Deck 4: Population Genetics and Natural Selection

Question 1

Many species of plants and animals that are associated with boreal forests also occur on mountains far to the south of the boreal forests. Using what you have learned about microclimates, predict how aspect and elevation would influence their distributions on these southern mountains.

Answer 1

Boreal forests, also called Taiga regions, are forests in the northern hemisphere characterized by coniferous trees. The plant and animal species found in the boreal forests are adapted to a climate characterized by the following:
• cold temperatures
• snowfall
• short and cool summers
• cold and long winters
If such a climate is found in another habitat, there is a possibility of finding the species of boreal forest in such habitats. For example, the mountains to the south of the boreal forests experience a climate similar to the boreal forests, and hence the species of boreal forests can also be seen on these mountains.
The organisms live in habitats characterized by microclimates. The microclimate may be different from the macroclimate of the geographical area. The factors influencing microclimate include the altitude and aspect of the region.
The cool microclimates in the mountains to the south of the boreal forests are at high altitudes. High altitude or elevation is responsible for low temperatures. Hence, the altitude favors a cool climate on the mountains.
Mountains can cause shading of land in adjacent regions. In the northern hemisphere, the regions shaded by the mountains are the ones facing the north. These regions will have cool microclimates.
Thus, the cool microclimates similar to the boreal forests can be present at high altitudes, and on the northern side of the mountains. These mountains are located to the south of the boreal forests can hence harbor the species of the boreal forest.

Question 2

What is the greatest strength of laboratory experiments in ecological research?

Answer 2

Experimentation is the best possible way to prove or disprove a hypothesis. Experiments are the only means of studying any science. Experiments can either be field experiments or they can be laboratory experiments. Field experiments are performed in the natural environment, whereas lab experiments are performed under much more controlled conditions.
The strength of lab experiments lies in the fact that the experimenter can control certain factors that influence the end result. There are numerous variable factors in a natural environment that influence a particular ecological process or phenomenon. When the effect of a single factor of interest is to be determined, it is essential to control the other factors in order to get conclusive results. Variable factors can be controlled in lab experiments. This is the strength of lab experiments.
For example, a lab experiment was designed to study the effect of basking on thermoregulation by a grasshopper Camnula pellucida. In this experiment, two populations of the grasshopper were grown at the same temperature, but one was exposed to light, while the other was not. Here, temperature, which is an important factor that determines the basking behavior of the grasshoppers, has been controlled. In this way, lab experiments allow the experimenters to control multiple variable factors that influence the ecological matter being studied. By controlling other factors, it is ensured that the result obtained is due to the influence of the factor of interest.
Thus, the strength of lab experiments is the ability to control variables to ensure comparability and validity of results.

Question 3

Imagine a desert beetle that uses behavior to regulate its body temperature above 35°C. How might this beetle's use of microclimates created by shrubs, burrows, and bare ground change with the season?

Answer 3

A desert beetle that uses behavior to regulate its body temperature above 35°C uses microclimates created by shrubs, burrows and bare ground in the following manner with changing seasons.
• In extreme summer, when the air temperature would be very high, the beetle would need to seek a cooler place in order to regulate its body temperature. It would inhabit the underground burrows in this season, since the burrows will be much cooler than the above ground temperature conditions. Staying inside of the burrows will help the beetle to avoid the heat of the day and stay cooler.
• In a slightly cooler season, the beetles would use shrubs to shade themselves from the Sun. The shrub microclimate will be ideal for this season, when the temperature is not very high and shading will be enough to allow them to regulate their body temperature in the optimum range.
• During the winter, when air temperature is low, the beetle would inhabit the bare ground in order to warm itself using the solar energy.

Question 4

Why do ecologists generally supplement information resulting from laboratory experiments with field obser­vations or experiments?

Question 5

L. Mosser and colleagues (1974) found that populations of the bacterium Sulfolobus living at different temperatures had different optimal temperatures for sulfur oxidation. Use natural selection to explain these patterns. Design an experiment to test your explanation. Assume you can create artificial springs and regulate their temperature as you like.

Question 6

Figure 4.8 shows how temperature influences the activity of acetylcholinesterase in rainbow trout. Assuming that the other enzymes of rainbow trout show similar responses to temperature, how would trout swimming speed change as environmental temperature increases above 20°C?

Question 7

The Applications section reviews how the studies of Bruno Baur and Anette Baur (1993) have documented the local extinction of the land snail Arianta arbustorum. Their research also shows that these extinctions may be due to reduced egg hatching at higher temperatures. Do these results show conclusively that the direct effect of higher temperatures on hatching success is responsible for the local extinctions of A. arbustorum? Propose and justify alternative hypotheses. Be sure you take into account all of the observations of the Baurs.

Question 8

Butterflies, which are ectothermic and diurnal, are found from the tropical rain forest to the Arctic. They can elevate their body temperatures by basking in sunlight. How would the percentage of time butterflies spend basking versus flying change with latitude? Would the amount of time butterflies spend basking change with daily changes in temperature?

Question 9

When we reviewed how some organisms use torpor, hibernation, and estivation to avoid extreme temperatures, we discussed the idea of energy savings. However, organisms do not always behave in a way that saves energy. For instance, when food is abundant hummingbirds do not go into torpor at night. This suggests that there may be some disadvantages associated with torpor. What are some of those potential disadvantages?

Question 10

The section on avoiding temperature extremes focused mainly on animals. What are some of the ways in which plants avoid temperature extremes? Bring cold and hot environments into your discussion. Some of the natural history included in chapter 2 might be useful as you formulate an answer.

Question 11

Some plants and grasshoppers in hot environments have reflective body surfaces, which make their radiative heat gain, Hr, less than it would be otherwise. If you were to design a tiger beetle that could best cope with thermal conditions on black beaches (see fig. 4.5), what color would it be? The beetles on the black beaches of New Zealand are black, and the beetles on the white beaches are white. What do the matches between the color of these beetles and their beaches tell us about the relative roles of thermoregulation and predation pressure in determining beetle color? What does this example imply about the ability of natural selection to "optimize" the characteristics of organisms?

Question 12

In most of the examples discussed in chapter 4, we saw a close match between the characteristics of organisms and their environment. However, natural selection does not always produce an optimal, or even a good, fit of organisms to their environments. To verify this you need only reflect on the fact that most of the species that have existed are now extinct. What are some of the reasons for a mismatch between organisms and environments? Develop your explanation using the environment, the characteristics of organisms, and the nature of natural selection.