CHAPTER 41 SPECIES INTERACTIONS
Scientific Skills Exercise
Teaching objective: This exercise reinforces the ability of students to make and interpret bar
graphs and scatter plots. As described below, it also provides an excellent opportunity to teach
students about evolution as well as invasive species ecology.
Teaching tips: A version of this Scientific Skills Exercise can be assigned in MasteringBiology.
Along with the technical skills it presents, the exercise provides a good opportunity to teach
about evolution, using invasive species ecology as an example. Through the answer to question
3, students should reason out that snakes that can produce an enzyme nullifying the toad toxin
more). This ability would likely increase the fitness of snakes with this ability compared to
snakes without it.
Answers:
1.
2. Black snakes will not prey on cane toads in areas where cane toads have been present for 40
4. Dependent variable: percentage reduction in snake swimming speed. Independent variable:
number of years cane toads were present in the area.
5. In part 1, the independent variable consists of two nonnumerical categories: cane toads present
Interpret the Data
Figure 41.4 The smallest beak depth observed for G. fortis on Santa María and San Cristóbal
Islands is 10 mm. Therefore, the predicted beak length is 10 mm × 1.12 = 11 mm.
Suggested Answers for End-of-Chapter Essay Questions
See the general information on grading short-answer essays and the suggested rubric at the
beginning of this document.
6. Scientific Inquiry
Hypothesis: The kangaroo rat is a keystone species in the desert. (Apparently, herbivory by the
7. Focus on Evolution
Character displacement means that there has been disruptive selection in two closely related
species with the result that some feature shared by both (perhaps an anatomical feature like a
8. Focus on Information
Sample key points:
On the island without predators, the bright coloration would offer no benefit, so it might fade
or disappear over time.
Sample top-scoring answer:
Based on this case of aposematic coloration and Batesian mimicry, evolutionary theory would
predict different outcomes for this fly species on different islands. On the first island, a lack of
9. Synthesize Your Knowledge
Two ecological interactions, pollination (a mutualism) and predation are suggested by the scene