population change chapter 8. principles of population ecology population ecologists ask: 1) how many...
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Population Change
Chapter 8
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Principles of Population Ecology
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?
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Principles of Population EcologyPopulation Density (because you can’t count them all!):• Not enough to know just how many.• Need to know per unit area.• Which environmental factors may influence population
density?
20 / 100 m220 / 25 m2
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Principles of Population Ecology
How Do Populations Change in Size?
On a global scale (closed system):
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Principles of Population Ecology
How Do Populations Change in Size?
On a local scale (open system):
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Principles of Population EcologyHow Do Populations Change in Size?
Global scale:
Births and deaths per 1,000 people per year
r = b/1,000 – d/1,000
Growth rate
Birth rate
Death rate
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Principles of Population Ecology
How Do Populations Change in Size?
Local scale (all per 1,000 people):
r = (b – d) + (i – e)
Growth rate
Birth rate
Death rate
Immigration rate
Emigration rate
What would a positive r or a negative r tell you about the population?
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Principles of Population Ecology• Maximum Population Growth- under ideal
conditions = intrinsic rate of increase (biotic potential)
• Which factors could influence the intrinsic rate of increase?
J-shaped curve (exponential growth)
All species follow J-curve based on intrinsic rate.
Major variable is pop. size and time!
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Principles of Population EcologyEnvironmental Resistance-• Exponential growth at intrinsic cannot occur forever.• What factors prevent it from doing so?• Crowding makes a pop. more susceptible to parasites,
viruses, predators, waste, food / space shortage
S-shaped curve (logistic growth)
• Environment influences K (ex. drought)
• How could one environmental influence have a “domino” effect on many species?
• Rate of population growth is proportional to the amount of resources
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Principles of Population EcologyOvershooting the carrying capacity can lead
to a population crash.
• Abrupt decline from high to low population density
• Over consumption of resources because of population size
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Reproductive StrategiesLife History Strategies - Trade offs!
r-selected K-selectedvs.
high growth rate slow growth rate
small body size large body size
early maturity late maturity
short life span long life span
large broods small broods
little / no parental care high parental care
“perfect”: continual reproduction at intrinsic rate of increase with all offspring surviving to reproduce
But… addt’l energy needed for their own survival
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Reproductive StrategiesSurvivorship: proportion of individuals alive at a
certain age (insurance companies used these!)
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Factors that Affect Population SizeDensity-Dependent Factors-
• Factors that have a greater influence on population growth when density is high.
• Predation, competition, disease.
• Living space, food, cover, water, minerals, sunlight in high demand
• Large population: parasites and predators have more hosts / prey– survive longer / reproduce more
• In lab: control all factors except one
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Factors that Affect Population SizeDensity-Dependence and Boom-or-Bust
Population Cycles • More prey - predator population increases
•Prey population decreases
•OR overwhelm food supply (plants=prey)
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Factors that Affect Population Size
Case-in-Point: Predatory Prey Dynamics on Isle Royale
Canine parvovirus outbreak
Tick outbreak
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Factors that Affect Population Size
Density-Independent Factors-
• Abiotic
• Regardless of population density, influences population growth.
• Frost, severe weather, fire.
• Example: Adult mosquitoes wiped out in winter. Species survives from hibernating larvae
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The Human Population: Demography
Human population size• Would not have occurred if not for:
•Food production technology
• Medical advancements
•Water quality
•Decline in birth rate and death rate
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The Human Population
Current Population Numbers
In 2004 = ~6.4 billion
Check out:
http://www.census.gov/main/www/popclock.html
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The Human PopulationCurrent Population Numbers
Rapid growth primarily due to drop in death rates
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The Human PopulationProjecting Future Population Numbers
When will zero population growth occur?
•K for Earth: 7.7 billion (most recent analysis)
•Past analyses: 4 - 11 billion
•Assumptions: standard of living, consumption, tech. advancements, waste generation
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Demographics of Countries
Most Populous Countries Insert Table 8.1
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Demographics of CountriesDeveloped vs. Developing Countries
Demographics (includes migration)
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Demographics of Countries
Developed vs. Developing Countries Demographics
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Demographics of Countries
Demographic Stages
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Demographics of CountriesAge Structure of Countries
Generalized Age Structure: Factors are age distribution and male-female ratio
Next Generation is larger
Next Generation is almost same size
Next Generation is smaller
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Demographics of Countries
Examples:
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Demographics of Countries
Examples:
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Demographics of Countries
Examples:
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Demographics of CountriesPopulation Under Age 15 (relative size of next
generation):
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Demographics of the USCase-in-Point: US Immigration
• Birth rate declining
• Increasing rate of immigration
• Consumption overpopulation
• Estimates 300,000 illegal per year, 1 million legal
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Demographics of the USCase-in-Point: US Immigration• Immigrate because of:
•Persecution
• High growth rate in developing countries reduces resources / jobs available
• Deteriorating environmental conditions in developing countries
• Top 5 immigrants: Mexico, Philippines, Vietnam, Dominican Republic, China
•70% poor with few skills, 30% college graduates
•Should the US increase or decrease immigrants?