Trap-lining

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Long-billed hermit (Phaethornis longirostris baroni), a species of traplining hummingbird adapted for flying long distances Phaethornis longirostris baroni.jpg
Long-billed hermit (Phaethornis longirostris baroni), a species of traplining hummingbird adapted for flying long distances
Rufous hummingbird (Selasphorus rufus), a species of territorial hummingbird, is more robust than traplining species Selasphorus rufus1.jpg
Rufous hummingbird (Selasphorus rufus), a species of territorial hummingbird, is more robust than traplining species

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. [1] Traplining is usually seen in species foraging for floral resources. [2] 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. [1] [3] 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, [4] although the concept was discussed by Charles Darwin and Nikolaas Tinbergen. [4]

Contents

Behavioral response

In the instance of hummingbirds and bumblebees, traplining is an evolutionary response to the allocation of resources between species. [5] Specifically, individual hummingbirds form their own specific routes in order to minimize competition and maximize nutrient availability. Some hummingbird species are territorial (e.g. rufous hummingbird, Selasphorus rufus,) and defend a specific territory, while others are trapliners (i.e. Long-billed hermit, Phaethornis longirostris) and constantly check different locations for food. Because of this, territorial hummingbirds will be more robust, while traplining hummingbirds have adaptations such as longer wings for more efficient flying. [6] Traplining hummingbirds will move from source to source, obtaining nectar from each. Over time, one hummingbird will be the primary visitor to a particular source. [7] In the case of bumblebees, when competitors are removed, there is an influx to the removal area and less time is spent traplining over long distances. This demonstrates the ability to behaviorally adapt based on surrounding competition. [8] In addition, bumblebees use traplining to distinguish between high nectar-producing flowers and low-nectar producing flowers by consistently recognizing and visiting those that produce higher levels. [9] Other types of bees, such as with euglossine bees (i.e. Euglossa imperialis ) use traplining to forage efficiently by flying rapidly from one precise flowering plant to the next in a set circuit, even ignoring newly blooming plants which are adjacent, but outside, of its daily route. By doing so, these euglossine bees significantly reduce the amount of time and energy spent searching for nectar each day. [10] In general, it is seen that traplining species have higher nutritional rewards than non-traplining species. [11]

Energy conservation

Traplining hummingbirds are known to be active proportionally to nectar production in flowers, decreasing throughout the day. Therefore, traplining hummingbirds can spend less time foraging, and obtain their energy intake from a few number of flowers. [12] Spending less time searching for food means less energy spent flying and searching. Traplining bumblebees prioritize their routes based on travel distance and reward quantity. [13] It is seen that the total distance of the trapline is related to the abundance of the reward (nectar) in the environment. [14]

Spatial cognition and memory

Traplining can also be an indication of the levels of spatial cognition of species that use the technique. For example, traplining in bumblebees is an indication that bumblebees have spatial reference memory, or spatial memory, that is used to create specific routes in short term foraging. [9] The ability to remember specific routes long-term cuts down foraging and flying time, consequently conserving energy. This theory has been tested, showing that bumblebees can remember the shortest route to the reward, even when the original path has been changed or obstructed. [15] Additionally, bees cut down the amount of time spent revisiting sites with little or no nutritive reward. [9] Bees with access to only short-term memory forage inefficiently. [9]

Advantages

One of the main advantages of traplining is that the route can be taught to other members of the population quickly or over a period of hours, leading all members to a reliable food source. When the group works together on finding a particular source of food they can quickly establish where it is and get the route information transferred to all the individuals in the population. This ensures that the entire community is able to quickly find and consume the nutrients that are needed.

Traplining helps foragers that are competing for resources that replenish in a decelerating way. For example, nectar in a plant is slowly replaced over time, while acorns only occur once a year. [16] Traplining can help plant diversity and evolution by keeping pollen with different genetics flowing from plant to plant. It is mostly pollinators that use traplining as a way to ensure they always know where the food sources they are looking for are. This means that organisms like bumblebees and hummingbirds can transfer pollen anywhere from the starting point of the route to the final food source along the path. Since the path is always the same, it greatly reduces the risk of self-pollination (iterogamy) because the pollinator won't return to the same flower on that particular foraging session. [16] [17]

Overall, plant species that are visited by trapliners have increased fitness and evolutionary advantages. [18] Because of this mutualistic relationship between traplining hummingbirds and plants, traplining hummingbirds have been referred to as "legitimate pollinators", while territorial hummingbirds have been referred to as "nectar thieves". [19] If an organism that traplines learns where a food source is once, they can always return to that food source because they can remember minute details about the location of the source. This allows them to adapt quickly if one of the major sources suddenly becomes scarce or destroyed. [20]

Disadvantages

Serious obstacles, such as the arrangement of plant life, can hamper traplining. If the route zig zags through the understory of the tropical rainforest, some of the organisms using the route can get lost because of very subtle changes, [16] such as a treefall gap or heavy rainfall. This could cause an individual to be separated from the entire group if it isn't able to find the path back to the original route. Some food sources can be overlooked because the traplining route in use does not lead the organisms to the area that these resources are in.

Since the route is very specific, the organisms following it may also miss out on opportunities to come in contact with potential mates. Male bumblebees going directly to the source of food have been observed to pass up on female bumblebees as potential mates that are along the same path, preferring to continue foraging and bring food back to the hive. [20] This can take away from species diversification and could possibly delete some traits in the gene pool that are useful.

Research

Observing traplining in the natural world has proven to be very difficult[ according to whom? ] and little is known about how and why species trapline, but the study of traplining in the natural environment does take place. In one particular study, individual bees trained on five artificial flowers of equal reward were observed traplining between those five flowers. When a new flower of higher reward gets included in the group, the bees subsequently adjust their trapline to include the higher reward flower. Under natural conditions they hypothesized that it would likely be beneficial for bees to prioritize higher reward flowers to either beat out competition or conserve energy.

In other field experiments, ecologists created a "competition vacuum" to observe whether or not bumblebees adjusted their feeding routes based on intense direct competition between other bumblebees. This study showed that bees in areas of higher competition are more productive than the control bees. Bumblebees opportunistically adjust their use of traplining routes in response to activity of other competing bees. [8] Another effective way to study the behavior of traplining species is via computer simulation and indoor flight cage experiments. Simulation models can be made to show the linkage between pollinator movement and pollen flow. This model considers how service by the pollinators with different foraging patterns would affect the flow of pollen.

Indoor flight cage experiments allow for easier determination between test subjects and easier observation of behavior and patterns. Bees in small study environments seem to demonstrate less traplining tendencies than bees that were studied in environments that stretched over several hectares. A larger working area increases the need for traplining techniques to further conserve energy and maximize nutrient intake and that bees most often trapline due strictly to travel distance. The bees remember these complex flight paths by breaking them into small segments using vectors, landmarks and other environmental factors, each one pointing to the next destination. [21]

Despite a long history of research on bee learning and navigation, most knowledge has been deduced from the behavior of foragers traveling between their nest and a single feeding location. [6] Only recently, studies of bumblebees foraging in arrays of artificial flowers fitted with automated tracking systems have started to describe the learning mechanisms behind complex route formation between multiple locations. The demonstration that all these observations can be accurately replicated by a single learning heuristic model holds considerable promises to further investigate these questions and fill a major gap in cognitive ecology. [21]

See also

Related Research Articles

<span class="mw-page-title-main">Pollinator</span> Animal that moves pollen from the male anther of a flower to the female stigma

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.

<span class="mw-page-title-main">Bumblebee</span> Genus of insect

A bumblebee is any of over 250 species in the genus Bombus, part of Apidae, one of the bee families. This genus is the only extant group in the tribe Bombini, though a few extinct related genera are known from fossils. They are found primarily in higher altitudes or latitudes in the Northern Hemisphere, although they are also found in South America, where a few lowland tropical species have been identified. European bumblebees have also been introduced to New Zealand and Tasmania. Female bumblebees can sting repeatedly, but generally ignore humans and other animals.

<span class="mw-page-title-main">Pollination</span> Biological process occurring in plants

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; birds, butterflies, 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.

<span class="mw-page-title-main">Zoophily</span> Pollination by animals

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.

<i>Bombus terrestris</i> Species of bee

Bombus terrestris, the buff-tailed bumblebee or large earth bumblebee, is one of the most numerous bumblebee species in Europe. It is one of the main species used in greenhouse pollination, and so can be found in many countries and areas where it is not native, such as Tasmania. Moreover, it is a eusocial insect with an overlap of generations, a division of labour, and cooperative brood care. The queen is monandrous which means she mates with only one male. B. terrestris workers learn flower colours and forage efficiently.

<span class="mw-page-title-main">Nectar</span> Sugar-rich liquid produced by many flowering plants, that attracts pollinators and insects

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.

<span class="mw-page-title-main">Nectarivore</span> Animal in which nectar is a main source of nutrition in their diet

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.

<span class="mw-page-title-main">Ornithophily</span> Pollination by birds

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.

<span class="mw-page-title-main">Palynivore</span> Group of herbivorous animals

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.

<span class="mw-page-title-main">Pollination syndrome</span> Flower traits that attract pollinators

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.

<span class="mw-page-title-main">Nectar robbing</span> Foraging behavior

Nectar robbing is a foraging behavior utilized 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.

<i>Bombus lapidarius</i> Species of bee

Bombus lapidarius is a species of bumblebee in the subgenus Melanobombus. Commonly known as the red-tailed bumblebee, B. lapidarius can be found throughout much of Central Europe. Known for its distinctive black and red body, this social bee is important in pollination.

<i>Bombus hortorum</i> Species of bee

Bombus hortorum, the garden bumblebee or small garden bumblebee, is a species of bumblebee found in most of Europe north to 70°N, as well as parts of Asia and New Zealand. It is distinguished from most other bumblebees by its long tongue used for feeding on pollen in deep-flowered plants. Accordingly, this bumblebee mainly visits flowers with deep corollae, such as deadnettles, ground ivy, vetches, clovers, comfrey, foxglove, and thistles. They have a good visual memory, which aids them in navigating the territory close to their habitat and seeking out food sources.

<span class="mw-page-title-main">Flower constancy</span> Tendency to visit certain flower species

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.

<i>Bombus occidentalis</i> Species of bee

Bombus occidentalis, the western bumblebee, is one of around 30 bumblebee species present in the western United States and western Canada. A recent review of all of its close relatives worldwide appears to have confirmed its status as a separate species.

<span class="mw-page-title-main">Frequency-dependent foraging by pollinators</span> Animal behavior

Frequency-dependent foraging is defined as the tendency of an individual to selectively forage on a certain species or morph based on its relative frequency within a population. Specifically for pollinators, this refers to the tendency to visit a particular floral morph or plant species based on its frequency within the local plant community, even if nectar rewards are equivalent amongst different morphs. Pollinators that forage in a frequency-dependent manner will exhibit flower constancy for a certain morph, but the preferred floral type will be dependent on its frequency. Additionally, frequency-dependent foraging differs from density-dependent foraging as the latter considers the absolute number of certain morphs per unit area as a factor influencing pollinator choice. Although density of a morph will be related to its frequency, common morphs are still preferred when overall plant densities are high.

<span class="mw-page-title-main">Bumblebee communication</span>

Bumblebees, like the honeybee collect nectar and pollen from flowers and store them for food. Many individuals must be recruited to forage for food to provide for the hive. Some bee species have highly developed ways of communicating with each other about the location and quality of food resources ranging from physical to chemical displays.

<i>Bombus impatiens</i> Species of insect

Bombus impatiens, the common eastern bumble bee, is the most commonly encountered bumblebee across much of eastern North America. They can be found in the Eastern temperate forest region of the eastern United States, southern Canada, and the eastern Great Plains. Because of their great adaptability, they can live in country, suburbs, and even urban cities. This adaptability makes them a great pollinator species, leading to an increase in their commercial use by the greenhouse industry. This increase consequently led to their farther spread outside their previous distribution range. They are considered one of the most important species of pollinator bees in North America.

<span class="mw-page-title-main">Insect cognition</span>

Insect cognition describes the mental capacities and study of those capacities in insects. The field developed from comparative psychology where early studies focused more on animal behavior. Researchers have examined insect cognition in bees, fruit flies, and wasps. 

<span class="mw-page-title-main">Floral isolation</span>

Floral Isolation is a form of reproductive isolation found in angiosperms. Reproductive isolation is the process of species evolving mechanisms to prevent reproduction with other species. In plants, this is accomplished through the manipulation of the pollinator’s behavior or through morphological characteristics of flowers that favor intraspecific pollen transfer. Preventing interbreeding prevents hybridization and gene flow between the species (introgression), and consequently protects genetic integrity of the species. Reproductive isolation occurs in many organisms, and floral isolation is one form present in plants. Floral isolation occurs prior to pollination, and is divided into two types of isolation: morphological isolation and ethological isolation. Floral isolation was championed by Verne Grant in the 1900s as an important mechanism of reproductive isolation in plants.

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