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Chapter 8Population Change
Overview of Chapter 8
• 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
CRUDE BIRTH/DEATH RATE are calculated per 1000 people
Growth Growth raterate
Birth Birth raterate
Death Death raterate
Immigration Immigration raterate
Emigration Emigration raterate
r = (b – d) + (i – e) r = (b – d) + (i – e)
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 speciesr-selected species k-selected speciesk-selected species
-Small body size-Small body size
- Early maturity- Early maturity
- Short life span- Short life span
- Large broods- Large broods
- Little or no parental - Little or no parental carecare- Probability of long Probability of long term survival is lowterm survival is low- Mosquitoes and Mosquitoes and DandelionsDandelions
-Small broodsSmall broods-Long life spanLong life span-Slow developmentSlow development-Large body sizeLarge body size-Late reproductionLate reproduction-Low reproductive rateLow reproductive rate-Parental careParental care-Redwood trees and Redwood trees and human beingshuman beings
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 Billion1 Billion 18001800
2 Billion2 Billion 19301930
3 Billion3 Billion 19601960
4 Billion4 Billion 19751975
5 Billion5 Billion 19871987
6 Billion6 Billion 19991999
6.6 Billion6.6 Billion 20062006
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.