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Populations

Populations. Understanding Populations Measuring Populations Human Population Growth. Understanding Populations. Properties of Populations Population Dynamics. Learning Objectives. Learning Objectives : TSW … Explain the differences btw population size, density, & dispersion

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Populations

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  1. Populations • Understanding Populations • Measuring Populations • Human Population Growth

  2. Understanding Populations • Properties of Populations • Population Dynamics

  3. LearningObjectives • Learning Objectives: TSW … • Explain the differences btw population size, density, & dispersion • Describe the 3 main patterns of population dispersion • Explain the importance of a population’s age structure • Contrast the 3 main types of survivorship curves

  4. Properties of Populations • What is a Population? • Population Size • Population Density • Population Dispersion

  5. Population • Group of organisms that… • …belong to the same species • …live in the same area at the same time • …are capable of interbreeding • The properties of a population differ from those of an individual organism Ex. Population Study: • How many individuals are born? • How many individuals die? • How many individuals reproduce?

  6. Population Size • Number of individuals in the population • May be determined directly • Species occurs in small area • Species immobile or relativelyimmobile Ex.Devils Hole pupfish in Devil’s Hole • May be estimated by sampling • Species occurs over a large area • Species is mobile Ex.Zebras on African savanna

  7. Population Density • Measures how crowded a population is • Expressed as a # of individuals perunit area or volume Ex.USA population is 30 people per km2 • Population densities in other countries

  8. Population Dispersion • The spatial distribution of individuals w/in a population • Clumped dispersion • Individuals are clustered (in groups) • Even (uniform) dispersion • Individuals are separated by a relatively consistent distance (even spacing) • Random dispersion • Each individual’s location is independent of the location of any other individual

  9. Population Dynamics • Birth Rates Death Rates & Life Expectancy • Age Structure • Patterns of Mortality

  10. PopulationDynamics • Birth rate= # births / time period • Death rate= # deaths / time period • Mortality rate • Life expectancy– how long an average individual is expected to live • Ex:In USA (1996), ♂ ~ 72;♀~ 79

  11. Age Structure BOOM! • The distribution of individuals among different ages in a population • Important factors • A large # of younger population members = higher birth rate • A large # of older population members = lower birth rate

  12. Patterns of Mortality • Mortality rate data for species tend to conform to one of three patterns • Survivorship curves • Type I – likelihood of dying early in lifeis small Ex: humans & elephants • Type II – likelihood of dying is the sameat any age Ex: squirrels & many birds • Type III – likelihood of dying early in life is great Ex: oysters, salmon, & insects

  13. Measuring Populations • Population Growth Rate • The Exponential Model • The Logistic Model • Population Regulation

  14. LearningObjectives • Learning Objectives: TSW … • Describe the exponential model of population growth • Compare the similarities & differences btw the logistic model & the exponential model • Distinguish btw density-dependent & density-independent regulatory factors • List 3 reasons why small populations are more vulnerable to extinction

  15. Population Growth Rate • Changes in Population Size • Immigration • Emigration • Birth Rates & Death Rates

  16. PopulationGrowth Rate • The amount by which a population’s size changes in a given time • Contributing Processes: • Birth • Death • Immigration – movement of individuals INTO a population • Emigration – movement of individuals OUT of a population

  17. Population Growth Rate 52 births & 14 deaths per 1,000 individuals: per capitabirth rate = 0.052 (52/1000) per capitadeath rate = 0.014 (14/1000) • Processes that ↑ population size • Birth • Immigration • Processes that ↓ population size • Death • Emigration • Demographers divide large populations into groups of 1,000 to present data “per capita” Birth rate – Death rate = Growth rate

  18. Growth Rate Calculation Per capitabirth rate = 0.052Per capitadeath rate = 0.014 Population size = 50,000 • Per capita growth rate Births per capita – Deaths per capita = Growth per capita 0.052 – 0.014 = 0.038 • Predicting yearly population growth Current population size X Growth per capita = Population increase 50,000 X 0.038 = 1,900 • Next year’s population will be 51,900

  19. Growth Rate Calculation Per capitabirth rate = 0.052Per capitadeath rate = 0.014 Population size = 51,900 • Per capita growth rate Births per capita – Deaths per capita = Growth per capita 0.052 – 0.014 = 0.038 • Predicting yearly population growth Current population size X Growth per capita = Population increase 51,900 X 0.038 = 1,972.2 = 1,972 • Second year’s population will be 51,900 + 1,972 = 53,872

  20. Population Models • The Exponential Model • Predictions & Limitations • The Logistic Model • Growth & Carrying Capacity

  21. The Exponential Model • Exponential Growth • The larger a population gets • The faster it grows • Predictions based on the Exponential Model • J-shaped curve • Population grows slowly when small • Population grows more rapidly as it gets larger • The rate of increase increases

  22. The Exponential Model Note: as density increases (space becomes limited), growth declines • Limiting Factor • Restrains the growth of a population • Limitations of the Exponential Model • Populations only grow exponentially under ideal conditions • No limit tofood, space –reduced competition • Waste removed Assumes that birth rate & death rate remain constant

  23. The Logistical Model • Logistic Growth • Population size is at carrying capacity • Birth rate = death rate • The logistical model accounts for limiting factors • Birth rates ↓ & death rates ↑ as a population grows • Carrying Capacity (symbol: K) • The number of individuals the environment can support over a long period of time

  24. Population Regulation • Population Fluctuations • Perils Of Small Populations

  25. Population Regulation • Limiting Factors • Density-independent factors • Density-dependent factors • Density-independent Factors • Reduce population regardless of its size (size-independent) • Density-dependent Factors • Reduce population because of its size(size-dependent)

  26. Population Regulation • Density-independent Factors • Weather conditions • Floods • Landslides • Wild fires • Population size decreases by the same proportion regardless of how many individuals there are

  27. Population Regulation • Density-dependent Factors • Competition for resources: food, space, etc. • Territoriality • Health • Predation • Intrinsic factors • Population size decreases because of competition for necessary resources or interactions w/ different species

  28. Population Fluctuations • Causes of Fluctuation • Seasonal changes • Temperate climes:spring/summer -v- fall/winter • Tropical climes:rainy season -v- dry season • Environmental changes • Cycle:drought years -v- wet years • Predator & prey interactions • Snowshoe hair & lynx populations

  29. Population Cycles:Ex: Dungeness Crab Population • Extreme Population Fluctuations • Due to complex interactions • Abiotic factors • Winds & ocean current carries larvae off shore • Temperature fluctuations due to storm systems • Biotic factors • Cannibalism by adult & older juvenile crabs • Competition among larvae for food Population variation: 9,000 low – 730,000 peak

  30. Population Cycles:Ex: Isle Royale Moose Population • Moderate Population Fluctuations • Due to complex interactions • Abiotic factors • Severity of winter temperatures • Duration of winter season • Biotic factors • Competition for food in winter • Wolf predation Population variation: 2,500 peak–500 low

  31. Perils of Small Populations • Inbreeding • Mating w/ close relatives • Increases likelihood of acquiring recessive alleles • Recessive alleles often lead to deleterious conditions • Loss of genetic diversity • Other perils • Vulnerability to natural & man-caused disasters: fires, disease, floods, etc.

  32. Small Populations

  33. Human Population Growth • History of Human Population Growth • The Effect of Agriculture • Population Explosion • Population Growth Today

  34. LearningObjectives • Learning Objectives: TSW … • Explain how the development of agriculture changed the pattern of human population growth • Describe the change in human population growth that began circa 1650 • Describe how growth rates have changed since WWII • Compare the general standard of living in developed countries w/ that in developing countries

  35. Human Population Growth • The Hunter-gatherer Lifestyle • The Agricultural Revolution • Population Fluctuations • Population Growth in Developed Countries • Population Growth in Developing Countries

  36. History of Human Population Growth • Hunter-gatherer Age • 500,000 – ~11,000 B.C.E. • Characteristic small population • Due to high infant mortality • Agricultural Age • 10 - 12,000 – 2,000 B.C.E. • Domestication of animals & cultivation of food plants • Stabilized & increased food supply Human Population: 10,000 years ago 2 - 20 million Human Population: 2,000 years ago 170 - 330 million

  37. History of Human Population Growth • Pre-industrial / Urbanization Age • 2,000 B.C.E. – 1650 C.E. • Steady but slow population growth • Due to lower death rate • Industrial Age • 1650 – 1930 C.E. • Population explosion • Due to ↑ birth rate – ↑ food supply • Due to ↓ death rate – better sanitation & hygiene Human Population: 350 years ago 500 million Human Population: 75 years ago 2 billion

  38. History of Human Population Growth • Post WWII • 1930 – 2000 C.E. • Explosive population growth continues • Due to large ↓ death rate – better sanitation & hygiene in poorer countries Human Population: 45 years ago 3 billion Human Population: 15 years ago 5 billion

  39. Population Growth Increases Despite Lower Growth Rate • Global Population Growth • Peak – late 1960s: 0.021 per capita • Current: 0.014 • Due to ↓ birth rate – better sanitation & hygiene in poorer countries 1970 pop. = 3.7 billionw/ 0.0196 growth rate Added 73 million people to world population 1999 pop. = 6 billionw/ 0.014 growth rate Added 84 million people to world population

  40. Population Growth Today • Developed Countries • Industrialized • USA, Canada, Japan, Europe, Russia, Australia • 20% of human population • Growth rates = 0.01 per capita(low) • Shrinking population in Germany, Russia, Hungary

  41. Population Growth Today • Developing Countries • Non-Industrialized; agrarian • Asia (most), Mexico, Central & South America, Africa • 80% of human population • Growth rates = 0.02 per capita(high) • Skyrocketing population in China, India,

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