Chapter 35: Population and Community Ecology
Concept Check 35.1
1. Give an example of boundaries that ecologists use to study populations.
-Natural boundaries such as a lake or other geographical boundaries such as a state line
2. Contrast population size with population density.
-Size is the overall number of individuals. Density is individuals per unit area.
3. Give an example of a population of organisms located near your school. Describe a
method you could use to measure the density of this population.
- Dandelions using quadrats.
4. What is the relationship between the terms species and population?
- Species is a unique kind of organism. Population is all the individuals of a particular
species within a defined area.
Concept Check 35.2
1. Describe how a population grows with unlimited food, space, and water.
-It tends to grow exponentially
2. Describe what happens when a population reaches its carrying capacity in a particular
environment.
- Its growth levels off – birth rate = death rate
3. Compare density-dependent and density-independent factors, and give an example of
each.
- Density-dependent factor (food supply, disease) affects a population more as the density
increases. A density independent factor (drought, flood) affects the population
independent of density.
4. What is a boom-and-bust population growth cycle? What might cause such a cycle?
-In a “boom-and-bust” cycle, a population increases rapidly, then decreases rapidly. This
might be caused by changes in the population’s food supply, for example.
Concept Check 35.3
Chapter 35: Population and Community Ecology
1. List some factors that have contributed to the rapid growth of the human population in
the last 500 years.
-Nutrition, sanitation, health care improved in the past few centuries.
2. What does an age-structure graph show? How might a scientist use this information to
make predictions about future population growth?
- Age-structure graphs show the number of people in each age range. A scientist might
use this to predict the population is likely to grow or shrink based on the number of
people of child-bearing age.
Concept Check 35.4
1. How did Gause's experiment with Paramecium demonstrate competitive exclusion?
-Growing separately, two species of Paramecium thrived. In the same container, the more
efficient food-gatherer excluded the other.
2. Describe two methods predators use to help them capture their prey and two methods
prey use to help them avoid being eaten.
- Predator adaptations: camouflage to ambush prey; outrunning prey. Prey adaptations:
fleeing, camouflage, mimicry, physical defenses.
3. Define and give an example of each of the three types of symbiotic relationships.
- Parasitism, one organism obtains food at the expense of the host (e.g., tapeworm in a
dog). Mutualism, both organisms benefit (bacteria in the intestine). Commensalism, one
benefits while the other is neither helped or harmed (crab using seaweed as camouflage).
Concept Check 35.5
1. Provide an example of an ecological disturbance and describe its effects on a
community.
- Forest fire may kill plants and animals, but it may also provide conditions for a new
plant to sprout and return nutrients to the soil.
2. What is the main difference between primary and secondary succession?
- In the primary succession, a community arises in an area with no soil. Secondary
succession is a change in a community where soil is intact
3. Give an example of an introduced species and describe its effect on species diversity.
- Kudzu took over much of the landscape in the American South, decreasing diversity.