Animal Ecology (Zoology 441) at UT Martin
Practice  Question Set #1 ? factors in ecology, scientific method, Connell study, types of error, statistics, sampling
  1. Ecology can be defines as "the scientific study of factors determining the distribution and abundance of organisms." (a) At what levels can distribution be measured? (b) At what levels can abundance be measured?
  2. What are the two categories of factor that determine the distribution and abundance of organisms?  Give examples of each.  Explain why the distinction between the two is not always clear cut.
  3. List the major types of biotic interaction discussed in lecture, state what causes each, and state whether each interacting species are positively or negatively impacted by the interaction.
  4. Explain why it is never possible to prove a hypothesis.
  5. Ecological studies can be descriptive or experimental; experimental studies can be lab-based or field-based.  What are the general pros and cons of each of these forms of study?
  6. Distinguish between systematic error and random error.  Which results in bias?  Which is most likely to be decreased by increasing sample size?  What are the major kinds of problem with interpretation caused by each type of error?  What are possible causes of each kind of error in ecological studies?
  7. In a scientific paper, you read that "the mean number of turtle nests per m2 in sandy soil is significantly higher than in clay soil (t= 8.2, df=34, p<0.01)." What does "significantly higher" mean in this statement?  What does p mean?
  8. Distinguish between the terms signficance and power.  Why do ecologists care about significance?  Why do ecologists care about power?
  9. What can ecologists do to increase statistical power in their studies?
  10. To study nest site choice in pileated woodpeckers (a species that excavates nest holes in trees), you sample large quadrats to describe the relationship between the number of woodpecker holes per quadrat and two vegetation variables: tree dbh (diameter at breast height, a standard measure of tree width), which you measure,  and amount of understory cover, which cannot be quantitatively measured but can be divided into two categories, high cover and low cover. If you sample quadrats at random, what kind of error will you avoid?  Suppose that you can only sample 10 quadrats.  How will this affect your conclusions if you find a significant association between number of holes and one of your variables? How will this affect your conclusions if you do NOT find a significant association between number of holes and one of your variables?
  11. An ecologist is interested in determining whether the abundance of beavers is related to the predominant tree type in woodlands.  The number of beaver lodges per hectare is compared between a pine forest, an oak-hickory forest, and a beech-maple forest.  Suppose there turn out to be significantly more lodges per hectare in the pine forest than in the oak-hickory or beech-maple forest.  The researcher wants to conclude that beavers are more abundant in pine forests.  Is this conclusion valid?  Why/why not?  If not, state an alternative hypothesis that could explain beaver abundance.  What would you do to better test between your hypothesis and the original hypothesis?
  12. You are studying vole (small rodent) density in a cow pasture by sampling the number of vole holes per m2 in a number of 1 m2 quadrats.  Since you notice that the cow pasture has two apparently different kinds of vegetation, one dominated by cheatgrass and one dominated by bluegrass,  you are careful to choose some of your quadrats in cheatgrass areas and some in bluegrass areas.  Why is this NOT the best way to sample vole density in this field?  What would be a better approach?
  13. In a study of territoriality in sparrows, researchers found that average territory size was larger during a cold year than it was during a warm year.  They concluded that temperature affects sparrow resources so they require larger territories during cold years.  What is wrong with this conclusion?  What information is needed to make this conclusion stronger?
  14. Suppose you are studying home range size in different habitats for two species of deer, mule deer and white-tailed deer.   You are using radio tracking to obtain accurate estimates of home range size.  You are able to study 8 mule deer in riparian habitats and 6 in upland habitats; you study 9 white-tailed deer in upland habitats and 7 in riparian habitats. Suppose you find that home range size is significantly larger for mule deer in upland habitats than mule deer in riparian habitats.  You find that there is no statistical difference in home range size between the two habitats for white-tailed deer.  In which conclusion do you have more confidence: (i) that home range size for mule deer is larger in upland than riparian habitats in the area you studied them, or (ii) that there is no difference in home range size of white-tailed deer between upland and riparian habitats in the area where you studied them?  Explain why you have more confidence in one conclusion than in the other.