Population Dynamics
Principles of Population Ecology
Objectives:
1. Define Population Ecology
2. Define growth rate and explain the factors that
produce changes in population size
3. Explain how human population change is
calculated
4. Understand how the following terms are related
to population growth: intrinsic rate of increase,
exponential population growth, environmental
resistance, and carrying capacity.
5. State how the J-curve and S-curve relate to
exponential population growth
Principles of Population Ecology
Population Ecology – the branch of biology
that deals with the numbers of a particular
species found in an area and how and why
those numbers change over time.
Population ecologists ask:
1) How many are in the population?
2) Are its numbers increasing /
decreasing?
3) What is its pattern of reproduction?
4) What is its pattern of mortality?
Principles of Population Ecology
Population Density:
• Not enough to know just how many.
• Need to know per unit area.
20 / 100 m2
20 / 25 m2
Principles of Population Ecology
How Do Populations Change in Size?
On a global scale (closed system):
Principles of Population Ecology
How Do Populations Change in Size?
Global scale:
Growth
rate
Death
rate
r= b–d
Birth
rate
Principles of Population Ecology
How Do Populations Change in Size?
On a local scale (open system):
Principles of Population Ecology
How Do Populations Change in Size?
Local scale:
Growth
rate
Death
rate
Emigration
rate
r = (b – d) + (i – e)
Birth
rate
Immigration
rate
Principles of Population Ecology
Maximum Population Growthunder ideal conditions = intrinsic rate of
increase
J-shaped curve
(exponential growth)
Principles of Population Ecology
Intrinsic rates of increase
for a species depend on:
•Age that reproduction
begins
•Fraction of life span
during which a species
can reproduce
•Number of reproductive
periods per lifetime
•Number of offspring
produced during
reproduction
Principles of Population Ecology
Environmental Resistance
Exponential growth cannot occur forever.
What factors prevent it from doing so?
S-shaped curve (logistic growth)
Principles of Population Ecology
Population growth depends on the interplay
between biotic potential and environmental
resistance
Biotic Potential
Environmental Resistance
•Reproductive rate
•Lack of food or nutrients
•Ability to migrate or
disperse
•Lack of water
•Lack of suitable habitat
•ability to invade new
habitats
•Adverse weather conditions
•Predators
•Defense mechanisms
•disease
•Ability to cope with
adverse conditions
•Parasites
•competitors
Principles of Population Ecology
Overshooting the carrying capacity can lead
to a population crash.
Reproductive Strategies
Objectives:
1. Compare r-selected species to K-selected
species with respect to survivorship
curves
Reproductive Strategies
Each species has its own unique life history
strategy that represents a tradeoff between
energy required for survival and energy
required for reproduction. This strategy
includes:
• Reproductive characteristics
• Body size
• Habitat requirements
• Migration patterns
• behaviors
Reproductive Strategies
Life History Strategies
r-selected
vs.
K-selected
high growth rate
small body size
slow growth rate
large body size
early maturity
short life span
large broods
late maturity
long life span
small broods
little / no parental care
high parental care
Reproductive Strategies
Survivorship- the proportion of newborn
individuals that are alive at a given age
Factors that Affect Population Size
Objectives:
1. Distinguish between density-dependent
and density-independent factors that
affect population size and give examples
of each.
Factors that Affect Population Size
Density-Dependent Factors• Factors with effects on population growth
that change as population density changes
Examples:
• Predation, competition, disease.
Factors that Affect Population Size
Density-Dependence and Boom-or-Bust
Population Cycles
Factors that Affect Population Size
Case-in-Point: Predatory Prey Dynamics on
Isle Royale
Factors that Affect Population Size
Density-Independent Factors• Factors that affect the size of a population
regardless of population density.
Examples:
• Extreme weather (frost, blizzard, hurricane,
etc.; fire.
The Human Population
Objectives:
1. Define demography and summarize the
history of human population growth
2. Identify Thomas Malthus, relate his ideas
on human population growth.
3. Explain why it is impossible to determine
the earth’s carrying capacity for humans.
The Human Population
Demography – the
science of population
structure and growth
Demographics – the
application of
population statistics
The Human Population
Current Population Numbers
Today = ~7.1 billion
Check out:
http://www.census.gov/main/www/popclock.html
• The world’s birth rate has declined over the last
200 years
• The large increases in population are a result of
decreased death rates.
The Human Population
Decreases in the death rate can be attributed
to:
•
•
•
•
Greater food production
Better medical care
Improvements in water quality
Sanitation practices
The Human Population
Current Population Numbers
Rapid growth primarily due to drop in
death rate
Mexico
(1900-2000)
The Human Population
Projecting Future Population Numbers
When will zero population growth occur?
Demographics of Countries
Objectives:
1. Explain how highly developed and
developing countries differ in population
characteristics such as infant mortality
rate, total fertility rate, and age structure.
2. Interpret age structure diagrams
Demographics of Countries
Most Populous Countries Insert Table 8.1
Demographics of Countries
Developed vs. Developing Countries
Insert Table 8.2 (note
Demographics
reconstruction)
Demographics of Countries
Developed vs. Developing Countries
Insert Table 8.2 (note
Demographics
reconstruction)
Demographics of Countries
Demographic Stages
Demographics of Countries
Age Structure of Countries
Generalized Age Structure
Demographics of Countries
Examples:
Demographics of Countries
Examples:
Demographics of Countries
Examples:
Demographics of Countries
Effects of an Aging Population
• Reduction in productive workforce
• Increasing tax burden
• Strain on social security, health, and
pension systems
• Lower crime rates????
Demographics of the US
Case-in-Point: US Immigration