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Chapter 44 Unit Questions
1. Describe the five main interspecific interactions and how each affects the species positively,
negatively, or neutrally.

Competition (-/-) refers to the interaction in which two or more different species use
the same resource. Interspecific competition can affect the population growth of a
species negatively because it can result in extinction if the competing species uses up
the resource.

Consumer-resource interactions (+/-) are those in which organisms gain nutrition by
eating other living organisms or are eaten themselves. This type of interaction is
positive for the consumer but negative for the resource.

Mutualism (+/+) is an interaction that benefits both species.

Commensalism (+/0) is an interaction in which one species benefits while the other is
unaffected.

Amensalism (-/0) is when one species is harmed while the other is unaffected.
2. Define competition, and distinguish between interspecific and intraspecific competition.

Competition is when two or more different species use the same resource.
Interspecific competition refers to competition involving organisms of the same species
(i.e. finding mating partners, territorial competition) while intraspecific competition
involves different species (i.e. food, sunlight).
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 the resource that is in the shortest supply relative to demand.

Resource partitioning, differences between competing species in resource use, is a
mechanism that can cause intraspecific competition to be stronger than interspecific
competition.

For example, if finches and bees both eat nectar, but finches can also eat seeds, then
finches will turn to seeds because there is less competition. Overtime, finches will
evolve to eat only seeds rather than nectar. This shows how resource partitioning
affects habits and lifestyles of different species.
4. Define predation or consumer-resource interactions, and describe the effects of natural
selection on predator-prey relationships.

Predation or consumer-resource interaction is when a predator/consumer consumes
another organism, the prey/resource, for an energy source. Predator-prey
relationships often result in an “evolutionary arms race” in which the prey evolves
better defenses and the predator evolves better offenses; however, neither gains any
significant advantage over the other.
5. Distinguish among mutualism, commensalism, amensalism, and parasitism, and give
examples of each.

Mutualism is an interaction between organisms of different species that benefits both
species. An example of mutualism is the relationship between mycorrhizal fungi and
plants, in which mycorrhizae expand a plant’s root surface, increasing the amount of
soil the plant can explore for nutrients. In return, the fungus obtains the products of
photosynthesis.

Commensalism is an interaction in which one species benefits while the other is
unaffected. An example is when cattle convert plants into dung, which dung beetles
can use for nutrition. In this interaction, the cattle are neutrally affected while the
beetles are positively affected.

Amensalism is an interaction in which one species is harmed while the other is
unaffected. An example is a herd of elephants or bison grazing the plains and crushing
insects, plants, or other small animals. This is amensalism because the elephants or
bison are unaffected while the organisms they crush are harmed.

Parasitism is an interaction in which one species benefits from or lives off of another
species, that is usually harmed. An example of this is fleas on a dog.
6. Read about the Kangaroo rats and explain their effect on grass growth. Highlight which
aspects of their behavior had the greatest effect on grass.

Kangaroo rats have a tendency to bury seeds in the ground for later use, if necessary.
This aspect of their behavior causes a greater abundance of grass if it is a good year
and the rats have more than enough seeds to eat, as the seeds buried in the ground
germinate and grow during rainfall.
7. Explain how competition and resource partitioning leads to changes in population distribution
and density.

Resource partitioning causes species to evolve overtime, whereas competition can lead
to extinction if one species beats out the other for resources. With resource
partitioning, as species switch over to alternate resources to reduce competition, the
species population shifts over to accommodate those new habits and traits.
8. **How does competition increase fitness of a species and can quickly lead to adaptation?

Competition can help species to get rid of inferior traits but keep useful traits. For
example, since small beaks can eat both big and tiny seeds, but the large beaks can
only eat big seeds, the small-beaked birds have greater fitness. Over time, the small
beaks would out-survive the big beaks, and there would be a greater small-beaked
bird population (natural selection).
9. How does mimicry increase fitness?

Mimicry gives advantage to prey by allowing them to mimic or disguise themselves as
something the predator is trying to avoid. For example, zebra butterflies lay eggs on
passionflower leaves for baby caterpillars to eat once they hatch, but they do not lay
eggs on leaves that already have eggs. Over time, passionflower leaves have adapted
to have yellow dots that mimic the butterfly eggs, so that butterflies avoid those
leaves. This increases the leaves’ fitness because it allows them to not be eaten by
baby caterpillars.
10. What kinds of attributes make a species invasive?

Invasive species are generally non-natives to an area, reproduce rapidly, spread
widely, and usually have negative effects on native species. An example of an invasive
species is the purple loosestrife, which was introduced into North America in the early
1800s. The purple loosestrife now dominates many wetlands and has crowded out
many native species such as cattails, affecting the life cycles of wetland organisms like
waterfowl and amphibians.