Unformatted text preview: L111 Quiz #3 ANSWER KEY 1. On the graph below draw two lines one showing a logistic growth curve and one showing an exponential population growth curve. Label curves. You only have to sketch in a curve showing a typical logistic growth curve and a typical exponential curve. (4pt) 2. Indicate carrying capacity on the above graph with a dotted line. Are both of these population growth curves influenced by a carrying capacity? If not, which one isn't? (3pts) Carrying capacity influences logistic growth; not exponential growth. Exponential growth is unconstrained no limits on growth. Logistic growth takes into consideration the resources available in the habitat that supports the population. 3. What is carrying capacity? Is it always constant? If so, why? If not, why might it change? (3pts) Carrying capacity is the amount of resources needed to support the population. No, carrying capacity is not constant. It could change as the resources or habitat changes. It could change as a result of a decrease/increase in food supply, increase/decrease in predation pressures, loss of habitat through storms, etc..... 4. When constrained by a carrying capacity, growth rate is slowest at what point(s) on the growth curve? (1pt) The growth rate will be slowest at the beginning with a small population size and as the population size reaches carrying capacity. 5. On the graph below, show two logistic growth curves with different growth rates. Label curves (Be sure to indicate which one has a higher and which one has a lower growth rate). (4pts) Note: The carrying capacity should be the same. 6. When might a population overshoot carrying capacity, even if only temporarily? (1pt) If the adults in the population have enough resources in order to reproduce then the population size will increase (due to the reproduction and the continuing presence of the adults). It is possible the reproduction pushes the population size above carrying capacity and as a result there will be pressure on the population (more competition, fewer resources to go around, etc.) and the population will decrease back towards carrying capacity. 7. When in nature are you most likely to see an exponential growth curve, even if not indefinitely? Briefly explain. (2pts) Seen in rebounding or reintroduced species which are well below capacity when put back into the environment. As a result of the low population size and the appropriate habitat requirements the population growth is quite rapid and so below carrying capacity as to appear to be unconstrained. Introduced species are also likely to show exponential growth as the constraints that they would normally face may not be present in the habitat in which they are introduced (e.g., no natural predators). 8. Give one densitydependent and one densityindependent factor that can influence population growth. What is meant by densitydependent vs. independent factors (how do they differ)? (2pts) Densitydependent factors have a different degree of impact on the population depending on the density of the population. For example, disease spreads more rapidly in a population that is very dense, and potentially killing more individuals than in a population that is not as dense. The impact varies with the density. Densityindependent impacts the population the same regardless of density. An entire population can be hurt if there is an extreme cold snap, and it will affect the population the same if it is a small or a large population ...
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 Fall '11
 Dr.SusanHengeveld
 2pts, 1pt, 4pt, 3pts

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