Supplemental Instruction
Iowa State University / Leader: / Steven F.
Course: / A ECL/BIOL 312
Instructor: / Dr. Jurik, Dr. Stewart
Date: / 12/6/2017
Population Dynamics
A population initially consists of 30 individuals (Nt = 30). Four individuals immigrate to the population and three individuals emigrate out of the population, and seven individuals are born and four die. What is new population size (value for Nt + 1)?
If population size changes in a way that is consistent with the model (Nt+1 = rNt), describe how this population will change over time. Under what conditions might a population’s actual growth pattern agree with predictions of this model?
Although some populations with low numbers and densities (e.g., endangered Whooping crane) can grow in an exponential manner until encountering limits to growth, dynamics of other small populations are inconsistent with exponential growth model predictions. These populations, when small, tend to continue to decline to extinction (an Allee effect). Using the demise of the heath hen on Martha’s Vineyard island as an example, describe environmental, genetic, and demographic factors that collectively can cause an Allee effect.
For a hypothetical population whose growth is consistent with a logistic growth pattern, and whose carrying capacity is 100 individuals, what would be the best estimate of the maximum sustainable yield? Justify your answer. What are the advantages of harvesting a population according to its maximum sustainable yield, instead of harvesting at levels that are above or below the maximum sustainable yield?
Draw age structure pyramids for two populations, one of which is likely to a) increase in the future and one of which is likely to b) a decline in the future.
Below are two survivorship curves. Provide the name of a species or taxon that is likely to have a survivorship curve resembling the curve on your left, and do the same for the curve on your right. Which of these survivorship curves best approximates the survivorship curve observed in a loggerhead sea turtle population? Based on the observed survivorship curve (and age-based survivorship), would the human-induced death of a single newborn individual, or a single young adult, have greater negative consequences on the welfare of this endangered species?
Based on lecture discussion and your understanding of ecology, provide specific examples of ecological factors (specifically density-dependent factors) and social factors that might eventually cause the global human population to stabilize or decline.
Communites
You measure species diversity in two communities that are located in the same geographic region. Species richness in communities A and B is identical, but community A has greater species evenness than community B. Provide two possible ecological explanations for differences in species evenness in the two communities.
Describe how evolutionary history and geographic isolation cause differences in species composition between continents? Specifically, what evolutionary processes cause these differences in species composition?
In terrestrial communities, there is a strong relationship between species richness and latitude. Describe this relationship and provide likely ecological explanations for it.
Species richness is strongly related to habitat size (habitat area) and degree of habitat isolation (distance between patches of similar habitat). Describe the relationship between habitat size and species richness that has been consistently observed. Describe the relationship between habitat isolation and species richness that has been consistently observed. Use your understanding of Island Biogeography Theory (and considering resource abundance and diversity, immigration, and genetic factors (or evolutionary mechanisms) to provide explanations for relationships between habitat area and species richness, and habitat isolation and species richness.
Although a habitat might appear to be homogenous in regard to environmental conditions, species richness can still be high in such a habitat. Use Hutchinson’s “Paradox of the Plankton” and additional knowledge of ecology to explain how species richness can be high in such an environment.
Describe how species diversity should change across a gradient of increasing intensity and frequency of disturbance events (e.g., physical disturbance, predation), according to the Intermediate Disturbance Hypothesis.
Multiple species of warblers (a family of birds) coexist in forests, even though each uses the same habitat (trees) for nesting and foraging, and each consumes the same food type (insects). These species appear to compete for the same resources, but a detailed study by MacArthur (1958) indicated that they use “resource partitioning” to avoid competing with each other. Describe MacArthur’s study results to demonstrate your understanding of resource partitioning. Describe an evolutionary mechanism that is likely to result in resource partitioning when two or more species use and potentially compete for the same resource.
In a study of ecological succession conducted in Glacier Bay, Alaska, investigators monitored effects of biotic interactions on spruce tree growth across four successional stages (pioneer species stage, Dryas shrub stage, alder stage, climax spruce stage). Describe their results, indicating if investigators observed a net negative (inhibitory) effect or net positive (facilitative) effect of existing plants on spruce growth at each stage. What ecological factor(s) appeared to be the reason for the observed net effect at each stage?
In a case study, Tilman and colleagues conducted an experiment to evaluate effects of plant species richness on subsequent plant abundance/production in a community experiencing adverse (drought) conditions. Results demonstrated that under drought conditions, plant production (and community resilience) were greater when species richness was high at the beginning of the experiment. Provide ecological explanations for these results.
Niche/Predation
What is Hutchinson’s concept of the niche? While mathematically elegant, his concept is somewhat harder to grasp than Elton’s definition (which is?)
In terms of the hypervolume concept of the niche, distinguish fundamental niche from realized niche.
In what types of environments would you expect to find “generalists” and “specialists”?
What are some characteristics of predators that enhance their ability to find and capture prey? (what are some major categories?)
Why are some plants predaceous (i.e., they are predators)?
What are characteristics of prey that enhance their survival? (what are some major categories?)
What are different types of adaptive coloration (e.g., cryptic, aposematic, disruptive) and how does each work?
Why does aposematic coloration depend on predators having some ability to learn?
What are some advantages of group living?
What is the confusion effect?
What are three common styles or strategies for hunting and what is each one?
Cycles in snowshoe hare and lynx populations:
Are lynx controlling the prey populations?
Is hare abundance, driven by food supply, controlling the lynx population?
What did Krebs et al.’s experiment demonstrate?
What does this experiment suggest about single factors versus multiple controlling factors in ecological interactions?
How might (what kind of) stress lead to physiological changes that affect hare reproduction?
What is mimicry, and what are some different types?
What is an amensal relationship? A commensal relationship? What is an example?
Why is “mutual exploitation system” a more accurate description than the normal human perception of “mutualism”?