Species Competition

Species Competition

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7.6 Intraspecific and interspecific competition
When resources in an ecosystem are scarce, there is competition between organisms for that resource. As the rate of
competition in an ecosystem increases, the rate of reproduction decreases (as there are fewer resources to be shared
amongst the individuals) and the death rate increases (as the organisms have fewer materials to survive on).
Intraspecific competition
Intraspecific competition is within members of the same species. This tends to be less common than competition
between members of different species, and so intraspecific competition mostly occurs when there is either a low level or
resources or a very high population of that species. When resources are abundant in the ecosystem, or when the
community is small, there is very little need for members of the same species to compete with each other.
An example of intraspecific competition might be found in lions. In a pack of lions, the dominant male will have the main
feed from a fresh kill, and the others will then compete for it once the dominant male has finished. By this method of
competition, the strongest (fittest) members of the species will succeed, getting more of the resource and having a larger
chance of survival.
Interspecific competition
Interspecific competition is between members of different species, which happens on a much wider scale. This can affect
both the population size of a species, and also the distribution of its members within an ecosystem. If two species
compete for the same resources in the same way (i.e. under very restricted conditions), then usually one will be more
effective than the other, and so the weaker species will be excluded.
However, species can avoid interspecific competition by means of niche specialisation, either by using different resources
to overcome competition, or to begin using resources in different ways. For example, a species may not necessarily
change the entire type of plant normally eaten, but perhaps just changing the time of day they go to feed on the plants.
Competition between different species is common when the
factor in question is space. This is common particularly when
beach sessile (non-mobile) organisms are involved. The diagram to
the left shows a beach shore. We can use the example of
barnacles to show interspecific competition.
For example, say species 1 (S1) was one species of barnacle,
species 1 existing only at high tide and is covered for a part of the day
high tide
by the high tide; and species 2 (S2) was another species which
lives only at low tide. When S2 is removed, the other species,
S1 thrives both at high tide and low tide, so why when S2 is
potential present does S1 only exist at high tide? We can decipher from
low tide range of species 2 this that S1 is able to survive in the whole range, as it can
species 1 resist desiccation (drying out when the high tide goes down),
however, it does not outcompete S2 at low tide.
We can also tell that S2 is quick to colonise and so competes well for space at the low water mark, where it is constantly
wet and so does not suffer desiccation, and so survive there but do not outcompete S1 at high tide regions because that
barnacle simply cannot survive there, allowing S1 to thrive.


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