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Populations How do they change over time? What is a population and how is it measured? • POPULATION: A group of organisms that belong to the same species living in the habitat at the same time. • GROWTH RATE = Births – Deaths – Immigration: moving INTO an area – Emigration: EXITING an area How are populations distributed? POPULATION DENSITY: Number of individuals per unit area. CLUMPED (in groups) RANDOM (all over) UNIFORM (spread evenly) How do populations grow? • Exponential Growth (J curve): population increases rapidly very quickly only after a few generations Exponential growth Peak population size Rapid decline Steady population size Steady population size Grow forever? Micro-organisms can if given enough nutrients and space! How do populations grow? • Logistic Growth (S curve): starts as exponential growth with limiting factors and levels off (due to carrying capacity) Carrying capacity • Carrying Capacity is the MAXIMUM number of individuals an environment and its resources can support Time (hours) As resources become less available the growth of a population slows or stops. Limiting factors prevent MOST populations from growing forever. What factors limit population growth? • Limiting Factors control the growth of a population – Available resources (food, space, mates) – Competition, predation, parasitism, disease – Natural disasters, unusual weather Limiting factors determine the carrying capacity for a species. What factors limit population growth? • Environmental changes (ex. drought) • Other species – Predators, prey, competitors – Lynx and snowshoe hare example How is the human population growing? 12 Human Population (Billions) 11 2100 10 9 Old Stone 7 Age 8 New Stone Age Bronze Age Modern Age Iron Middle Age Ages 6 2000 Future 5 4 1975 3 1950 2 1 Black Death—The Plague 1900 1800 1+ million7000 6000 5000 4000 3000 2000 1000 A.D. A.D. A.D. A.D. A.D. A.D. years B.C. B.C. B.C. B.C. B.C. B.C. B.C. 1 1000 2000 3000 4000 5000 • Earth - 5 Billion Years • Multi-cell Biota - 600 Million Years • Human Beings ~ 2 Million Years • Human Population Growth into Billions- Last 200 years What’s Behind the Human Population Explosion? • Three Factors • – Fertility – Infant Mortality – Longevity • Animal Domestication and Agriculture – Provided for a few to feed many Industrial Revolution – Growth of Cities and Infrastructure •Water •Energy •Transportation – Increased Productivity – Nutrition – Sanitation – Medicine How are humans affecting the environment? • Limited Resources – Land, food, water • Agriculture • Industries • Ecosystem Goods – Renewable – Nonrenewable • Desertification & Deforestation • Water pollution • Biological magnification • Air pollution • Acid rain • Habitat Fragmentation • Introduced Species What is the size of YOUR ecological footprint? (take the quiz online!) Any Questions?