POLLINATORS: TYPES AND THEIR CHARACTERISTICS, IMPORTANCE - BIOLOGY - 2024

The pollinators are responsible biotic agents of sexual reproduction of plants, which need to transport and exchange of pollen between their male and female flower structures. Most angiosperm plants depend on vertebrate or invertebrate animals for pollination.

Plants can be pollinated by biotic or abiotic agents. Abiotic agents do not establish relationships with the plant and can be wind or water. In biotic pollination, on the other hand, a second organism participates, the pollinator, which regularly visits the flower and establishes a flower-pollinator interaction.

Bee visiting flower (Source: pixabay.com/)

The relationship between the flower and its pollinator is mutualistic, since there is generally some type of attractant (smell and color) or direct reward (nectar and pollen) for the pollinator, while the flower uses the animal to transport its pollen and reproduce..

Most pollinators are "generalist" species that visit a wide variety of different plant species. However, some have exclusive preferences for specific plant species and these are known as "specialists." The plants visited by these specialists have complex and specific adaptations for interaction with their pollinator.

The different types of pollinators cause a divergence in floral traits that include morphology, smell and color, size, reward, phenology, among others. Each trait is effectively selected for the reward need of particular pollinator groups.

Rudolf Jakob Camerarius was the first to observe pollination in bisexual flowers in 1694. However, it was Dobbs and Müller in 1750 and 1751, respectively, who detailed cross-pollination and the importance of animals such as insects in the transport of pollen., coining the term "pollinators".

Types and their characteristics

Currently four types of biotic pollinators are known: insects, birds, mammals and a species of reptile.

-Insects

For insects, flowers are structures capable of satisfying a large part of their nutritional needs, obtaining much of the energy they need from carbohydrates in nectar or pollen.

Beetles

Beetles are the least specialized group of insects in pollination and typically establish relationships with flowers from tropical areas. These insects can only extract nectar and pollen from flat, open flowers, since they do not have specialized mouth structures.

Flower-eating beetles have bodies covered with hairs and scales that are very useful for the adherence of pollen grains. Plants of the genus Magnolia are visited by many beetles.

Flies

Flies or diptera are more specialized pollinators than beetles: thanks to their small size they reach the interior of the flowers of most species and since they have specialized jaws, they can easily feed on nectar.

These insects are responsible for the pollination of plant species that flourish in adverse conditions.

The world's largest flowering plant, Amorphophallus titanum, known as the "corpse flower," is typically pollinated by flies that are attracted to the foul odor that emanates from the flower.

Hymenoptera

Bee on Sunflower flower (Source: pixabay.com/)

Hymenopterans are among the most evolved, specialized and economically important pollinators. This group includes wasps, ants, and bees.

Wasps

Wasps have the most varied life cycles and have pollination mechanisms very similar to those of flies. They do not have great oral specializations, therefore they can only access the most open flowers.

Wasps, like flies, look for nectar and pollen as part of their diet, but they are not as specialized as bees and recognize only one color and smell in flowers. These insects present complex societies: they bring food to their young, which can lick their jaws after ingesting nectar.

In the tropics, warns have been evidenced pollinating orchid species such as Celosía argentea, however, no plant species have been found to date that have only been pollinated by wasps.

Ants

Ant visiting a flower (Source: pixabay.com/)

Ants are mainly interested in the sugar in flowers, either in the flower per se or in the nectaries. Despite this, they are so small that they can enter and leave the flowers without even touching the anthers or the stigma, and their hard, waxed bodies do not seem to adhere considerable amounts of pollen to speak of pollinating agents.

Ants are thought of as nectar stealers rather than pollinators, so plants have developed innumerable mechanisms to prevent their access to the flower.

Ants are mainly associated with the pollination of plants in desert areas, an example is the visit of the flowers of succulent Polycarpon to lick their nectar, with which they also carry pollen.

Bees

Bees are the group of insects best adapted for pollination. Such animals have a wide range of behaviors, from the simplest (such as parasites or solitary bees) to the most complex with highly structured and hierarchical societies.

The life of bees is oriented towards their function as pollinators, proof of this are their functional and morphological characteristics to find and collect nectar and pollen. They have a great sense of smell, which helps them distinguish between the species of flowers they frequent.

They can create scent marks on a flower to point the way from the hive to other bees; these marks can vary between 1 and 20 meters depending on the species.

In addition, they have “communication” strategies similar to a zigzag dance, which they use to indicate to other bees in the hive the location of a flower, its nutritional content, direction and distance.

Bees are sensitive to seasonality, since most of them use the sun to maintain their orientation.

Lepidoptera

Monarch Butterfly visiting a flower (Source: pixabay.com/)

Lepidoptera encompass both moths and butterflies, which are separated more by a difference in behavior than in morphology. Butterflies are diurnal in habit while moths are twilight or nocturnal habit.

The most basal species have jaws for chewing pollen, while the more evolved ones have exclusively a long and thin suction tube. Most butterflies feed on pollen extracted from flowers using their suction tube-shaped mouth or proboscis apparatus.

The olfactory attraction plays an important role in the flowers that pollinate the moths, they flood the tropical night air with overwhelming fragrances that can be recognized by the moths.

The species visited by these Lepidoptera generally have their buttons closed during the day and open at night to allow the entry of the pollinator.

-Vertebrates

Vertebrate pollinators are of great importance in the African and American continent. They are animals much larger than insects, generally warm-blooded and with different nutritional needs.

These pollinators need large amounts of substances such as protein, carbohydrates, and high-calorie fats, so the nutritional requirement is usually covered by another food source.

There are few cases of birds and bats that feed on pollen to fully cover their protein requirement.

Orioles, hummingbirds and even tropical woodpeckers have the tip of the tongue with highly specialized fringes in the collection of nectar and pollen, so it is conjectured that perhaps these specialized structures and flower structures could have evolved together.

Hummingbirds

Hummingbird (Source: pixabay.com/)

Hummingbirds are the main birds with a pollinator character. They have small bodies and extremely active metabolisms, which is why they are able to make numerous tours in vast flower fields in order to satisfy their high nutritional requirements.

Hummingbirds are territorial birds capable of fiercely defending flowers with high nectar content, especially during the breeding season.

The flowers preferred by hummingbirds are those that hang, exposing their organs to free space and that have large reservoirs of nectar inside the flower. An example of these flowers are those of the genus Heliconia.

Bats

Image via naturalista.mx

Bats have, like birds, a rough surface with a great capacity to transport pollen. These animals move quickly and travel great distances when they come out to feed. Pollen has been found in bat feces from plants more than 30 km away.

Bats specialized in consuming pollen or nectar have huge eyes, a more important sense of smell than usual (septate) and a less developed sonar apparatus.

Some have the ability to float or maintain flight while consuming pollen from flowers, a characteristic similar to hummingbirds.

Most of the bats in the American continent, like those of the genus Leptonycteris, cover all their protein requirement from pollen, this is sufficient both in quantity and in caloric quality.

Importance

Plant-pollinator relationships are one of the most important kinds of plant-animal interaction in nature. Plants could not produce seeds and reproduce were it not for pollinators, and without plants pollinators could not feed on nectar, so both animal and plant populations would disappear without this interaction.

Biotic pollination is a key element of biodiversity in most groups of plants and even animals, and is an important ecosystem service for man, since a large part of cereal consumption depends on the biotic pollination of cultivars.

Biotic pollination is essential for most wild plants, which also provide food and sustenance for many other organisms on which man depends.

A decline in pollinator populations would automatically imply a drastic decline in plant species whose reproduction depends on them.

Apis mellifera bees are one of the most economically valuable pollinators for cereal monocultures worldwide, also important for coffee, fruit and other seed crops.

References

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