Consumer–resource interactions are the core motif of ecological food chains or food webs, and are an umbrella term for a variety of more specialized types of biological species interactions including prey-predator (see predation), host-parasite (see parasitism), plant-herbivore and victim-exploiter systems. These kinds of interactions have been studied and modeled by population ecologists for nearly a century. Species at the bottom of the food chain, such as algae and other autotrophs, consume non-biological resources, such as minerals and nutrients of various kinds, and they derive their energy from light (photons) or chemical sources. Species higher up in the food chain survive by consuming other species and can be classified by what they eat and how they obtain or find their food.
Various terms have arisen to define consumers by what they eat, such as meat-eating carnivores, fish-eating piscivores, insect-eating insectivores, plant-eating herbivores, seed-eating granivores, and fruit-eating frugivores and omnivores are meat eaters and plant eaters. An extensive classification of consumer categories based on a list of feeding behaviors exists.
Another way of categorizing consumers, proposed by the American ecologist Wayne Getz, is based on a biomass transformation web (BTW) formulation that organizes resources into five components: live and dead animal, live and dead plant, and particulate (i.e. broken down plant and animal) matter. It also distinguishes between consumers that gather their resources by moving across landscapes from those that mine their resources by becoming sessile once they have located a stock of resources large enough for them to feed on during completion of a full life history stage.
In Getz's scheme, words for miners are of Greek etymology and words for gatherers are of Latin etymology. Thus a bestivore, such as a cat, preys on live animals (Latin: bestia=animal) while a sarcophage, such as a botfly larva mines live flesh and a zontanophage (Greek: zontanos=alive), such as a leaf miner, mines live plant material. A carcasivore (Latin: carcasium=carcass), such as white-backed vulture, scavenge animal carcasses while a necrophage (Greek: nekros=dead body), such as a blowfly, mines dead flesh. Victivores (Latin: victus=living) gather live plant material and thus include frugivores, nectivores, graminivores, granivores and folivores as subcategories. Lectivores, such as many termites, gather dead plant material (Latin: lectus=bed which is the root of the word litter, as in leaf-litter) and thanatophages (Greek: thanatos=death), such as pillbugs mine piles of dead plant material. Carnivore and herbivore are generic multigroup categories for gathers respectively of animal and plant material, irrespective of whether live or dead. Croppers, scavengers, and detritivores are gatherers respectively of live, dead, and particulate material. Parasites, saprophages, and decomposers are miners respectively of live, dead, and particulate material.
Exploitative interactions, also known as enemy–victim interactions, is a part of consumer–resource interactions where one organism (the enemy) is the consumer of another organism (the victim), typically in a harmful manner. Some examples of this include predator–prey interactions, host–pathogen interactions, and brood parasitism.In exploitative interactions, the enemy and the victim may often coevolve with each other. How exactly they coevolve depends on many factors, such as population density. One evolutionary consequence of exploitative interactions is antagonistic coevolution. This can occur because of resistance, where the victim attempts to decrease the number of successful attacks by the enemy, which encourages the enemy to evolve in response, thus resulting in a coevolutionary arms race. On the other hand, toleration, where the victim attempts to decrease the effect on fitness that successful enemy attacks have, may also evolve.Exploitative interactions can have significant biological effects. For example, exploitative interactions between a predator and prey can result in the extinction of the victim (the prey, in this case), as the predator, by definition, kills the prey, and thus reduces its population. Another effect of these interactions is in the coevolutionary "hot" and "cold spots" put forth by geographic mosaic theory. In this case, coevolution caused by resistance would create "hot spots" of coevolutionary activity in an otherwise uniform environment, whereas "cold spots" would be created by the evolution of tolerance, which generally does not create a coevolutionary arms race.Mutualism (biology)
Mutualism describes the ecological interaction between two or more species where each species benefits. Mutualism is thought to be the most common type of ecological interaction, and it is often dominant in most communities worldwide. 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.
Mutualism is often conflated with two other types of ecological phenomena: cooperation and symbiosis. Cooperation refers to increases in fitness through within-species (intraspecific) interactions. Symbiosis involves two species living in close proximity and may be mutualistic, parasitic, or commensal, so symbiotic relationships are not always mutualistic.
Mutualism plays a key part in ecology. For example, mutualistic interactions are vital for terrestrial ecosystem function as more than 48% of land plants rely on mycorrhizal relationships with fungi to provide them with inorganic compounds and trace elements. As another example, the estimate of tropical forest trees with seed dispersal mutualisms with animals ranges from 70–90%. In addition, mutualism is thought to have driven the evolution of much of the biological diversity we see, such as flower forms (important for pollination mutualisms) and co-evolution between groups of species. However, mutualism has historically received less attention than other interactions such as predation and parasitism.The term mutualism was introduced by Pierre-Joseph van Beneden in his 1876 book Animal Parasites and Messmates.