Pollination is the transfer of pollen grains from male to female parts of plants, thereby enabling fertilization and, subsequently, the development of seeds. Pollinating agents include birds, bats, wind, insects, and other animals. When pollination occurs within a species, then the offspring is of similar species to the parents, but when it occurs between different species, then a hybrid species is produced. In flowering plants ( angiosperms), pollen on the stigma grows and develop pollen tubes that reach the ovary. Two male gametes travel to the carpel where female gametes are contained. One fertilizes the ovule to create the embryo while the other fertilizes the polar bodies to give rise to endosperm tissues. When both are successful, then double fertilization has occurred, and the process results in the development of a seed made of the embryo and nutritious tissue. In gymnosperms such as conifers, gnetophytes, cycads, and ginkgoes, the ovule is not within the carpel but is exposed to allow fertilization without penetration of the carpel tissue. Understanding pollination brings together several disciplines, such as horticulture, botany, ecology, and entomology. Pollination is vital in agriculture and horticulture since fertilization results in fruiting.
Many plants require external agents such as wind, animals, birds, insects, and water to aid in the pollination process. However, the presence of these agents does not necessarily assure that pollination will take place. Factors such as diseases, extreme temperatures, and drought may prevent fertilization from occurring. Flowering plants have coexisted with their pollinators for millions of years, creating a floral diversity. The variations in form, scent, and color we see in flowers are due to the association between flowers and pollinators. Animals account for 80% of pollination, while wind and water account for the remaining 20%.
Plants that depend on the wind forecast pollination flower in early spring before the leaves emerge. This allows pollen from anthers to be dispersed and received by the stigmas. In plants such as cottonwood, birch, and oaks, male flowers align in upright inflorescence flowers and grouped to produce a lot of pollen. Wind-pollinated pollens are smooth, small, and lightweight.
Plants that are pollinated by water are mostly aquatic. They release the pollen or seeds into the water, which are then carried downstream and received by other plants. They are buoyant and can stay afloat for long. Coconuts can float on water and grow on the banks of rivers.
Plants have developed intricate methods for attracting animals and using them as pollinators. These include scent, food, visual cues, entrapment, and mimicry. Likewise, animals have developed features and behaviors to assist in pollination, such as fur. Animal-pollinated pollen is sticky and attaches to animals.
Mechanisms Of Pollination
Pollination can either be cross or self. Cross-pollination occurs when pollen from is transmitted from the stamen to the stigma of different plants of the same species. Cross-pollinating plants develop mechanisms to deter self-pollination, such as growing reproductive organs at different ends of the flower or maturing the carpel and stamens at different times. Self-pollination plants transfer pollen from the stamen to the stigma of the same flower or another flower on the same plant. Self-pollination evolved due to the lack of a reliable pollinator to transfer pollen between flowers and is common in annual or introduced plants. These plants develop reproductive organs of the same length and close together. About 48% of plant species cannot self pollinate, while 42% have a mixed mating system. In horticulture, a good pollenizer provides plentiful and compatible pollen and blooms at the same period as the plants to be pollinated.
Honeybees As Pollinators
Honeybees are perhaps the most useful pollinators. They travel from one plant to the other in search of nectar and pollen and spread pollen grains in the process. Bees gain energy from nectar and protein from pollen. When the insects are reared in hives, they gather pollen to meet the requirements of the brood. A bee that is actively gathering pollen is a better pollinator than one that is gathering nectar. Farmers relying on bees for pollination ought to synchronize the blooming period of their crops with the "building" state of the insects to maximize pollination. About 80% of cross-pollinations are performed honey bees. This includes fruits, vegetables, nuts, spices, crops, forage, and herbs. European honey bees were introduced to North America in the 1600s by colonists. Many escaped into the wild and displaced more than 4,000 native species. The feral bees played a vital role in the development of the agricultural industry throughout the 20th century. Between 1990 and 1991, varroa and tracheal mites were accidentally introduced to North America from Asia, resulting in a severe decline of the honey bees within a short period. Fewer pollinators affect agricultural production. Every year millions of honey bees are transported from there are winter residences to agricultural farms to aid in the pollination of crops in bloom. During the winter season between 2006 and 2009, a large number of bee colonies died mysteriously in what was termed as Colony Collapse Disorder (CCD). Though the death of bees is not likely to result in a widespread shortage of food, it leads to an increase in the cost of production.
Impacts On The Environment
Pollinator decline causes disturbance in plant regeneration by preventing the development of seeds, pollination, and seed dispersal. Early plant regeneration depends on animal-plant interactions, and disturbances interrupt biodiversity in the ecosystem. More than 87% of angiosperms, 75% of tropical trees, and 30% of plant species in temperate environments depend on seed dispersal and pollination. Human activities such as habitat destruction, use of pesticides, and logging contribute to the decline of pollinators. Research has also found that a lack of pollinators leads to a decrease in genetic variations within a species.
Pollination By Birds
Bird pollination (ornithophily) is similar to bee pollination. The hummingbirds of South and North America are the most renowned nectar-eating birds. Others include sunbirds flowerpeckers, bananaquits, honeyeaters, and honeycreepers. Plants pollinated by birds are characterized by bright petals and no odor since birds have a poor sense of smell. These plants are typically sturdy to allow for perching. The anthers are long and thin so than the pollen can fall on the head or neck of birds as they reach for nectar.
Pollination management seeks to enhance and protect pollinators that aid in agriculture. It is mostly applied in monoculture situations, primarily fruit orchards. The almond orchards of California contain about one million hives during spring. The blueberry farms of Maine have about 50,000, while the Apple farmlands of New York host more than 30,000. Bees are also introduced to plantations of squash, cucumbers, strawberries, melons, and several other crops. Honey bees are the most common pollinators, but others include the alfalfa leafcutter bees and bumblebees. The economic and ecological importance of pollination in agricultural lands cannot be underestimated. The proximity of agricultural lands close to wild grasslands or forests increases the production of crops by over 20%.