Experiments on Competition, Theories on Competition and Significance, Practice Problems and FAQs

How do we select our representative to the parliament (MP) in India? If it is a democratic country, then it will be through the process of election, right? So whomever we select should be powerful and able to represent us in the parliament. Before the election, there will be tight competition with all the candidates. To win they will show all their skills. They will offer many things that they will do for you if you make them win. But we always try to vote for the candidate which is fit for a particular position.

This kind of competition is seen everywhere in nature. The fittest species will survive, just like the theory of Darwin. But the existence of the species also depends on the ability of the other species competing with them. If you are competing with a weak opponent, there is more chance of victory for you. 

In the same way in the ecosystem all the organisms compete with each other for their better survival. Some can live with other organisms but some cannot. In such cases the weakest organism will be eliminated by the strongest one. Most of the competitions depend on the availability of resources needed for them to survive. So how do we know about these kinds of competitions among the organisms? For that we need to do some experiments or studies on them. Right? So many scientists conducted experiments on different species to know how they are behaving during the competition and also to find out the techniques they used to survive. Here in this article we are going to discuss in depth about some of the experiments on competition. 

Table of contents

• Competition
• Experiments on competition
• Significance of competition
• Practice Problems
• FAQs

Competition 

It is a type of population interaction between two or more organisms for obtaining the same resources. These resources can be water, nutrients, space, sunlight, food, mating etc. 

                             Fig: Outcome of competition between species A and B

When there are competing species present, the fitness of one species is noticeably reduced. The term ‘fitness’ in this context refers to an organism's capacity for reproduction and the delivery of healthy, fruitful progeny. Natural selection favours the more superior and fit species, which survive and are chosen, while the less superior and unfit species are eliminated from the competition. This interaction has a negative effect on both the interacting species (-/- interaction). 

Types of Competition

There are two types of competitions based on the type of species involved in the competition. They are the intraspecific competition and interspecific competition. 

Intraspecific competition

It is the competition between individuals of a single species. The members of the Silver gorilla population is an example for this. Within their group, the dominant or alpha male mates with the female gorillas. They engage in a fight with other male members who want to mate with the same female. Intraspecific competition normally reduces birth rates and raises death rates. This is required to manage population size in the ecosystem.

GIF: Gorillas competing with each other for proving dominance

Interspecific competition

It is the competition for a shared resource between members of various species. For example, zooplankton is a food source for both the local fish and the visiting flamingos in the lakes of South America. These two species compete for the same food source while having no connection at all. It demonstrates that animals that are entirely unrelated can also compete for the same resource.

                          Fig: Flamingos and fishes feeding on the zooplankton

Interference competition 

There is another type of competition called interference competition which demonstrates that, even in times with ample resources, competition might still exist. 

Even when resources like food, shelter, and space are plentiful, the presence of one species may interfere with the ability of another species to feed effectively. This type of rivalry, called interference competition, demonstrates that competing species do not necessarily clash over scarce resources. Even in times with ample resources, competition might still exist. When one organism or species physically restricts another species or organism's access to resources, it is called 'interference competition'.

For example, the Abingdon tortoise in the Galapagos Islands went extinct within a decade of the introduction of goats to the island, perhaps as a result of the better browsing efficiency of goats. Therefore, even though there were plenty of resources available, such as grazing areas, the presence of the goats interfered and inhibited the Abingdon tortoise's ability to efficiently forage.

                  Fig: Competition between goats and Abingdon tortoises in Galapagos island

Experiments on Competition

Since competition is a very interesting topic to observe and study, scientists have done many experiments on this. Through that they could know about the techniques and methods of competition adapted by different organisms. 

Gause’s exclusion principle

Based on his research with various Paramoecium species, a Russian biologist named Georgy F. Gause proposed his theory regarding interspecific competition in nature in the 1930s. It states that two closely related species competing for the same resources cannot coexist indefinitely and the competitively inferior one will be eliminated eventually. 

                Fig: Georgy F. Gause 

Experiment by Gause

An aquatic single-celled ciliated protozoan called Paramoecium feeds on bacteria, yeast, algae, and other tiny protozoans to survive. In petri plates, he cultured P. caudatum and P. aurelia separately and together in one plate. Each petri plate received the same quantity of nutrients.

                             Fig: Culture plates on the first day of the experiment

For three weeks, he counted the number of organisms on each plate every day. He noticed that the distinct cultures in the petri plates expanded tremendously. However, in the petri plate containing the combined culture, P. aurelia increased while the numbers of P. caudatum decreased. So, here in the competition for resources, P. aurelia defeated P. caudatum. This he called competitive exclusion.

                                Fig: The petri dishes after three weeks

The competitively inferior species will eventually be eliminated, according to Gause's competitive exclusion principle. This argues that two closely related species competing for the same resources cannot coexist permanently. However, this rule only applies if a certain quantity of the resources are available in the system under study.

Competitive release

 A species whose distribution is mainly restricted to a small geographical area, that means it is space constraint, because of the presence of a particular competitively superior species, is found to expand its distributional geographical range dramatically once the competing species is removed experimentally. It is referred to as a competitive release. It is evident that competition exists in nature.

Joseph Connell demonstrated competitive release with his study on two barnacle species, Balanus and Chthamalus, that competed for the same space on the rocky sea coasts of Scotland. Barnacles are sessile organisms in the adult stage. Larval barnacles attach to a substrate and grow into adults in that spot.

Experiment by Joseph Connell

In Scotland's rocky intertidal zones, the barnacle Balanus predominates and pushes out the barnacle Chathamalus.

Joseph Connell carried out a well-known series of removal experiments in the 1950s to look for possible competitive interactions between these two kinds of barnacles. Connell documented that Balanus normally occupies the intertidal zone, while Chthamalus normally occupies the coast above high tide. When he experimentally removed Balanus, Chathamalus colonised the intertidal zone and overgrown. The experimental removal of Balanus allowed Chthamalus to undergo competitive release (relief from competition). 

Thus, in the presence of Balanus, Chthamalus can occupy only its realised niche (above high tide), but when Balanus is absent, Chthamalus can occupy its fundamental niche (above high tide and the intertidal zone).

                Figure : Competitive release shown by Chthamalus

He discovered that the Chathamalus grew more quickly after the superior Balanus was eliminated from the area because there was less competition. The term ‘competitive release’ refers to this behaviour.

Therefore, competitive release happens when a species, whose distribution is constrained to a narrow geographic area, drastically increases its range of distribution after the superior competitor species is eliminated. This is due to the fact that the presence of the superior species was making the competition tough to survive.

Resource Partitioning

Resource partitioning is a mechanism evolved when more than one species competes for the same resource in nature. It promotes coexistence and reduces the intensity of competition. For example, five closely related species of birds like warblers living on the same tree were able to withstand competition and stay together due to behavioural differences in their foraging activities. 

Experiment by Gause on resource partitioning

Gause cultivated P. caudatum and P. bursaria with the same quantity of nutrients in a series of tests. In petri plates, he cultured P. caudatum and P. bursaria separately and together in one plate. Each petri plate received the same quantity of nutrients.

                          Fig: Culture plates on day one of the experiment

He observed that neither species reached the point of extinction; rather, they coexisted and they both thrived. In the nutritional medium, P. caudatum consumed the bacteria whereas P. bursaria consumed the yeast. They were still in competition with one another, though, as evidenced by the fact that their growth was slower than when they were raised independently. Resource partitioning is the term used to describe this type of interaction.

                          Fig: Culture plates after some weeks of the experimen

When two species compete for the same resource, a phenomenon known as resource partitioning allows them to avoid conflict by utilising distinct feeding schedules, different foraging habits, etc.

MacArthur’s experiment on resource partitioning

MacArthur's research revealed that different warbler species that live in a tree distribute their feeding time among various portions of the tree in different ways. He discovered that they also have various foraging habits.

                           Fig: MacArthur

MacArthur studied five closely related species of insectivorous birds called warblers like Cape May, Black-throated green, Yellow-rumped, Bay-breasted and Blackburnian. They lived on the same coniferous trees and appeared to be an exception to the competitive exclusion principle which states that two species with the same niche essentially cannot coexist as one will always out-compete the other and displace it. Niche refers to the interrelationship of a species with all the biotic and abiotic factors affecting it.

He divided the trees into different zones. Then he recorded feeding positions of the given different warblers within each of them. One species of warbler was found to feed more among the abundant newly formed needles and buds of the tip of the branch, between 20 and 30 feet from the top of the tree. A different species of warbler fed mostly dead needles almost at the same height but normally in the middle zone of a branch. A third warbler species fed on the bare, lichen-covered base of the branch. Similarly, various different positions on trees were distinguished. 

MacArthur also tried to record the details of the foraging habits of warblers and discovered that they also differed. They also had different sleeping times, and thus the times of their peak food requirements are not the same. They are partitioning a limiting resource, their supply of insects and is hence called ‘resource partitioning’. It allows them to coexist despite competition.

For example, the Cape May warbler lives on the outer side of the tree because it feeds on flying insects. In the deeper interior of the tree, the other warblers that eat insects are observed. The warblers feed at various times throughout the day since they have varying sleeping schedules. Due to this their peak feeding requirements were not occuring at the same time. They were dividing their limited supply of food resources, that mainly include insects.

                              Fig: Different types of warbler species and their foraging habitats

Experiment by Crombie on competition

Crombie revealed that Trilobium completely eliminates Oryzaephilus among the two kinds of beetles grown in flour. The immature forms of Oryzaephilus were discovered to be actively being destroyed by Trilobium. However, both groups were discovered to be alive when they were separated by small glass plates.

                                    Fig: Flour beetles

Significance of competition

The population interaction called competition has more significance in an ecosystem. Some of them are as follows: 

• Continuous competition for food resources results in adaptations in organisms. For example, drongos have adapted themselves to human habitats. Burning farm lands give them an opportunity to capture insects. The agile bird will manoeuvre inside and across fire flames catching fleeing insects on the move. It shows that they have adapted to the heat of the flames. This reduces their competition for food with other creatures 

                                                                  Fig: Drongo

• It results in resource partitioning and coexistence of different species. For example, Five closely related species of warblers living on the same tree were able to avoid competition and co-exist due to behavioural differences in their foraging activities.

                Fig: Different types of warbler species and their foraging habitats 

• It results in the elimination of the weaker individuals from the population. For example, if there is a high population of rabbits in an area, it will result in competition. As rabbits are herbivores, they will be depending on the grasses, shrubs or plant products for their food (carrots, turnips etc.). Hence they will develop a competition among themselves for the available resources (food, shelter and mating) and the fittest one will survive at the end. 

                     Fig: Intraspecific competition among rabbits for food

• It is required for the balance of food webs and sustainability in the ecosystem. 

Practice Problems

Q 1. Niche overlap denotes ____________.

a. two species exhibiting mutualism
b. two species actively cooperating
c. both a and b
d. Sharing of one or more resources by two species

Answer: Each organism has a niche, which is a consistently defined range of environmental circumstances that it can withstand, diversity in the resources it uses, and a specific functional role within the ecological system. The niches of two species overlap when they compete for the same resources, such as food, habitat, and mates. For example, lions and hyenas compete with each other for deers. Lions typically pursue and kill deer. The hyena will consume the leftover meat once the lion has finished eating. In this case, lions and hyenas are sharing the same food source. Hence the correct option is d.

                             Fig: Niche overlap for sharing food

Q 2. Two typical population interactions are listed below. Select the answer that accurately fits both A and B.

a. A - Parasitism, B - Competition
b. A - Competition, B - Parasitism
c. A - Competition, B - Commensalism
d. A - Parasitism, B - Commensalism

Answer: When two species compete for the same scarce resources, it is referred to as a type of population interaction called competition. Both of the interacting species are negatively impacted by this (-/- interaction). An example of this is the competition between resident fish and visiting flamingos for zooplanktons, which is a common food source, in several shallow lakes in South America. As a result, A is a competition. A sort of population interaction known as parasitism occurs when one organism benefits at the expense of another. The parasite is the creature that benefits (+), whereas the host is the organism that suffers (-). A good example is the presence of ticks on dogs. B is therefore parasitism. Hence the correct option is b.

                                    Fig: Ticks on dog

Q 3. It is possible for two species competing for the same resource to coexist by using distinct feeding techniques. It was supported by ___A________ and is known as ___B_____.

a. A - Gause, B - competitive exclusion
b. A - MacArthur, B - competitive exclusion
c. A - MacArthur, B - resource partitioning
d. A - Gause, B - resource partitioning

Answer: In nature, while competing for the same resource, many species may develop strategies that encourage cohabitation. MacArthur did research on five kinds of warblers, which are insectivorous birds. They shared a single coniferous tree. He noticed that the various warbler species spent varied amounts of time in various regions of the tree. It was discovered that one type of bird preferred to eat near the ends of branches while another species preferred to eat largely in the centre of the tree. At the trunk of the tree, a third kind of warbler was feeding. Similar distinctions were made among various tree locations. The foraging strategies of the warblers were also noted by MacArthur, who found that they varied. Their differing sleeping schedules meant that their peak eating needs did not occur at the same times. As a result, they were able to coexist by lowering the level of competition for the same resource, such as the availability of insects. Resource partitioning is the term used for this phenomenon. Hence the correct option is c.

Q 4. What is a competitive release?

Answer: Competitive release happens when a species, whose distribution is constrained to a narrow geographic area, drastically increases its range of distribution after the superior competitor species is eliminated. It is due to the fact that the presence of the superior species was making the competition tough to survive.

FAQs

Q 1. What are keystone species?
Answer: Keystone species are any species whose elimination would significantly alter the composition of the community. It is comparable to the central keystone of an arch, whose removal causes the building to collapse. For example, starfish mostly eat mussels and barnacles. When the starfishes are removed, the population of mussels takes over and the algae, whelks, and limpets are driven out.

Q 2. What is a local extinction?
Answer: Extirpation, another term for local extinction, is the disappearance of a species (or other taxon) of plants or animals from a particular geographic region while it continues to exist elsewhere. Extinction rates locally and globally are contrasted. Local extinctions indicate a shift in the local environment.

Q 3. What are umbrella species?
Answer: Umbrella species is referred to as a species whose conservation will protect a large number of naturally co-occurring other species. 

Q 4. What is meant by character displacement?
Answer: When two closely related species coexist in the same environment, an evolutionary shift known as character displacement takes place. Natural selection favours a divergence in the characteristics (morphology, ecology, behaviour, or physiology) of the species under such circumstances. Character displacement often reduces interactions which reduce the fitness that might otherwise result in competitive or reproductive exclusion. Reproductive exclusion is believed to promote species coexistence.

Related Topics