ICA 5 COMPETITION PROBLEMS Group Name ____________Your name ________
Question 1. Buttercups growing on ridge and furrow.
1. In one sentence summarize the results. The two species each have their peak
abundance in either furrow or ridge. OR Sp 1 is largely on the ridge and Sp 2 is
largely on the furrow.
2. Provide two alternative hypotheses (if…then) for the observed pattern.
A. If…. tolerance of environmental (abiotic) conditions explains the distribution
then when grown alone, sp 1 grows better on F than R; sp 2 grows better on R than F.
OR Each species grows better than the other species on its home site
B. If (symmetric) interspecific competition explains the distribution,
Sp 1 grows better than sp 2 on F, but sp 1 grows worse than sp 2 on R.
Sp 2 grows better than sp 1 on R, but sp 2 grows worse than sp 1 on F.
3. Draw one complete experiment that would test both hypotheses.
Grow each species alone and with the other species in both ridge and furrow sites.
4. What specific results from the experiment would provide support for your
hypothesis 1. above?
Environmental tolerance Hypothesis:
When grown alone, sp 1 grows better on F than R; sp 2 grows better on R than F.
OR Each species grows better than the other species on its home site.
OR Competition Hypothesis:
When grown together:
Sp 1 grows better than sp 2 on F, but sp 1 grows worse than sp 2 on R.
Sp 2 grows better than sp 1 on R, but sp 2 grows worse than sp 1 on F.
Question 2. Barnacle zonation in intertidal area. 16.11
1. What are two alternative hypotheses to explain the zonation of barnacle sp B and C?
A. If…environmental tolerance explains the zonation…
B. If…interspecific competition explains the zonation…
2. Draw one complete experiment to test the two hypotheses.
Grow each species alone and with the other species in both sites.
3. Given these results, what are two conclusions:
1. Competitive exclusion: Sp B outcompetes Sp C and prevents Sp C from using
the same space in B zone.
2. Sp B is prevented from zone C by physiological intolerance.
Question 3. Galium sp. 1 and Galium sp. 2 don’t grow together. 16.1
1. What are two alternative hypotheses to explain their growing on different soil types?
A. If…tolerance of soil types explains their distribution…
B. If…competition explains their distribution…
2. Describe the experiment illustrated to test possible hypotheses.
Grow each species alone and with the other species in both soil types.
3. Summarize in two sentences the key results
A. When grown alone, each species grows best in its native soil, but it can
grow on the non-native soil.
B. When grown together in its native soil, each native species is dominant over the
non-native species.
4. What is the main conclusion? The two species are excluded from the other site by
competition from the other species; they grow poorly on the non-native soil and
are easily out-competed.
5. Is competition symmetric between the two species? Yes; they depress the other
species equally when on their native soil.
Question 4. Desmodium sp. 1 and Desmodium sp. 2
1. What are the two key questions being addressed by this experiment?
A. Does interspecific- or intraspecific-competition have a greater negative impact on
growth?
B. Is the answer to A different between the two species?
2. Summarize in two sentences the key results.
A. Both intra- and interspecific competition depressed plant growth in both species.
B. For D.n., inter- was stronger than intra-specific competition; the reverse held for
D.g.
3. What is the main conclusion? Species differ in inter0 and intra-specific competitive
ability.
4. Which species is the better competitor? Under interspecific competition, D.g.
depresssed growth of D.n. more than D.n did on D.g. So D.g. is the better competitor.
5. Grass 1 on granite soil and Grass two on serpentine soil.
1. What are two alternative hypotheses that explain the species’ distributions?
A. Tolerance of the soil conditions explains the distributions…
B. Interspecific competition explains the distributions…
2. Design an experiment to address the role of soil factors limiting distributions.
Grow the two species in absence of competition on each of the two soils.
3. What is the main conclusion for:
Grass 1 can’t grow on serpentine because of its intolerance of some inherent factor
and not because of competition from Grass 2.
Grass 2 can grow on granite soil, so intolerance of soil conditions does not explain its
absence from granite soils.
4. Design two experiments to determine whether competition limits the distribution of
the two grasses (hint: think of addition and removal).
A. Plant two species together on each soil type.
B. Remove each grass in areas of contact zone.
5. Is competition symmetric or asymmetric? asymmetric
What is the main conclusion about Grass 1’s competitive ability? Competition from
Grass 1 limits Grass 2 on granite because Grass 2 grows well when Grass 1 is
eliminated
What is Grass 1’s tolerance of the stressful serpentine soil? Despite its competitive
ability, Grass 1 is intolerant of serpentine soils, even when Grass 2 is absent.
What may be a general principle relating to competitive ability vs. tolerance of
stressful conditions? Trade-off: stress tolerant = poor competitor under favorable
conditions; strong competitor = unable to tolerate stressful conditions.