat depends directly on animals pollinating crops.[3] At least 800 cultivated plants rely on animal pollinators, and about 73 per cent of these are pollinated by bees.[18] Pollinators also affect which plants grow in a community and where, and disruption of pollination is now seen as a major issue.[22][22]

Evolution

Insects and flowering plants have evolved together. One textbook sums this up: "The reason why angiosperms are so diverse today is because there are so many insects, while there are so many insects because the angiosperms are so diverse!"[17] Animal pollination probably arose at least twice, in different groups of plants.[23] Rainforests contain many plants with specialised ways of being pollinated, which need an equally varied set of insects.[24]

See also

References

  1. ↑ 1.0 1.1 1.2 Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 55. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  2. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. pp. 3–5. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  3. ↑ 3.0 3.1 Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 4. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  4. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 56. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  5. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 3. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  6. ↑ 6.0 6.1 Begon, Michael; Howarth, Robert W.; Townsend, Colin R. (2014). Essentials of Ecology (4th ed.). Hoboken, NJ: Wiley. p. 232. ISBN 978-0-470-90913-3. {{cite book}}: |access-date= requires |url= (help)
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Begon, Michael; Howarth, Robert W.; Townsend, Colin R. (2014). Essentials of Ecology (4th ed.). Hoboken, NJ: Wiley. p. 235. ISBN 978-0-470-90913-3. {{cite book}}: |access-date= requires |url= (help)
  8. ↑ Chapman, J. L.; Reiss, M. J. (1999). Ecology: Principles and Applications (2nd ed.). Cambridge: Cambridge University Press. p. 258. ISBN 978-0-521-58802-7. {{cite book}}: |access-date= requires |url= (help)
  9. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 5. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  10. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 378. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  11. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 379. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  12. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 304. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  13. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 322. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  14. ↑ 14.0 14.1 14.2 Chapman, J. L.; Reiss, M. J. (1999). Ecology: Principles and Applications (2nd ed.). Cambridge: Cambridge University Press. p. 259. ISBN 978-0-521-58802-7. {{cite book}}: |access-date= requires |url= (help)
  15. ↑ Chapman, J. L.; Reiss, M. J. (1999). Ecology: Principles and Applications (2nd ed.). Cambridge: Cambridge University Press. pp. 259–260. ISBN 978-0-521-58802-7. {{cite book}}: |access-date= requires |url= (help)
  16. ↑ Chapman, J. L.; Reiss, M. J. (1999). Ecology: Principles and Applications (2nd ed.). Cambridge: Cambridge University Press. p. 260. ISBN 978-0-521-58802-7. {{cite book}}: |access-date= requires |url= (help)
  17. ↑ 17.0 17.1 Chapman, J. L.; Reiss, M. J. (1999). Ecology: Principles and Applications (2nd ed.). Cambridge: Cambridge University Press. p. 261. ISBN 978-0-521-58802-7. {{cite book}}: |access-date= requires |url= (help)
  18. ↑ 18.0 18.1 Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 606. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  19. ↑ 19.0 19.1 Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 418. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  20. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. pp. 418–419. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  21. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 605. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  22. ↑ 22.0 22.1 Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 620. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  23. ↑ Willmer, Pat (2011). Pollination and Floral Ecology. Princeton, NJ: Princeton University Press. p. 89. ISBN 978-0-691-12861-0. {{cite book}}: |access-date= requires |url= (help)
  24. ↑ Begon, Michael; Howarth, Robert W.; Townsend, Colin R. (2014). Essentials of Ecology (4th ed.). Hoboken, NJ: Wiley. p. 103. ISBN 978-0-470-90913-3. {{cite book}}: |access-date= requires |url= (help)
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