1.8+Interaction+Among+Organisms

 =__**Competition**__ =

**//Interspecific Competition //** Interspecific competition occurs between members of two, or more, different species. Individuals may compete over a variety of limiting resources including food, water, light,  [|soil] resources, or space. Members of different species may compete by [|exploitative competition] or by interference competition. Interspecific competition is an important factor limiting the population size of many species. In addition, interspecific competition can limit the number of species that can coexist in a community and affect the phenotypic characteristics of organisms in an attempt to reduce the effects of competition.  **//Interspecific competition and population regulation //** 

Interspecific interference competition between lions and hyenas.

Interspecific competition is an important factor limiting the population size of many species. The growth rate of a species will be limited as the population size of their competitors increases, either because they have access to fewer limiting resources ( [|exploitative competition] ) or because of the negative effects of the direct interactions of their competitor (interference competition).  <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;">**//<span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 14pt; line-height: 150%;">Interspecific competition and community structure //** <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 150%;">Interspecific competition can plan an important role in influencing aspects of community structure such as [|species richness], [|species diversity] , and patterns of species abundance. <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;">**//<span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 14pt; line-height: 150%;">Species richness //** <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 150%;">Interspecific competition can limit the number of species that can coexist in a community. The [|competitive exclusion principle] suggests that two species with exactly the same niche are not able to coexist. Thus, when the niches of two competing species are too similar, one of the species will be driven to extinction or be extirpated from the range of the other (competitive exclusion). <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;">**//<span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 14pt; line-height: 150%;">Limiting the effects of interspecific competition //** <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 150%;">Species may respond to the effects of interspecific competition by evolving to fill slightly different niches (niche differentiation). The divergence in phenotype produced by [|natural selection] to reduce the effects of competition are known as character displacement. 

<span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;">**<span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 14pt; line-height: 150%;">Intraspecific Competition ** <span style="display: block; line-height: 150%; margin-bottom: 12pt; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 10.5pt; line-height: 150%;">Intraspecific competition occurs between members of the same species. Individuals may compete over food, water, light, space, safe sites, or mates. Intraspecific competition is an important factor limiting the population size of many species. <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;">**<span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 14pt; line-height: 150%;">Intraspecific population regulation ** <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="font-family: 'Times New Roman',serif;"> <span style="display: block; line-height: 150%; margin-bottom: 7.85pt; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 8pt; line-height: 150%;">Competition among individuals of the bunchgrass //Hilaria rigida// (big galleta grass) results in an even spatial dispersion of individuals. (Photo by R. Robberecht) <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 10.5pt; line-height: 150%;">If members of the same species are competing for limited resources, then each individual would receive fewer resources when the population size of intraspecific competitors increases. Fewer resources per individual will (1) decrease the growth rates of individuals, (2) increase the chance that individuals die of starvation, or (3) decrease the number of offspring that a female can produce. Thus, as population density increases, there will be a resultant decrease in population growth rate. Intraspecific competition can cause populations to stop growing when they reach their [|carrying capacity]. <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;">**<span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 14pt; line-height: 150%;">Intraspecific competition and patterns of spatial dispersion ** <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 10.5pt; line-height: 150%;">Intraspecific competition can influence the spatial dispersion of organisms in a population. For example, if plants are competing for [|soil] resources, there may be a limit to how close together individual plants of the same species can live. Thus, intraspecific competition can result in plants having an even pattern of distribution across the environment. <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;">**<span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 14pt; line-height: 150%;">Limiting the effects of intraspecific competition ** <span style="display: block; line-height: 150%; margin-bottom: 0in; text-align: justify; vertical-align: baseline;"> <span style="font-family: 'Times New Roman',serif;"> <span style="display: block; line-height: 150%; margin-bottom: 7.85pt; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 8pt; line-height: 150%;">Tiger marking territory. (Photo from [|Save the Tiger Fund] ) <span style="display: block; line-height: 150%; margin-bottom: 12pt; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 10.5pt; line-height: 150%;">Individuals may try to limit competition for resources by defending limited resources from use by other members of their species. The physical defense of resources from other members of the same species is an example of interference competition. In some cases animals may defend territories to allow them to have exclusive use of the resources in the territory. Animals may defend territories to provide them with access to food or other resources or to provide them with a space where they can safely raise their young. Males of many species defend territories from other males of their own species for exclusive access rights to mating with the females living in their territory. <span style="display: block; line-height: 150%; margin-bottom: 12pt; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 12pt; text-align: justify; vertical-align: baseline;"> <span style="display: block; line-height: 150%; margin-bottom: 12pt; text-align: justify; vertical-align: baseline;">

<span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 10.5pt; line-height: 150%;"> = **<span style="font-family: 'Times New Roman',serif; font-size: 16pt; line-height: 150%;">__Predator Prey Relationships__ ** = <span style="display: block; line-height: 150%; margin-bottom: 12pt; text-align: justify; vertical-align: baseline;">media type="youtube" key="GFTBFDPfMh8?fs=1" height="385" width="480" <span style="display: block; line-height: 150%; margin-bottom: 12pt; text-align: justify; vertical-align: baseline;"><span style="color: #404040; font-family: 'Times New Roman',serif; font-size: 10.5pt; line-height: 150%;"><span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 150%; text-align: justify;">A predator is an organism that eats another organism. The prey is the organism that the predator eats. Some examples of predator and prey are lion and zebra, bear and fish, and fox and rabbit. The words "predator" and "prey" are almost always used to mean only animals that eat animals, but the same concept also applies to plants: Bear and berry, rabbit and lettuce, grasshopper and leaf.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 150%; text-align: justify;">

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 150%; text-align: justify;">Predator and prey evolve together. The prey is part of the predator's environment, and the predator dies if it does not get food, so it evolves whatever is necessary in order to eat the prey: speed, stealth, camouflage (to hide while approaching the prey), a good sense of smell, sight, or hearing (to find the prey), immunity to the prey's poison, poison (to kill the prey) the right kind of mouth parts or digestive system, etc. Likewise, the predator is part of the prey's environment, and the prey dies if it is eaten by the predator, so it evolves whatever is necessary to avoid being eaten: speed, camouflage (to hide from the predator), a good sense of smell, sight, or hearing (to detect the predator), thorns, poison (to spray when approached or bitten), etc.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 150%; margin-bottom: 0in; text-align: justify;">The fastest lions are able to catch food and eat, so they survive and reproduce, and gradually, faster lions make up more and more of the population. The fastest zebras are able to escape the lions, so they survive and reproduce, and gradually, faster zebras make up more and more of the population. An important thing to realize is that as both organisms become faster to adapt to their environments, their relationship remains the same: because they are both getting faster, neither gets faster in relation to the other. This is true in all predator-prey relationships.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 150%; text-align: justify;">Another example of predator-prey evolution is that of the Galapagos tortoise. Galapagos tortoises eat the branches of the cactus plants that grow on the [|Galapagos Islands]. On one of the islands, where long-necked tortoises live, the branches are higher off the ground. On another island, where short-necked tortoises live, the branches are lower down. The cactuses, the prey, may have evolved high branches so that the tortoises, the predators, cannot reach them

= =  Most of the interactions between species involve food: These interactions are often brief. There are many cases, however, where two species live in close association for long periods. Such associations are called ** symbiotic ** ("living together"). In symbiosis, at least one member of the pair benefits from the relationship. The other member may be
 * competing for the same food supply
 * eating (predation)
 * avoiding being eaten (avoiding predation)
 * injured = **parasitism**
 * relatively unaffected ( = **commensalism**)
 * may also benefit ( = **mutualism**).

media type="youtube" key="8YKAalZAqO4?fs=1" height="385" width="640" Symbiotic relationships in which ** each species benefits ** are mutualistic. There are hundreds of examples of mutualism between a heterotroph and an [|alga]. also harbor algae within their cells. Mutualistic relations between plants and fungi are very common. The fungus invades and lives in or among the cortex cells of the secondary [|roots]. The association is called a **mycorrhiza**. The fungus helps the host plant absorb inorganic nitrogen and phosphorus from the soil. Some mycorrhizal fungi also secrete antibiotics which may help protect their host from invasion by parasitic fungi and bacteria.
 * ** Paramecium bursaria ** is a [|ciliate] that engulfs unicellular green algae into vacuoles within its cell.
 * The paramecium certainly benefits from the food synthesized by the alga. It can be cultured apart from the alga but then must be given extra food.
 * The alga presumably benefits from the carbon dioxide produced by its host as well as the host's ability to transport it to a spot where there is ample light.
 * Many other aquatic heterotrophs
 * [|sponges]
 * [|sea anemones]
 * [|planarians]
 * [|clams]

One of the most important examples of mutualism in the overall economy of the biosphere is the endosymbiotic relationship between certain nitrogen-fixing bacteria and their legume hosts. A large body of evidence supports the view that intracellular endosymbiotic relationships gave rise to eukaryotes with their mitochondria and chloroplasts.

The drawing shows the Nile crocodile opening its mouth to permit the Egyptian plover to feed on any leeches attached to its gums. Cleaning symbiosis is more common in fish.

media type="youtube" key="48eKFw7DDbY?fs=1" height="385" width="480" Commensalism means "at table together". It is used for symbiotic relationships in which one organism consumes the unused food of another. Some examples:
 * the remora and the shark. The dorsal fin of the remora (a [|bony fish]) is modified into a sucker with which it forms a temporary attachment to the shark. When the shark feeds, the remora picks up scraps. The shark makes no attempt to prey on the remora.
 * Some species of [|barnacles] are found only as commensals on the jaws of whales. And there are other species of barnacles found only as commensals on those barnacles!
 * Many of the bacteria living in our large intestine. They feed on food in the gut and do not harm us. And some probably help us; that is, the relationship is mutualistic Animals (e.g., mice) raised under germfree conditions are abnormal in several ways, and it is now standard practice to deliberately infect them with several species of microorganisms so that the animals develop normally.

Epiphytes are plants that live perched on sturdier plants. They do not take any nourishment from their host and simply benefit from being better exposed to sunlight. Some examples:
 * many orchids
 * many bromeliads (e.g., "Spanish moss" and other members of the pineapple family).

media type="youtube" key="rLtUk-W5Gpk?fs=1" height="385" width="480" A parasite is an organism that Animals are parasitized by viruses, bacteria, fungi, protozoans, flatworms (tapeworms and flukes), nematodes, insects (fleas, lice), and arachnids (mites). Plants are parasitized by viruses, bacteria, fungi, nematodes, and a few other plants. Parasites damage their host in two major ways: The relationship between parasite and host varies along a spectrum that extends from > to
 * lives on or in the body of another organism (the host)
 * from whose tissues it gets its nourishment, and
 * to whom it does some damage
 * consuming its tissues, e.g., hookworms
 * liberating toxins, for example,
 * Tetanus bacilli secrete tetanus toxin which interferes with synaptic transmission.
 * Diphtheria bacilli secrete a toxin that inhibits protein synthesis by ribosomes.
 * "hit and run" parasites that live in their host for a brief period and then move on to another with or without killing the first
 * Parasites that establish chronic infections. Both parasite and host must evolve to ensure the survival of both because if the parasite kills its host before it can move on, it destroys its own meal ticket.