AP Biology
ECOLOGY
Chapter 53.1,2,3,4,5,6
Formula sheet for population formulae
Big Idea 2: Biological systems
utilize free energy and molecular
building blocks to grow, to
reproduce and to maintain dynamic
homeostasis. Essential knowledge
Chapters/sections
Illustrative examples covered
2.a.1 All living systems require
constant input of free energy.
53.3, 53.4
4.A.5: Communities are composed
of populations of organisms that
interact in complex ways.
53.1, 53.2, 53.3,
53.5, 53.6
54.1, 54.2
• Life-history strategy (biennial
plants, reproductive diapause)
• Change in the producer level can
affect the number and size of other
trophic levels
• Change in energy resources levels
such as sunlight can affect the
number and size of the trophic
levels
• Predator/prey relationships
spreadsheet model
• Symbiotic relationship
• Graphical representation of field
data
• Introduction of species
• Global climate change models
View video: On the Edge – Wildlife in the Columbia Mountains. 21 minutes
AP Biology: Chapter 53 Population Ecology guided notes
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Chapter 53 Population Ecology
What is a population?
What is Population ecology?
How is population density different from population dispersion?
Describe the three main patterns of dispersal within a population.
The study of vital statistics that affect population size is called ____________.
Additions to the population are caused by ____________________________ and
________________________________.
Deletions from the population are caused by ______________________________ and
_____________________________.
A life table is an age-specific summary of the survival pattern of a population.
The best way to construct a life table is to follow the fate of a cohort, a group of individuals
of the same age, from birth throughout their lifetimes until all are dead.
To build a life table, researchers need to determine the number of individuals that die in each
age group and calculate the proportion of the cohort surviving from one age to the next.
Examine table 53.1

A graphic way of representing the data in a life table is a survivorship curve, a plot of the
numbers or proportion of individuals in a cohort of 1,000 individuals still alive at each age.
AP Biology: Chapter 53 Population Ecology guided notes
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A survivorship curve is a plot of the proportion or numbers of a cohort still alive at each
age. Compare Type I, II and III survivorship curves. Each type of organism has a
particular survivorship curve.
Describe each type of curve and relate it to a real organism.
What do we mean by the life history of an organism? ____________________________
________________________________________________________________________
AP Biology: Chapter 53 Population Ecology guided notes
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Population Growth 53.2

Change in population size =

Using mathematical notation, we can express this relationship more concisely.
o If N represents population size and t represents time,
o then N is the change in population size and t is the time interval.
We can rewrite the verbal equation as: N/t = B − D where B is the number of births during
the time interval and D is the number of deaths. (this is if we ignore immigrants and emmigrants)

The per capita birth rate is the number of offspring produced per unit time by an average
member of the population.
Calculate:
If there are 34 births per year in a population of 1,000 individuals, the annual per capita
birth rate is

If we know the annual per capita birth rate (expressed as b), we can use the formula B = bN to
calculate the expected number of births per unit time in a population of any size.

Similarly, knowing the per capita death rate (symbolized by m for mortality) allows us to
calculate the expected number of deaths per unit time in a population of any size using the
formula.
o If m = 0.016 per year , we would expect 16 deaths per year in a population of 1,000
individuals.
If the mortality rate of a population is 0.05 per year. How many deaths can be expected in
a population of I million people?

Now we can revise the population growth equation, using per capita birth and death rates:
N/t = bN − mN

Population ecologists are most interested in the difference between the per capita birth rate
and the per capita death rate.

This difference is the per capita rate of increase, or r:
r=b−m

The value of r indicates whether a population is growing (r > 0) or declining (r < 0).
o When r = 0, there is zero population growth (ZPG).
o Births and deaths still occur, but they balance exactly.

Using the per capita rate of increase, we rewrite the equation for the change in population size
as:
N/t = rN

Ecologists use differential calculus to express population growth instantaneously, as the
growth rate at a particular instant in time:
where rinst

dN/dt = rinstN
is the instantaneous per capita rate of increase.
Population growth under ideal conditions is called exponential population growth.
AP Biology: Chapter 53 Population Ecology guided notes
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o

Under these conditions, we may assume the maximum growth rate for the population
(rmax), called the intrinsic rate of increase.
The equation for exponential population growth is
dN/dt = rmaxN
a) Exponential model of population growth (J-curve)
This type of growth pattern can occur when a
population is small and resources are unlimited.
________________________________________________________________________
________________________________________________________________________
The recovery of the whooping crane population illustrates ______________ population
growth.
________________________________________________________________________
_____________________________________________________
AP Biology: Chapter 53 Population Ecology guided notes
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Do concept check 53.2 # 3.
https://www.youtube.com/watch?v=1tvfmWdZHR4 Coral population recovery.
Concep53.3 The logistic growth model describes how a population grows more
slowly as it nears its carrying capacity.
The logistic model of population growth incorporates the concept of carrying capacity.
What is ‘carrying capacity’?
This model incorporates the idea that the growth rate of the population slows down as the
population size reaches the carrying capacity of the environment (K):
Logistic growth gives a ‘J-shaped’ growth curve:
AP Biology: Chapter 53 Population Ecology guided notes
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Few populations actually follow the logistic growth pattern exactly, but it is used as a
starting point for analyzing population growth. Here are some examples:
The logistic growth model can be used to analyze various types of life histories.
What type of life history traits are favoured in crowded conditions (high density) where
the population is near the carrying capacity of the environment?
____________________________________________________________
Do concept check 53.3 #2
Concept 53.4 Life history traits are products of natural selection.

Natural selection favors traits that improve an organism’s chances of survival and
reproductive success.

In every species, there are trade-offs between survival and traits such as frequency of
reproduction, number of offspring produced, and investment in parental care.

The traits that affect an organism’s schedule of reproduction and survival make up its life
history.
Read and understand the Inquiry in Figure 53.13
AP Biology: Chapter 53 Population Ecology guided notes
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Selection for life history traits that are sensitive to population density is known as ____
selection, or density-____________ selection.
○
K-selection tends to maximize population size and operates in populations living at a
density near K, where competition between individuals is strong.
○
Mature trees growing in an old-growth forest are an example of K-selected organisms.
Review Fig 53.17 on page 1183 and 1184

Selection for life history traits that maximize reproductive success at low densities is known
as _____-selection, or density-___________ selection.
o r-selection tends to maximize r, the per capita rate of increase.
o This occurs in environments in which population densities fluctuate well below K or
when individuals face little competition.
o Such conditions are often found in disturbed habitats, such as weeds growing in an
abandoned agricultural field.
What type of life history traits are favoured in less dense environments?
Why do we say these traits are a result of ‘r-selection’?
Complete this table of the Two Life Strategies
r – strategists
Many young
K - strategists
Intensive parenting
Rapid maturation/
Large young
Reproduce once
Example: mammals, birds, reptiles
AP Biology: Chapter 53 Population Ecology guided notes
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Population Limiting Factors
Limiting factors are those factors that limit population growth. They are divided into two
categories:
1. Density – dependent factors are those factors that increase directly as the
population increases. They include competition for food, the buildup of wastes,
predation and disease.
2. Density – independent factors are those whose occurrence is unrelated to
population density. For example earthquakes, storms, and naturally occurring fires
and floods.
How do the rates of birth, death, immigration and emigration change as population
density rises?
Population equilibrium is reached when the birth rate equals the death rate (assuming no
immigration or emigration).
What is the difference between a ‘density dependent’ and a ‘density-independent’ birth or
death rate?
Density independent birth or death rates do not change regardless of population density.
Analyse these graphs.
Negative feedback prevents unlimited population growth:
AP Biology: Chapter 53 Population Ecology guided notes
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What does population dynamics explain?
Some populations have regular ‘boom-and-bust’ cycles
What could account for the regular fluctuations in the snowshoe hare and lynx
populations?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________

There are three main hypotheses. What are these?
1.
2.
3.

The availability of prey is the major factor influencing population changes for predators such
as lynx, great-horned owls, and weasels, which depend heavily on a single prey species.

When prey become scarce, predators often turn on one another.
o Coyotes kill both foxes and lynx, and great-horned owls kill smaller birds of prey as well
as weasels, thus accelerating the collapse of the predator populations.

Immigration and emigration also influence populations: When a population becomes crowded
and resource competition increases, emigration often increases.
AP Biology: Chapter 53 Population Ecology guided notes
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Concept 53.6 The human population is no longer growing exponentially, but it is
still increasing rapidly.

The concepts of population dynamics can be applied to the specific case of the human
population.

It is unlikely that any other population of large
animals has ever sustained so much population growth
for so long.

The human population increased relatively slowly
until about 1650, when approximately 500 million
people inhabited Earth.
http://www.worldometers.info/world-population/
Activity: Human Population Growth
To maintain population stability, a regional human population can exist in one of two
configurations:
Zero population growth = High birth rates − High death rates
Zero population growth = Low birth rates − Low death rates
The movement from the first toward the second state is called the demographic transition.
As countries go through the ‘demographic transition’, their population growth rate can be
very high because the death rate is much lower than the birth rate:
AP Biology: Chapter 53 Population Ecology guided notes
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The age structure of the population in a given country determines to some extent its
future population growth pattern:
Activity: Analyzing Age-Structure Pyramids
How are age structure diagrams useful?
________________________________________________________________________
________________________________________________________________________
_______________________________________________________
Which country in the diagrams above represents a developing nation? ______________
What determines our human footprint?
Population growth and economics
The Demographic Transition - Differences in a country's population growth correlate
with economic development




Pre-industrial: Birth rates high, but death rates high too. Population growth is
LOW
Transitional: Industrial society begins. More foor, more medical care. Birth rates
high, death rates lowered. Population growth is HIGH
Industrial: Population is "well off" and realtively wealthy. Birth and death rates
are low, but population size grows rapidly!
Post-industrial: Zero to negative growth: Birth rate very low, even less that death
rate, but population size is still high
AP Biology: Chapter 53 Population Ecology guided notes
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http://www.nature.com/scitable/knowledge/library/how-populations-grow-theexponential-and-logistic-13240157 good website
AP Biology: Chapter 53 Population Ecology guided notes
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