Biology 104-41 -- Changing Natural Environment (Kasmer)

Answers to short-answer questions on Exam 3

 1. When it comes to identifying species, some scientists are "splitters" (recognize many different species), and others are "lumpers" (recognize fewer different species). If you owned a very valuable piece of property that happened to contain habitat for a species that is being considered for protection under the Endangered Species Act, would you want your legislators in Congress to consult a lumper or a splitter when trying to decide whether to protect the species? Why?

Given the premise that you have a valuable piece of land and that you would like to be able to profit from its value, you would want your legislators to consult a lumper. Such an individual would be likely to identify the population on your property as belonging to a species with a larger range and larger total number of individuals than if a splitter, and the species would therefore be less likely to be listed as endangered. In turn, if it is not listed as endangered, you are likely to be able to profit by the sale or development of your property. (You may have argued that personally you would want to protect the species, but this ignores the premise in the question that deals with the economic value of the land.)

2. Leucaena has been widely hailed as a miracle tree and the solution to many of the problems that lead to (or result from) deforestation in the tropics. Identify two characteristics that make it so useful, and two potential problems that might result from its widespread use.

Characteristics that make it useful include that it is a nitrogen-fixer (and can therefore thrive on poor soils, and can actually enrich the soil), and that it can provide not only fuelwood, but construction materials and animal forage as well. Potential problems involved with widespread planting include the potential that it will escape from areas of cultivation and cause additional loss of biodiversity in remaining natural communities, and the problems associated with depending on monocultures of a single species (including the potential that a single pest species could lead to loss of a resource that people have come to depend upon, and the attraction of and maintenance of populations of pest species).

3. Define what is meant by the term "essential amino acids". How would someone consuming a vegetarian diet make sure that they are getting all of the essential amino acids?

Essential amino acids are amino acids that we (or other organisms) are incapable of synthesizing ourselves, and that therefore must be consumed as proteins in our diets. A vegetarian can ensure that they are getting all of the essential amino acids in their diet by eating a varied diet that includes both corn (or other grains, such as rice) and legumes (i.e., beans), because each of these types of foods contains some essential amino acids that are lacking in the other.

4. Identify two factors that increase the water- and nutrient-holding capacities of soil. Explain how each of these factors helps increase the ability of soil to retain water and/or nutrients.

Characteristics of soil that increase nutrient- and water-holding capacities include humus and other organic matter (that provide structure to the soil (makes it less massive) and that can attract and hold onto both water and mineral nutrients), and loamy texture (i.e., that is a mix of sand, silt and clay: the sand helps provide pore spaces, and the fine particles have lots of surface area to hold onto water, and lots of negative charges that can attract and hold on to mineral nutrients). I also accepted answers that dealt with agricultural practices that prevent erosion and help keep the soil cool and moist.

5. Folks in an area where rainfall is sparse and soils are generally poor are interested in maximizing the productivity of their herds. Describe an appropriate grazing plan for them, considering whether the herd should be one or more species (and what the characteristics of those species should be), how much land would be required for grazing to be sustainable, and how long animals should spend in a given area before being moved on to another area. Explain the reasoning behind each of your decisions.

In order to maximize production on marginal lands, the people should use mixed-species herds (so that all different components of the vegetation are utilized) that are moved from place to place (before soils and vegetation are degraded, and so that grazed areas have a chance to recover before they are grazed again). Because plant growth in the area is likely to be slow, a large total area of land would be required so that individual patches have a chance to fully recover before being grazed again.

6. Describe three important ecological services provided by forests, and describe how forests are able to provide these services.