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Chapter 19

POPULATIONS. Chapter 19. Population. A population is a group of organisms that belong to the same species and live in a particular place at the same time . Ex. all the bass living in a pond during a certain period of time. . Properties of Populations.

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Chapter 19

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  1. POPULATIONS Chapter 19

  2. Population • A population is a group of organisms that belong to the same species and live in a particular place at the same time. • Ex. all the bass living in a pond during a certain period of time.

  3. Properties of Populations • Population Size- the number of individuals it contains

  4. Properties of Populations 2. Population Density- measures how crowded a population is. It is expressed as the number of individuals per unit of area or volume Ex. U.S. states with greatest population density New Jersey and lowest population density Alaska.

  5. Properties of Populations 3. Dispersion- the spatial distribution of individuals within a population. Ex. random, clumped, even

  6. Change in Populations • Birth Rate ex. U.S. 4 million births/year • Death Rate ex U.S. 2.6 million death/year • Life Expectancy- or how long an average individual is expected to live. Ex. In 2003- Man= 74 Woman= 80

  7. Change in Population 4. Immigration- the movement of individuals into a population 5. Emigration- the movement of individuals out of a population

  8. Growth Rate • Growth Rate- the amount by which a population’s size changes in a given time. • Scientist assume that immigrations and emigration are zero when calculating a populations growth rate ***birth rate - death rate = growth rate US

  9. Exponential Growth • When a population increases rapidly, only after a few generations and the larger the population gets, the faster it grows. • Exponential population growth forms a characteristic J- shaped curve • Ex. bacteria

  10. Limiting Factor • A factor that restrains the growth of a population • Ex. food water living space • In reality populations cannot grow indefinitely because the resources they depend upon become scarce and wastes accumulate.

  11. Logistic Model of Pop. Growth • The logistic model builds on the exponential model but accounts for the influence of limiting factors.

  12. Logistic Model of Pop. Growth • Carrying Capacity- the number of individuals the environment can support over a long period of time. • A graph of logistic growth is S- shaped

  13. Limiting Factors 1. Density-Independent Factors -Reduce the population size by the same proportion, regardless of the population’s size. Ex. weather, flood, fires

  14. Limiting Factors 2. Density-Dependent Factors -Reduce the population size and are triggered by increasing population density. Ex. Shortage of food, nesting sites, resource limitations, Disease

  15. Fluctuation in Size • Environmental changes Ex. drought, fires, floods, storms, freeze • Availability of Food/prey Ex. lynx -snowshoe hare population • Habitat availability -nesting sites • Hunting

  16. Problem of Small Populations • The members of a small population may be descended from only a few individual, increasing the likelihood of inbreeding, mating with relatives. Inbreeding in small populations often leads to decreased genetic variability which then results in a less likely chance that they will be able to adapt to changing environmental conditions. Ex. Cheetahs

  17. Growth of Human Population • From the origin of Homo sapiens more than 500,000 years ago, until about 10,000-12,000 years ago, the human population grew very slowly because humans lived in small, nomatic groups living a hunter-gatherer lifestyle.

  18. 10,000-12,000 years ago • The Agricultural revolution- humans began to domesticate animals and cultivate certain plants for food

  19. Acceleration of Growth • After 1650 human population growth began to accelerate because of a sharp decline in death rates. Why? • Better Sanitation and hygene • Better Control of Disease • Increased Availability of Food • Improved Economic Conditions

  20. Acceleration of Growth • While death rates fell, Birth rate remained high, resulting in rapid population growth. • The human population increased from 500 million in 1650 to 1 billion by 1800 and 2 billion by 1930 • After WWII more health improvements took place and the population increased to 3 billion by 1960 and then to 5 billion by 1987!!!!! • Today the current world population is 7,076,970,928

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