Transcript ch. 8 population change

Chapter 8
Population Change
Overview of Chapter 8
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Principles of Population Ecology
Reproductive Strategies
The Human Population
Demographics of Countries
Demographics of United States
Principles of Population Ecology
• Population Ecology
– Study of populations and why their numbers change over
time
– Important for
• Endangered species
• Invasive species
• Population
– Group of individuals of same species living in the same
geographic area at the same time
Population Density
• Population density
– The number of individuals of a species per unit area or
volume at a given time
– Ex: minnows per Liter of pond water
Change in Population Size
Change in Population Size
Calculating Population Change
Growth
rate
Death
rate
Emigration
rate
r = (b – d) + (i – e)
Birth
rate
Immigration
rate
CRUDE BIRTH/DEATH RATE are calculated per 1000 people
Maximum Population Growth
• Intrinsic Rate of Growth (Biotic Potential)
– Growth rate under ideal conditions
– J- Shaped Curve (exponential growth)
Environmental Resistance
• Environmental limits (resistance)
– Prevent indefinite reproduction
– Unfavorable food, water, shelter, predation, etc.
• Carrying Capacity (K)
– Maximum # of individuals an environment can support
– Causes leveling off of exponential growth
– S- shaped curve of logistic population growth
Check for understanding
• 4 - I can explain to my peers why populations
cant grow in size forever.
• 3 - I understand what limits populations from
growing in size unstopped.
• 2 - I understand carrying capacity, but need
more practice.
• 1 - huh? Exponential growth? Carrying
capacity?
Population Crash
• Overshooting carrying capacity can lead to
population crash
– Abrupt decline in population density
Factors That Affect Population Size
• Density Dependent Factor
– Factor whose effect on population changes as
population density changes
– Examples:
• Predation
• Disease
• Competition
– Sometimes cause Boom-or-Bust Population Cycles
Boom-Or-Bust Population Cycles
Case Study- Predator Prey Dynamics on Isle
Royale
• As wolf population increases, moose
population decreases (and vice versa)
Factors That Affect Population Size
• Density Independent Factors
– Factors that affects population size, but is not
influenced by changes in population density
– Examples:
• Killing frost
• Severe blizzard
• Fire
Check for understanding
• 4 - I can explain to my peers different ways
that populations increase in size and factors
that limit uncontrollable population growth.
• 3 - I understand different ways that
populations grow and limitations to their
growth.
• 2 - I understand how exponential growth,
boom and bust, and carrying capacity, but I
need more practice.
• 1 - I am lost population growth.
Reproductive Strategies
r-selected species
k-selected species
-Small body size
-Small broods
- Early maturity
-Long life span
- Short life span
-Slow development
- Large broods
-Large body size
- Little or no parental
-Late reproduction
care
-Low reproductive rate
- Probability of long term -Parental care
survival is low
-Redwood trees and
- Mosquitoes and
human beings
Dandelions
Survivorship
Some populations fit two curves
• Herring Gulls
• Type III (young)
& Type II
Check for understanding
• 4 - I can explain to my peers how
reproductive strategies vary from survivorship
types.
• 3 - I understand how reproductive strategies
vary from survivorship types .
• 2 - I understand, I think, but need to review
my notes on reproductive strategies and
survivorship types.
• 1 - Aren’t all organisms the same????
Human Population
• Demography
– Science of population
structure and growth
• Human Population is
J-shaped curve
• Thomas Malthus
– food for people?? 
famine & disease!!!
• better crop yields
Human Population
1 Billion
1800
2 Billion
1930
3 Billion
1960
4 Billion
1975
5 Billion
1987
6 Billion
1999
6.6 Billion
2006
Population Increase in Mexico
Projecting Future
Populations
• Population is increasing; why is
death rate going down?
• Growth rate (r) has started to
decline
• Zero-population growth: birth
rate and death rate are equal (S –
shaped curve)
• Projections for 2050 – variation
due to fertility rate of less
developed countries
– Low = 7.7 billion
– High = 10.6 billion
– Most likely = 9.1 billion
Demographics of Countries
• Highly developed countries – Ex: US, Japan,
Germany –
– low birth rates, low infant mortality rates (6% US;
54% world), long life expectancy (77 US, 67
world), high per-capita GNI PPP ($34,000, $7,000)
• Developing countries:
– moderately developed countries (Ex: Mexico,
Thailand) – high infant mortality/birth rates, but
declining
– less developed countries (Bangladesh, Niger,
Ethiopia)
Growth rate
• Doubling time!! – amount of time for an area
to double = 70/r (r = growth rate as %)
– Which type of country has shorter doubling time?
• Replacement-level fertility – typically 2.1
children
– Total fertility rate (world) is above replacement
level (about 2.5)
– Impacting factors: infant mortality rate, population
momentum by ## of young females, need/lack of
need for children to work (rural), education
(especially of women!!)
Check for understanding
• 4 - I can explain to my peers zero population growth,
total fertility rate, replacement level fertility, and
doubling time.
• 3 - I understand zero population growth, total
fertility rate, replacement level fertility, and doubling
time.
• 2 - I understand, I think, but need to review my
notes on zero population growth, total fertility rate,
replacement level fertility, and doubling time
• 1 - I understand some of the terms, but not all.
Demographic Stages
• Pre-industrial Stage
– Birth and death rates high – poor medical care, limited food supply
– Modest population growth
• Transitional Stage
– Lowered death rate – higher education/improved conditions
– Rapid population growth
• Industrial Stage
– Birth rate decline – urbanization decreases economic reason for
many kids, women educated/work, retirement safety nets reduce it
– Population growth slow
• Post Industrial Stage
– Low birth and death rates
– Population growth very slow
Demographic Stages
Age Structure
• The number and proportion of people at each
age in a population
Demographics of Specific Countries
World-wide
• 29% of human
population is under
age 15
• Could cause large
increase in birth
rates
Check for understanding
• 4 - I can explain to my peers all the different
demographic stages, why they occur AND how
to read age structure graphs. I should just
drop out of HS now .
• 3 - I understand all the different demographic
stages, why they occur AND how to read age
structure graphs .
• 2 - I understand demographic transition and
age structure graphs, BUT…..
• 1 - I am lost and need to hear it all again.