Antipredator adaptation: Wikis

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Silver Gulls will often mob predators who approach their nesting site.[1]

Antipredator adaptations are evolutionary adaptations developed over time, which assist prey organisms in their constant struggle against their predators. There are several ways antipredator adaptations can be classified, such as behavioral or non-behavioral or by taxonomic groups.

The act of a predator acquiring a food source can be divided into four stages: detection, attack, capture and consumption.[1] At each stage adaptations that maximize the prey organism's chance of survival have evolved, which in turn drives responding adaptation in their predators. This interaction over long periods of time is known as co-evolution.

Contents

Animal adaptations

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Avoiding detection as prey

A camouflaged Orange Oak Leaf butterfly (centre)

For a predator to locate a potential meal, it must first identify an organism as prey. Prey, however, have many adaptive characteristics which make such a task difficult. Crypsis is the ability of prey to evade detection by predators (or vice versa).

Camouflage is one heavily utilised method, and can be either inactive pigmentation, or as with many marine species, active redistribution of pigment in the skin. Some animals provide structures on their bodies for algae to grow, and thus camouflage the host. Some unpalatable animals make use of bright warning colouration, so as to advertise their poisonousness.[2] Batesian mimicry is the imitation by a harmless species of the warning signals of a harmful species directed at a common predator.

Polymorphism is a strategy adopted by an organism (mostly insects) to reduce predation. Experiments have shown that polymorphic prey suffered less predation than single-morph species at a particular density, and, conversely, polymorphic prey could maintain higher population densities for a given rate of predation. [3]:11

Animals adapt their waking patterns to avoid predators. Generally, animals are either diurnal, active during the day, nocturnal, active during the night, or crepuscular, active during twilight, depending of food availability, and predator prevalence.

Some animals, particularly gazelles, are known to stot, which, among other things, may advertise their unprofitability to predators.[4]

Avoiding capture by predators

A herd of wildebeest in Tanzania; the leader in the centre is watching the others

Many animals have highly developed senses of sight, smell, and hearing so that they can detect danger and escape. By frequently scanning and monitoring their surroundings, especially when in the open, prey can avoid attack by hoping to see a predator before it reaches the critical distance for an attack. This is a standard defence mechanism for animals in open grasslands and prairies. It is also common for arboreal animals to scan both the ground around them for terrestrial predators, and the sky for aerial predators.

Animals that are the frequent target of predation often make use of 'safety in numbers'. This results in a situation where any one herd member is unlikely to be preyed upon, and in high populations, predator satiation is likely to occur. Grazing mammals often feed in social groups, also known as herds. When a predator attacks, the herd runs and scatters, causing difficulty for the predator and allowing most, if not all, of the prey animals to escape. Prey animals may use alarm signals to alert the other herd members when a predator is sighted or sensed. Animals usually have a breeding season, where all the members of the species spawn at the same time, in order to maximise their young's chance of survival. This is particularly pronounced in insects such as Magicicada and the Mayfly, where millions of individuals emerge from pupation on the same day.[5]

Many animals have horns or claws to fight off predators, and some even spray noxious chemicals to deter attackers. Mobbing behaviour is common in birds, and is usually done to protect the young in social colonies. The eastern honeybee mobs invading hornets, vibrating their flight muscles in order to raise the temperature around the hornet scout to lethal levels, rather than allowing the scout to bring others to their beehive.[6]

An injured Virginia Opossum plays dead in front a dog

Some smaller animals may freeze in cover or play dead when seen. Smaller animals may not venture too far from their cover in the undergrowth of dense vegetation, where they can quickly hide when danger approaches.

Unconventional adaptations

Sea cucumbers utilise an odd defence behaviour, in that they eviscerate (effectively turn themselves inside out) by excreting part or all of their digestive tract. This is done to either anchor the cucumber into a rock fissure, or to eject toxins at the predator.[7] They are able to survive this, and later regrow the lost tissues.

Horned lizards also have an odd defence mechanism. When threatened, the lizard increases pressure in its sinus cavities until the blood vessels in the corners of its eyes burst, squirting blood at the attacker.[8]

Camponotus saundersi, an ant species found in Malaysia, also has an interesting defence. One caste within their colonies is the soldier ant, which is charged with defending the colony at all costs. The soldier ants have two large glands that run the entire length of their body, and when stressed during battle, abdominal muscles contract, causing the glands to explode, killing the ant, but spraying poison in all directions.

Plant adaptations

Aphid feeding on plant sap

Many plant species have, over the course of their evolutionary history, developed physical and chemical defense mechanisms to deter herbivores. Prickles, spines, and thorns are examples of physical mechanisms. Stinging nettles are covered in small hairs that contain chemicals that are a skin irritant to many mammals, including humans.

See also

References

  1. ^ a b John Alcock (1998). Animal Behavior: An Evolutionary Approach (8th ed.). Sinauer. ISBN 0-87893-009-4. 
  2. ^ Juan Carlos Santos, Luis A. Coloma, David C. Cannatella (28 October 2003). "Multiple, recurring origins of aposematism and diet specialization in poison frogs". National Academy of Sciences. http://www.pnas.org/cgi/content/abstract/100/22/12792. Retrieved 2008-12-22. 
  3. ^ Edmunds, Malcolm. The Evolution of Cryptic Colour. in Insect defenses: adaptive mechanisms and strategies of prey and predators (1990) Eds. David L. Evans, Justin O. Schmidt, pg 11.
  4. ^ Caro, T. M. (1986). "The functions of stotting in Thomson's gazelles: Some tests of the predictions.". Animal Behaviour (34): 663–684. 
  5. ^ John Cooley & Dave Marshall (9 January 2000). "Periodical Cicada". University of Michigan. http://insects.ummz.lsa.umich.edu/fauna/. Retrieved 2008-12-22. 
  6. ^ Masato Ono, Takeshi Igarashi, Eishi Ohno, and Masami Sasaki (28 September 1995). "Unusual thermal defence by a honeybee against mass attack by hornets". Nature 377 (377): 334–336. doi:10.1038/377334a0. http://www.nature.com/nature/journal/v377/n6547/abs/377334a0.html. Retrieved 2008-12-22. 
  7. ^ Patrick Flammang, Jerome Ribesse, Michel Jangoux (2002-12-01). "Biomechanics of adhesion in sea cucumber cuvierian tubules (echinodermata, holothuroidea)". Integrative and Comparative Biology. http://findarticles.com/p/articles/mi_qa4054/is_200212/ai_n9160035/pg_1. Retrieved 2008-12-22. 
  8. ^ Dr. Wendy Hodges. "About Horned Lizards". DigiMorph. http://www.digimorph.org/resources/horned.phtml. Retrieved 2008-12-22. 

Further reading

  • Edmunds, M. 1974. Defence in Animals: A Survey of Anti-Predator Defences. Harlow, Essex & NY: Longman ISBN 0582441323
  • Ruxton, G. D.; Speed, M. P.; Sherratt, T. N. (2004). Avoiding Attack. The Evolutionary Ecology of Crypsis, Warning Signals and Mimicry. Oxford: Oxford University Press. ISBN 0198528604
  • Caro, T. 2005. Antipredator Defenses in Birds and Mammals. Chicago : University of Chicago Press. 591 pp. ISBN 0226094359 (hardcover version)
  • Steen, J.B., Gabrielsen, G.W. & Kanwischer, J.W.: Physological aspects of freezing behavior in Willow ptarmigan hens. Acta Phys. Scand. 134: 299-304. 1988.
  • Gabrielsen, G.W. & Smith, E.N.: Physiological responses assosiated with feigned death in the American opossum. Acta Phys. Scand. 123: 393-398. 1985.
  • Gabrielsen, G.W. & E.N. Smith. Physiological responses to disturbance in animals. In; Wildlife and recreationists (R. Knight and K. Utzwiller. Island Press, Washington, D.C. pp. 137-153. 1995.

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