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ECOL111 Module 3 - Species Interactions
Questions and Correct Answers
What are the two main mechanisms by which interspecific
competition can occur and what do they mean? Ans: Exploitation
competition - Indirect competition through shared resources.
When a species uses a resource, there are less resources available
for other species, there is no active competition.
Interference competition - Direct competition involving one
species actively preventing access to resources, or inhibiting
growth or survival of another species. This doesn't just involve
behaviour meaning it can involve plants as well. An example of
this is allelochemicals being secreted by some plants to inhibit the
growth rate of other species.
What is the difference between functional and numerical
responses? Ans: Functional responses - where the use of resources
by a species is changed based on the presence of another species.
A change in the behaviour or physiology of a species.
Numerical response - where the presence of one species is lower
when the competitor is present, than if they are not. This is
generally easier to recognise as competition by ecologists.
Explain when and why competitive exclusion might occur. Ans:
The superior competitor could cause the extinction of the other
competitor, but this is a very extreme occasion. It's rare because:
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- Competitive advantages may depend on conditions
- The environment is patchy
- Species can adjust their niche.
These factors suggest that extinction due to competition does not
occur very often and only in extreme cases.
Describe evolution in the face of sustained competition. Ans:
Where we see a highly diverse community (e.g. fish on a coral reef
very high biodiversity) there must have been strong competition
and so they have evolved super specialised niches so that these
species don't have to compete for resources.
Sometimes due to a long history of fundamental responses and
evolution, some species may perform better in the presence of a
(historical) competitor due to niche modifications.
Explain the role of niche complementarity in structuring
communities. Ans: Niche complementarity is where, due to a
history of competition, partitioning of resources and reduced
niche overlap occurs. This is because of functional responses and
evolution causes different dimensions of niches to shift between
species and coexisting can occur.
What are the different types of consumers and how do they differ?
Ans: Predators
-Invariably kill their prey during attack
-Consume several prey in their lifetime
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Grazers (herbivores)
-Normally they don't eat the whole plant, meaning they don't kill
the organism
-Attack several plant victims in their lifetime
Parasites
-Also don't kill victim, they need their host alive
-Differ as they typically attack a single victim (or just a few) in
their lifetime
Parasitoids (properties of parasites and predators)
-They invariably kill their host as they eat it from within
-Attack only one host in their lifetime
Explain how coevolution has shaped adaptations in both predators
and prey. Ans: Predator-prey relationships have evolved in
response to each other based on selection pressures, most
commonly the predators exert selection pressures onto the prey as
the predator will use the prey as a food source initially. The prey
therefore adapt over time and the predators must adapt to this to
be able to catch their prey. This keeps repeating over time.
© 2025 All rights reserved
ECOL111 Module 3 - Species Interactions
Questions and Correct Answers
What are the two main mechanisms by which interspecific
competition can occur and what do they mean? Ans: Exploitation
competition - Indirect competition through shared resources.
When a species uses a resource, there are less resources available
for other species, there is no active competition.
Interference competition - Direct competition involving one
species actively preventing access to resources, or inhibiting
growth or survival of another species. This doesn't just involve
behaviour meaning it can involve plants as well. An example of
this is allelochemicals being secreted by some plants to inhibit the
growth rate of other species.
What is the difference between functional and numerical
responses? Ans: Functional responses - where the use of resources
by a species is changed based on the presence of another species.
A change in the behaviour or physiology of a species.
Numerical response - where the presence of one species is lower
when the competitor is present, than if they are not. This is
generally easier to recognise as competition by ecologists.
Explain when and why competitive exclusion might occur. Ans:
The superior competitor could cause the extinction of the other
competitor, but this is a very extreme occasion. It's rare because:
© 2025 All rights reserved
, 2 | Page
- Competitive advantages may depend on conditions
- The environment is patchy
- Species can adjust their niche.
These factors suggest that extinction due to competition does not
occur very often and only in extreme cases.
Describe evolution in the face of sustained competition. Ans:
Where we see a highly diverse community (e.g. fish on a coral reef
very high biodiversity) there must have been strong competition
and so they have evolved super specialised niches so that these
species don't have to compete for resources.
Sometimes due to a long history of fundamental responses and
evolution, some species may perform better in the presence of a
(historical) competitor due to niche modifications.
Explain the role of niche complementarity in structuring
communities. Ans: Niche complementarity is where, due to a
history of competition, partitioning of resources and reduced
niche overlap occurs. This is because of functional responses and
evolution causes different dimensions of niches to shift between
species and coexisting can occur.
What are the different types of consumers and how do they differ?
Ans: Predators
-Invariably kill their prey during attack
-Consume several prey in their lifetime
© 2025 All rights reserved
, 3 | Page
Grazers (herbivores)
-Normally they don't eat the whole plant, meaning they don't kill
the organism
-Attack several plant victims in their lifetime
Parasites
-Also don't kill victim, they need their host alive
-Differ as they typically attack a single victim (or just a few) in
their lifetime
Parasitoids (properties of parasites and predators)
-They invariably kill their host as they eat it from within
-Attack only one host in their lifetime
Explain how coevolution has shaped adaptations in both predators
and prey. Ans: Predator-prey relationships have evolved in
response to each other based on selection pressures, most
commonly the predators exert selection pressures onto the prey as
the predator will use the prey as a food source initially. The prey
therefore adapt over time and the predators must adapt to this to
be able to catch their prey. This keeps repeating over time.
© 2025 All rights reserved
