19.3 - Competition

Question 1

Where such competition arises between members of the same species it is called…

Answer 1

intraspecific competition.

Question 2

Where competition arises between members of different species it is called…

Answer 2

interspecific competition.

Question 3

What determines the size of populations

Answer 3

• availability of resources
• The greater the availability = the larger the population.
• The lower the availability = the smaller the population.
• Availability of resources also affects the degree of competition between individuals which results in a smaller population.

Question 4

Give some examples of infraspecific competion
1) for limpets
2) for oak trees
3) for Robins

Answer 4

1) limpets competing for algae, which is their main food. The more algae available, the larger the limpet population becomes.
2) oak trees competing for resources. In a large population of small oak trees some will grow larger and restrict the availability of light, water and minerals to the rest, which then die. In time the population will be reduced to relatively few large dominant oaks.
3) robins competing for breeding territory. Female birds are normally only attracted to males who have established territories. Each territory provides adequate food for one family of birds. When food is scarce, territories become larger to provide enough food. There are therefore fewer territories in a given area and fewer breeding pairs, leading to a smaller population size.

Question 5

Explain competitive exclusion principle

Answer 5

• When populations of two species are in competition one will normally have a competitive advantage over the other.
• The population of this species will gradually increase in size while the population of the other will diminish.
• If conditions remain the same, this will lead to the complete removal of one species.
• therefore no two species can occupy the same niche indefinitely when resources are limiting.
• This is known as the competitive exclusion principle.

Question 6

In many cases we suspect that competition is the reason for variations in population. In practice it is difficult to prove for a number of reasons, these reasons include:

Answer 6

• There are many other factors that influence population size, such as abiotic factors.
• A causal link has to be established to show that competition is the cause of an observed correlation.
• There is atime lag in many cases of competition and so a population change may be due to competition that took place many years earlier.
• Data on natural population sizes are hard to obtain and not always reliable

Question 7

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Answer 7

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