n., plural: interspecific competitions
Definition: a type of competition that involves different species
Interspecific Competition Definition
In Biology, competition is defined as the process that occurs among species that have to compete for limited resources in order to survive. This competition over resources occurs between organisms because these species have niches that overlap and so they are forced to use the same resources such as food, water, and shelter. Competition is a perfect example of one of the many symbiotic relationships that happen in ecosystems.
Competition can be interspecfic or intraspecific. In biology, intraspecific competition is defined as the relationship of competition between organisms of the same species. If this is an interspecific competition, how can we define interspecific competition? What is the interspecific competition?
Interspecific competition is the symbiotic relationship of competition between species that are completely different. This interspecific competition science definition takes place in two ways — those based on mechanism and those based on the outcome.
Interspecific competition is a form of competition between different species inhabiting the same ecological area. In biology, competition means rivalry for a limited resource, such as food, mate, shelter, etc. In interspecific competition, though, the rivalry is between different species as opposed to another form of competition, intraspecific competition, which is a form of rivalry between the same species.
Examples: interspecific competition between lions and leopards that vie for similar prey and interspecific competition between rice paddies with weeds growing in the field.
There are many different types of examples of competition in nature and interspecies competition examples as well. One of the most common ones is the lion and hyena symbiotic relationship. The two have been captured in Figure 1 above. In Maasi Mara, the adult male lion and spotted hyena share the same ecosystem, Hence, the two animals must compete for the same prey, both being carnivorous hunters. However, this can negatively impact the living of the other as the presence of one will bring about less food for the other.
Another simple example of interspecific competition happens in the ocean where, though fish are abundant, some species are often the same prey for several dolphins, birds, and sharks. Different plant species compete with each other regularly in their environments. In fact, plants often secrete chemicals in their leaves and roots to prevent other plants from growing too close to them so they can avoid competing for resources like nutrients, water, and sunlight.
There are two types of interspecific competition in ecology. These are those interspecies competitions that are based on the mechanism of competition and those based on the outcome of the competition. The mechanism is the way that the competition occurs and the outcome is the result of the competition happening, the aftermath.
Based on mechanism
Exploitative competition occurs as species indirectly compete for the same resources in an ecosystem. This would be like plants that all grow in the same area. However, some plants are able to absorb water and nutrients at a quicker pace than others. Another form of competition based on the mechanism is the interference mechanism. This is direct and can even be termed as aggressive behavior. This is because these competing species will physically fight each other for whatever they are competing for whether it is a resource or a potential mating partner.
For instance, aphids often need to defend their feedings sites from other competing animals. They do this by sending out their younger aphids from the better sites. This can also happen within the plant communities.
In fact, within the forests, the top or emergent layer of trees controls the nutrients and how they are distributed. This is because they are massive and often need more of all the resources than the shrubs and other grass-like plants (forest floor). Even their branches and leaves determine how much sunlight the smaller plants will get by blocking access to the sun. This can be easily viewed in Figure 2 below. All these competition relationships are all based on the way the competition happens and how it occurs.
Based on outcome
The two competition types that are based on outcome are scramble and contest competition in an ecosystem. Scramble competition between species occurs when the competitors are vying for the same resource. Nevertheless, the resources may be evenly shared among the species individually and so when the population begins to increase, there are not enough resources for numerous individuals to thrive at optimum. In contrast, contest competition happens when some individuals control or take over the resources so, despite population growth or decline, these individuals will always survive. In scramble competition, the competition for a finite resource — when becomes inadequate over time — may lower the survival chances of all competing species (or to mass extinction in extreme cases). That is because the resource is not contested, rather, it is partitioned equally among the competing species.
In intraspecific competition, a scramble competition is one that is exhibited by a flock of sheep grazing in a particular pasture area. Since the area is limited, there will only be that specific amount of food in the area. However, as time goes by and the flock multiplies, there are more mouths to feed but the same area of pasture. This then becomes scramble competition as the sheep must battle for the limited amount of grass to consume. The white-faced monkey shows a great example of contest competition when the alpha males take control of the resources of the group. These males tend to be larger, stronger, and easily get a mate as they dominate the pack and take charge. No matter what occurs within the group or in the surroundings, the alpha males will usually survive due to this advantage.
As for interspecific competition, a scramble competition could be a competition for a limited resource. Think of it as two different species of aerobic bacteria thriving in a limited source of oxygen. Both bacterial species could eventually die as the oxygen continues to deplete over time. Take for instance the sheep grazing on pasture from the passage above. If cows were added to this field, there would be interspecific scramble competition. This is because the sheep and the cows would now have to compete for the grass not only among their own but also among the other species. As for contest competition, a hypothetical example is when two different species compete for the same limited resource, and only one of them “wins”. This form of competition is fairly seen in the animal kingdom. For example, two predators “compete” for prey; one of them wins especially if it is physically stronger or more adapted than the other.
Apparent competition can be defined as a type of indirect competition that occurs between two organisms. These organisms are both of completely different species but are both preyed upon by the same predator. These prey indirectly compete against each other in terms of survival. Often this can occurs when one of the prey has an abundant or sudden growth in their population. This causes the predator to have more food since there is more prey around. The predator population will then grow as well because of the accessibility to more food. However, this is often detrimental to the other prey whose population does not grow but now has more predators present to hunt it. This is the indirect competition between the two prey as now they must both fight to not be eaten by the predator.
We see apparent competition within ecosystems through both plants and animals. In plants, it is more common – but not limited to – when an invasive species comes into a niche in abundance, causing a herbivore to have more options for food. In animals, it could be a random population boom or decline via more or fewer resources or also an invasive species.
Apparent competition can often be hard to distinguish in nature as it can be very complex and overlap with other kinds of competition. For instance, both chipmunks and squirrels are prey for the hawk. In the beginning, an increase in the chipmunk’s population will benefit the squirrels as there will be more chipmunks for the hawks to feed on and so the squirrels may be targeted less. However, the more chipmunks available to the hawks, the more nutrients they will obtain and so live at optimum which will cause a rise in the population of the hawks as well. Thus, increased predation will decrease the population of both the chipmunks and the squirrel, but since the squirrels already have a lower population, they suffer more. On the other hand, if the chipmunk’s population decreases, this will also affect the squirrels as they will now become the more regular source of nutrients for the hawk. This will also cause a decrease in the squirrel population.
All interspecific interactions have consequences. The interspecies competition will have negative impacts on either one or all of the species involved. These can lead to one of the species being forced to leave the ecosystem, one of the organisms having to find new ways to use resources, or even the entire population of a species being completely wiped out. All of these and many more consequences all affect the community and how it will develop in the future.
The competitive exclusion principle occurs when two species that use the same limiting resource can no longer co-exist in an environment. This was discovered through much mathematical analysis and study models, and concludes that eventually, one of the organisms must leave the area in order for them to both survive. If they both stay, one species will die off. This is also sometimes known as Gause’s Law.
The superior species will often take advantage of the way they use the resource and drive the other away. The inferior species will suffer and show a great declination in their population and so eventually move away before they become too endangered. If a forest has many carnivorous animals but a limited amount of prey, eventually there will not be enough prey for every species to get their required amount of nutrition. The top species will remain and the others will be forced to leave in order to continue to survive. They will find enough food for themselves in another location.
Niche differentiation is referred to as the process by which species that compete for the same resources begin to use their environments in different ways so that they are now able to coexist. If the species do not undergo niche differentiation, the competitive exclusion will force one of the species out of the environment. If the organism then does not want to move, nor does it want to die, it must begin to use other resources in the ecosystem or use them in other ways so that it can continue to thrive.
In the Caribbean, Central, and South America, there are thousands of species of lizards among which many may end up living in the same ecosystems. They will all share the same niche and resources. In order for them to be able to survive, the lizards have adapted to their surroundings each in their unique way physically, so that they all have their specific microhabitats. This allows the reptiles to become “masters” of their own spaces and so live in harmony with the rest of the lizards while still being able to obtain all their necessary resources.
Once competition exclusion and niche differentiation do not work, it is inevitable that a species will become extinct if it remains in an intense form of interspecific competition. Too much pressure on one species will cause a rapid population decline and eventually, the population of that organism will die out. This has been seen before with zooplankton who lived in the same rockpool. Since it is a rockpool, often there is nowhere else to go (so competition exclusion cannot occur) and a limited number of ways resources can be used (no niche differentiation either). Hence, eventually, species of zooplankton will die out and go extinct for lack of availability of resources. Figure 4 below shows the seclusion that a rockpool often has.
Impacts on communities
All the effects mentioned above and many others can contribute to the numerous impacts that interspecific interactive competition can have on communities within an ecosystem. These competitions have serious and long-term effects on how communities continue or change as they happen. Consider organisms that rely on seeds to feed on. These organisms come every year and eat many seeds from plants, which results in plants not being able to continue to reproduce. To combat this, many plants have adapted into the process of mast seeding, where the plants overproduce seeds. This allows the animals to be able to eat all the seeds they need while the plants are still able to get seeds in order to reproduce.
Competitive Lotka–Volterra Model
The competitive Lotka-Volterra model comes from the many impacts and effects interspecific competition has brought about. This is a mathematical model that takes into consideration the effects both species have on each other. They do this by using the formula below. N stands for the size of the population, t represents time. The carrying capacity is represented by K, the intrinsic rate is r and both α and β are representing different coefficients relative to the competition. When calculated, the results will show the effects that one species will have on the other and vice versa. The results can be turned into a graph which makes it easier to see what may happen next with the populations or to point out any trends.
The Equation used for the Competitive Lotka-Volterrra Model: (watch the video below to understand more about this equation)
Species 1: dN1/dt = r1N1 [(K1 – N1 – αN2)/K1]
Species 2: dN2/dt = r2N2 [(K2 – N2 – βN1)/K2]
Of course, for this model to work, as with all models in ecology, many assumptions must be made to obtain data. For instance, one must assume that there is no migration within any of the populations being observed. It must also be assumed that the carrying capacity for these models must remain constant as well as the competition coefficients for both the organisms being studied. Of course, assumptions are very rare when in the field and you cannot control the outcome of organisms and what they do. However, this model still makes for a fairly accurate tool to use when one wants to know the effect interspecific competition will have on different species of animals.
Try to answer the quiz below to check what you have learned so far about the interspecific competition.
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