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
View population ecology video and/or ppt from Campbell download.

What is a population? A population is a group of individuals of a single species that live in
the same general area.
o Members of a population rely on the same resources, are influenced by similar
environmental factors, and are likely to interact and breed with one another.
What is Population ecology? is the study of populations in relation to their environment.
Population ecology explores how biotic and abiotic influences on population density,
distribution, size, and age structure.
How is population density different from population dispersion? The density of a population
is the number of individuals per unit area or volume.
The dispersion of a population is the pattern of spacing among individuals within the
geographic boundaries.
Describe the three main patterns of dispersal within a population.
Clumped
Uniform
Random
The study of vital statistics that affect population size is called demography.
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.

A Type I curve is relatively flat at the start, reflecting a low death rate in early and middle
life, and drops steeply as death rates increase among older age groups.
o Humans and many other large mammals that produce few offspring but provide them
with care exhibit Type I survivorship curves.

The Type II curve is intermediate, with constant mortality over an organism’s life span.
o Many species of rodent, various invertebrates, and some annual plants show Type II
survivorship curves.

A Type III curve drops sharply at the start, reflecting very high death rates early in life, but
flattens out as death rates decline for the few individuals surviving to a critical age.
○
o
Type III survivorship curves are associated with organisms that produce large numbers of
offspring but provide little or no parental care.
Examples are many fishes, long-lived plants, and most marine invertebrates.
AP Biology: Chapter 53 Population Ecology guided notes
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What do we mean by the life history of an organism? ____________________________
________________________________________________________________________
Life histories are inherited traits, and are therefore subject to evolutionary pressures. The
life history that has evolved is the one that most suits the organism to its particular
environment.
Population Growth 53.2

Change in population size =
Births + Immigrants −
entering population
Deaths
– Emigrants
leaving population

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 34/1000, or 0.034.

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 D = mN.
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?
D = mN = 0.05 x 1 x 106 = 5 x 104 individuals

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.
AP Biology: Chapter 53 Population Ecology guided notes
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
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.
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.

J-shaped curves are characteristic of populations
that are introduced into a new or unfilled
environment or whose numbers have been
drastically reduced by a catastrophic event and are
rebounding.
________________________________________
___________________
The recovery of the whooping crane population
illustrates exponential population growth.
_____________________________________
_____________________________________
_____________________________________
______________
Do concept check 53.2 # 3.
https://www.youtube.com/watch?v=1tvfmWd
ZHR4 Coral population recovery.
AP Biology: Chapter 53 Population Ecology guided notes
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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’?
____The maximum population size that a particular environment can sustain. _____K
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):
N represents population size and t
represents time.
Value of r indicates whether a population
is growing or declining.
Logistic growth gives a ‘Jshaped’ 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?
___Population close to carrying capacity, strong competition for survival.
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 Kselection, or density-dependent 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 r-selection, or density-independent 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? Rapid
reproduction with numerous small offspring. Little competition and population density
well below carrying capacity.
Why do we say these traits are a result of ‘r-selection’? These are density independent.
Complete this table of the Two Life Strategies
r – strategists
Many young
Little or no parenting
Rapid maturation/ rapid growth
J shaped curve
Opportunistic species
Small young
Reproduce once
Insects, salmon, arachnids,
K - strategists
Few young
Intensive parenting
Slow , population size relatively constant at
carrying capacity, K
Large young
Many times
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?
Death rate that rises as population density rises or birth rate that falls with rising density
is density dependent.
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?
The study of population dynamics focuses on the complex interactions between biotic and
abiotic factors that cause variations in population size.
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.
1. The cycles may be caused by food shortages during the winter.
2. The cycles may be due to predator-prey interactions.
3. Snowshoe hare population size may vary with cyclic changes in sunspot activity.

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?
________________________________________________________________________
Age structure diagrams can predict a population’s growth trends and future social
conditions.
________________________________________________________________________
_______________________________________________________
Which country in the diagrams above represents a developing nation? ______________
What determines our human footprint?
Ultimately, the combination of resource use per person and population density determines our
global ecological 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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