1.When Semibalanus is excluded from below the tidal zone:
Many Chthamalus individuals grow well in the Semibalanus exclusion area.
Semibalanus quickly overrun areas above the tidal zone.
Chthamalus individuals do not grow at all in the exclusion area because they cannot reach and settle there.
Any of the above are possible on different rocks (e.g., in different runs of the simulation).
2. When Chthamalus is excluded from high up in the tidal zone:
Many Semibalanus individuals grow well in the Chthamalus exclusion area.
Occasional Semibalanus individuals grow in the Chthamalus exclusion area but they tend to die quickly through too much exposure to air.
Semibalanus individuals do not grow at all in the exclusion area because they cannot reach and settle there.
All of the above are equally likely.
3. In 1917, biologist A. G. Tansley performed a famous series of studies on two species of bedstraw, a plant that was used to stuff beds. In nature, heath bedstraw grows on peat soil, and slender bedstraw grows on limestone soil. Tansley discovered both species can grow on both types of soil when the other species is absent. He hypothesized competition explains why, in nature, the two species do not coexist. Which experimental approach would best test his competition hypothesis?
A transplantation experiment, where both species are grown together in each soil type, and the number of plants of each species is counted after the duration of the experiment
An exclusion experiment, where slender bedstraw is planted in a plot of peat soil, and heath bedstraw is excluded from the plot for the duration of the experiment
An exclusion experiment, where heath bedstraw is planted in a plot of limestone soil, and slender bedstraw is excluded from the plot for the duration of the experiment
An experiment where peat and limestone soils are mixed together, and both species of bedstraw are planted
You are studying the intertidal zone of a previously unstudied island. You find three species of barnacles on the rocks. Species A is most abundant in the upper intertidal zone, Species B in the middle, and Species C in the lower, as shown below.
4. You conduct an exclusion experiment: You locate three experimental areas on rock faces that are the same size and span all three intertidal zones (upper, middle, and lower). In each experimental area, you exclude all but one species of barnacle for the duration of the experiment, as illustrated in the diagram below.
The diagram also shows the numbers of individuals for the unexcluded species in each intertidal zone at the end of your experiment. Based on the data, what can you conclude?
Species A and B compete with Species C in the upper intertidal zone.
All three species are equally well adapted to all three habitats.
Species C may lack the adaptations necessary to survive in the upper intertidal zone.
Species A has the best adaptations to all three zones.
5. Based on the results above, you study the settlement patterns of the three species. You establish transects on each of your experimental areas (which are evenly distributed among the upper, middle and lower intertidal zones) and remove all barnacles. Each day, you count the number of colonizers of each species in each transect, then remove them. This allows you to measure colonizing ability (not competition).For 30 days. Based on your results in the table below, and your knowledge of the distribution of these barnacles in the wild (see diagram above) which statement is most likely to be true?
Species C is the superior competitor in all three intertidal zones.
Competition between species A and B explains their distributions in the wild.
Competition is not a factor that influences the distributions of these species.
Species A is better adapted to the upper intertidal zone than the middle or lower.
6. Continuing your studies, you perform a transplant experiment. You chisel up multiple rocks from the upper intertidal zone, each holding 10 individuals of Species A, and move them to the lower intertidal zone among individuals of Species C. You count the number of individuals of each species present at the end of 30 days. Based on your findings, what can you conclude? (Remember that all 3 species settle in this zone at equal rates.)
Species A and B lack the necessary adaptations to survive in the lower intertidal zone.
Species C likely outcompetes Species A and B in the lower intertidal zone.
Species A and B compete with one another for space in the lower intertidal zone, reducing the number of individuals of both species.
Species A outcompetes Species B in the lower intertidal zone.
7. Remember that Species B is more abundant than the other two species in the middle intertidal. Both Species A and B settle in that range at the same rate and both survive in that zone equally well when the other is excluded. You conduct a transplant experiment similar to that in question 8, transplanting multiple rocks, each with 10 individuals of Species A, into the middle intertidal zone. You count the number of individuals of each species present at the end of 30 days. Based on your findings below, what can you conclude?
Species B outcompetes species A in the middle intertidal zone.
Species B has better adaptations to the physical environment of the middle intertidal zone than does Species A.
The presence of Species C in the samples means that no conclusions can be drawn.
Neither competition nor differences in adaptation to the physical environment alone explain the distributions of Species A and B.
8. You now turn your attention again to the lower intertidal zone. Individuals of all three species can survive there in the absence of the others, and all three species settle there at the same rate. If a predator were present that fed only on Species C, you would expect to see fewer individuals of Species C. What else would you reasonably expect to observe, based on the data you’ve collected?
You would expect a sparsely populated lower intertidal zone, because individuals of Species A and B would still be rare.
Species B would dominate the region because it is better adapted to the lower intertidal zone than is Species A.
Species A would dominate the region because it is the best adapted of all three species.
You would expect an increase in the number of individuals of Species A, Species B, or both, but you can’t predict which would dominate.
