11.2: Foraging Ecology

Foraging

Figure \(\PageIndex{1}\): Grizzly bear (Ursus arctos horribilis) mother and cubs foraging in Denali National Park, Alaska.

Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce.^[1] Foraging theory is a branch of behavioral ecology that studies the foraging behavior of animals in response to the environment where the animal lives.

Behavioral ecologists use economic models to understand foraging; many of these models are a type of optimal model. Thus foraging theory is discussed in terms of optimizing a payoff from a foraging decision. The payoff for many of these models is the amount of energy an animal receives per unit time, more specifically, the highest ratio of energetic gain to cost while foraging.^[2] Foraging theory predicts that the decisions that maximize energy per unit time and thus deliver the highest payoff will be selected for and persist. Key words used to describe foraging behavior include resources, the elements necessary for survival and reproduction which have a limited supply, predator, any organism that consumes others, prey, an organism that is eaten in part or whole by another,^[1] and patches, concentrations of resources.

Behavioral ecologists first tackled this topic in the 1960s and 1970s. Their goal was to quantify and formalize a set of models to test their null hypothesis that animals forage randomly. Important contributions to foraging theory have been made by:

• Eric Charnov, who developed the marginal value theorem to predict the behavior of foragers using patches;
• Sir John Krebs, with work on the optimal diet model in relation to tits and chickadees;
• John Goss-Custard, who first tested the optimal diet model against behavior in the field, using redshank, and then proceeded to an extensive study of foraging in the common pied oystercatcher

 

Factors influencing foraging behavior

Several factors affect an animal's ability to forage and acquire profitable resources.

Learning

Learning is defined as an adaptive change or modification of a behavior based on a previous experience.^[3] Since an animal's environment is constantly changing, the ability to adjust foraging behavior is essential for maximization of fitness. Studies in social insects have shown that there is a significant correlation between learning and foraging performance.^[3]

In nonhuman primates, young individuals learn foraging behavior from their peers and elders by watching other group members forage and by copying their behavior.^[4] Observing and learning from other members of the group ensure that the younger members of the group learn what is safe to eat and become proficient foragers (Figure \(\PageIndex{2}\)).

Figure \(\PageIndex{2}\): A troop of olive baboons (Papio anubis) foraging in Laikipia, Kenya. Young primates learn from elders in their group about proper foraging.

One measure of learning is 'foraging innovation'—an animal consuming new food, or using a new foraging technique in response to their dynamic living environment.^[5] Foraging innovation is considered learning because it involves behavioral plasticity on the animal's part. The animal recognizes the need to come up with a new foraging strategy and introduce something it has never used before to maximize his or her fitness (survival). Forebrain size has been associated with learning behavior. Animals with larger brain sizes are expected to learn better.^[5] A higher ability to innovate has been linked to larger forebrain sizes in North American and British Isle birds according to Lefebvre et al. (1997).^[6] In this study, bird orders that contained individuals with larger forebrain sizes displayed a higher amount of foraging innovation. Examples of innovations recorded in birds include following tractors and eating frogs or other insects killed by it and using swaying trees to catch their prey.^[5]

Another measure of learning is spatio-temporal learning (also called time-place learning), which refers to an individual's ability to associate the time of an event with the place of that event.^[7] This type of learning has been documented in the foraging behaviors of individuals of the stingless bee species Trigona fulviventris.^[7] Studies showed that T. fulviventris individuals learned the locations and times of feeding events, and arrived to those locations up to thirty minutes before the feeding event in anticipation of the food reward.^[7]

 

Genetics

Figure \(\PageIndex{3}\): A European honey bee extracts nectar. According to Hunt (2007), two genes have been associated with the sugar concentration of the nectar honey bees collect.

Foraging behavior can also be influenced by genetics. The genes associated with foraging behavior have been widely studied in honeybees with reference to the following; onset of foraging behavior, task division between foragers and workers, and bias in foraging for either pollen or nectar.^[5][8] Honey bee foraging activity occurs both inside and outside the hive for either pollen or nectar. Similar behavior is seen in many social wasps, such as the species Apoica flavissima. Studies using quantitative trait loci (QTL) mapping have associated the following loci with the matched functions; Pln-1 and Pln-4 with onset of foraging age, Pln-1 and 2 with the size of the pollen loads collected by workers, and Pln-2 and pln-3 were shown to influence the sugar concentration of the nectar collected (Figure \(\PageIndex{3}\)).^[8] 

 

Predators and parasites

The presence of predators while a (prey) animal is foraging affects its behaviour. In general, foragers balance the risk of predation with their needs, thus deviating from the foraging behaviour that would be expected in the absence of predators.^[9]

Similarly, parasitism can affect the way in which animals forage. Parasitism can affect foraging at several levels. Animals might simply avoid food items that increase their risk of being parasitized, as when the prey items are intermediate hosts of parasites. Animals might also avoid areas that would expose them to a high risk of parasitism. Finally, animals might effectively self-medicate, either prophylactically or therapeutically.^[10]

 

Types of foraging

Foraging can be categorized into two main types. The first is solitary foraging, when animals forage by themselves. The second is group foraging.

 

Solitary foraging

Solitary foraging includes the variety of foraging in which animals find, capture and consume their prey alone. Individuals can manually exploit patches or they can use tools to exploit their prey. For example, Bolas spiders attack their prey by luring them with a scent identical to the female moth's sex pheromones.^[11] Animals may choose to forage on their own when the resources are abundant, which can occur when the habitat is rich or when the number of conspecifics foraging are few. In these cases there may be no need for group foraging.^[12] In addition, foraging alone can result in less interaction with other foragers, which can decrease the amount of competition and dominance interactions an animal deals with. It will also ensure that a solitary forager is less conspicuous to predators.^[13] Solitary foraging strategies characterize many of the phocids (the true seals) such as the elephant and harbor seals. An example of an exclusive solitary forager is the South American species of the harvester ant, Pogonomyrmex vermiculatus.^[14][15]. The theory scientists use to understand solitary foraging is called optimal foraging theory, which predicts that foragers alter their behavior (e.g., when to move to the next foraging area) to maximize energy intake. See the book section on "Optimal Foraging Theory" for more information. 

 

Group foraging

Group foraging is when animals find, capture and consume prey in the presence of other individuals. In other words, it is foraging when success depends not only on your own foraging behaviors but the behaviors of others as well.^[16] An important note here is that group foraging can emerge in two types of situations. The first situation is frequently thought of and occurs when foraging in a group is beneficial and brings greater rewards known as an aggregation economy. The second situation occurs when a group of animals forage together but it may not be in an animal's best interest to do so known as a dispersion economy. Think of a cardinal at a bird feeder for the dispersion economy. We might see a group of birds foraging at that bird feeder but it is not in the best interest of the cardinal for any of the other birds to be there too (Figure \(\PageIndex{4}\)). The amount of food the cardinal can get from that bird feeder depends on how much it can take from the bird feeder but also depends on how much the other birds take as well.

Figure \(\PageIndex{4}\): A male northern cardinal at a bird feeder. Birds feeding at a bird feeder is an example of a dispersion economy. This is when it may not be in an animal's best interest to forage in a group.

In red harvester ants, the foraging process is divided between three different types of workers: nest patrollers, trail patrollers, and foragers. These workers can utilize many different methods of communicating while foraging in a group, such as guiding flights, scent paths, and "jostling runs", as seen in the eusocial bee Melipona scutellaris.^[17]

Chimpanzees in the Taï Forest in Côte d'Ivoire also engage in foraging for meats when they can, which is achieved through group foraging. Positive correlation has been observed between the success of the hunt and the size of the foraging group. The chimps have also been observed implying rules with their foraging, where there is a benefit to becoming involved through allowing successful hunters first access to their kills.^[22][23][24]

 

Cost and benefits of group foraging

Figure \(\PageIndex{5}\): Female lions make foraging decisions and more specifically decisions about hunting group size with protection of their cubs and territory defense in mind.^[21]

As already mentioned, group foraging brings both costs and benefits to the members of that group. Some of the benefits of group foraging include being able to capture larger prey,^[21] being able to create aggregations of prey,^[22] being able to capture prey that are difficult or dangerous and most importantly reduction of predation threat.^[16] With regard to costs, however, group foraging results in competition for available resources by other group members. Competition for resources can be characterized by either scramble competition whereby each individual strives to get a portion of the shared resource, or by interference competition whereby the presence of competitors prevents a forager's accessibility to resources.^[1] Group foraging can thus reduce an animal's foraging payoff.^[16]

Group foraging may be influenced by the size of a group. In some species like lions and wild dogs, foraging success increases with an increase in group size then declines once the optimal size is exceeded. A myriad number of factors affect the group sizes in different species. For example, lionesses (female lions) do not make decisions about foraging in a vacuum (Figure \(\PageIndex{5}\)). They make decisions that reflect a balance between obtaining food, defending their territory and protecting their young. In fact, we see that lion foraging behavior does not maximize their energy gain. They are not behaving optimally with respect to foraging because they have to defend their territory and protect young so they hunt in small groups to reduce the risk of being caught alone.^[21] Another factor that may influence group size is the cost of hunting. To understand the behavior of wild dogs and the average group size we must incorporate the distance the dogs run.^[23]

 

 

References

1. Danchin, E., Giraldeau, L., & Cezilly, F. (2008). Behavioural Ecology. New York: Oxford University Press. ISBN 978-0-19-920629-2.
2. Hughes, R.N, ed. (1989). Behavioural Mechanisms of Food Selection. London & New York: Springer-Verlag, p. v. ISBN 978-0-387-51762-9
3. Raine, N.E., & Chittka, L. (2008). The correlation of learning speed and natural foraging success in bumble-bees. Proceedings of the Royal Society B: Biological Sciences, 275(1636), pp. 803–08. doi:10.1098/rspb.2007.1652. PMC 2596909. PMID 18198141.
4. Rapaport, L.G., & Brown, G.R. (2008). Social influences on foraging behavior in young nonhuman primates:learning what, where and how to eat. Evolutionary Anthropology: Issues, News, and Reviews, 17(4), pp. 189–201. doi:10.1002/evan.20180. S2CID 86010867.
5. Dugatkin, L.A. (2004). Principles of Animal Behavior.
6. Lefebvre, L., Whittle, P., Lascaris, E., & Finkelstein, A. (1997). Feeding innovations and forebrain size in birds. Animal Behaviour, 53(3), pp. 549–60. doi:10.1006/anbe.1996.0330. S2CID 53146859.
7. Murphy, C.M., & Breed, M.D. (2008). Time-place learning in a neotropical stingless bee, Trigona fulviventris Guérin (Hymenoptera: Apidae). Journal of the Kansas Entomological Society, 81(1), pp. 73–76. doi:10.2317/JKES-704.23.1. ISSN 0022-8567. S2CID 86256384.
8. Hunt, G.J., et al. (2007). Behavioral genomics of honeybee foraging and nest defense. Naturwissenschaften, 94(4), pp. 247–67. doi:10.1007/s00114-006-0183-1. PMC 1829419. PMID 17171388.
9. Roch, S., von Ammon, L., Geist, J., & Brinker, A. (2018). Foraging habits of invasive three-spined sticklebacks (Gasterosteus aculeatus) – impacts on fisheries yield in Upper Lake Constance. Fisheries Research, 204, pp. 172–80. doi:10.1016/j.fishres.2018.02.014.
10. Hutchings, M.R., Athanasiadou, S., Kyriazakis, I., Gordon, I.J. (2008). Can animals use foraging behaviour to combat parasites? Proceedings of the Nutrition Society, 62(2), pp. 361–370. doi:10.1079/PNS2003243. ISSN 1475-2719.
11. Foraging Strategies | Encyclopedia.com. www.encyclopedia.com. Retrieved 2021-09-26.
12. Riedman, M. (1990). The pinnipeds: seals, sea lions, and walruses. Berkeley: University of California Press. ISBN 978-0-520-06497-3. ISBN The pinnipeds: seals, sea lions, and walruses By Marianne Riedman 1990.
13. le Roux, Aliza; Michael I. Cherry; Lorenz Gygax (5 May 2009). "Vigilance behaviour and fitness consequences: comparing a solitary foraging and an obligate group-foraging mammal". Behavioral Ecology and Sociobiology. 63 (8): 1097–1107. doi:10.1007/s00265-009-0762-1. S2CID 21961356.
14. Torres-Contreras, H., Olivares-Donoso, R., & Niemeyer, H.M. (2007). Solitary foraging in the ancestral South American ant, Pogonomyrmex vermiculatus. Is it due to constraints in the production or perception of trail pheromones? Journal of Chemical Ecology, 33(2), pp. 435–40. doi:10.1007/s10886-006-9240-7. PMID 17187299. S2CID 23930353.
15.  About Forest to Food. Harvesting Nature's Bounty, One Step at a Time. 2023-06-05. Retrieved 2023-06-29.
16. Stephens, D.W., Brown, J.S. & Ydenberg, R.C. (2007). Foraging: Behavior and Ecology. Chicago: University of Chicago Press.
17. Hrncir, M., Jarau, S., Zucchi, R., Barth, F.G. (2000). Recruitment behavior in stingless bees, Melipona scutellaris and M. quadrifasciata. II. Possible mechanisms of communication. Apidologie, 31(1), pp. 93–113. doi:10.1051/apido:2000109.
18. Boesch, C. (1994). Cooperative hunting in wild Chimpanzees. Animal Behaviour, 48(3), pp. 653–67. doi:10.1006/anbe.1994.1285. S2CID 53177700
19. Gomes, C.M., & Boesch, C. (2009). Wild chimpanzees exchange meat for sex on a long term basis. PLOS ONE, 4(4): e5116. doi:10.1371/journal.pone.0005116. PMC 2663035. PMID 19352509
20. Gomes, C.M., & Boesch, C. (2011). Reciprocity and trades in wild west African chimpanzees. Behavioral Ecology and Sociobiology, 65(11), pp. 2183–96. doi:10.1007/s00265-011-1227-x. S2CID 37432514.
21. Packer, C., Scheel, D., & Pusey, A.E. (1990). Why lions form groups: Food is not enough. American Naturalist, 136, pp. 1–19. doi:10.1086/285079. S2CID 85145653.
22. Benoit-Bird, K., & Whitlow, W.L. (2009). Cooperative prey herding by the pelagic dolphin, Stenella longirostris. The Journal of the Acoustical Society of America, 125(1), pp. 125–37. doi:10.1121/1.2967480. PMID 19173400. Archived from the original (PDF) on 2012-04-25. Retrieved 2011-11-29
23. Creel, S., & Creel, N.M. (1995). Communal hunting and pack size in African wild dogs, Lycaon pictus. Animal Behaviour, 50(5), pp. 1325–39. doi:10.1016/0003-3472(95)80048-4. S2CID 53180378.

Contributors and Attributions  

Modified by Dan Wetzel (University of Pittsburgh) and Natasha Gownaris (Gettysburg College) from the following sources:

• Wikipedia, the free Encyclopedia, article on Foraging