Book cover for Biology

Biology

Sylvia S. Mader, Michael Windelspecht

ISBN #9780078024269

12th Edition

687 Questions

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Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

Chapter 44 on Population Ecology provides an in-depth exploration of how populations are studied within ecology. It covers the hierarchical levels of biological organization and delves into the methods used to analyze population dynamics, including demography, survivorship curves, and growth models such as exponential and logistic growth. Furthermore, the chapter emphasizes the role of both density-dependent and independent factors in regulating population sizes, contrasts the reproductive strategies of r-selected versus K-selected species, and considers the unique aspects of human population growth and its environmental consequences. These concepts are vital for both understanding natural ecosystems and managing human impacts on the environment.

Learning Objectives

1

Explain the levels of biological organization from individual organisms to the biosphere.

2

Describe and analyze key population dynamics concepts including demography, survivorship curves, and growth models.

3

Compare exponential (J-shaped) and logistic (S-shaped) growth models and understand the factors regulating population size.

4

Evaluate the roles of density-dependent and density-independent factors in controlling population dynamics.

5

Examine the contrasting life history strategies of r-selected versus K-selected species and assess the unique factors influencing human population growth.

Key Concepts

CONCEPT

DEFINITION

Ecology

The branch of biology that studies the interactions of organisms with each other and their physical environment.

Population Ecology

A subfield of ecology focused on population dynamics, including birth rates, death rates, and growth patterns within populations.

Demography

The statistical study of populations, including the structure, size, and distribution, as well as birth and death rates.

Survivorship Curves

Graphs that depict the number or proportion of individuals surviving to different ages within a population.

Exponential Growth

A population growth model where the population size increases in a J-shaped curve under ideal and unlimited growth conditions.

Logistic Growth

A population growth model where growth speed decreases as the population nears the environment's carrying capacity, producing an S-shaped curve.

Density-dependent Factors

Environmental factors whose effects on a population vary with population density, such as competition or predation.

Density-independent Factors

Environmental factors that influence population size regardless of the population’s density, such as weather events or natural disasters.

r-selected Species

Organisms that reproduce quickly with many offspring and typically have high growth rates in unstable environments.

K-selected Species

Organisms that invest more in fewer offspring in stable environments, emphasizing survival and competitive ability.

Example Problems

Example 1

Which of these levels of ecological study involves an interaction between abiotic and biotic components? a. organisms b. populations c. communities d. ecosystem e. All of these are correct.

Example 2

In which pair is the first included in the second? a. habitat population b. population community c. community ecosystem d. ecosystem biosphere e. All of these except a are correct.

Example 3

When phosphorus is made available to an aquatic community, the algal populations suddenly bloom. This indicates that phosphorus is a. a density-dependent regulating factor. b. a reproductive factor. c. a limiting factor. d. an r-selection factor. e. All of these are correct.

Example 4

If a population has a type I survivorship curve (most have a long lifespan), which of these would you also expect? a. a single reproductive event per adult b. overlapping generations c. reproduction occurring near the end of the lifespan d. a very low birthrate e. None of these are correct.

Example 5

A pyramid-shaped age distribution means that a. the prereproductive group is the largest group. b. the population will grow for some time in the future. c. the country is more likely an LDC than an MDC. d. fewer women are leaving the reproductive years than entering them. e. All of these are correct.
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Step-by-Step Explanations

QUESTION

How does the exponential growth model describe a population's increase under ideal conditions?

STEP-BY-STEP ANSWER:

Step 1: Recognize that exponential growth occurs when resources are unlimited and there are no constraints on reproduction.
Step 2: Understand that the growth rate is proportional to the current population size, leading to a constant rate of increase over time.
Step 3: Visualize the J-shaped curve that results from this model, where the population rapidly increases as each generation builds on a larger base.
Step 4: Conclude that in an exponential growth scenario, small changes in initial conditions can lead to large differences in later population sizes.
Final Answer: Exponential growth describes populations that increase at a constant percentage rate, resulting in a rapidly expanding, J-shaped growth curve under ideal conditions.

Exponential Growth

QUESTION

What factors cause the transition from exponential to logistic (S-shaped) growth in population dynamics?

STEP-BY-STEP ANSWER:

Step 1: Begin with understanding that logistic growth initially follows exponential growth when a population is small relative to the environment's resources.
Step 2: Identify that as the population size grows, resources become limited, leading to increased competition among individuals.
Step 3: Recognize that the environment has a carrying capacity, which is the maximum population size that can be supported sustainably.
Step 4: Note that density-dependent factors, such as competition for food and space, slow the growth rate as the population nears the carrying capacity.
Step 5: Understand that these factors cause the growth rate to decrease, resulting in an S-shaped curve where the population stabilizes at the carrying capacity.
Final Answer: Logistic growth occurs as limiting resources and density-dependent factors cause the growth rate to decline, leading to an S-shaped curve that levels off at the carrying capacity.

Logistic Growth

QUESTION

How do density-dependent and density-independent factors regulate population size?

STEP-BY-STEP ANSWER:

Step 1: Define density-dependent factors as those whose influence increases with population density, for example, competition, predation, and disease.
Step 2: Define density-independent factors as those that impact the population regardless of its size, such as weather events and natural disasters.
Step 3: Understand that in high-density scenarios, density-dependent factors can limit population growth by increasing mortality or reducing birth rates.
Step 4: Recognize that density-independent factors can cause sudden changes in population size regardless of current density, adding an element of unpredictability.
Step 5: Conclude that the balance between these factors determines whether a population stabilizes, declines, or experiences bursts of growth.
Final Answer: Population size is regulated by density-dependent factors that intensify with growing populations and by density-independent factors that impact populations regardless of their size.

Population Regulation

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Common Mistakes

  • Confusing exponential growth with logistic growth by neglecting the role of resource limitations and carrying capacity.
  • Overlooking the importance of density-dependent factors in regulating population sizes.
  • Misinterpreting survivorship curves and failing to link them with species’ life history strategies.
  • Assuming that human population growth follows the same patterns as non-human populations without considering unique social and technological influences.