Name:____________________________________

BIOL425: Population Ecology, Exam 2, Fall 2020

Use math and logic to answer each of the following. Where appropriate, use complete sentences arranged in a logical sequence to support your ideas. Points available per question are indicated in parentheses. If calculations are required, you must show your work to receive full credit. 78 points are available; your score will be the percentage of those points you earn.

1. What does it mean for a process to be density-independent? Provide an example of a density-independent factor that might influence population size or growth. (3)

2. The eastern screech owl (Megascops asio) roosts in tree cavities. As long as there are enough tree cavities available for all the owls in the population, the number of tree cavities has no effect on per capita birth or death rates. If there are more owls than the number of tree cavities, the per capita death rate increases with increased population size (because of increased rates of predation or death by exposure). How does this scenario differ from the traditional idea of density-dependent population regulation, as described by Nicholson (1956) or Turchin (1995)? Does it make more or less sense, and why? (8)

3. Briefly explain why habitat fragmentation greatly increases extinction rates. (3)

4. Invasive species are an important contributor to current extinction rates. After being introduced into a new habitat, invasive species are able to grow to unusually large population sizes, and therefore have negative effects on native species. What makes it possible for populations of invasive species to grow so much and so rapidly? (The best answers will address the Principle of Allocation.) (3)

5. Why are species with low body size and low population size probably rare? (2)
6. Consider a metapopulation of iguanas inhabiting a chain of small islands off the coast of South America. In year 1, there are iguanas on 15 of the 60 islands. The probability of a given empty island being colonized in a given year is 0.11, and the probability of the population going extinct on any particular occupied island in a given year is 0.12.

a. In year 1, what will be the rate of change in the proportion of islands occupied by iguanas, based on the Levins metapopulation model? (6)

b. Determine the number of islands that should be occupied when the metapopulation reaches equilibrium. (6)

c. Should this metapopulation go extinct, or should it persist? How do you know? (2)

 Table 1. Annual extinction and colonization rates for three species of shrew (genus Sorex) on small islands. From Hanski (1999). Species Body size (g) C E S. araneus 9 0.20 0.04 S. caecutiens 5 0.05 0.33 S. minutus 3 0.13 0.46

7. a. Based on the Levins model, which of the shrew metapopulations in Table 1 is most likely to persist long-term? (2)
i. S. araneus
ii. S. caecutiens
iii. S. minutus
iv. i and ii
v. i and iii
vi. ii and iii
vii. i, ii, and iii
viii. None

8. A follow-up study indicated that the effect of environmental stochasticity on extinction risk was negatively correlated with body size (i.e., larger shrews were less affected by environmental variation). Does this make biological sense? Why or why not? (2)

9. In a 13-year study of population dynamics of the invasive Asian shore crab (Hemigrapsus sanguineus) in Long Island Sound, Kraemer (2019) found that density declined over time, and the largest size classes declined the most. At the same time, average size of breeding females also declined (see figures below). Based on your understanding of life-history strategies, develop a hypothesis that would explain this pattern. Explain the reasoning behind it in enough detail that another student would be able to understand it. (8)

.

10. Two ecologists walk into a bar. After a few drinks, they begin to argue about which would be at greater risk of extinction: a population of 100 African elephants (Loxodonta africana) or a population of 100 house mice (Mus musculus). Provide the best argument you can in favor of each. (2.5 points each)

Why elephants are at greater risk:

Why mice are at greater risk:

11. Low population size is probably the single best predictor of extinction risk. Why are small populations generally at much greater risk of extinction than larger populations? (4)

12. Suppose that you discover a new species of gastropod in a deep-sea hydrothermal vent community. This species grows rapidly, reproduces at 3 months of age, and has several clutches of >20,000 eggs each year. It appears to follow a Type I survivorship curve (i.e., juvenile mortality is low, and most individuals survive to adulthood). The largest individual you observed is at least 150 years old.

When you submit your results for publication, one reviewer recommends rejection, saying your data are clearly flawed, while the second reviewer says you’ve made the most important discovery in modern population biology. Their reasoning is exactly the same. What is it about your results that is causing these reactions? (6)

13. Large animals should have higher lifetime probabilities of cancer than small animals because each cell division carries a risk of mutating towards a tumor lineage, and large animals have many more cells. However, this is not observed—a paradox that suggests large and/or long-lived species tend to evolve effective cancer suppression mechanisms. Based on the principle of allocation, the evolutionary value of cancer suppression should be determined by the ‘cost’ of suppression (decreased fecundity) vs. the ‘cost’ of cancer (reduced survivorship). Should effective cancer suppression be more common in more r-selected (fast life history) or K-selected (slow life history) species? Explain your reasoning. (5)

14. Modern humans have an unusually high lifetime risk of developing cancer (~43%). Based on the information above, what does this suggest about the life-history of pre-industrial humans compared to modern humans? (3)
15. Gotelli and Taylor (1999) found that the classical, Levins-style metapopulation model did not accurately reflect the dynamics of a stream fish metapopulation. Describe the major assumptions of the Levins model and explain how they were violated by the fish metapopulation. (8)
Bonus (1 point each)

1. There’s a terrible, horrible, egregious error somewhere in this exam. (Don’t worry, it doesn’t affect your answers.) What is it?

2. On an episode of the science fiction television program Doctor Who, the “Progenation Machine” can take a tissue sample from an individual, duplicate all their chromosomes many times, then assemble a new individual with a complete set of homologous pairs by randomly selecting two of each set of chromosomes. If this actually worked, and wasn’t just a fictional construct, what is the maximum number of genetically distinct individuals that could be produced in this way from a human?

3. Follow up: suppose a male human entered the Progenation Machine. Would it be possible for the machine to produce a female from his chromosomes? Why, or why not?

4. An Idaho Falls man recently was banned from Yellowstone National Park because he tried to do what?

5. What is the most interesting thing you’ve learned in one of your other classes in the last week? (BIOL396, 485, 497, or 499 don’t count. It’s got to be a regular class.)

## Why US?

##### 100% Confidentiality

Information about customers is confidential and never disclosed to third parties.

##### Timely Delivery

No missed deadlines – 97% of assignments are completed in time.

##### Original Writing

We complete all papers from scratch. You can get a plagiarism report.

##### Money Back

If you are convinced that our writer has not followed your requirements, feel free to ask for a refund.