1 | Page
ECOL111 - Species Interaction Questions
and Correct Answers
22. What are the two mechanisms by which interspecific
competition can occur? Ans: Exploitative competition - passive and
indirect competition through shared use of resources
Interference competition - direct competition with one species
actively inhibiting success/ survival of another species
22. What is the difference between functional and numerical
responses? Ans: Functional response - a change in resource
utilisation and physiology or behaviour of one species due to the
presence of another
Numerical response - decrease in the number of individuals/
biomass of a species in the presence of another (stronger evidence
for competition)
22. When does competitive exclusion occur? Ans: When a superior
species eliminates another species from an environment over
time/ generations
22. When does coexistence occur? Ans: When competition is
weaker i.e. through environmental heterogeneity, aggregated
distributions and resource partitioning with functional responses
22. How does competition cause evolution of species? Ans: Natural
select favours adaptations that minimise niche overlap and avoid
reductions in fitness due to competition i.e. Brooke sticklebacks
evolved specialised planktonic diet in lakes with benthic Ninespine
sticklebacks to reduce competition with modified narrowed
feeding niche
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, 2 | Page
22. What is niche complementarity? Ans: The use of specific niche
ranges and gaps by species to allow coexistence and habitation of
the entire niche i.e. Buttercups with soil dryness and aeration
preferences
22. What is interspecific competition? Ans: The process by which
individuals of one species suffer reductions in fecundity,
survivorship or growth as a result of the presence or activities of a
second species
22. What is plasticity? Ans: The ability of an organism to adapt
and cope in response to changes in it's environment usually
physiologically or behaviourally
22. How does functional responses affect the realised niche of
Voles? (Case study) Ans: Realised niche is smaller than potential
niche as Voles change use of niche moving to grasslands from
forested areas in order to reduce competition and overlap in
resource use with Shrews
22. How does numerical responses affect species? Ans: Lowers
carry capacity and equilibrium density of one or both species i.e.
Balanus and Chthamalus Barnacles
22. The Lotka-Volterra equation for two competing species Ans:
dN1/dt = r1N1 (K1[N1 + a12*N2]/K1)
22. Why is competitive exclusion rare in nature (i.e. Blue muscles
displacing seaweed)? Ans: - Competitive advantage may be
depending on conditions
- Environment is patchy/ unstable
- Niche adjustments
© 2025 All rights reserved
ECOL111 - Species Interaction Questions
and Correct Answers
22. What are the two mechanisms by which interspecific
competition can occur? Ans: Exploitative competition - passive and
indirect competition through shared use of resources
Interference competition - direct competition with one species
actively inhibiting success/ survival of another species
22. What is the difference between functional and numerical
responses? Ans: Functional response - a change in resource
utilisation and physiology or behaviour of one species due to the
presence of another
Numerical response - decrease in the number of individuals/
biomass of a species in the presence of another (stronger evidence
for competition)
22. When does competitive exclusion occur? Ans: When a superior
species eliminates another species from an environment over
time/ generations
22. When does coexistence occur? Ans: When competition is
weaker i.e. through environmental heterogeneity, aggregated
distributions and resource partitioning with functional responses
22. How does competition cause evolution of species? Ans: Natural
select favours adaptations that minimise niche overlap and avoid
reductions in fitness due to competition i.e. Brooke sticklebacks
evolved specialised planktonic diet in lakes with benthic Ninespine
sticklebacks to reduce competition with modified narrowed
feeding niche
© 2025 All rights reserved
, 2 | Page
22. What is niche complementarity? Ans: The use of specific niche
ranges and gaps by species to allow coexistence and habitation of
the entire niche i.e. Buttercups with soil dryness and aeration
preferences
22. What is interspecific competition? Ans: The process by which
individuals of one species suffer reductions in fecundity,
survivorship or growth as a result of the presence or activities of a
second species
22. What is plasticity? Ans: The ability of an organism to adapt
and cope in response to changes in it's environment usually
physiologically or behaviourally
22. How does functional responses affect the realised niche of
Voles? (Case study) Ans: Realised niche is smaller than potential
niche as Voles change use of niche moving to grasslands from
forested areas in order to reduce competition and overlap in
resource use with Shrews
22. How does numerical responses affect species? Ans: Lowers
carry capacity and equilibrium density of one or both species i.e.
Balanus and Chthamalus Barnacles
22. The Lotka-Volterra equation for two competing species Ans:
dN1/dt = r1N1 (K1[N1 + a12*N2]/K1)
22. Why is competitive exclusion rare in nature (i.e. Blue muscles
displacing seaweed)? Ans: - Competitive advantage may be
depending on conditions
- Environment is patchy/ unstable
- Niche adjustments
© 2025 All rights reserved
