Ch. 44 – Ecological and Evolutionary Consequences of Species Interactions – Questions
1. Describe the five main interspecific interactions and how each affects the species either
positively, negatively or neutrally.
Interspecific Competition: members of two or more different species use the same resource
(-/-)
Consumer-Resource Interactions – organisms gain their nutrition by eating other living
organisms or are eaten themselves (+/-)
Mutualism – both organisms are benefited (+/+)
Commensalism – one organism is benefited while the other is unaffected (+/0)
Amensalism – one participant is harmed while the other is unaffected (-/0)
2. Define competition, and distinguish between interspecific and intraspecific competition.
Competition is an interaction between two organisms where one’s fitness is lowered in the
presence of the other. Interspecific is competition that is outside a species (a lion against a
tiger) and intraspecific in competition that takes place inside a species (a lion against a lion).
3. What is a limiting resource and summarize the concepts of resource partitioning and how it
affects the habits and lifestyles of a species.
A limiting resource is food, water, sunlight, space that is in the shortest supply relative to
the demand. Resource partitioning is when species divide a niche to avoid competition for
resources. For example, some plants evolve to reproduce at different times of the year so
that there is less competition for pollinators. Resource partitioning essentially changes the
habits and lifestyles of a species because they have to adapt to reduce competition and fit
the needs of others.
4. Define predation or consumer-resource interactions, and describe the effects of natural
selection on predator–prey relationships.
Consumer-resource interactions (predation) are interactions in which one organism feeds
on another to attain nutrients. Natural selection sides with the prey because if all the white
butterflies that cannot camouflage are eaten, then the ones that can camouflage will
survive and will no longer be prey.
5. Distinguish among mutualism, commensalism, amensalism, and parasitism, and give
examples of each.
Mutualism: both organisms are benefited; ex: mycorrhizae in the roots of orchids
Commensalism: one organism is benefited while the other is unaffected; ex: puffins use the
burrows made by rabbits to lay their eggs
Amensalism: one species is harmed and the other is unaffected; ex: elephants stepping
through a forest and crushing insects with every step
Parasitism: a parasitic organism invades the host, usually consuming part of it, but not
killing it; ex: tapeworms in the intestines of cows
6. Page 862. Read about the Kangaroo rats and explain their effect on grass growth. Highlight
which aspects of their behavior had the greatest effect on grass.
The kangaroo rats were very beneficial to grass growth, creating a large increase in grass
growth. Their natural behavior of burying excess food for later creates more grass growth.
7. Explain how competition and resource partitioning leads to changes in population
distribution and density.
Competition reduces the population density and distribution because with competition,
only one organism benefits. Resource partitioning positively affects the population
distribution and density by increasing or keeping it neutral. It reduces competition between
species making the environment easier for organisms to survive in.
8. How does competition increase fitness of a species and quickly lead to adaptation?
Competition increases the fitness of a species by winning that species more resources. With
competition, only one wins, so the species that wins gets all the benefit, increases its
fitness. This can quickly lead to an adaptation because if an organism possesses a rare trait
that is very beneficial, it will survive to pass that trait on, eventually leading to an
adaptation.
9. How does mimicry increase fitness?
Mimicry is an organisms close resemblance to an inanimate object, such as a plant leaf or
tree bark. This helps an organism by blending in to its surroundings and avoiding predators,
therefore increasing fitness.
10. What kinds of attributes make a species invasive? Give an example.
Invasive species reproduce rapidly and spread widely. They have negative effects on the
native species that are unable to compete and defend themselves against the new species.
Examples of invasive species include the emerald ash borer, various types of carp, and the
Asian tiger mosquito.