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Populations

Populations. Chapter 4. Properties of Populations. Population: a group of organisms of 1 species in the same area 1) Population Size (usually estimated) 2) Population Density = how crowded a popltn. is Expressed as # of individual. per area or volume. Properties of Populations (con’t).

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Populations

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  1. Populations Chapter 4

  2. Properties of Populations • Population: a group of organisms of 1 species in the same area • 1) Population Size (usually estimated) • 2) Population Density = how crowded a popltn. is • Expressed as # of individual. per area or volume

  3. Properties of Populations (con’t) • 3) Dispersion = the spatial distribution of individuals • 3 types: • A) Even (due to social interactions) • B) Clumped (due to resource availability) • C) Random (due to seed dispersal by wind or birds)

  4. Population Dynamics • Reflects changes in size and composition of popltn. • Birth Rate: # births in 1 period of time • US = ~4.2 million/year • Death Rate: # deaths in 1 period of time • US = ~2.5 million/year • Life Expectancy: average length of life • US = 72 (male); 79 (female)

  5. Population Dynamics (con’t) • Age Structure: distribution of individuals of different ages in a popltn. • As % young increases, growth rate increases • Survivorship Curves: show likelihood of survival at different ages throughout lifetime

  6. Population Growth Rate • Growth Rate: the amount by which a popltn. changes over time • Calculated by: • Growth Rate = Birth rate – Death Rate • Depends on: • 1) birth rate • 2) death rate • 3) immigration (moving in) • 4) emigration (moving out)

  7. Exponential Growth • Describes a popltn. that grows rapidly after only a few generations • Larger popltn. = faster growth • In reality, resources will run out • Limiting Factor: a factor that restrains popltn. growth

  8. Logistic Growth • Describes a realistic popltn. (birth/death rates vary with popltn. size) • Accounts for limiting factors • Carrying Capacity: the maximum # of individuals the environment can support over time

  9. Population Regulation • Factors in place to help control popltn. size • 2 Types: • 1) Density-dependant: depend on popltn. density • i.e. availability of resources • 2) Density-independent: popltn. density does not matter • i.e. weather, floods, etc.

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