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Section Outline Section 5-1 5–1 How Populations Grow A. Characteristics of Populations B. Population Growth C. Exponential Growth D. Logistic Growth Go to Section: 5-1 How Populations Grow Population - group of organisms belonging to a single species that lives in a given area. 3 Characteristics of any Population 1. Geographic distribution – area inhabited by population 2. Density - # per unit of space 3. Growth rate – how fast it grows Go to Section: Population Growth Four factors that influence population size 1. Birth – duh. 2. Mortality - death 3. Emigration – out of an area 4. Immigration – into an area • • When these factors are balanced = no growth (negative or positive) What factors would increase size? Decrease size? Go to Section: What environmental factors influence these? •Birth and immigration? – Abundance of resources (food, mates, shelter) – Organisms reproduce and move into the area for the resources •Mortality and emigration? – Resources on the decline – Organisms faced with dilemmas • Adapt to other resources • Death/extinction • Move out - emigrate Go to Section: Exponential Growth •Bacteria reproduce on average every 20 minutes •In a matter of 1day, one bacteria reproduce into…. – 4720000000000000000000 bacteria – mass of bacteria size of earth in 3 days •Represented with a “J-curve©” •Only occurs under ideal conditions (unlimited resources/no predation) Go to Section: 9000000 Number of bacteria 8000000 Exponential Growth Chart 7000000 6000000 5000000 4000000 3000000 2000000 1000000 0 1 Go to Section: 3 5 7 9 11 13 15 17 19 21 23 Hours Logistic Growth •Normal growth curves •Populations that grow exponentially use resources exponentially! – “carrying capacity” – The limit to which any population ceases to grow due to depletion of resources • Run out of food • Nowhere to live Go to Section: Figure 5-4 Logistic Growth of Yeast Population Section 5-1 Carrying capacity Time (hours) Go to Section: Concept Map Section 5-1 Population Growth can be Logistic growth Exponential growth characterized by No limits on growth Unlimited resources represented by Constant growth rate J-shaped curve characterized by Limits on growth which cause a Falling growth rate Go to Section: represented by S-shaped curve Interest Grabber Section 5-2 Name That Resource! A situation that causes the growth of a population to decrease is called a limiting factor. Some limiting factors depend on the size of the population. Other limiting factors affect all populations in similar ways, regardless of the population size. Go to Section: Interest Grabber continued Section 5-2 1. Imagine a small island that has a population of five rabbits. How might each of the following factors affect the rabbit population? a. climate b. food supply c. predation 2. Now imagine another small island that has a population of 500 rabbits. How would the same factors affect this population? 3 Which of the factors depend on population size? Which factors do not depend on population size? Go to Section: Section Outline Section 5-2 5–2 Limits to Growth A.Limiting Factors B.Density-Dependent Factors 1. Competition 2. Predation 3. Parasitism and Disease C. Density-Independent Factors Go to Section: Limiting Factors • Factors that influence negative population growth • can be anything from…. – Climate – Predators – Food availability – Parasites – Human influences • Clearing of forests – destroy natural habitat Go to Section: Density-Dependent Factors •Any factor that is influenced by the density of the population. •Competition – When populations become crowded, resources are used up at a faster rate. – Occurs within species as well as among groups of species. – Species that compete will change to ease the competition – Drives evolution • Ex: plants and sunlight (canopies/black walnut) Go to Section: A Density-Dependent Limiting Factor Section 5-2 Growth of Aphids Exponential growth Peak population size Rapid decline Steady population size Steady population size Go to Section: •Predation – Predator-prey relationship – regulation of populations by predators – Most effective population control “technique” – Ex: wolves and moose in Isle Royale – Graph usually fluctuates often over time • Predator and prey charts are inverse of each other 60 2400 50 2000 40 1600 30 1200 20 800 10 400 0 1955 1960 Go to Section: 0 1965 1970 1975 Moose 1980 Wolves 1985 1990 1995 Parasitism and Disease •Disease and parasites very effective – Ability to spread directly related to density of population • Higher density = faster spread = higher death rate – May be what eventually causes human population decline • Ex: Bubonic plague Go to Section: Density – Independent Factors •Factors not caused by population size – Climatic change – Human disturbances • Damming rivers, clearing forests •Most populations will shrink in response – Unless these events are recurring or large in magnitude Go to Section: Interest Grabber Section 5-3 How Fast Are We Growing? Until about 500 years ago, the world’s human population remained fairly stable. Then, as advances in medicine, agriculture, and technology occurred, the human population began growing very rapidly. Today, the world’s human population is greater than 6 billion people, and it continues to grow, but at a slower rate. Go to Section: Interest Grabber continued Section 5-3 1. The human population is increasing by about 1.4 percent each year. Assume that the population is 6 billion (6,000,000,000). How large will the population be in one year? 2. If the human population continues to grow at a rate of 1.4 percent per year, the population would double in size (to 12 billion people) in only 51 years! What effect might this increase in population have on the environment and on other people? Go to Section: Section Outline Section 5-3 5–3 Human Population Growth A.Historical Overview B.Patterns of Population Growth 1.The Demographic Transition 2.Age Structure C.Future Population Growth Go to Section: Historical Overview • Populations of humans were regulated by the same limiting factors influencing other animals. – Harsh climate – Food supply – Predators •50% infant mortality rate as soon as 500 years ago. •8500 years ago – agriculture – Now instead of nomads, humans domesticated in one area – Increased the food supply – Coupled with high birth rate already, population increased Go to Section: Human Population Growth Section 5-3 Industrial Revolution begins Agriculture begins Bubonic plague Plowing and irrigation Go to Section: Patterns of Population Growth •Human populations will cease to grow exponentially because of lack of resources. •Today’s limiting factors: – Disease – Famine – War •Demography – study of human populations •Examine: – Birth rates – Death rates – Age structure •Can predict future trends in growth or decline of population Go to Section: Demographic Transition •When the demography shifts in a population – Go from high birth rate/high death rate to…. – Low birth rate/low death rate •How does a society do that? •Occurred in the United States, Japan, and Europe •Africa, S. America, and Asia, still have exponential growth….world overall still growing exponentially. Go to Section: United States Demographic Transition Go to Section: Figure 5-13 Age Distribution Section 5-3 U.S. Population Males Go to Section: Females Rwandan Population Males Females Go to Section: Go to Section: What Can Age Structure Diagrams Tell Us? •Trends by…. – Age group – Gender – Birth rate – Life Expectancy •Overall quality of life Go to Section: Future Population Growth •By 2050 population may increase to 9 billion •Growth rate will slow to 0.43% from 1.4% currently and 2.1% in the ’60’s. •Some feel this is very bad for the environment •Others feel technology and changes in society will allow us to cope. Go to Section: Go Online Links from the authors on the gray wolf Interactive test For links on populations, go to www.SciLinks.org and enter the Web Code as follows: cbn-2051. For links on population growth, go to www.SciLinks.org and enter the Web Code as follows: cbn-2053. 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