When pollen is delivered to stigmas by animal vectors the term Biotic Pollination is used. There are many species of animals that pollinate plants, and many adaptations of flowers to enhance pollination by various animals.

(1) Floral Function

The parts of flowers that function to enhance animal pollination can be thought of as performing one of two functions; signal or reward. Realize that animals that pollinate are not doing so for the plant - they are reaping some product (usually food) from the flower. Therefore, some signal is required to notify the animal that food is present in the flower. Then, there must be food when the animal visits the flower. If these two conditions are et, there is a good chance that the animal will pick up pollen in one flower and transport it to another flower. If this occurs between flowers of the same species, pollination will occur.

(a) Signals

The types of signals displayed by flowers to animals varies quite a bit. they may be visual (color, texture, pattern), olfactory (scent), or in some cases even motion. It is not uncommon to have more than one signal operating in one flower. Examine the examples on display and list the various kinds of signals that might attract pollinators.

(b) Rewards

Rewards offered to pollinating animals by flowers almost always involve a food source. the most common food source is generally called nectar, and is a complex of sugars, amino acids, and aromatic compounds. Note that nectar is usually NOT what gives flowers their scent (differentiate signal and reward). In some species waxes are harvested by pollinators, and sometimes the pollen itself may be used for a food supply.

(2) Animal Syndromes

It is important to realize that most species of plant are not pollinated by only one kind of pollinator. There are cases of species-specific pollination in some species (e.g., some orchids), but these are the exception. Despite the general nature of pollination in many species of plant, you can make some generalized statements about different animal groups that pollinate flowers. Click on the links below to see representatives of flowers that you might expect to be pollinated by the respective animals.

(a) Insects

Insects are the most common type of animal pollinator; however, just as there are many types of insects, we can expect that there are many insect-pollination syndromes.

1. Coleoptera (beetles) - Beetle pollination is generally regarded as among the least-specialized of animal pollination. Beetles seem to favor large, strong-scented flowers, and it is common for beetles to chew the entire flower as a food source. Pollination by beetles, therefore, is regarded as a bit sloppy, but efficient enough to get the job done. Examples:

2. Lepidoptera (butterflies and moths) - Butterflies and moths constitute a diverse group, but many species of pollinating butterflies are diurnal (fly, hence pollinate by day), while many species of pollinating moths are vespertine (evening flying). Diurnal pollinators rely on visual signals, at least in part, while vespertine pollinators must rely more heavily on olfactory signals. Examples: Asclepias; Grindelia; Linanthus dichotomus (night bloomer)

Some evening-pollinated species of plants even produce differing amounts of odor at different times of the day, with the strongest scent being produced just after dusk. The well-known “night blooming jasmine” is a good example of this pattern.

Lepidopterans also have long mouth parts that can probe deeply into structures containing food resources. Consequently, Lepidopteran-pollinated plants commonly have tubular corollas with nectar produced at the bottom of the tube.

3. Diptera (flies and mosquitoes) - Many species of flies are important pollinators of flowers (there are many different kinds of flies - not just house flies and horse flies). Indeed, some species of flies, such as hoverflies, are capable of helicopter-like movement that allows them to hover over flowers and probe into tubular corollas with their elongate mouth parts. Example: Leptosiphon

Some flies are attracted to carrion, and curiously there are flowers that are carrion-colored, -textured, and even -scented. These flowers probably have no trouble attracting certain species of flies. Examples: Heurnia;

4. Hymenoptera (bees and wasps) - Many Hymenopterans are known for their elaborate vision capability, and this is reflected in the often elaborate visual signals that have evolved in species that are pollinated primarily by bees and wasps. Example: Koehleria.

In particular, some bees are noted or their ability to see into the ultraviolet range of visible wavelengths. Hence, some corollas are “colored” with pigments that reflect ultraviolet “colors”. These compounds are not visible to normal human vision, but can be visualize with the aid of an ultraviolet lamp

(b) Birds

Birds represent another group of animals that have evolved in parallel with flowering plants along lines of pollination syndromes. There are some major differences in the basic biology of birds versus insects that are reflected in the features of flowers pollinated by these animals. Foremost, most birds do not have the capability of olfaction, and this is true for pollinating birds. Thus, olfactory signals do not work on birds. On the other hand, birds are known for their good vision, so you can expect the visual signals to be well-developed in bird pollinated flowers.

Another point about pollinating birds is that, while they are not very large compared to most other bird species, they are generally much larger that insect pollinators. Therefore, expect bird pollinated flowers to be adapted to being visited by larger animals. Larger corollas, stronger corollas, and larger volumes of nectar per flower are features common in bird-pollinated species.

Examples: Fouquieria; Polemonium;

(c) Mammals

Mammals are not generally known for their pollinating activities, but one group stands out as an exception - the nectar feeding bats. When you think about it, bats, while much larger than insects and pollinating birds, have many of the same features that would make them excellent pollinators. The basic differences between bats and birds as pollinators are 1) bats are larger, and therefore “require” larger flowers with even more nectar, and 2) pollinating bats are active at night, so bat pollinated flowers probably rely more heavily on non-visual signals. Indeed, bats have fine olfactory capability. Example: Cobaea

There are also examples of marsupial mammals serving as pollinators, as shown by the “honey possum” of Australia, and there have even been reports of pollination being effected by rodent species.

(3) Nectar Thieves

Nectar-producing flowers are obviously a good source of nutrition for many animal species; however, not every visit by an animal to a flower results in pollination. There are species of animals that have adapted to a life style of “robbing” corollas of nectar without ever coming into contact with either anthers or stigmas. Examine the material in lab for evidence of nectar thievery.