Question Set 3_ENVI

Topics: Population ecology, Population, Population growth Pages: 8 (2580 words) Published: December 2, 2014
ENVS 105 Question Set Section #3 Fall 2014
Answer the following questions for your homework. Work on the questions after we have covered the topic in class. Bring any questions to class or office hours. These questions will help you on the exam. If you do not do them, the points will add up and hurt your grade.

To get credit, you must:
Answer all questions
Answer all parts of each question
Type your answers
Do complete and conscientious work
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1) Explain how the logistic population growth model modifies the exponential population growth model to incorporate the idea of resource limitation?

Exponential growth is possible only when infinite natural resources are available; this is not the case in the real world. Individuals will compete (with members of their own or other species) for limited resources. The successful ones will survive to pass on their own characteristics and traits (which we know now are transferred by genes) to the next generation at a greater rate: a process known as natural. To model the reality of limited resources, population ecologists developed the logistic growth model.

2) Using the Exponential Growth Model determine which of the following populations would be growing the fastest. Show your work. You can use a calculator.

A population with an r of .015 and N of 7000

A population with an r of .17 and N of 70

A population with an r or .093 and N of 573

3) Using the Logistic Growth Model, determine which of the following populations would be growing the slowest. Show your work. You can use a calculator.

A population with an r of .027, N of 7000, and K of 8400

A population with an r of .17, N of 70, and K of 750

A population with an r or .093, N of 573, and K of 800

4) Why can’t density independent factors regulate the size of a population to prevent it from overshooting carrying capacity? When the density of a population is low (few individuals in a given area), resources are not limiting. There are plenty of resources for everyone. More individuals can give birth, and fewer individuals will die. Overall, the population will grow in size and become denser. When the density of a population is high (many individuals in a given area), resources are more limited for each individual. Because of this, more individuals will die, fewer individuals will be born, and the population size will decrease and become less dense.

5) Read section 10.11 of the textbook. Explain the difference between the life history characteristics of r-strategists and K-strategists.

6) For competition to occur, (1) the competing individuals must overlap in the use of the resource that they are competing for and (2) the resource must be in limited supply relative to the demand that the competing individuals have for that resource. Using the information and graph below explain why these 2 conditions need to be true for competition to occur.

Planthoppers feed on protein,
chlorophyll, and moisture produced
by salt marsh grass.
Salt marsh grass (Spatina
alterniflora) heavily populated
by planthoppers (Prokelesisia
marginata) show reduced
concentrations of protein,
chlorophyll, and moisture.
As shown in the graph to the
right, planthopper survival
and reproduction declines
as the number of planthoppers
feeding on a plant increases.

The planthopper, chlorophyll, and moisture lives on the salt marsh grass. The population density of them were controlled by enclosing the insects with Spartina seedlings at densities of. At the highest density, they showed reduced survivorship, decreased body length, and increased developmental time. These signs of intraspecific competition were probably the result of reduced food quality at high planthopper densities. Plants heavily populated...
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