Key for Exam 3 Biology 260 Fall 2003
Average on the exam was 73% - add 5 points to your total for a conservative estimate of your
grade on this exam.
Multiple Choice – average on the multiple choice part was also 73% or 11 out of 15 correct
1. a. 2. a. 3. b. 4. d. 5. b. 6. d. 7. a. 8. c. 9. a. 10. d. 11. c. 12. d. 13. d. 14. c. 15. c.
16. obligate 17. climax 18. I was looking for physical or structural but constitutive or passive are
also correct 19. satiation 20. indirect
21. In general, you did a good job on this one.
Examples:
An herbivore consumes plants and algae, but can be further defined by whether the organisms eat
part or the whole of the plant. When an animal eats the whole plant, such as when a deer eats a
whole sapling, it is considered to be predation because the plant is removed from the population.
When an animal eats only part of the plant, like a giraffe browsing on a tree, it is parasitism
because the plant is being consumed but the tree remains alive.
An herbivore can act as both a predator and a parasite. When an herbivore acts as a parasite it
eats only part of the plant or algae, not the whole thing (damaging it but still allowing it to
survive). An example of this is when a deer grazes and eats only the tops of the grass not the
whole plant. A predator herbivore eats the whole plant or algae, killing it. An example of this is
where an elephant tears a whole shrub out of the ground to eat it.
The herbivore-plant, predator-prey, and parasite-host relationships are types of consumerresource relationships. The predator-prey relationship involves the consumer killing the resource
like the lion kills the antelope. The parasite-host relationship does not involve killing the
resource (except in parasitoids). In parasite-host, the host is kept alive like a tick in humans. A
tick feeds off the human but does not kill it. The herbivore-plant relationship can kill the plant or
not. For example, a deer can eat a whole bush, bark, leaves and all and kill it. This would be an
example of predator-prey relationship because the resource is killed. But a ladybug can also eat
just a leaf on a bush and the resource is still living. This is an example of a parasite-host
relationship.
22. 4 points for the graph, 1 point for the explanation. Most people did well on this one. Graph
should have 4 bars for Bannow woods that add up to 100% with the bars more equal than the 4
bars that add up to 100% for Audubon woods. E.g., for Bannow Woods, 4 bars at 25% each and
for Audubon woods, 1 bar at 40%, 1 bar at 10% and 2 bars at 25%.
Examples:
Bannow Woods has higher diversity. Diversity is a measure of both species richness and
evenness. The two communities are equal in richness but Bannow Woods has higher evenness.
Bannow Woods has higher diversity because the diversity is defined by the combination of
evenness and richness. So if Bannow Woods has higher evenness and both have equal richness
then Bannow Woods is more diverse than Audubon Woods.
23. Most people did pretty well on this one. Most common mistakes were combining multiple
examples into one (e.g., mycorrhizal nitrogen-fixing bacteria) or describing other kinds of
mutualisms (dispersal or defensive).
A trophic mutualism involves two individuals who positively affect each other’s growth rates by
supplying one another with energy or nutrients. Lichens are an example of a trophic mutualism.
Lichens are symbiotic association between fungus and algae. The fungus benefits the algae by
increasing surface area and aiding in extraction of nutrients. The algae benefits the fungus by
supplying it with food in the form of photosynthetic products like carbohydrates and sugars.
Because each individual positively benefits the other by increasing growth rates by the
energy/nutrient transfers lichens are an example of a trophic mutualism.
A trophic mutualism is a mutualism in which the mutualism benefits the species involved in a
way that provides resources such as food, water, or nutrients. An example is the bacteria that
grow in the gut of a deer. The bacteria help digest tough plant material that the deer has eaten.
The deer provides a favorable habitat for the bacteria where it has a constant food source.
Trophic mutualisms exist between two organisms who aid each other in attaining energy, water,
or nutrients. Both organisms benefit from the relationship. For example, nitrogen fixing bacteria
fix nitrogen into a form that plants can use. The plant provides the bacteria with reduced carbon
compounds formed during photosynthesis. It is a mutual relationship in which the plant and
bacteria both benefit.
24. If you had trouble with this one, please review the table and associated text in Ch. 22 that
covers this (page 433).
One characteristic of early successional plants is that they produce small seeds. Late
successional plants, on the other hand, produce large seeds. This difference makes early
successional plants well-adapted to dispersing to an area through wind and water. Both provide
a very rapid dispersal to grow in areas before competitors arrive. Also, this allows them to travel
to bare areas through wind or water, areas that animals would not travel to before the smallseeded early successional plants provided a better environment. Early successional plants
produce lots of seeds whereas late successional plants provide few seeds. Since they are
dispersed by wind and water, early successional plants are well-adapted by producing many
seeds because most seeds end up traveling to unfavorable areas where they do not grow.
Without producing a lot of seeds, early successional plants likelihood of finding freshly
uninhabited areas would be greatly reduced. Many seeds allow many seeds to be lost but still
enough to survive and produce more seeds.
The early plants have fast growth rates compared to the late plants. This allows them to quickly
establish themselves and quickly reproduce to produce seeds to colonize other places. By
growing quickly, they have an advantage over the slower growing late plants by being able to
reproduce before they are replaced by them. The early plants also have many seeds which are
carried by wind and sea. This allows them to colonize new land before other plants colonize and
take over. They face little competition compared to later plants which may have lots of
competition. Having lots of wind dispersed seeds allows the plants to establish in lots of places
instead of the climax species replacing the climax species in the later plants.
One characteristic of early successional plants is that they have good seed dispersal mechanisms,
most late successional plants have poor seed dispersal mechanisms. This allows the early
successional plant to get to an area first after a disturbance or after formation of a new substrate.
Another characteristic of early successional plants is that they produce a large amount of small
seeds. Late successional plants produce a small amount of large seeds. The smaller seeds are
more easily dispersed into new habitats and the large amount of seeds helps ensure that not all
are lost to predation or unfavorable habitats.
25. a. Intraspecific competition is competition between members of the same species. The
information on survival of each tadpole species when grown alone gives you the relative
importance of intraspecific competition. Interspecific competition is competition between
members of more than one species. Because the two tadpoles species eat the same thing (small
invertebrates) and have reciprocal negative effects on each other’s growth rates, there is
interspecific competition. You don’t need to use the information from the experiment with the
fish predator to answer this question although some people used it to point out how predation
can affect competition.
Examples:
Tadpole species 1 exhibits some degree of intraspecific competition, enough to reduce the
survival of the species by about 30%. There is no evidence of intraspecific competition in
tadpole species 2, because growth with only members of its own species survival remains high at
100%. Interspecific competition is less significant in tadpole species 1 than tadpole species 2.
Tadpole species 2 hardly decreased the survival of tadpole species 1 whereas tadpole species 1
nearly killed off tadpole species 2. Interspecific competition is more important for tadpole
species 2 and intraspecific competition is more important for tadpole species 1.
For tadpole species 1, intraspecific competition has higher importance then interspecific
competition. When grown alone, it has 70% survival and when grown with tadpole species 2,
with no predators, it has 90% survival. For tadpole species 2, interspecific competition has
higher importance than intraspecific competition. When grown alone, it has 100% survival but
when grown with tadpole specie 1 with no predators, it has low survival (about 5%).
Intraspecific competition has higher relative importance for tadpole 1 than does interspecific
competition. When alone, with only intraspecific competition, Tadpole 1 had 70% survival but
when mixed with tadpole 2, with interspecific competition, it had 90% survival. For tadpole 2,
intraspecific competition did not have any impact on survival (100% when grown alone) but
interspecific competition had a large impact reducing survival by 80%.
25. b. The functional or interaction web should have 3 species, tadpole 1, tadpole 2, and the fish
predator. You don’t have information about the impact of the tadpoles on the population growth
of the invertebrates or vice versa so the invertebrates should not be included. Likewise, you
don’t have information about the impact of the tadpoles on the growth rate of the fish so leave
those out as well. There should be negative arrows going back and forth between the two
tadpole species with the arrow towards tadpole 2 (the impact of tadpole 1 on tadpole 2) being
much larger(thicker) than the arrow going the other direction. There should be a negative
intraspecific arrow going from tadpole 1 to itself. There should be negative arrows going from
the fish predator to each of the tadpole species but the arrow pointed to tadpole 1 should be
larger. Common mistakes here were not labeling the arrows with pluses or minuses and not
representing the strength of the interactions with different sized arrows. For the final, make sure
you understand the difference between the 3 kinds of webs we talked about in class.