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Chapter 44: Ecological and Evolutionary Consequences of Species Interactions
Questions:
1. Competition (-/-)
Consumer-resource, predation, herbivory, parasitism (+/-)
Mutualism, sometimes symbiosis (+/+)
Commensalism (+/0)
Amensalism (-/0)
2. Competition is a symbiotic relationship where two or more species want the same
resources. Interspecific is when two separate species compete. Intraspecific is when two
organisms of the same species compete.
3. A limiting resource is in the shortest supply relative to demand. It is a resource that is most
competed for. Resource partitioning is differences in species for resource use. For example,
if a finch and a bee both seek the nectar from a flower, but the finch can also eat seeds, then
the finch will usually turn to seeds because there is less competition. Over time, the finch
will evolve to only eat seeds, not nectar. Resource partitioning decreases interspecific
competition, but increases intraspecific competition.
4. (see vocab for definitions) The interests of a consumer species and a resource species are at
odds. Over time, a predator-prey arms race takes place for survival. Each species continually
evolves better defenses and better offenses to gain an advantage.
5. Mutualism is how humans benefit from bacteria in our guts because we need them to break
down our food, and they need us as a host to survive because we give them food. An
example of commensalism is how cow-birds follow cattle in order to feed on insects that the
cows’ grazing interrupts. The cow is unaffected, but the cow-bird benefits. Amensalism is
like when a herd of elephants stampedes through a jungle. They are unaffected, but the
insects and small organisms they trample are harmed. With parasitism, one organism
benefits, but the other is harmed. When paramecium enters a human, the protist thrives in
its new habitat, but the human is hurt and possibly dies.
6. Kangaroo Rats always bury seeds in the ground for later use whenever possible. If there is a
good year and the rats have plenty of seeds, then the seeds buried in the ground can
germinate and grow when the rains come.
7. When organisms use resource partitioning over competition, the species will evolve. In the
example above, the small finches that seek nectar become less common than the large
finches that eat seeds as the finch population shifts to a seed only diet. Now, the finch
population has mostly large finches.
8. In an environment with both small and large beaked birds, where the small beaks can eat big
and tiny seeds but the large beaks can only eat big seeds, the small beaked birds would have
greater fitness. Over time, the population would have more small beaked birds than large
beaked birds and the population would grow because more of that species would be able to
eat a larger variety of seeds. This is directional selection.
9. As with the evolutionary arms race, mimicry gives the advantage to the prey. The prey will
disguise themselves as something the predator wishes to avoid. For example, zebra
butterflies lay their small yellow eggs on the leaves of the passionflower plant so that the
baby caterpillars will have an immediate food source when they hatch. The passionflower
plant uses mimicry by adapting to have yellow dots on its leaves so that the butterflies move
on to other plants that haven’t already been taken. The plants with fake yellow dots have
increased fitness because they will survive and won’t be eaten by baby caterpillars. Thus,
passionflowers will survive to reproduce more of their kind.
10. Invasive species are non-native, reproduce quickly, spread wildly, and negatively affect
native species. An invasive species includes buckthorn. It chokes out all other native
underbrush and flowers, even trees. It spreads like a weed. It was imported as an
ornamental plant from somewhere in Europe.