Review & Rehearse

Chapter 15: Ecosystems and Communities

Chapter 15. Chapter 15: Ecosystems and Communities

Review & Rehearse

true

You must read each slide, and complete any questions on the slide, in sequence.

Instructions

Review the visual summaries and answer the essay questions below.

Make sure to enter a brief response that completely answers each question and explains your reasoning. When you click "Submit," you will be provided instant feedback, allowing you to check if your response is correct.

(This activity contains 15 total essay questions. Each new question will be revealed once you complete the preceding question.)

1.

1. Describe the two elements of an organism’s physical or abiotic environment.

The two elements of an organism’s abiotic environment are: (a) chemical resources, such as soil, water, carbon, nitrogen, and phosphorus; and (b) physical conditions, including factors such as temperature, salt levels, moisture, humidity, sunlight, and air pressure.

2.

2. What changes in climate occur on moving from the equator toward the Poles? Which two aspects of weather determine the type of biome found at any location?

The temperature generally decreases on moving from the equator toward the Poles. The type of biome located in a geographic region is determined by: (a) temperature: average temperature and whether it varies seasonally or is constant; and (b) precipitation: average amount and whether it varies seasonally.

3.

3. Why are areas at lower latitudes typically warmer than high-latitude areas?

At lower latitudes, closer to the equator, the sun’s rays hit the earth more directly, and the solar energy spreads out over a smaller area (is more concentrated). Closer to the Poles, energy from the sun’s rays is spread out over a greater area, The greater the concentration of sunlight reaching the earth, the higher the temperature.

4.

4. You are charged with creating a “greener” city that will be cooler and use less air
conditioning. Describe three strategies by which you could help achieve this goal.

By reducing the amount of solar radiation they absorb, cities can become cooler without the expenditure of energy. Steps that could be taken include: (a) making rooftops lighter in color to reflect sunlight, (b) planting trees and plants around buildings to provide shade and cool areas, and (c) creating rooftop green areas and gardens.

5.

5. Why is the water on the beaches of southern California so cold relative to water on east coast beaches?

Winds blow more strongly when they are higher above the earth, freed from the earth’s frictional drag. When strong elevated winds encounter tall buildings, they are deflected, and much of the wind is pushed downward, increasing speed as it reaches street level.

6.

6. Why is the term food web more accurate than food chain when describing the pathway of energy flow?

Many organisms are omnivores, which eat both plants and animals and thus can occupy more than one trophic level in a food chain. These multiple connections between organisms, not apparent in a food chain, are better represented by a food web.

7.

7. Describe the energy flow that occurs through an ecosystem. How does this energy flow influence the number of top carnivores?

Energy flows from producers to consumers through several levels called trophic levels. Producers, the photosynthesizers, are at the base of the food chain and outnumber all consumers. Primary consumers, the herbivores, feed on the producers. Energy then passes to secondary consumers as they feed on the primary consumers. Finally, at the very top of the food chain are the tertiary consumers: the top carnivores. Only about 10% of the energy at each trophic level is available for consumers at the next higher trophic level. Very little energy originally absorbed by producers is available to top carnivores, so a relatively small number of these animals can be supported.

8.

8. Why do levels of CO₂ in the northern hemisphere have ups and downs throughout the year?

Carbon dioxide levels reflect fluctuations in plant growth during different seasons. Photosynthetic rates decrease during the winter, resulting in higher atmospheric carbon dioxide levels. The carbon dioxide levels decrease during the summer as photosynthetic levels increase.

9.

9. Give an example to demonstrate that “natural selection does not distinguish between biotic and abiotic resources as selective forces.”

Natural selection selects for characteristics that improve reproductive success, regardless of whether the trait evolves in response to the selective pressure of physical resources or of biotic resources. For instance, an animal may develop a thick fur coat in response to cold temperatures and develop a light-colored coat to improve camouflage as a defense against predators. Evolution of a thick fur coat is in response to an abiotic resource; camouflage is in response to biotic resources.

10.

10. What is a niche? What is the potential fate of two species that occupy the same niche?

An organism’s niche can be described as its place in a community. The features of a niche include space and food requirements; the time of year the organism reproduces; its temperature, moisture, and other living requirements; the plants or other organisms it feeds on; and how it influences competitors. If two species occupy the same niche, two outcomes are possible. Competitive exclusion occurs when the two species compete until the one that uses resources more efficiently drives the other specie to extinction. Resource partitioning occurs when the two species alter their use of the niche through behavioral or structural changes, so that one or both species become restricted to just part of their niche.

11.

11. When the niches of species overlap, the result is competition. Describe the two possible outcomes from competition.

Competitive exclusion: The two species compete until the one that uses resources more efficiently drives the other specie to extinction. Resource partitioning: The two species alter their use of the niche through behavioral or structural changes, so that one or both species become restricted to just part of their niche.

12.

12. Why would you expect plants to have chemical defense mechanisms to reduce
predation?

Unlike animals, plants are immobile and unable to move away from danger. They have developed chemical defenses that can injure or kill organisms that try to eat or otherwise harm them.

13.

13. Describe a feature of rabies that reflects the mechanism by which the disease is
transmitted from one host to the next.

Rabies is spread through the transfer of saliva from one mammal to another. This disease causes an infected animal to become aggressive and to foam at the mouth, which increases the chance of its biting and transferring saliva to another animal.

14.

14. Why is commensalism described as an interaction with a winner but no loser?

Commensalism is a relationship involving one specie that benefits and another specie that neither benefits nor is harmed. In other words, one species is a winner, while the other derives no benefit from the relationship, but does not lose anything either.

15.

15. Which feature is crucial for the colonizers seen in the earliest stages of primary
succession?

A crucial feature of a colonizer in primary succession is its ability to disperse far from its site of origin. Because of their ability to travel far, these species can reach remote environments that have been disturbed. Generally, they face few if any competitors at first and can flourish, but in later stages of succession they do not compete well with other species.

Activity results are being submitted...