Unit 3
Populations
10-15% of AP Exam
Unit Focus:
Populations within ecosystems change over time in response to a variety of factors. This unit examines the relationship between the type of species and the changes in a habitat over time. Specialist species are advantaged by habitats that remain constant, while generalist species tend to be advantaged by habitats that are changing. Different reproductive patterns, including those exhibited by K- and r-selected species, also impact changes to population. Population growth is limited by environmental factors, especially by the availability of resources and space. In subsequent units, You will explore how increases in populations affect earth systems and resources, land and water use, and energy resources.
Exam Prep:
On the AP Exam, you must be able to explain trends in population data for organisms. To practice this, we will look at a variety of human population graphs from various countries and then explain the trends in the data to draw conclusions about changes in the populations. This is also an opportunity for you to explain population density and population growth. We will also practice interpreting population growth curves for other species. When explaining the survival of a species, you should consider population size and emphasize problems associated with reduced genetic diversity. It is helpful for you to connect data represented by tables, charts, and graphs to real-life examples of population changes.
Essential Questions:
What are the factors that cause populations to change over time and how can we use data to make useful predictions?
How do social and cultural factors affect Human population sizes?
This Unit Focuses on the following Science Practices:
SP1 Concept Explanation: Explain environmental concepts, processes, and models presented in written format.
SP5 Data Analysis: Analyze and interpret quantitative data represented in tables, charts, and graphs.
SP6 Mathematical Routines: Apply quantitative methods to address environmental concepts.
SP7 Environmental Solutions: Propose and justify solutions to environmental problems.
Assessment
Thursday October 26th
Will Assess:
Unit 3 Learning Objectives
SP 1: Concept Explanation
SP 5: Data Analysis
SP 6: Mathematical Routines
Learning Objectives
to show mastery a student should be able to:
3.1 Identify differences between generalist and specialist species.
Essential Knowledge:
Specialist species tend to be advantaged in habitats that remain constant, while generalist species tend to be advantaged in habitats that are changing.
Resources and Book References:
(Ch 5) Module 17 (pages 173 - 175)
3.2 Identify differences between K- and r-selected species.
Essential Knowledge:
K-selected species tend to be large, have few offspring per reproduction event, live in stable environments, expend significant energy for each offspring, mature after many years of extended youth and parental care, have long life spans/life expectancy, and reproduce more than once in their lifetime. Competition for resources in K-selected species’ habitats is usually relatively high.
r-selected species tend to be small, have many offspring, expend or invest minimal energy for each offspring, mature early, have short life spans, and may reproduce only once in their lifetime. Competition for resources in r-selected species’ habitats is typically relatively low.
Biotic potential refers to the maximum reproductive rate of a population in ideal conditions.
Many species have reproductive strategies that are not uniquely r-selected or K-selected, or they change in different conditions at different times.
K-selected species are typically more adversely affected by invasive species than r-selected species, which are minimally affected by invasive species. Most invasive species are r-selected species.
Resources and Book References:
(Ch 6) Module 19 (pages 204-209)
3.3 Explain survivorship curves.
Essential Knowledge:
A survivorship curve is a line that displays the relative survival rates of a cohort—a group of individuals of the same age—in a population, from birth to the maximum age reached by any one cohort member. There are Type I, Type II, and Type III curves.
Survivorship curves differ for K-selected and r-selected species, with K-selected species typically following a Type I or Type II curve and r-selected species following a Type III curve.
Resources and Book References:
(Ch 6) Module 19 (pages 209-211)
3.4 Describe carrying capacity.
Essential Knowledge:
When a population exceeds its carrying capacity (carrying capacity can be denoted as K), overshoot occurs. There are environmental impacts of population overshoot, including resource depletion.
Describe the impact of carrying capacity on ecosystems.
Essential Knowledge:
A major ecological effect of population overshoot is dieback of the population (often severe to catastrophic) because the lack of available resources leads to famine, disease, and/or conflict.
Resources and Book References:
(Ch 6) Module 18 (pages 201-203)
3.5 Explain how resource availability affects population growth.
Essential Knowledge:
Population growth is limited by environmental factors, especially by the available resources and space.
Resource availability and the total resource base are limited and finite over all scales of time.
When the resources needed by a population for growth are abundant, population growth usually accelerates.
When the resource base of a population shrinks, the increased potential for unequal distribution of resources will ultimately result in increased mortality, decreased fecundity, or both, resulting in population growth declining to, or below, carrying capacity.
Resources and Book References:
(Ch 6) Module 18 (pages 198-201)
3.6 Explain age structure diagrams.
Essential Knowledge:
Population growth rates can be interpreted from age structure diagrams by the shape of the structure.
A rapidly growing population will, as a rule, have a higher proportion of younger people compared to stable or declining populations.
Resources and Book References:
(Ch 7) Module 22 (pages 242 - 244)
3.7 Explain factors that affect total fertility rate in human populations.
Essential Knowledge:
Total fertility rate (TFR) is affected by the age at which females have their first child, educational opportunities for females, access to family planning, and government acts and policies.
If fertility rate is at replacement levels, a population is considered relatively stable.
Factors associated with infant mortality rates include whether mothers have access to good healthcare and nutrition. Changes in these factors can lead to changes in infant mortality rates over time.
Resources and Book References:
(Ch 7) Module 22 (235-242)
3.8 Explain how human populations experience growth and decline.
Essential Knowledge:
Birth rates, infant mortality rates, and overall death rates, access to family planning, access to good nutrition, access to education, and postponement of marriage all affect whether a human population is growing or declining.
Factors limiting global human population include the Earth’s carrying capacity and the basic factors that limit human population growth as set forth by Malthusian theory.
Population growth can be affected by both density-independent factors, such as major storms, fires, heat waves, or droughts, and density-dependent factors, such as access to clean water and air, food availability, disease transmission, or territory size.
The rule of 70 states that dividing the number 70 by the percentage population growth rate approximates the population’s doubling time.
Resources and Book References:
(Ch 7) Module 22 (pages 233-234)
(Ch 7) Module 23 (pages 248-254)
3.9 Define the demographic transition.
Essential Knowledge:
The demographic transition refers to the transition from high to lower birth and death rates in a country or region as development occurs and that country moves from a preindustrial to an industrialized economic system. This transition is typically demonstrated through a four-stage demographic transition model (DTM).
Characteristics of developing countries include higher infant mortality rates and more children in the workforce than developed countries.