{"id":3318,"date":"2017-02-14T18:47:53","date_gmt":"2017-02-14T18:47:53","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&p=3318"},"modified":"2017-07-05T17:46:04","modified_gmt":"2017-07-05T17:46:04","slug":"community-ecology","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-wmopen-biology2\/chapter\/community-ecology\/","title":{"raw":"Community Ecology","rendered":"Community Ecology"},"content":{"raw":"

Discuss the scope and study of community ecology<\/h2>\r\nPopulations rarely, if ever, live in isolation from populations of other species. In most cases, numerous species share a habitat. The interactions between these populations play a major role in regulating population growth and abundance. All populations occupying the same habitat form a community: populations inhabiting a specific area at the same time. The number of species occupying the same habitat and their relative abundance is known as species diversity. Areas with low diversity, such as the glaciers of Antarctica, still contain a wide variety of living things, whereas the diversity of tropical rainforests is so great that it cannot be counted. Ecology is studied at the community level to understand how species interact with each other and compete for the same resources.\r\n
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Learning Objectives<\/h3>\r\n
    \r\n \t
  • Discuss the importance of predation and herbivory in the ecosystem, including how organisms defend against these<\/li>\r\n \t
  • Define the competitive exclusion principle<\/li>\r\n \t
  • Compare and contrast the three different types of symbiotic relationships<\/li>\r\n \t
  • Identify different species roles that structure communities<\/li>\r\n \t
  • Describe community dynamics as the changes in community structure that take place over time<\/li>\r\n \t
  • Define behavioral biology<\/li>\r\n \t
  • Identify different types of innate behaviors in animals<\/li>\r\n \t
  • Identify different types of learned behaviors in animals<\/li>\r\n<\/ul>\r\n<\/div>\r\n

    Predation and Herbivory<\/h2>\r\nPerhaps the classical example of species interaction is predation: the hunting of prey by its predator. Nature shows on television highlight the drama of one living organism killing another. Populations of predators and prey in a community are not constant over time: in most cases, they vary in cycles that appear to be related. The most often cited example of predator-prey dynamics is seen in the cycling of the lynx (predator) and the snowshoe hare (prey), using nearly 200 year-old trapping data from North American forests (Figure\u00a01). This cycle of predator and prey lasts approximately 10 years, with the predator population lagging 1\u20132 years behind that of the prey population. As the hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, however, they kill so many hares that hare population begins to decline, followed by a decline in the lynx population because of scarcity of food. When the lynx population is low, the hare population size begins to increase due, at least in part, to low predation pressure, starting the cycle anew.\r\n\r\n[caption id=\"attachment_3325\" align=\"aligncenter\" width=\"700\"]\"The Figure\u00a01. The cycling of lynx and snowshoe hare populations in Northern Ontario is an example of predator-prey dynamics.[\/caption]\r\n\r\nThe idea that the population cycling of the two species is entirely controlled by predation models has come under question. More recent studies have pointed to undefined density-dependent factors as being important in the cycling, in addition to predation. One possibility is that the cycling is inherent in the hare population due to density-dependent effects such as lower fecundity (maternal stress) caused by crowding when the hare population gets too dense. The hare cycling would then induce the cycling of the lynx because it is the lynxes\u2019 major food source. The more we study communities, the more complexities we find, allowing ecologists to derive more accurate and sophisticated models of population dynamics.\r\n\r\nHerbivory describes the consumption of plants by insects and other animals, and it is another interspecific relationship that affects populations. Unlike animals, most plants cannot outrun predators or use mimicry to hide from hungry animals. Some plants have developed mechanisms to defend against herbivory. Other species have developed mutualistic relationships; for example, herbivory provides a mechanism of seed distribution that aids in plant reproduction.\r\n

    Defense Mechanisms against Predation and Herbivory<\/h3>\r\nThe study of communities must consider evolutionary forces that act on the members of the various populations contained within it. Species are not static, but slowly changing and adapting to their environment by natural selection and other evolutionary forces. Species have evolved numerous mechanisms to escape predation and herbivory. These defenses may be mechanical, chemical, physical, or behavioral.\r\n\r\nMechanical defenses, such as the presence of thorns on plants or the hard shell on turtles, discourage animal predation and herbivory by causing physical pain to the predator or by physically preventing the predator from being able to eat the prey. Chemical defenses are produced by many animals as well as plants, such as the foxglove which is extremely toxic when eaten. Figure\u00a02 shows some organisms\u2019 defenses against predation and herbivory.\r\n\r\n[caption id=\"attachment_3326\" align=\"aligncenter\" width=\"700\"]\"Photo Figure\u00a02. The (a) honey locust tree (Gleditsia triacanthos) uses thorns, a mechanical defense, against herbivores, while the (b) Florida red-bellied turtle (Pseudemys nelsoni) uses its shell as a mechanical defense against predators. (c) Foxglove (Digitalis sp.) uses a chemical defense: toxins produced by the plant can cause nausea, vomiting, hallucinations, convulsions, or death when consumed. (d) The North American millipede (Narceus americanus) uses both mechanical and chemical defenses: when threatened, the millipede curls into a defensive ball and produces a noxious substance that irritates eyes and skin. (credit a: modification of work by Huw Williams; credit b: modification of work by \u201cJamieS93\u201d\/Flickr; credit c: modification of work by Philip J\u00e4genstedt; credit d: modification of work by Cory Zanker)[\/caption]\r\n\r\nMany species use their body shape and coloration to avoid being detected by predators. The tropical walking stick is an insect with the coloration and body shape of a twig which makes it very hard to see when stationary against a background of real twigs (Figure\u00a03a). In another example, the chameleon can change its color to match its surroundings (Figure\u00a03b). Both of these are examples of\u00a0camouflage<\/strong>, or avoiding detection by blending in with the background.\r\n\r\n[caption id=\"attachment_3327\" align=\"aligncenter\" width=\"700\"]\"Photo Figure\u00a03. (a) The tropical walking stick and (b) the chameleon use body shape and\/or coloration to prevent detection by predators. (credit a: modification of work by Linda Tanner; credit b: modification of work by Frank Vassen)[\/caption]\r\n\r\nSome species use coloration as a way of warning predators that they are not good to eat. For example, the cinnabar moth caterpillar, the fire-bellied toad, and many species of beetle have bright colors that warn of a foul taste, the presence of toxic chemical, and\/or the ability to sting or bite, respectively. Predators that ignore this coloration and eat the organisms will experience their unpleasant taste or presence of toxic chemicals and learn not to eat them in the future. This type of defensive mechanism is called aposematic coloration<\/strong>, or warning coloration.\r\n\r\n[caption id=\"attachment_3328\" align=\"aligncenter\" width=\"700\"]\"Photo Figure\u00a04. (a) The strawberry poison dart frog (Oophaga pumilio<\/em>) uses aposematic coloration to warn predators that it is toxic, while the (b) striped skunk (Mephitis mephitis<\/em>) uses aposematic coloration to warn predators of the unpleasant odor it produces. (credit a: modification of work by Jay Iwasaki; credit b: modification of work by Dan Dzurisin)[\/caption]\r\n\r\nWhile some predators learn to avoid eating certain potential prey because of their coloration, other species have evolved mechanisms to mimic this coloration to avoid being eaten, even though they themselves may not be unpleasant to eat or contain toxic chemicals. In Batesian mimicry<\/strong>, a harmless species imitates the warning coloration of a harmful one. Assuming they share the same predators, this coloration then protects the harmless ones, even though they do not have the same level of physical or chemical defenses against predation as the organism they mimic. Many insect species mimic the coloration of wasps or bees, which are stinging, venomous insects, thereby discouraging predation (Figure\u00a05).\r\n\r\n[caption id=\"attachment_3329\" align=\"aligncenter\" width=\"700\"]\"Photos Figure\u00a05.\u00a0Batesian mimicry occurs when a harmless species mimics the coloration of a harmful species, as is seen with the (a) bumblebee and (b) bee-like robber fly. (credit a, b: modification of work by Cory Zanker)[\/caption]\r\n\r\n[caption id=\"attachment_3330\" align=\"alignright\" width=\"350\"]\"Photos Figure\u00a06. Several unpleasant-tasting Heliconius butterfly species share a similar color pattern with better-tasting varieties. (credit: Joron M, Papa R, Beltr\u00e1n M, Chamberlain N, Mav\u00e1rez J, et al.)[\/caption]\r\n\r\nIn M\u00fcllerian mimicry<\/strong>, multiple species share the same warning coloration, but all of them actually have defenses. Figure\u00a06\u00a0shows a variety of foul-tasting butterflies with similar coloration.\r\n\r\nIn Emsleyan\/Mertensian mimicry<\/strong>, a deadly prey mimics a less dangerous one, such as the venomous coral snake mimicking the non-venomous milk snake. This type of mimicry is extremely rare and more difficult to understand than the previous two types. For this type of mimicry to work, it is essential that eating the milk snake has unpleasant, but not fatal, consequences. Then, these predators learn not to eat snakes with this coloration, protecting the coral snake as well. If the snake were fatal to the predator, there would be no opportunity for the predator to learn not to eat it, and the benefit for the less toxic species would disappear.\r\n

    Competition<\/h2>\r\nResources are often limited within a habitat and multiple species may compete to obtain them. All species have an ecological niche in the ecosystem, which describes how they acquire the resources they need and how they interact with other species in the community. The competitive exclusion principle<\/strong> states that two species cannot occupy the same niche in a habitat. In other words, different species cannot coexist in a community if they are competing for all the same resources. An example of this principle is shown in\u00a0Figure\u00a07, with two protozoan species, Paramecium aurelia<\/em> and Paramecium caudatum<\/em>. When grown individually in the laboratory, they both thrive. But when they are placed together in the same test tube (habitat), P. aurelia<\/em> outcompetes P. caudatum <\/em>for food, leading to the latter\u2019s eventual extinction.\r\n\r\n[caption id=\"attachment_3335\" align=\"aligncenter\" width=\"1024\"]\"Graphs Figure\u00a07. Paramecium aurelia<\/em> and Paramecium caudatum<\/em> grow well individually, but when they compete for the same resources, the P. aurelia<\/em> outcompetes the P. caudatum<\/em>.[\/caption]\r\n

    Resource Partitioning<\/h3>\r\nCompetitive exclusion may be avoided if one or both of the competing species evolves to use a different resource, occupy a different area of the habitat, or feed during a different time of day. The result of this kind of evolution is that two similar species use largely non-overlapping resources and thus have different niches. This is called resource partitioning<\/strong>, and it helps the species coexist because there is less direct competition between them.\r\n\r\nThe anole lizards found on the island of Puerto Rico are a good example of resource partitioning. In this group, natural selection has led to the evolution of different species that make use of different resources. Figure\u00a08\u00a0shows resource partitioning among 11 species of anole lizards. Each species lives in its own preferred habitat, which is defined by type and height of vegetation (trees, shrubs, cactus, etc.), sunlight, and moisture, among other factors.\r\n\r\n[caption id=\"attachment_3673\" align=\"aligncenter\" width=\"720\"]\"Diagram Figure\u00a08. Resource partitioning among anole lizards[\/caption]\r\n\r\n
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    Video Review<\/h3>\r\nWatch this video to\u00a0review competition and how populations share resources in a community:\r\n\r\nhttps:\/\/youtu.be\/GxE1SSqbSn4\r\n\r\n<\/div>\r\n

    Symbiosis<\/h2>\r\nSymbiotic relationships, or symbioses<\/strong> (plural), are close interactions between individuals of different species over an extended period of time which impact the abundance and distribution of the associating populations. Most scientists accept this definition, but some restrict the term to only those species that are mutualistic, where both individuals benefit from the interaction. In this discussion, the broader definition will be used.\r\n

    Commensalism<\/h3>\r\n[caption id=\"attachment_3336\" align=\"alignright\" width=\"350\"]\"Photo Figure\u00a09.\u00a0The southern masked-weaver bird is starting to make a nest in a tree in Zambezi Valley, Zambia. This is an example of a commensal relationship, in which one species (the bird) benefits, while the other (the tree) neither benefits nor is harmed. (credit: \u201cHanay\u201d\/Wikimedia Commons)[\/caption]\r\n\r\nA commensal<\/strong> relationship occurs when one species benefits from the close, prolonged interaction, while the other neither benefits nor is harmed. Birds nesting in trees provide an example of a commensal relationship (Figure\u00a09). The tree is not harmed by the presence of the nest among its branches. The nests are light and produce little strain on the structural integrity of the branch, and most of the leaves, which the tree uses to get energy by photosynthesis, are above the nest so they are unaffected. The bird, on the other hand, benefits greatly. If the bird had to nest in the open, its eggs and young would be vulnerable to predators. Another example of a commensal relationship is the clown fish and the sea anemone. The sea anemone is not harmed by the fish, and the fish benefits with protection from predators who would be stung upon nearing the sea anemone.\r\n

    Mutualism<\/h3>\r\nA second type of symbiotic relationship is called mutualism<\/strong>, where two species benefit from their interaction. Some scientists believe that these are the only true examples of symbiosis. For example, termites have a mutualistic relationship with protozoa that live in the insect\u2019s gut (Figure\u00a010a). The termite benefits from the ability of bacterial symbionts within the protozoa to digest cellulose. The termite itself cannot do this, and without the protozoa, it would not be able to obtain energy from its food (cellulose from the wood it chews and eats). The protozoa and the bacterial symbionts benefit by having a protective environment and a constant supply of food from the wood chewing actions of the termite. Lichens have a mutualistic relationship between fungus and photosynthetic algae or bacteria (Figure\u00a010b). As these symbionts grow together, the glucose produced by the algae provides nourishment for both organisms, whereas the physical structure of the lichen protects the algae from the elements and makes certain nutrients in the atmosphere more available to the algae.\r\n\r\n[caption id=\"attachment_3337\" align=\"aligncenter\" width=\"765\"]\"Photo Figure\u00a010. (a) Termites form a mutualistic relationship with symbiotic protozoa in their guts, which allow both organisms to obtain energy from the cellulose the termite consumes. (b) Lichen is a fungus that has symbiotic photosynthetic algae living inside its cells. (credit a: modification of work by Scott Bauer, USDA; credit b: modification of work by Cory Zanker)[\/caption]\r\n

    Parasitism<\/h3>\r\nA parasite<\/strong> is an organism that lives in or on another living organism and derives nutrients from it. In this relationship, the parasite benefits, but the organism being fed upon, the host<\/strong> is harmed. The host is usually weakened by the parasite as it siphons resources the host would normally use to maintain itself. The parasite, however, is unlikely to kill the host, especially not quickly, because this would allow no time for the organism to complete its reproductive cycle by spreading to another host.\r\n\r\nThe reproductive cycles of parasites are often very complex, sometimes requiring more than one host species. A tapeworm is a parasite that causes disease in humans when contaminated, undercooked meat such as pork, fish, or beef is consumed (Figure\u00a011). The tapeworm can live inside the intestine of the host for several years, benefiting from the food the host is bringing into its gut by eating, and may grow to be over 50 ft long by adding segments. The parasite moves from species to species in a cycle, making two hosts necessary to complete its life cycle. Another common parasite is Plasmodium falciparum<\/em>, the protozoan cause of malaria, a significant disease in many parts of the world. Living in human liver and red blood cells, the organism reproduces asexually in the gut of blood-feeding mosquitoes to complete its life cycle. Thus malaria is spread from human to human by mosquitoes, one of many arthropod-borne infectious diseases.\r\n\r\n[caption id=\"attachment_3338\" align=\"aligncenter\" width=\"1024\"]\"The Figure\u00a011.\u00a0This diagram shows the life cycle of a pork tapeworm (Taenia solium<\/em>), a human worm parasite. (credit: modification of work by CDC)[\/caption]\r\n

    Community Structure<\/h2>\r\nCommunities are complex entities that can be characterized by their structure (the types and numbers of species present) and dynamics (how communities change over time). Understanding community structure and dynamics enables community ecologists to manage ecosystems more effectively.\r\n

    Foundation Species<\/h3>\r\n[caption id=\"attachment_3340\" align=\"alignright\" width=\"400\"]\"Photo Figure\u00a012.\u00a0Coral is the foundation species of coral reef ecosystems. (credit: Jim E. Maragos, USFWS)[\/caption]\r\n\r\nFoundation species<\/strong> are considered the \u201cbase\u201d or \u201cbedrock\u201d of a community, having the greatest influence on its overall structure. They are usually the primary producers: organisms that bring most of the energy into the community. Kelp, brown algae, is a foundation species, forming the basis of the kelp forests off the coast of California.\r\n\r\nFoundation species may physically modify the environment to produce and maintain habitats that benefit the other organisms that use them. An example is the photosynthetic corals of the coral reef (Figure\u00a012). Corals themselves are not photosynthetic, but harbor symbionts within their body tissues (dinoflagellates called zooxanthellae) that perform photosynthesis; this is another example of a mutualism. The exoskeletons of living and dead coral make up most of the reef structure, which protects many other species from waves and ocean currents.\r\n

    Biodiversity, Species Richness, and Relative Species Abundance<\/h3>\r\nBiodiversity describes a community\u2019s biological complexity: it is measured by the number of different species (species richness) in a particular area and their relative abundance (species evenness). The area in question could be a habitat, a biome, or the entire biosphere. Species richness<\/strong> is the term that is used to describe the number of species living in a habitat or biome. Species richness varies across the globe (Figure\u00a013). One factor in determining species richness is latitude, with the greatest species richness occurring in ecosystems near the equator, which often have warmer temperatures, large amounts of rainfall, and low seasonality. The lowest species richness occurs near the poles, which are much colder, drier, and thus less conducive to life in Geologic time (time since glaciations). The predictability of climate or productivity is also an important factor. Other factors influence species richness as well. For example, the study of island biogeography<\/strong> attempts to explain the relatively high species richness found in certain isolated island chains, including the Gal\u00e1pagos Islands that inspired the young Darwin. Relative species abundance<\/strong> is the number of individuals in a species relative to the total number of individuals in all species within a habitat, ecosystem, or biome. Foundation species often have the highest relative abundance of species.\r\n\r\n[caption id=\"attachment_3341\" align=\"aligncenter\" width=\"538\"]\"Map Figure\u00a013. The greatest species richness for mammals in North and South America is associated with the equatorial latitudes. (credit: modification of work by NASA, CIESIN, Columbia University)[\/caption]\r\n

    Keystone Species<\/h3>\r\n[caption id=\"attachment_3342\" align=\"alignright\" width=\"400\"]\"Photo Figure\u00a014. The Pisaster ochraceus<\/em> sea star is a keystone species. (credit: Jerry Kirkhart)[\/caption]\r\n\r\nA keystone species<\/strong> is one whose presence is key to maintaining biodiversity within an ecosystem and to upholding an ecological community\u2019s structure. The intertidal sea star, Pisaster ochraceus<\/em>, of the northwestern United States is a keystone species (Figure\u00a014).\r\n\r\nStudies have shown that when this organism is removed from communities, populations of their natural prey (mussels) increase, completely altering the species composition and reducing biodiversity. Another keystone species is the banded tetra, a fish in tropical streams, which supplies nearly all of the phosphorus, a necessary inorganic nutrient, to the rest of the community. If these fish were to become extinct, the community would be greatly affected.\r\n

    Invasive Species<\/h3>\r\n[caption id=\"attachment_4571\" align=\"alignright\" width=\"450\"]\"Photo Figure\u00a015. Aquatic invasive species in the United States: (a) purple loosestrife and (b) zebra mussel. (credit a: modification of work by Liz West; credit b: modification of work by M. McCormick, NOAA)[\/caption]\r\n\r\nInvasive species are non-native organisms that, when introduced to an area out of their native range, threaten the ecosystem balance of that habitat. Many such species exist in the United States, as shown in Figures 4\u20136. Whether enjoying a forest hike, taking a summer boat trip, or simply walking down an urban street, you have likely encountered an invasive species.\r\n\r\nInvasive species like purple loosestrife (Lythrum salicaria<\/em>) and the zebra mussel (Dreissena polymorpha<\/em>) threaten certain aquatic ecosystems (Figure\u00a015).\r\n\r\nSome forests are threatened by the spread of common buckthorn (Rhamnus cathartica<\/em>), garlic mustard (Alliaria petiolata<\/em>), and the emerald ash borer (Agrilus planipennis<\/em>) (Figure\u00a016). The European starling (Sturnus vulgaris<\/em>) may compete with native bird species for nest holes.\r\n\r\n[caption id=\"attachment_4572\" align=\"aligncenter\" width=\"1067\"]\"Photo Figure\u00a016. Invasive species in US forests: (a) common buckthorn, (b) garlic mustard, and (c) the emerald ash borer. (credit a: modification of work by E. Dronkert; credit b: modification of work by Dan Davison; credit c: modification of work by USDA)[\/caption]\r\n

    Community Dynamics<\/h2>\r\nCommunity dynamics are the changes in community structure and composition over time. Sometimes these changes are induced by\u00a0environmental disturbances<\/strong> such as volcanoes, earthquakes, storms, fires, and climate change. Communities with a stable structure are said to be at equilibrium. Following a disturbance, the community may or may not return to the equilibrium state.\r\n\r\nSuccession describes the sequential appearance and disappearance of species in a community over time. In primary succession<\/strong>, newly exposed or newly formed land is colonized by living things; in secondary succession<\/strong>, part of an ecosystem is disturbed and remnants of the previous community remain.\r\n

    Primary Succession and Pioneer Species<\/h3>\r\n[caption id=\"attachment_3346\" align=\"alignright\" width=\"400\"]\"Photo Figure\u00a017. During primary succession in lava on Maui, Hawaii, succulent plants are the pioneer species. (credit: Forest and Kim Starr)[\/caption]\r\n\r\nPrimary succession occurs when new land is formed or rock is exposed: for example, following the eruption of volcanoes, such as those on the Big Island of Hawaii. As lava flows into the ocean, new land is continually being formed. On the Big Island, approximately 32 acres of land is added each year. First, weathering and other natural forces break down the substrate enough for the establishment of certain hearty plants and lichens with few soil requirements, known as pioneer species<\/strong> (Figure\u00a017). These species help to further break down the mineral rich lava into soil where other, less hardy species will grow and eventually replace the pioneer species. In addition, as these early species grow and die, they add to an ever-growing layer of decomposing organic material and contribute to soil formation. Over time the area will reach an equilibrium state, with a set of organisms quite different from the pioneer species.\r\n

    Secondary Succession<\/h3>\r\nA classic example of secondary succession occurs in oak and hickory forests cleared by wildfire (Figure\u00a018). Wildfires will burn most vegetation and kill those animals unable to flee the area. Their nutrients, however, are returned to the ground in the form of ash. Thus, even when areas are devoid of life due to severe fires, the area will soon be ready for new life to take hold.\r\n\r\nBefore the fire, the vegetation was dominated by tall trees with access to the major plant energy resource: sunlight. Their height gave them access to sunlight while also shading the ground and other low-lying species. After the fire, though, these trees are no longer dominant. Thus, the first plants to grow back are usually annual plants followed within a few years by quickly growing and spreading grasses and other pioneer species. Due to, at least in part, changes in the environment brought on by the growth of the grasses and other species, over many years, shrubs will emerge along with small pine, oak, and hickory trees. These organisms are called intermediate species. Eventually, over 150 years, the forest will reach its equilibrium point where species composition is no longer changing and resembles the community before the fire. This equilibrium state is referred to as the climax community<\/strong>, which will remain stable until the next disturbance.\r\n\r\n[caption id=\"attachment_3347\" align=\"aligncenter\" width=\"1024\"]\"The Figure\u00a018. Secondary succession is shown in an oak and hickory forest after a forest fire.[\/caption]\r\n

    Behavioral Biology<\/h2>\r\nBehavior<\/strong> is the change in activity of an organism in response to a stimulus. Behavioral biology<\/strong> is the study of the biological and evolutionary bases for such changes. The idea that behaviors evolved as a result of the pressures of natural selection is not new. Animal behavior has been studied for decades, by biologists in the science of ethology<\/strong>, by psychologists in the science of comparative psychology, and by scientists of many disciplines in the study of neurobiology. Although there is overlap between these disciplines, scientists in these behavioral fields take different approaches. Comparative psychology is an extension of work done in human and behavioral psychology. Ethology is an extension of genetics, evolution, anatomy, physiology, and other biological disciplines. Still, one cannot study behavioral biology without touching on both comparative psychology and ethology.\r\n

    Innate Behaviors<\/h2>\r\nOne goal of behavioral biology is to dissect out the innate behaviors<\/strong>, which have a strong genetic component and are largely independent of environmental influences, from the learned behaviors<\/strong>, which result from environmental conditioning. Innate behavior, or instinct, is important because there is no risk of an incorrect behavior being learned. They are \u201chard wired\u201d into the system. On the other hand, learned behaviors, although riskier, are flexible, dynamic, and can be altered according to changes in the environment.\r\n

    Movement and Migration<\/h3>\r\nInnate or instinctual behaviors rely on response to stimuli. The simplest example of this is a reflex action<\/strong>, an involuntary and rapid response to stimulus. To test the \u201cknee-jerk\u201d reflex, a doctor taps the patellar tendon below the kneecap with a rubber hammer. The stimulation of the nerves there leads to the reflex of extending the leg at the knee. This is similar to the reaction of someone who touches a hot stove and instinctually pulls his or her hand away. Even humans, with our great capacity to learn, still exhibit a variety of innate behaviors.\r\n

    Kinesis and Taxis<\/h4>\r\nAnother activity or movement of innate behavior is kinesis<\/strong>, or the undirected movement in response to a stimulus. Orthokinesis is the increased or decreased speed of movement of an organism in response to a stimulus. Woodlice, for example, increase their speed of movement when exposed to high or low temperatures. This movement, although random, increases the probability that the insect spends less time in the unfavorable environment. Another example is klinokinesis, an increase in turning behaviors. It is exhibited by bacteria such as E. coli<\/em> which, in association with orthokinesis, helps the organisms randomly find a more hospitable environment.\r\n\r\nA similar, but more directed version of kinesis is taxis<\/strong>: the directed movement towards or away from a stimulus. This movement can be in response to light (phototaxis), chemical signals (chemotaxis), or gravity (geotaxis) and can be directed toward (positive) or away (negative) from the source of the stimulus. An example of a positive chemotaxis is exhibited by the unicellular protozoan Tetrahymena thermophila<\/em>. This organism swims using its cilia, at times moving in a straight line, and at other times making turns. The attracting chemotactic agent alters the frequency of turning as the organism moves directly toward the source, following the increasing concentration gradient.\r\n

    Fixed Action Patterns<\/h4>\r\nA fixed action pattern<\/strong> is a series of movements elicited by a stimulus such that even when the stimulus is removed, the pattern goes on to completion. An example of such a behavior occurs in the three-spined stickleback, a small freshwater fish (Figure\u00a019). Males of this species develop a red belly during breeding season and show instinctual aggressiveness to other males during this time. In laboratory experiments, researchers exposed such fish to objects that in no way resemble a fish in their shape, but which were painted red on their lower halves. The male sticklebacks responded aggressively to the objects just as if they were real male sticklebacks.\r\n\r\n[caption id=\"attachment_3350\" align=\"aligncenter\" width=\"881\"]\"Photo Figure\u00a019. Male three-spined stickleback fish exhibit a fixed action pattern. During mating season, the males, which develop a bright red belly, react strongly to red-bottomed objects that in no way resemble fish.[\/caption]\r\n

    Migration<\/h4>\r\n[caption id=\"attachment_3351\" align=\"alignright\" width=\"400\"]\"Photo Figure\u00a020. Wildebeests migrate in a clockwise fashion over 1800 miles each year in search of rain-ripened grass. (credit: Eric Inafuku)[\/caption]\r\n\r\nMigration<\/strong> is the long-range seasonal movement of animals. It is an evolved, adapted response to variation in resource availability, and it is a common phenomenon found in all major groups of animals. Birds fly south for the winter to get to warmer climates with sufficient food, and salmon migrate to their spawning grounds. The popular 2005 documentary March of the Penguins <\/em>followed the 62-mile migration of emperor penguins through Antarctica to bring food back to their breeding site and to their young. Wildebeests (Figure\u00a020) migrate over 1800 miles each year in search of new grasslands.\r\n\r\nAlthough migration is thought of as innate behavior, only some migrating species always migrate (obligate migration). Animals that exhibit facultative migration can choose to migrate or not. Additionally, in some animals, only a portion of the population migrates, whereas the rest does not migrate (incomplete migration). For example, owls that live in the tundra may migrate in years when their food source, small rodents, is relatively scarce, but not migrate during the years when rodents are plentiful.\r\n

    Foraging<\/h4>\r\n[caption id=\"attachment_3352\" align=\"alignright\" width=\"400\"]\"Photo Figure\u00a021. The painted stork uses its long beak to forage. (credit: J.M. Garg)[\/caption]\r\n\r\nForaging<\/strong> is the act of searching for and exploiting food resources. Feeding behaviors that maximize energy gain and minimize energy expenditure are called optimal foraging behaviors, and these are favored by natural section. The painted stork, for example, uses its long beak to search the bottom of a freshwater marshland for crabs and other food (Figure\u00a021).\r\n

    Living in Groups<\/h3>\r\nNot all animals live in groups, but even those that live relatively solitary lives, with the exception of those that can reproduce asexually, must mate. Mating usually involves one animal signaling another so as to communicate the desire to mate. There are several types of energy-intensive behaviors or displays associated with mating, called mating rituals. Other behaviors found in populations that live in groups are described in terms of which animal benefits from the behavior. In selfish behavior, only the animal in question benefits; in altruistic behavior, one animal\u2019s actions benefit another animal; cooperative behavior describes when both animals benefit. All of these behaviors involve some sort of communication between population members.\r\n

    Communication within a Species<\/h4>\r\nAnimals communicate with each other using stimuli known as signals<\/strong>. An example of this is seen in the three-spined stickleback, where the visual signal of a red region in the lower half of a fish signals males to become aggressive and signals females to mate. Other signals are chemical (pheromones), aural (sound), visual (courtship and aggressive displays), or tactile (touch). These types of communication may be instinctual or learned or a combination of both. These are not the same as the communication we associate with language, which has been observed only in humans and perhaps in some species of primates and cetaceans.\r\n\r\nA pheromone is a secreted chemical signal used to obtain a response from another individual of the same species. The purpose of pheromones is to elicit a specific behavior from the receiving individual. Pheromones are especially common among social insects, but they are used by many species to attract the opposite sex, to sound alarms, to mark food trails, and to elicit other, more complex behaviors. Even humans are thought to respond to certain pheromones called axillary steroids. These chemicals influence human perception of other people, and in one study were responsible for a group of women synchronizing their menstrual cycles. The role of pheromones in human-to-human communication is still somewhat controversial and continues to be researched.\r\n\r\nSongs are an example of an aural signal, one that needs to be heard by the recipient. Perhaps the best known of these are songs of birds, which identify the species and are used to attract mates. Other well-known songs are those of whales, which are of such low frequency that they can travel long distances underwater. Dolphins communicate with each other using a wide variety of vocalizations. Male crickets make chirping sounds using a specialized organ to attract a mate, repel other males, and to announce a successful mating.\r\n\r\n[caption id=\"attachment_3353\" align=\"alignright\" width=\"400\"]\"Photo Figure\u00a022. This stork\u2019s courtship display is designed to attract potential mates. (credit: Linda \u201cjinterwas\u201d\/Flickr)[\/caption]\r\n\r\nCourtship displays<\/strong> are a series of ritualized visual behaviors (signals) designed to attract and convince a member of the opposite sex to mate. These displays are ubiquitous in the animal kingdom. Often these displays involve a series of steps, including an initial display by one member followed by a response from the other. If at any point, the display is performed incorrectly or a proper response is not given, the mating ritual is abandoned and the mating attempt will be unsuccessful. The mating display of the common stork is shown in Figure\u00a022.\r\n\r\nAggressive displays<\/strong> are also common in the animal kingdom. An example is when a dog bares its teeth when it wants another dog to back down. Presumably, these displays communicate not only the willingness of the animal to fight, but also its fighting ability. Although these displays do signal aggression on the part of the sender, it is thought that these displays are actually a mechanism to reduce the amount of actual fighting that occurs between members of the same species: they allow individuals to assess the fighting ability of their opponent and thus decide whether it is \u201cworth the fight.\u201d The testing of certain hypotheses using game theory has led to the conclusion that some of these displays may overstate an animal\u2019s actual fighting ability and are used to \u201cbluff\u201d the opponent. This type of interaction, even if \u201cdishonest,\u201d would be favored by natural selection if it is successful more times than not.\r\n\r\nDistraction displays<\/strong> are seen in birds and some fish. They are designed to attract a predator away from the nest that contains their young. This is an example of an altruistic behavior: it benefits the young more than the individual performing the display, which is putting itself at risk by doing so.\r\n\r\nMany animals, especially primates, communicate with other members in the group through touch. Activities such as grooming, touching the shoulder or root of the tail, embracing, lip contact, and greeting ceremonies have all been observed in the Indian langur, an Old World monkey. Similar behaviors are found in other primates, especially in the great apes.\r\n
    \r\n\r\nThe killdeer bird distracts predators from its eggs by faking a broken wing display in this video taken in Boise, Idaho. Note that this video has no narration.\r\n\r\nhttps:\/\/youtu.be\/TNG7y0caqj0\r\n\r\n<\/div>\r\n

    Altruistic Behaviors<\/h4>\r\nBehaviors that lower the fitness of the individual but increase the fitness of another individual are termed altruistic. Examples of such behaviors are seen widely across the animal kingdom. Social insects such as worker bees have no ability to reproduce, yet they maintain the queen so she can populate the hive with her offspring. Meerkats keep a sentry standing guard to warn the rest of the colony about intruders, even though the sentry is putting itself at risk. Wolves and wild dogs bring meat to pack members not present during a hunt. Lemurs take care of infants unrelated to them. Although on the surface, these behaviors appear to be altruistic, it may not be so simple.\r\n\r\nThere has been much discussion over why altruistic behaviors exist. Do these behaviors lead to overall evolutionary advantages for their species? Do they help the altruistic individual pass on its own genes? And what about such activities between unrelated individuals? One explanation for altruistic-type behaviors is found in the genetics of natural selection. In the 1976 book, The Selfish Gene, <\/em>scientist Richard Dawkins attempted to explain many seemingly altruistic behaviors from the viewpoint of the gene itself. Although a gene obviously cannot be selfish in the human sense, it may appear that way if the sacrifice of an individual benefits related individuals that share genes that are identical by descent (present in relatives because of common lineage). Mammal parents make this sacrifice to take care of their offspring. Emperor penguins migrate miles in harsh conditions to bring food back for their young. Selfish gene theory has been controversial over the years and is still discussed among scientists in related fields.\r\n\r\nEven less-related individuals, those with less genetic identity than that shared by parent and offspring, benefit from seemingly altruistic behavior. The activities of social insects such as bees, wasps, ants, and termites are good examples. Sterile workers in these societies take care of the queen because they are closely related to it, and as the queen has offspring, she is passing on genes from the workers indirectly. Thus, it is of fitness benefit for the worker to maintain the queen without having any direct chance of passing on its genes due to its sterility. The lowering of individual fitness to enhance the reproductive fitness of a relative and thus one\u2019s inclusive fitness evolves through kin selection<\/strong>. This phenomenon can explain many superficially altruistic behaviors seen in animals. However, these behaviors may not be truly defined as altruism in these cases because the actor is actually increasing its own fitness either directly (through its own offspring) or indirectly (through the inclusive fitness it gains through relatives that share genes with it).\r\n\r\nUnrelated individuals may also act altruistically to each other, and this seems to defy the \u201cselfish gene\u201d explanation. An example of this observed in many monkey species where a monkey will present its back to an unrelated monkey to have that individual pick the parasites from its fur. After a certain amount of time, the roles are reversed and the first monkey now grooms the second monkey. Thus, there is reciprocity in the behavior. Both benefit from the interaction and their fitness is raised more than if neither cooperated nor if one cooperated and the other did not cooperate. This behavior is still not necessarily altruism, as the \u201cgiving\u201d behavior of the actor is based on the expectation that it will be the \u201creceiver\u201d of the behavior in the future, termed reciprocal altruism. Reciprocal altruism requires that individuals repeatedly encounter each other, often the result of living in the same social group, and that cheaters (those that never \u201cgive back\u201d) are punished.\r\n\r\nEvolutionary game theory, a modification of classical game theory in mathematics, has shown that many of these so-called \u201caltruistic behaviors\u201d are not altruistic at all. The definition of \u201cpure\u201d altruism, based on human behavior, is an action that benefits another without any direct benefit to oneself. Most of the behaviors previously described do not seem to satisfy this definition, and game theorists are good at finding \u201cselfish\u201d components in them. Others have argued that the terms \u201cselfish\u201d and \u201caltruistic\u201d should be dropped completely when discussing animal behavior, as they describe human behavior and may not be directly applicable to instinctual animal activity. What is clear, though, is that heritable behaviors that improve the chances of passing on one\u2019s genes or a portion of one\u2019s genes are favored by natural selection and will be retained in future generations as long as those behaviors convey a fitness advantage. These instinctual behaviors may then be applied, in special circumstances, to other species, as long as it doesn\u2019t lower the animal\u2019s fitness.\r\n

    Finding Sex Partners<\/h4>\r\nNot all animals reproduce sexually, but many that do have the same challenge: they need to find a suitable mate and often have to compete with other individuals to obtain one. Significant energy is spent in the process of locating, attracting, and mating with the sex partner. Two types of selection occur during this process and can lead to traits that are important to reproduction called secondary sexual characteristics: intersexual selection<\/strong>, the choosing of a mate where individuals of one sex choose mates of the other sex, and intrasexual selection<\/strong>, the competition for mates between species members of the same sex. Intersexual selection is often complex because choosing a mate may be based on a variety of visual, aural, tactile, and chemical cues. An example of intersexual selection is when female peacocks choose to mate with the male with the brightest plumage. This type of selection often leads to traits in the chosen sex that do not enhance survival, but are those traits most attractive to the opposite sex (often at the expense of survival). Intrasexual selection involves mating displays and aggressive mating rituals such as rams butting heads\u2014the winner of these battles is the one that is able to mate. Many of these rituals use up considerable energy but result in the selection of the healthiest, strongest, and\/or most dominant individuals for mating. Three general mating systems, all involving innate as opposed to learned behaviors, are seen in animal populations: monogamous, polygynous, and polyandrous.\r\n
    \r\n\r\nWatch this informative video on sexual selection.\r\n\r\n