What is Competition Interaction?

Competition is defined as an interaction between two or more individuals of the same population or between two or more populations in which each adversely affects the other’s access to limited resource(s) (food, water, nesting sites, shelter, mates, etc.). Mutualism is defined as a population interaction that benefits both parties.

• Competition is the interaction between organisms or species that require a resource that is in short supply (such as food, water, or territory).
• Competition decreases the fitness of both animals involved since the presence of one creature reduces the amount of the resource accessible to the other.
• An essential biological interaction in the study of community ecology is intra- and interspecific competition.
• Competition is one of numerous biotic and abiotic elements that combine to influence community structure, species diversity, and population dynamics (shifts in a population over time).
• Interference, exploitation, and seeming competition are the three basic mechanisms of competition (in order from most direct to least direct).
• Interference and exploitation competition are “actual” forms of competition, whereas seeming competition is not, because organisms do not share a resource but rather a predator.
• Competition between members of the same species is referred to as intraspecific rivalry, whereas competition between members of different species is referred to as interspecific competition.
• According to the idea of competitive exclusion, species less adapted to compete for resources must either adapt or perish, but competitive exclusion is rarely observed in natural ecosystems.
• In natural selection, according to the idea of evolution, competition within and between species for resources is crucial.
• This idea is known as the “Room to Roam” notion.

Competitive exclusion principle

• In 1934, Georgii Gause established the competitive exclusion principle, often known as the Gause principle, to explain how species coexist: species with the same ecological niche cannot coexist.
• The term “niche” refers to the survival and reproductive requirements of a species. This includes both resources (such as food) and suitable habitat conditions (like temperature or pH).
• Gause reasoned that if two species had identical niches (needed the same resources and habitats), they would compete for the same resources and attempt to reside in the same region.
• If this were to occur, the species with the greatest competitive advantage would always eliminate its competitors from the area. To cohabit, species must therefore occupy somewhat distinct ecological niches.

Types of Competition Interaction On the basis of the taxonomical relationship

On the basis of their taxonomic relationship, interspecific and intraspecific competition are distinguished.

1. Intraspecific competition

• Intraspecific competition is a sort of competition that is density-dependent. “intra” refers to within a species, but “inter” means between species.
• Intraspecific competition is competition among members of the same species (cospecifics).
• The effect of competition on each individual within a species is contingent on the nature of the competition.
• The term ‘contest-competition’ may be passive or active, with varying outcomes. A species that fights for a finite resource in which all individuals consume the same amount until the resource is depleted may end in the extinction of the entire population.
• On the other hand, and more frequently, one individual competes and gains control of the resource, and by utilising it, it continues to exist.
• Not only does the nature of competition influence intraspecific competition, but so does the type of resource. A non-depletable land will influence the survival of future generations.
• Consumables, such as food, may become less accessible to future generations, and it may take time for these resources to recover.
• Density-dependent intraspecific competition can lead to density-dependent death. At low concentrations, there is no intraspecific rivalry and resource competition plays no role in survival.
• As population densities increase, a threshold is reached at which resource availability begins to influence mortality.
• When population growth rate is plotted as a graph, the outcome is either a J-shaped growth or an S-shaped/sigmoidal curve, both of which are known as logistic growth.

Types of Intraspecific competition

Two basic types of intraspecific competition have been identified:

1. Interference (adapted) intraspecific competition

• This occurs in species that develop social hierarchies by violent behaviour, where one or more individuals in the community retain a dominant position over the others.
• Through direct involvement, these individuals will restrict or block access to a resource for subordinates.
• When individuals within a species form territories and restrict the access of others to a resource, this type of competition may also arise.
• In this sort of competition, only dominant or territorial individuals will increase their reproductive success.
• It is frequently referred to as “contest competition” to denote displays and contents between individuals competing for access to a resource (usually mates).

2. Exploitation (contest) intraspecific competition

• This occurs when members of the same population exploit the same resources, thereby diminishing or exhausting their availability for others.
• This competition involves indirect interactions, such as the elimination of a food supply, between individuals.

Why Intraspecific Competition is density dependent?

• There is a concept in ecology known as carrying capacity, which calculates the maximum population number that an ecosystem can support, taking into account the amount of available resources.
• Therefore, as carrying capacity is reached, rivalry between individuals becomes more intense. This tendency can result in dramatic population declines.
• This sort of competition is hence “density dependent.” At low population densities, competition has little effect on the survival of individuals, in contrast to when the population size increases.
• As population density rises, resources become scarcer, increasing competition between members of a species.

Factors affecting intraspecific competition

1. Influence of the age of the competitor

• If we consider all conceivable situations of competition between members of the same species, we must consider whether competition is limited to members of the same cohort or whether it extends to members of different age groups, i.e., between members of different ages.
• Observations from the natural world indicate that adult and juvenile members of the same species have limited possibility of competing with one another because they often utilise distinct resources.
• In the case of anemones, for instance, the usage of resources is clearly circumscribed. The mature species have significantly larger tentacles than the youngsters.
• As their mode of predation involves of waiting for the prey to come and then capturing it, adult individuals have a different prey range than the species that juveniles capture with their little tentacles.
• This trend has been observed in other organism groupings. There is a spatial separation of resources between age groups among fish, with adults inhabiting distinct environments.

2. Competitors’ spatial arrangement

• The pattern of disposition in a population’s physical environment influences competition. This is exemplified by the exclusive hunting and feeding territories possessed by predators.
• Despite the inability of some individuals to secure a territory for themselves, those who are able to do so are able to ensure the availability of prey until reproduction. In this instance, the competition is not for the food itself, but rather for the territory.

Mechanisms of Intraspecific Competition

Direct

• Interference competition is the process wherein individuals compete directly with one another for a resource. It may involve violence, theft, or ritualised battle.
• Direct intraspecific competition comprises animals claiming a region and excluding other animals from entering.
• It is possible that there is no actual conflict between the two rivals, but the animal banned from the territory suffers a fitness loss due to a restricted foraging area and is unable to access the area because it fears conflict with a more dominant member of the population.
• During interference competition, animals are able to adapt behavioural tactics and morphologies to outcompete rivals in their population as they encounter one another.
• Depending on the severity of intraspecific rivalry, various populations of the northern slimy salamander (Plethodon glutinosus) have evolved varying levels of hostility.
• More violent behaviour is likely to arise in communities where resources are scarcer. Due to a dearth of food, it is more beneficial to battle rivals within the species with greater vigour than to seek out alternative possibilities.
• Aggression can spread throughout the community because more aggressive salamanders are more likely to obtain the resources they need to reproduce, whereas timid salamanders may starve before reproducing.

Indirect

• Organisms can engage in indirect competition through either exploitative or ostensible means. Individuals engage in exploitative competition when they deplete a shared resource and both suffer a fitness decline as a result.
• The organisms may not come into physical touch and may only interact indirectly via the shared resource.
• Experiments have demonstrated, for instance, that exploitative rivalry exists between juvenile wolf spiders (Schizocosa ocreata). Both an increase in the population density of juvenile spiders and a decrease in the food supply slowed the growth of individual spiders. Food is obviously a scarce resource for wolf spiders, yet there was no direct competition amongst juveniles for food; rather, there was a decline in fitness due to the increasing population density.
• The negative density dependence is obvious in young wolf spiders; as population densities increase, growth rates continue to decline and could reach zero (as predicted by the logistic growth model).
• This is also observed in the Viviparous lizard, Lacerta vivipara, in which the existence of colour morphs within a population is dependent on the population density and intraspecific competition.
• Exploitative competition has a significantly larger significance than interference competition in stationary species, such as plants, because individuals are anchored to a single area and utilise resources in their immediate surroundings. Saplings will compete for light, with taller trees blocking and utilising the majority of it.
• One of the reasons why seed distribution distances can be so great is that the saplings can be easily outcompeted by larger individuals of their own species. It is possible that seeds that germinate near to their parents will be outcompeted and perish.

Significance of Intraspecific Competition

• For many species, intraspecific competition has a significant impact on the variation in population size across time. At high population density, development is stifled, reproduction is inhibited, and survival is compromised. As a result, the population grows more slowly, stabilises, and then finally begins to decrease.
• Once the population returns to a smaller size, fertility and survival improve, putting the population back on a growth trajectory. These variations prevent the population from becoming excessively high or low, and this regulating effect is a well-established result of intraspecific competition.

Examples of Intraspecific Competition

Competition between moths of the genus Lymantria

• In the northern United States, the persistence of a moth of the genus Lymantria regarded a pest.
• It is an example of intense intraspecific competition, as the population grows rapidly and depletes resources due to this disproportionate rise.
• The insect’s life cycle does not correspond to the availability of resources; hence, as the caterpillars complete metamorphosis, there is no longer any food, and the population declines with the same vigour with which it increased.

2. Interspecific Competition

• Interspecific competition is competition between distinct species.
• Any competition between populations has an effect on both populations’ fitness. The investment of resources (energy, time, and matter) in competition or its avoidance diminishes the availability of these resources and has a negative impact on the reproductive success of populations.
• When one population completely or partially depletes a finite resource, the competitor’s access to that resource is diminished.
• It is important for each population to avoid competition, as natural selection has favoured niche separation, specialisation, and diversification.

Type of Interspecific Competition

Under this sort of competition, we also recognise two types of competition, but the interaction is between individuals of different species, as opposed to individuals of the same population as in intraspecific competition.

1. Exploitation (consumption) competition

In an indirect interaction between species (populations) over a restricted resource, one population deprives the other population of the resource. Indirect interactions involving three or more distinct species populations can fall into one of three categories.

• Classical exploitative competition due to resource depression: Two consumers that share a similar prey may engage in indirect competition if one consumes the resource before the other, so denying its opponent access to the resource.
• Apparent competition: Two prey species may appear to be in competition because, as one population grows, so does that of a common predator, to the cost of the other population.
• Competitive mutualism: Two populations are weak competitors, but a third population is a formidable competitor. By each of the weak competitors impeding the third (strong) competitor, they each gain an advantage. This situation can also occur in a four-species system (facilitation) when two species consume one of the two competing prey species. In this scenario, the expansion of one predator species leads in the decrease of its prey species, which allows the competing prey species to increase. As a result, predator 2 increases as its prey becomes more common, but over time it limits the supply of prey, which benefits prey 1, and so on.

2. Interference competition : allelopathy or interspecific territoriality

• This entails direct competition between species (populations) over a restricted resource by limiting access to that resource for one population.
• This can be performed by establishing a territory, achieving dominance within a hierarchical species, or releasing toxins into the soil to hinder the establishment of other plant populations.
• If the competition is for space, “preemptive competition” may occur, which is mostly determined by which species arrives at the resource first.

Consequences of Interference competition

1. Competitive exclusion

• The competitive exclusion principle, commonly known as “Gause’s law,” is based on mathematical analysis and simple competition models. It argues that two species that use the same limiting resource in the same space and time cannot cohabit and must diverge through time in order to coexist. Typically, one species will have an edge in resource usage.
• This superior competitor will outcompete the other by utilising the scarce resource more effectively.
• Consequently, the inferior competitor’s population will diminish over time. It will be removed from the region and replaced with the greater rival.

2. Niche differentiation

• Differentiation in a niche is the process by which competitive exclusion results in distinct resource utilisation.
• In other instances, it may result in additional adjustments designed to avoid competition. If it is possible to avoid rivalry, each species will occupy a niche edge and become more specialised in that region, hence reducing competition.
• This tendency frequently occurs in niche differentiation, the separation of species through time as they become increasingly specialised to their niche’s edge.
• To avoid niche overlap, however, the species need not inhabit separate areas. To escape competition, certain animals have evolved regionally to utilise different resources than they would normally.

3. Local extinction

• Although less well-documented than niche separation or competitive exclusion, local extinction of one or more competitors does occur.
• In an experiment involving zooplankton in artificial rock pools, local extinction rates were considerably greater in interspecifically competitive areas.
• In these instances, detrimental effects are not only observed at the population level but also at the species diversity of communities.

4. Impacts on communities

• As stated previously, interspecific competition has a significant effect on the composition and organisation of communities.
• Species niche separation, local extinction, and competitive exclusion are only a few of the potential outcomes. In addition to this, interspecific rivalry may be the cause of a cascade of cumulative consequences.
• An example of such an effect is the introduction of the invasive species purple loosestrife to the United States. When introduced to wetland areas, this plant frequently outcompetes the local flora and reduces species diversity, food, and shelter for several species at higher trophic levels.
• One species can influence the populations of numerous other species in this way, as well as through a vast array of other relationships. Because every ecosystem and habitat is comprised of a complex web of interconnections, the outcomes of interspecific competition are complex and site-specific.

Example of Interference competition

• Corals are found near the ocean’s base, where they line rocks and compete with other organisms.
• These corals fulfil their energy needs by filtering organic matter present in the water and diverse autotrophic microorganisms.
• In addition, they compete with other aquatic animals, such as fish, for nutrients and sunlight.
• They cover broad areas of the ocean floor in order to provide sufficient sunlight for autotrophic bacteria.

Types of Competition Interaction On the basis of mechanism

On the basis of mechanism, competition can be classified as interfering, exploitative, or obvious.

1. Interference competition

• Interference competition, also known as contest competition, involves species directly competing for finite resources.
• For instance, large aphids protect feeding spots on cottonwood leaves by excluding smaller aphids from more desirable locations. Male-male competition during the rut in red deer is an example of intraspecific interference competition.
• Interference competition occurs directly between individuals through violence when they interfere with the feeding, survival, or reproduction of others, or by inhibiting their physical settlement in a sector of the habitat.
• In the case of Novomessor cockerelli and red harvester ants, the former prevents the latter from foraging by blocking their colony entrances with small rocks.
• Male bowerbirds, which construct ornate buildings known as bowers to lure potential mates, may directly lower the fitness of their neighbours by taking ornaments from their bowers.
• Interference competition is a strategy utilised by larger and more powerful creatures in an environment. Consequently, populations with high interference competition have generation cycles driven by adults.
• Initially, larger adult rivals inhibit the development of youngsters. Once juveniles reach adulthood, however, they undergo a secondary growth cycle. In contrast, plants engage mostly in interference rivalry with their neighbours via allelopathy or the synthesis of biochemicals.
• Interference competition is a tactic with a clear cost (injury or death) and benefit (advantage) (obtaining resources that would have gone to other organisms).
• Other creatures frequently participate in interference competition or exploitation competition in response to intense interference competition.
• Due of interference competition, larger male red deer ungulates are competitively dominant during certain seasons. However, does and fawns have adapted by utilising temporal resource partitioning, or foraging exclusively when adult males are absent.

Example of interference competition

• Interference competition can be found in flamingos, where paired flamingos are more aggressive against single birds in order to obtain food and ensure their survival.
• The paired flamingos interact directly with a single flamingo and may engage in fights to defend their mates and young.

2. Exploitative competition

• Exploitation competition, also known as scramble competition, happens when two organisms utilise a shared limiting resource or food item.
• Instead of fighting or displaying aggressive behaviour to win resources, exploitative competition happens when resource utilisation by one organism depletes the total amount of resources available to another organism.
• These organisms may never contact physically, yet they compete by reacting to fluctuations in resource availability.
• This phenomena is exemplified by diurnal and nocturnal organisms that share the same resources or a plant that competes with its neighbours for light, nutrients, and room for root growth.
• Typically, this sort of competition rewards organisms that claim a resource early. Consequently, exploitation competition is frequently size-dependent, and smaller species are typically preferred due to their typically higher foraging rates.
• Since smaller organisms have an advantage when exploitative competition is essential in an ecosystem, this form of competition may lead to a juvenile-driven generation cycle: individual juveniles are successful and develop quickly, but once they mature they are outcompeted by smaller species.
• Exploitative competition can occur both above and below ground in plants. Aboveground, plants lower the fitness of their neighbours by competing for sunlight. Plants consume nitrogen by absorbing it into their roots, rendering it inaccessible to neighbouring plants. Plants that develop a large number of roots frequently deplete the soil of nitrogen, resulting in the death of nearby plants.
• It has also been demonstrated that exploitative competition occurs both within species (intraspecific) and between species (interspecific).
• In addition, many competitive interactions between organisms involve a combination of exploitative and interference competition, indicating that the two mechanisms are not mutually exclusive.
• A 2019 study demonstrated, for instance, that the native thrip species Frankliniella intonsa was competitively dominant over the invading thrip species Frankliniella occidentalis because it not only spent more time feeding (exploitative competition) but also spent more time guarding its resources (interference competition).
• Plants may also exhibit both forms of competition, not only competing for space for root development but also hindering the development of other plants through allelopathy.

Example of exploitative competition

• The spider population comprised of young spiders is characterised by exploitative competition.
• When population density grows and food resources decrease, the rate of spider reproduction decreases.
• Despite the fact that there is no direct connection amongst juvenile spiders, the number of fit spiders tends to decline. The fitter species consume the available nutrients, leaving fewer nutrients for the weaker individuals.

3. Apparent competition

• Apparent competition occurs when two non-related prey species indirectly compete for survival by sharing a predator.
• Typically, this type of competition results in new equilibrium abundances of each prey species.
• Suppose, for instance, that two species (species A and species B) are prey for a food-limited predator species C. Scientists observe a rise in the population of species A and a decrease in the population of species B.
• This relationship is discovered to be mediated by predator C in an apparent competition model; a population explosion of species A enhances the abundance of predator species C due to a bigger total food source.
• Since there are now more predators, A and B will be hunted at a higher rate than in the past. Consequently, the success of species A was detrimental to species B, not because they fought for resources, but because their increasing population had indirect consequences on the predator population.
• This one-predator/two-prey paradigm has been studied by ecologists since 1925, but Robert D. Holt of the University of Florida popularised the phrase “apparent competition” in 1977.
• Holt discovered that at the time, field ecologists incorrectly attributed unfavourable interactions between prey species to niche partitioning and competitive exclusion, ignoring the impact of food-limited predators.

Example of apparent competition- Skinks

• The introduction of rabbits diminishes the number of skins in a region.
• This is due to the fact that both skinks and rabbits are prey for ferrets. The introduction of rabbits to a region results in the influx of ferrets into the same region.
• Thus, the ferrets reduce the populations of both the skinks and the rabbits by feeding on them.

Types of Competition Interaction  On the basis of influence

On the basis of influence, competition is classified as either direct or indirect. A portion of the competitive engagement falls into more than one of these categories.

1. Direct Competition

• Direct competition is an interaction in which species within an ecosystem directly influence one another by influencing the availability of resources within the ecosystem.
• Whenever two or more animals fight or engage in a symbolic encounter, there is likely a rivalry over a resource.

Example of Direct competition

• In the instance of zebras inhabiting the same ecological niche, direct rivalry among animals might be observed.
• When grass and leaves become sparse in their environment, zebras compete for a limited supply.

2. Indirect competition

• Indirect competition is a type of rivalry in which species indirectly affect the availability of resources.
• Species engaged in indirect competition typically occupy distinct ecological niches.

Example of Indirect competition

• Additionally, indirect competition can arise between zebras inhabiting distinct but similar environments.
• By limiting the amount of water in the river, zebras near the pond may have an impact on zebras found elsewhere. This is a sort of indirect competition in which the species do not interact with one another but share a resource.

Outcomes of Competition

The process of competition is not static. Once in motion, there are numerous possible outcomes. In spite of the fact that the models predict that it would eventually lead to the extinction of one species, a number of other outcomes are possible. First, an environmental disturbance, such as a fire or a strong wave, might disrupt the ecosystem and nullify the greatest competitor’s advantage. Pine trees typically dominate a pinewood forest because they are the best competitors in the ecosystem. However, the most abundant plants following a forest fire are small, opportunistic plants that grow rapidly. The fire alters the environment, which drastically alters the dynamics of competition.

In addition, the majority of rivalry exerts an evolutionary strain on both parties. Surviving and reproducing are possible for animals from both sides that compete well. Consequently, rivalry tends to settle itself over time. More often than not, competition can deteriorate when species adapt to utilise other resources or alter how they use a resource. The term for this is character displacement. It has been extensively studied in finches. When two distinct species of finches inhabit separate islands, their beaks are identical in size because they prefer the same seeds. When they reside on the same island, one of their beaks shrinks while the other grows. This divides the resources they utilise and reduces rivalry.

What is Size-asymmetric competition?

• Competition can be complete symmetric (all individuals receive the same quantity of resources regardless of size), perfectly size symmetric (all individuals exploit the same amount of resource per unit biomass), or completely size asymmetric (the largest individuals exploit all the available resource).
• Size asymmetries in plants are context-dependent, and competition can be asymmetric or symmetric depending on the most limiting resource.
• In forest stands, below-ground competition for nutrients and water is size-symmetric, as the root system of a tree is proportional to its total biomass.
• In contrast, above-ground competition for light is size-asymmetric; as light has directionality, only the largest trees dominate the forest canopy. These trees use a disproportionate amount of the resource for their biomass, resulting in a size-asymmetric interaction.
• Whether above-ground or below-ground resources are more limiting can have significant effects on the structure and variety of ecological communities; for example, in mixed beech stands, size-asymmetric competition for light is a better predictor of growth than competition for soil resources.

References

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• Norbury, Grant. (2002). Conserving dryland lizards by reducing predator‐mediated apparent competition and direct competition with introduced rabbits. Journal of Applied Ecology. 38. 1350 – 1361. 10.1046/j.0021-8901.2001.00685.x. 
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