Scramble competition
In general terms, scramble competition is a type of competition in which equally rationed yet perpetually limited resources within an environment result in decreased survival rates for all competitors. Scramble competition is known in the field of ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

 as a situation where, “animals have to share a limited resource but there is no way in which an individual can limit the access of that resource to other individuals”. 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 is partitioned equally among contestants, so no competitor obtains the amount it needs and in extreme cases all die.

Types of intraspecific competition

Researchers recognize two main forms of intraspecific competition
Intraspecific competition
Intraspecific competition is a particular form of competition in which members of the same species vie for the same resource in an ecosystem...

, where living organisms are all using a shared resource in short supply. Intraspecific competition, more specifically, is when individuals are in competition with members of their own species. The two types of intraspecific competition are (1) contest competition, and (2) scramble competition

Contest competition

Contest competition is a form of competition where there is a winner and a loser and where resources can be completely attained or not at all. Contest competition sets up a situation where “each successful competitor obtains all resources it requires for survival or reproduction”. In contest competition resources are stable, involves competition with food and mates, oftentimes contests can be for a ritual objective such as territory or status, and losers may return to the competition another day to gain increased benefits.

Scramble competition

In scramble competition resources are limited, and the lack of necessary amount of resources per individual can and often does lead to group member starvation
Contest competition is often the result of aggressive social domains, including hierarchies or social chains. Conversely, scramble competition is what occurs by accident when naturally competitors want the same resources. These two forms of competition can be interwoven into one another; some researchers have even noted the parallels between intraspecific behaviors of both competition and cooperation. These two processes can be evolutionarily adopted and they can also be accidental, which makes sense given the aggressive competition and collaborative cooperation aspects of social behavior in humans and animals. To date, few studies have looked at the interplay between contest and scramble competition, despite the fact that it is not as “cut and dry” to have two distinct types of solitary, unfaltering competition. In the insect social dynamic there appears to be a lack of understanding around the interface of contest competition within otherwise scramble competition systems. In fact, much research still needs to be conducted concerning the overlap of contest and scramble competition systems Contests can pop up even within a scramble competition system and, vice versa, scramble competition “may play a role in a system characterized by interference”.

Population effects

A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

 can be greatly affected by scramble competition (and contest competition). Intraspecific competition normally leads to a decline of organisms. Wikibooks furthermore describes scramble competition as an illustration of a population that is so dense that all individuals compete for survival. Overtime all members of the population are affected negatively, and eventually all individuals cease to exist. The effects of competition on survival can be high, resulting oftentimes in a decline of population, due to lack of resources. The more time that an individual spends seeking food and reproduction opportunities, the less energy that organism naturally has to defend oneself against predators, resulting in a “zero-sum game”. Competition is a density dependent effect, and scramble competition is no exception. Scramble competition usually involves interactions among individuals of the same species, which makes competition balanced and often leads to a decline of population growth rate as the amount of resources depletes.

The Ricker Model
Ricker model
The Ricker model, named after Bill Ricker, is a classic discrete population model which gives the expected number a t+1 of individuals in generation t + 1 as a function of the number of individuals in the previous generation,Here r is interpreted as an intrinsic growth rate and k as...

, is used to model scramble competition. It was originally formulated to study the growth of salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

 populations and is given by the equation Pn+1 = R(Pn) = aPnexp(-bPn), where Pn is the population at the nth time period, r is the Malthusian growth rate, and M is the carrying capacity of the population.

Some researchers have noted that in certain species, such as the horseshoe crab
Horseshoe crab
The Atlantic horseshoe crab, Limulus polyphemus, is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders, ticks, and scorpions than to crabs. Horseshoe crabs are most commonly found in the Gulf of Mexico and along the northern Atlantic coast of North America...

, males are most successful at mating when they are able to practice scramble competition polygyny where they do not defend their territory but rather mate and move on, thus providing the highest likelihood of species survival and reproductive prowess.

Examples of scramble competition

There are many examples of scramble competition within the environment. For example, cows grazing in a grassland could be operating under a scramble competition. This illustration of cows eating grass is scramble competition because there are limited resources, there is only so much grass to be eaten before all the food resource is depleted. Additionally, there is no way that others can limit the amount of resources or the access to resources that the other cows receive.

Another example of scramble competition is forest defoliators. If their larvae can find shelter and food then survival is possible, but when all the foliage is destroyed then the population decreases. Their synchronized life cycle increases competition for specific resources this greatly affects their ability to receive resources including food and shelter due to the overwhelming population increase at certain times of the year.

Another example of scramble competition can be seen with the example of red spotted newts
Eastern Newt
The Eastern Newt or Red-spotted Newt is a common salamander of eastern North America. Eastern newts dwell in wet forests with small lakes or ponds. They can coexist in an aquatic environment with fish, however, their skin secretes a poisonous substance when the newt is threatened or injured...

. Interestingly, Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...

 (1871) first explored the concept of “sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

” which stats that, “most sexually dimorphic species are also the most polygynous” which would enable males to “outcompete other males through female choice, combat, or scrambles to encounter females would be favored by selection, and sexual dimorphism would result”. The key to red-spotted newts increased success in scramble competition is the newts enhanced or strengthened tailfins.

Another example of scramble competition is the success of small beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...

s over large beetles. Interestingly, while larger beetles, similar to larger animals in general, tend to win more often in contest competition, the opposite can be true in a scramble competition. Specifically with beetles, scramble competition is dependent on male movement and locomotion so that the beetle that can move faster is more likely to be successful in attaining resources, mates and food. Smaller beetles fair better in scramble competition for shelter, which could one day lead to the evolutionary adaptation of smaller beetle structures for survival purposes. The flux of contest and scramble competition in this example is important to note because it truly depends on the context of each individual to determine which type of competition is most suitable.
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