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CHAPTER 5: POPULATIONS
How Populations Grow (5-1)
Limits to Population Growth (5-2)
Human Population Growth (5-3)
5-1: How Populations
Grow
POPULATION

A population is a
group of organisms that
belong to the same
species and live in a
given area.
A. 3 Factors That Influence Population
Size
1. Birth Rate
2. Death Rate
3. Migration
a.
b.
immigration = movement of organisms into
an area
emigration = movement of organisms out of
an area
4. Calculation of Population Growth

Population Growth Rate =
(Birth Rate+Immigration) – (Death Rate+Emigration)

Zero population growth is when:
Birth Rate+Immigration = Death Rate+Emigration
B. Population Dynamics
= Change in population size over time
Biotic
Potential
+
Environmental
Resistance
= Carrying
Capacity
1. Biotic Potential
= The maximum rate at which a species can
increase if unchecked
1. Biotic Potential
Considerations Include:
a. age at which reproduction begins
b. frequency of reproduction during life
c. # of offspring per reproductive event
d. survival rate of offspring to reproductive
age
e. length of reproductive ability
1. Biotic Potential

Creates a growth curve that is exponential
(logarithmic, J-shaped curve).

Many species, particularly herbivores,
generally have higher birth rates
2. Environmental Resistance
= The sum of all the forces that cause death
or lowers reproduction
This includes:
 Resource Availability (food/water)
 Predation
 Disease/parasites
 Climatic factors
 Numerous human created elements
3. Carrying Capacity
= The number of organisms that can be
supported in a given area at a given time
Carrying Capacity – The Kaibab

If humans do not harvest part of the herd by
using licensed hunters, natural forces of
disease and starvation will bring about the
reduction with starvation and disease.
QUESTION:
Are human populations ultimately
controlled by the same equation?
C. Change in Population Size Over Time

Population increases for living things are
generally exponential
1. Exponential Growth (J-Shaped)
a. Type of exponential growth that shows
slow growth at first, followed by
increasingly faster rates of growth
b. Under natural conditions, the exponential
phase of growth may drop off sharply due
to environmental constraints
c. Note: Happens to a population only
briefly when encountering a new habitat.
J-Shaped Growth Curve
2. Logistic Growth (S-Shaped)
a. A growth model that starts off like the Jshaped form, but eventually the rate of
growth slows and stabilizes at a certain
level
2. Logistic Growth (S-Shaped)
2. Logistic Growth (S-Shaped)
b. Environmental resistance ultimately limits
growth in the S-shaped growth model.
c. Real-world populations vary in complex ways,
and may show either a J- or an S-shaped growth
form at different times in their history.
5-2: Limits to Population
Growth
1. Density Dependent Controls

Remove higher % of individuals as
population size increases
Density Dependent Controls:
a. INTRASPECIFIC COMPETITION

Intraspecific competition = Among same
species
•Includes mate
competition
Chuckwallas
Density Dependent Controls:
b. INTERSPECIFIC COMPETITION


Interspecific Competition – Between
species
Does not include mate competition
Big Horn Sheep
and Burros
Density Dependent Controls:
c. PREDATION

one organism feeding on another
C. PREDATION
1. Types
a) Equilibrium – prey can avoid predator
b) Boom-Bust cycle – lynx and hare
c. PREDATION
2. Plant Defenses
a) Morphological (body
forms) – thorns, spines
b) Chemical – poisons
c. PREDATION
3. Animal Defenses
a) Morphological
1. size – hide, frighten
2. coloration – camouflage, warning, mimicry
3. other - sting, bite, run
c. PREDATION
3. Animal Defenses
b) Chemical – poison
c. PREDATION
3. Animal Defenses
c) Vigilance (intelligence) – watch for
predators, learned behavior
c. PREDATION
3. Animal Defenses
d) Broken wing display
1. Density Dependent Controls
d. PARASITISM
d) Parasitism - Predators feed on prey but
do not kill it immediately
Freshwater Leech
1. Density Dependent Controls
e. CROWDING AND STRESS
e) Crowding and Stress
1. Density Dependent Controls
f. MIGRATION
f) Migration
Zebra and Wildebeest Migration
2. Density Independent Controls
a) Remove a certain % of the population
regardless of number of individuals in
the population
b) Are typically random or extreme abiotic
events (weather, natural disaster)
2. Density Independent Controls
Floods are an example of a density-independent factor.
This is the aftermath of Katrina in New Orleans.
2. Density Independent Controls
c. After extreme abiotic events, new habitats are
opened for organisms to create new logistic
growth
5-3: Human Population
Growth
5-3 Human Population Growth
A. Human Populations
1. Growth rates were low for much of human
history, but rates started increasing in the
1700’s and became exponential in the
1950’s, exhibiting a J-shaped curve ever
since.
Time
PreIndustrial
Transition
al
Culture
Agriculture
Moving
into
cities
B
D
High
High
Large
Family
Large
Family
High
DECREASING
DECREASING
Industrial
Living
in cities
Post
Industrial
Strategy
Technology
Smaller
Families
and Labor
Laws
College
degree
to
compete
Low
LOW LOW
Graph
How Can Economic Development
Help Reduce Birth Rates
• Demographic Transition
Human Population Growth:
Past History and Current Conditions
YEAR
POPULATION
1804
1 billion
1974
4 billion
2005
6.2 billion
2011
6.9 billion
End of 21st Century
Estimated 8.5 – 11
billion
Human Population Growth:
Past History and Current Conditions
2. World population growth is fastest in
developing countries
3. Education is a key in developing countries:
a) If educated to 2nd or 3rd grade = 8
babies/female
b) Women with higher education/careers =
delay childbirth and typically have fewer
children
Human Population Growth:
Past History and Current Conditions
COUNTRY
Developed
Less-developed:
China, India, parts of
Africa, and Latin America
ANNUAL GROWTH RATE
0.4%
1.8 - 3%
B. Effects of Large Human Population
1. Food and agriculture
a) Only three plants provide 50% of our food
supply - wheat, rice and corn
b) Crops are genetically identical - not
resistant to disease or weather, lose 70 to
80% of a crop
Effects of a Large Human Population
2. Usable land
a) high percentage of potentially
usable land is being cultivated
b) agricultural land is the fastest growing
area of land being destroyed
c) removal of tropical forest removes
circulating water and deserts are
getting bigger
Deforestation in
the Tropics
Effects of a Large Human Population
3. Other human impacts
a) Global warming – the increase in
atmospheric CO2 concentrations
during the last 150 years concerns
ecologists because of its potential
effect on global temperature through
the greenhouse effect.
Effects of a Large Human Population
b) Ozone depletion - increased UV radiation hits the
earth
1979
2003
Effects of a Large Human Population
c) Acid rain/Water pollution
The Parthenon in Greece
shows discoloration and
chemical weathering effects
from air pollution and acid
rain
Statue of Queen Victoria - England
Effects of a Large Human Population
d) Habitat destruction/soil destruction
Effects of a Large Human Population
e) Biodiversity loss
Fragmentation of
habitat causes
species to go
extinct.
Habitat Loss, Pollution,
Invasive Species,
Overuse/Killing by
Humans
Effects of a Large Human Population
f) Waste build-up Example: Open Pit Mining
Effects of a Large Human Population
g) Non-native/exotic
species – would not be
present without the
direct or indirect help of
humans
Termites, Africanized
Honey Bees,
Myconia,
Ice Plant,
Tiger Mosquito
Walking catfish
Starlings