22 Biological interactions

In ecology, a biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species, or of different species. These effects may be short-term, like pollination and predation, or long-term; both often strongly influence the evolution of the species involved. A long-term interaction is called a symbiosis. Symbioses range from mutualism, beneficial to both partners, to competition, harmful to both partners. Interactions can be indirect, through intermediaries such as shared resources or common enemies. This type of relationship can be shown by net effect based on individual effects on both organisms arising out of relationship.

Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the battledress of a modern soldier, and the leaf-mimic katydid's wings. A third approach, motion dazzle, confuses the observer with a conspicuous pattern, making the object visible but momentarily harder to locate. The majority of camouflage methods aim for crypsis, often through a general resemblance to the background, high contrast disruptive coloration, eliminating shadow, and countershading. In the open ocean, where there is no background, the principal methods of camouflage are transparency, silvering, and countershading, while the ability to produce light is among other things used for counter-illumination on the undersides of cephalopods such as squid. Some animals, such as chameleons and octopuses, are capable of actively changing their skin pattern and colours, whether for camouflage or for signalling. It is possible that some plants use camouflage to evade being eaten by herbivores.

A carnivore, meaning "meat eater", is an animal whose food and energy requirements derive solely from animal tissue or meat, whether through hunting or scavenging. Animals that depend solely on animal flesh for their nutrient requirements are called obligate carnivores while those that also consume non-animal food are called facultative carnivores. Omnivores also consume both animal and non-animal food, and, apart from the more general definition, there is no clearly defined ratio of plant to animal material that would distinguish a facultative carnivore from an omnivore. A carnivore at the top of the food chain, not preyed upon by other animals, is termed an apex predator.

Competition is an interaction between organisms or species in which both the organisms or species are harmed. Limited supply of at least one resource used by both can be a factor. Competition both within and between species is an important topic in ecology, especially community ecology. Competition is one of many interacting biotic and abiotic factors that affect community structure. Competition among members of the same species is known as intraspecific competition, while competition between individuals of different species is known as interspecific competition. Competition is not always straightforward, and can occur in both a direct and indirect fashion.

In ecology, the competitive exclusion principle, sometimes referred to as Gause's law, is a proposition named for Georgy Gause that two species competing for the same limited resource cannot coexist at constant population values. When one species has even the slightest advantage over another, the one with the advantage will dominate in the long term. This leads either to the extinction of the weaker competitor or to an evolutionary or behavioral shift toward a different ecological niche. The principle has been paraphrased in the maxim "complete competitors can not coexist".

In ecology, crypsis is the ability of an animal to avoid observation or detection by other animals. It may be a predation strategy or an antipredator adaptation. Methods include camouflage, nocturnality, subterranean lifestyle and mimicry. Crypsis can involve visual, olfactory, or auditory concealment. When it is visual, the term cryptic coloration, effectively a synonym for animal camouflage, is sometimes used, but many different methods of camouflage are employed by animals.

An epibiont is an organism that lives on the surface of another living organism. An epibiont is, by definition, harmless to its host. In this sense, the interaction between the two organisms can be considered neutralistic or commensalistic; as opposed to being, for example, parasitic, in which case one organism benefits at the expense of the other, or mutualistic, in which both organisms obtain some explicit benefit from their coexistence). Examples of common epibionts are barnacles, remoras, and algae, many of which live on the surfaces of larger marine organisms such as whales, sharks, sea turtles, and mangrove trees. The host of the epibiont is typically referred to as the basibiont.

Fecundity selection, also known as fertility selection, is the fitness advantage resulting from the preference of traits that increase the number of offspring. Charles Darwin formulated the theory of fecundity selection between 1871 and 1874 to explain the widespread evolution of female-biased sexual size dimorphism (SSD), where females were larger than males.

Holozoic nutrition is a type of heterotrophic nutrition that is characterized by the internalization (ingestion) and internal processing of gaseous, liquids or solid food particles. Protozoa, such as amoebas, and most of the free living animals, such as humans, exhibit this type of nutrition where food is taken into the body as a liquid or solid and then further broken down is called holozoic nutrition most animals exhibit this kind of nutrition.

In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist guest (symbiont). The guest is typically provided with nourishment and shelter. Examples include animals playing host to parasitic worms, cells harbouring pathogenic (disease-causing) viruses, a bean plant hosting mutualistic (helpful) nitrogen-fixing bacteria. More specifically in botany, a host plant supplies food resources to micropredators, which have an evolutionarily stable relationship with their hosts similar to ectoparasitism. The host range is the collection of hosts that an organism can use as a partner.

Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resources in an ecosystem. This can be contrasted with mutualism, a type of symbiosis. Competition between members of the same species is called intraspecific competition.

Intraguild predation, or IGP, is the killing and sometimes eating of a potential competitor of a different species. This interaction represents a combination of predation and competition, because both species rely on the same prey resources and also benefit from preying upon one another. Intraguild predation is common in nature and can be asymmetrical, in which one species feeds upon the other, or symmetrical, in which both species prey upon each other. Because the dominant intraguild predator gains the dual benefits of feeding and eliminating a potential competitor, IGP interactions can have considerable effects on the structure of ecological communities.

Intraspecific competition is an interaction in population ecology, whereby members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals, but the more fit individual survives and is able to reproduce. By contrast, interspecific competition occurs when members of different species compete for a shared resource. Members of the same species have rather similar requirements for resources, whereas different species have a smaller contested resource overlap, resulting in intraspecific competition generally being a stronger force than interspecific competition.

Isotricha is a genus of protozoa which are commensals of the rumen of ruminant animals. They are approximately 150 μm (0.0059 in) long.

Mutualism describes the ecological interaction between two or more species where each species has a net benefit. Mutualism is a common type of ecological interaction. Prominent examples include most vascular plants engaged in mutualistic interactions with mycorrhizae, flowering plants being pollinated by animals, vascular plants being dispersed by animals, and corals with zooxanthellae, among many others. Mutualism can be contrasted with interspecific competition, in which each species experiences reduced fitness, and exploitation, or parasitism, in which one species benefits at the "expense" of the other.

Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which in his view is intentional, whereas natural selection is not.

Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.

In aquatic biology, the paradox of the plankton describes the situation in which a limited range of resources supports an unexpectedly wide range of plankton species, apparently flouting the competitive exclusion principle which holds that when two species compete for the same resource, one will be driven to extinction.

The Pathogen-Host Interaction database (PHI-base) is a biological database that contains curated information on genes experimentally proven to affect the outcome of pathogen-host interactions. The database is maintained by researchers at Rothamsted Research, together with external collaborators since 2005. Since April 2017 PHI-base is part of ELIXIR, the European life-science infrastructure for biological information via its ELIXIR-UK node.

In sociology, popularity is how much a person, idea, place, item or other concept is either liked or accorded status by other people. Liking can be due to reciprocal liking, interpersonal attraction, and similar factors. Social status can be due to dominance, superiority, and similar factors. For example, a kind person may be considered likable and therefore more popular than another person, and a wealthy person may be considered superior and therefore more popular than another person.

In ecology, scramble competition refers to a situation in which a resource is accessible to all competitors. However, since the particular resource is usually finite, scramble competition may lead to decreased survival rates for all competitors if the resource is used to its carrying capacity. Scramble competition is also defined as "[a] finite resource [that] is shared equally amongst the competitors so that the quantity of food per individual declines with increasing population density". A further description of scramble competition is "competition for a resource that is inadequate for the needs of all, but which is partitioned equally among contestants, so that no competitor obtains the amount it needs and all would die in extreme cases."

In ethology, territory is the sociographical area that an animal of a particular species consistently defends against conspecifics. Animals that defend territories in this way are referred to as territorial.