Summary

Communities include all the different species living in a given area. The variety of these species is referred to as biodiversity. Species may form symbiotic relationships such as commensalism, mutualism, or parasitism. Community structure is described by its foundation and keystone species. Communities respond to environmental disturbances by succession: the predictable appearance of different types of plant species, until a stable community structure is established.

Populations are individuals of a species that live in a particular habitat. Ecologists measure characteristics of populations: size, density, and distribution pattern. Life tables are useful to calculate life expectancies of individual population members. Survivorship curves show the number of individuals surviving at each age interval plotted versus time.

Populations with unlimited resources grow exponentially—with an accelerating growth rate. When resources become limiting, populations follow a logistic growth curve in which population size will level off at the carrying capacity.

Humans have increased their carrying capacity through technology, urbanization, and harnessing the energy of fossil fuels. Unchecked human population growth could have dire long-term effects on human welfare and Earth’s ecosystems, especially if resource use per individual rises to the level of the average use in the United States.

Review Questions

1. You are working as a biologist and perform the “mark and recapture” technique to estimate the number of endangered lemurs living within a particular habitat. You initially capture 37 lemurs, marking them all before releasing them. Two months later, you capture 49 lemurs, of which 11 are those originally captured and marked. What is the estimated size of the lemur population, rounded to the nearest whole number?

A. 60

B. 86

C. 97

D. 165

E. 407

2. Which one of the following measuring techniques would best enable you to determine the distribution pattern of a population of zebra?

A. Track how many and which individuals use a central watering hole

B. Use a drone to capture aerial photographs of their habitat range

C. Employ a camera trap in the middle of their habitat

D. Use the mark-recapture method

E. Collect and analyze DNA from hair samples collected at 2 locations

3. A species that you are studying has a type III survivorship curve. Which one of the following describes this type of curve?

A. Survivorship rates are lowest during early parts of its lifecycle

B. Survivorship rates are lowest during the late parts of its lifecycle

C. Survivorship rates are highest during early parts of its lifecycle

D. Survivorship rates are consistent through the lifecycle

E. Survivorship rates are highest in the early and middle parts of its lifecycle

4. A population has unlimited resources and exhibits rapid and sustained population growth. This type of growth would be best described by which one of the following?

A. Exponential

B. Logistic

C. Sigmoidal

D. Parabolic

E. Inverse

5. What single factor has most strongly contributed to the rapid population growth in the human population witnessed over the last 150 years?

A. Increased fertility rates

B. Reduced death rates

C. Longer life spans

D. Economic growth

E. Increased morbidity

6. Which one of the following age groups would most likely to lead to rapid population growth in the future if it contained the greatest relative abundance within that population?

A. 0-15 years old

B. 16-30 years old

C. 31-45 years old

D. 46-60 years old

E. 61 years old and greater

7. Two species have the same ecological niche. If they lived in the same habitat, both would compete until one species became predominant and the other became locally extinct. This process is summarized by which one of the following?

A. Niche warfare

B. Competitive exclusion principle

C. Species selection principle

D. Exclusion through competition theorem

E. Exclusive ecological fractioning

8. Which form of symbiosis benefits one member of the interaction, but neither benefits nor harms the other member?

A. Parasitism

B. Commensalism

C. Sequentialism

D. Mutualism

E. Natural selection

9. Biologists examined the effects of reintroducing wolves into Yellowstone National Park of the United States. They found that by preying on elk, wolves altered the foraging behavior of the elk; the elk spent less time browsing near streambanks. This allowed the regrowth of important vegetation, which had large positive impacts on the ecosystem at large. When a relatively small number of individuals, like wolves, have disproportionate impacts on the ecosystem, they are referred to as a…

A. Foundation species

B. Portal species

C. Keystone species

D. Cornerstone species

E. Pivotal species

10. The 1980 volcanic explosion of Mt. St. Helens in the United States devasted the north side of the mountain and it’s forests. The forests were demolished and replaced with volcanic debris that formed the new soil, free of any remnants of the previous ecosystem (such as seeds stored in the soil). Such an event would lead to which one of the following processes?

A. Primary succession

B. Secondary succession

C. Tertiary succession

D. Quaternary succession

E. Pioneering succession

See Appendix for answers

Attributions

Concepts of biology by OpenStax. Licensed under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from Original by Matthew R. Fisher.

Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0.

“Review Questions” is licensed under CC BY 4.0 by Matthew R. Fisher.