Population Ecology

Basic ecological principles govern the growth and sustainability of all populations

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Population Characteristics(Demographics)

Population Size Population DensityPopulation Distribution

Age Structure = number of individuals in age categories Pre-reproductive, reproductive, post-reproductive Reproductive Base

POPULATION SIZE = Number of individuals that contribute to population’s gene pool within the same geographic area

• Birth rate vs. Death rate• Immigration vs. emigration

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Population DensityNumber of individuals per specified area or habitat

2011 World Population density (individuals per square km) 3

General pattern in which individuals are distributed

Population Distribution

Clumping is MOST COMMON, due to ???• environmental conditions• behavioral issues• reproductive concerns

Random Sampling

Capture/ recapture

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Population Growth Immigration Emigration Migration Birth/death

rate

With NO limiting factors

J-Shaped curve = exponential curve

Doubling Time Biotic Potential5

Population Growth LimitsReality•Limiting Factors•Short supply of any essential resource = ?Carrying capacity•Maximum number of individuals that an environment can sustain•NATURAL SELECTION?•S-shaped curve = logistic curve

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Limiting FactorsIn nature, most populations are never able to reach biotic potential

Density-dependent

Density-independent

Abiotic factors

Biotic factors

Predator

CompetitionParasitism

Weather

Elevation9

Typical biotic carrying capacity relationship

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World Population GrowthWhat differentiates humans from other species found in nature? How does this impact population growth?

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The rate of national population growth is expressed as a percentage for each country, commonly between about 0.1% and 3% annually. You'll find two percentages associated with population - natural growth and overall growth. Natural growth represents the births and deaths in a country's population and does not take into account migration. The overall growth rate takes migration into account.

In the U.S., the natural growth rate is 0.6% and overall growth is 0.9%. The growth rate of a country provides demographers and geographers with a good contemporary variable for current growth and for comparison between countries or regions. For most purposes, the overall growth rate is the more frequently utilized.

The world's current growth rate is about 1.3%, representing a doubling time of 54 years. We can expect the world's population of approximately 6 billion (2000) to become 12 billion by 2054 if the current rate of growth continues. The world's growth rate peaked in the 1960s at 2% and a doubling time of 35 years.

Doubling Time

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World Population Distribution by Region, 1800–2050

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Age Structure Diagrams

Rapid Growth•High pre-reproductive and productive populationSlow Growth•Steady declining population with ageZero Growth•Equal distribution of agesNegative Growth•Low pre-reproductive and productive population

Fertility RateReplacement Levels

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Demographic TransitionRelates economic conditions to population growthStages:

Pre-Industrial• High birth & death rates

Transitional• Declining death rates

Industrial• Declining birth rates

Post-Industrial• Low birth & death rates

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