In zoology, a nectarivore is an animal which derives its energy and nutrient requirements from a diet consisting mainly or exclusively of the sugar-rich nectar produced by flowering plants.
Nectar as a food source presents a number of benefits as well as challenges. It is essentially a solution of (as much as 80%) the simple sugars sucrose, glucose and fructose, which are easily ingested and digested, representing a rich and efficient source of nutrition. This solution is often diluted either by the plant that produces it or by rain falling on a flower and many nectarivores possess adaptations to effectively rid themselves of any excess water ingested this way.
However, nectar is an incomplete source of nutrition. While it does contain proteins and amino acids, [1] these are found in low quantities, and it is severely deficient in minerals and vitamins. [2] Very few organisms consume nectar exclusively over their whole life cycle, either supplementing it with other sources, particularly insects (thus overlapping with insectivores) or only consuming it exclusively for a set period. [3] Many species are nectar robbers or nectar thieves, performing no pollination while still consuming nectar. Many species are both nectar robbers and pollinators, depending on the plant species they encounter.
Nectar is produced by flowering plants to attract pollinators to visit the flowers and transport pollen between them. Flowers often have specialized structures that make the nectar accessible only for animals possessing appropriate morphological structures, and there are numerous examples of coevolution between nectarivores and the flowers they pollinate. For example, hummingbirds and hawkmoths have long narrow beaks that can reach nectar at the bottom of long tubular flowers. [4] [5]
The majority of nectar feeders are insects or birds, but instances can also be found in other animal groups.
Nectarivory is extremely common in insects. Key families with large proportions of nectarivores include the Coleoptera, Lepidoptera, Diptera, Hymenoptera and Hemiptera. Some, but not all, are also pollinators: others engage in nectar robbing by avoiding the reproductive organs of plants altogether, particularly those with deep corollas, by piercing into the base of the flower to reach the nectary directly, such as carpenter bees and secondarily honey bees (who consume nectar from holes made by others), [6] as well as ants, who frequently consume nectar and pollen where available despite actively inhibiting germination of pollen at the flowers they visit to the detriment of the plant. [7]
Nectar-feeding insects gain enough water from nectar to rarely need to drink, though adult butterflies and moths may engage in puddling in order to obtain dissolved substances not abundant in nectar, particularly salts and amino acids. [8] Some flying nectarivores, particularly larger bees, do not lose enough water by evaporation while on the wing to offset their high intake due to nectar-feeding, as well as water produced metabolically while flying. They must excrete while on the wing to prevent water loading, and may wait at the nest entrance to evaporate off some of their water load before flying out. [9]
There is evidence that some spiders, though normally thought to be exclusively carnivorous, consume nectar indirectly by consuming nectarivorous insects, and/or directly from flowers. This behavior is thought to be more common among spiders that live among foliage. A few make nectar their primary food source, such as Bagheera kiplingi , a member of the jumping spiders, [10] [11] [12] while others such as the crab spiders, feed more rarely and opportunistically. None of the spider groups observed feeding on nectar build webs, they are all wandering species. [13]
Nectar-feeding is widespread among birds, but no species consumes nectar exclusively. Most combine it with insectivory for a mixed diet. Of particular interest are three lineages of specialized nectarivorous birds: the hummingbirds (Trochilidae), sunbirds (Nectariniidae) and honeyeaters (Meliphagidae). These groups have adapted to permit a nectar-central diet, showing higher activity of digestive enzymes which break down sugars, higher rates of absorption of sugars, and altered kidney function. To maintain flight a bird must rapidly excrete much of the water content of the nectar it consumes. A hummingbird's kidneys are capable of rapidly producing large quantities of hyposmotic urine i.e. urine containing a lower concentration of dissolved substances than the blood. [14] Some other bird groups have one or more similar specializations – for instance, the Lories, one group of Australasian parrots within the larger parrot family Psittacidae, possess similar digestive modifications. [15] These are examples of parallel evolution. The Hawaiian honeycreepers have several species adapted to feed on nectar. The Hawaiian tree Metrosideros polymorpha is heavily dependant on the pollination of the more or less nectarivorous honeycreepers. [16]
Many species of bat feed on nectar, their lifestyle similar to that of nectarivorous birds. In the Americas there is significant overlap between flowers pollinated by bats and hummingbirds – both need similarly-composed nectar to keep up energy-intensive hovering flight. In this part of the world there is particularly close association between some species of columnar cacti and bat species, who provide pollination in exchange for nectar with composition matching their nutritional needs. [17] Nectarivorous bats might be at particular risk of extinction due to their reliance on particular species of flowering plants. [18]
A single marsupial species, the honey possum, feeds on nectar and pollen exclusively. It raises fewer young which grow more slowly than other marsupials of its size, because of the time-consuming effort of nectar-drinking from many flowers to support itself. It may spend periods in deep sleep to reduce its need for food, and shows the typical nectarivore adaptations for excess water-removal. [19]
Hummingbirds are birds native to the Americas and comprise the biological family Trochilidae. With approximately 366 species and 113 genera, they occur from Alaska to Tierra del Fuego, but most species are found in Central and South America. About 28 hummingbird species are listed as endangered or critically endangered, with numerous species declining in population.
A pollinator is an animal that moves pollen from the male anther of a flower to the female stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains.
In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well as gene-culture coevolution.
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, for example beetles or butterflies; birds, and bats; water; wind; and even plants themselves. Pollinating animals travel from plant to plant carrying pollen on their bodies in a vital interaction that allows the transfer of genetic material critical to the reproductive system of most flowering plants. When self-pollination occurs within a closed flower. Pollination often occurs within a species. When pollination occurs between species, it can produce hybrid offspring in nature and in plant breeding work.
Heliconia is a genus of flowering plants in the monotypic family Heliconiaceae. Most of the 194 known species are native to the tropical Americas, but a few are indigenous to certain islands of the western Pacific and Maluku in Indonesia. Many species of Heliconia are found in the tropical forests of these regions. Most species are listed as either vulnerable or data deficient by the IUCN Red List of threatened species. Several species are widely cultivated as ornamentals, and a few are naturalized in Florida, Gambia, and Thailand.
Parallel evolution is the similar development of a trait in distinct species that are not closely related, but share a similar original trait in response to similar evolutionary pressure.
Entomophily or insect pollination is a form of pollination whereby pollen of plants, especially but not only of flowering plants, is distributed by insects. Flowers pollinated by insects typically advertise themselves with bright colours, sometimes with conspicuous patterns leading to rewards of pollen and nectar; they may also have an attractive scent which in some cases mimics insect pheromones. Insect pollinators such as bees have adaptations for their role, such as lapping or sucking mouthparts to take in nectar, and in some species also pollen baskets on their hind legs. This required the coevolution of insects and flowering plants in the development of pollination behaviour by the insects and pollination mechanisms by the flowers, benefiting both groups. Both the size and the density of a population are known to affect pollination and subsequent reproductive performance.
Zoophily, or zoogamy, is a form of pollination whereby pollen is transferred by animals, usually by invertebrates but in some cases vertebrates, particularly birds and bats, but also by other animals. Zoophilous species frequently have evolved mechanisms to make themselves more appealing to the particular type of pollinator, e.g. brightly colored or scented flowers, nectar, and appealing shapes and patterns. These plant-animal relationships are often mutually beneficial because of the food source provided in exchange for pollination.
Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide herbivore protection. Common nectar-consuming pollinators include mosquitoes, hoverflies, wasps, bees, butterflies and moths, hummingbirds, honeyeaters and bats. Nectar plays a crucial role in the foraging economics and evolution of nectar-eating species; for example, nectar foraging behavior is largely responsible for the divergent evolution of the African honey bee, A. m. scutellata and the western honey bee.
Ornithophily or bird pollination is the pollination of flowering plants by birds. This sometimes coevolutionary association is derived from insect pollination (entomophily) and is particularly well developed in some parts of the world, especially in the tropics, Southern Africa, and on some island chains. The association involves several distinctive plant adaptations forming a "pollination syndrome". The plants typically have colourful, often red, flowers with long tubular structures holding ample nectar and orientations of the stamen and stigma that ensure contact with the pollinator. Birds involved in ornithophily tend to be specialist nectarivores with brushy tongues and long bills, that are either capable of hovering flight or light enough to perch on the flower structures.
In zoology, a palynivore /pəˈlɪnəvɔːɹ/, meaning "pollen eater" is an herbivorous animal which selectively eats the nutrient-rich pollen produced by angiosperms and gymnosperms. Most true palynivores are insects or mites. The category in its strictest application includes most bees, and a few kinds of wasps, as pollen is often the only solid food consumed by all life stages in these insects. However, the category can be extended to include more diverse species. For example, palynivorous mites and thrips typically feed on the liquid content of the pollen grains without actually consuming the exine, or the solid portion of the grain. Additionally, the list is expanded greatly if one takes into consideration species where either the larval or adult stage feeds on pollen, but not both. There are other wasps which are in this category, as well as many beetles, flies, butterflies, and moths. One such example of a bee species that only consumes pollen in its larval stage is the Apis mellifera carnica. There is a vast array of insects that will feed opportunistically on pollen, as will various birds, orb-weaving spiders and other nectarivores.
Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic or biotic, such as birds, bees, flies, and so forth through a process called pollinator-mediated selection. These traits include flower shape, size, colour, odour, reward type and amount, nectar composition, timing of flowering, etc. For example, tubular red flowers with copious nectar often attract birds; foul smelling flowers attract carrion flies or beetles, etc.
The buffy hummingbird is a species of bird in the hummingbird family Trochilidae. It is the only species placed in the genus Leucippus. This bird lives in dry forest and scrubland in northern South America where it feeds on insects and the nectar, flesh, and juice of cactus fruits.
Leach's single leaf bat, also known as Greater Antillean long-tongued bat, is a species of bat in the family Phyllostomidae. It is found in the southern Bahamas and in all the Greater Antilles. It forms large colonies, with up to a few hundred thousand individuals, and feeds on a relatively wide variety of food items including pollen, nectar, fruit and insects.
The banana bat is an endangered species of bat in the family Phyllostomidae. It is also commonly known as the trumpet-nosed bat or the Colima long-nosed bat.
Nectar robbing is a foraging behavior used by some organisms that feed on floral nectar, carried out by feeding from holes bitten in flowers, rather than by entering through the flowers' natural openings. "Nectar robbers" usually feed in this way, avoiding contact with the floral reproductive structures, and therefore do not facilitate plant reproduction via pollination. Because many species that act as pollinators also act as nectar robbers, nectar robbing is considered to be a form of exploitation of plant-pollinator mutualism. While there is variation in the dependency on nectar for robber species, most species rob facultatively.
In ethology and behavioral ecology, trap-lining or traplining is a feeding strategy in which an individual visits food sources on a regular, repeatable sequence, much as trappers check their lines of traps. Traplining is usually seen in species foraging for floral resources. This involves a specified route in which the individual traverses in the same order repeatedly to check specific plants for flowers that hold nectar, even over long distances. Trap-lining has been described in several taxa, including bees, butterflies, tamarins, bats, rats, and hummingbirds and tropical fruit-eating mammals such as opossums, capuchins and kinkajous. Traplining is used to term the method in which bumblebees and hummingbirds go about collecting nectar, and consequently, pollinating each plant they visit. The term "traplining" was originally coined by Daniel Janzen, although the concept was discussed by Charles Darwin and Nikolaas Tinbergen.
Bombylius major is a parasitic bee mimic fly. B. major is the most common type of fly within the Bombylius genus. The fly derives its name from its close resemblance to bumblebees and are often mistaken for them.
Flower constancy or pollinator constancy is the tendency of individual pollinators to exclusively visit certain flower species or morphs within a species, bypassing other available flower species that could potentially contain more nectar. This type of foraging behavior puts selective pressures on floral traits in a process called pollinator-mediated selection. Flower constancy is different from other types of insect specialization such as innate preferences for certain colors or flower types, or the tendency of pollinators to visit the most rewarding and abundant flowers.
In zoology, a florivore is an animal which mainly eats products of flowers. Florivores are types of herbivores, yet within the feeding behaviour of florivory, there are a range of other more specific feeding behaviours, including, but not limited to: