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Leyda 1. Geographic distribution: the area inhabited by a population. 2. Population density: the number of individuals per unit area. 2. Population density: the number of individuals per unit area. a. high density: lots of individuals per unit area 2. Population density: the number of individuals per unit area. a. high density: lots of individuals per unit area b. low density: few individuals per unit area 3. Growth Rate: how quickly a population changes in size. Fast Growth Rate: Slow Growth Rate: 55 Minutes! 55 Years! Birth rate ________ Death rate ________ 1. 2. stays the same birth rate = death rate population size _________________ increases b. birth rate > death rate population size _________________ decreases c. birth rate < death rate population size _________________ a. movement of individuals into an area 3. immigration: _________________________________ bison immigrates to a meadow full of grass a. example: ___________________________________________ movement of individuals out of an area 4. emigration: _________________________________ bison emigrates out of a meadow without grass a. example: ___________________________________________ Individuals reproduce at a constant rate Exponential growth: _________________________________ 1. ______________ 1. Individuals reproduce at a constant rate Exponential growth: ________________________________ ____________ a. Conditions necessary for exponential growth 1. Unlimited resources 2. Absence of disease and predators b. Example: Bacteria will double their population in 20 mins Staphylococcus aureus c. Shape of graph: J-shaped d. Graph example: Notice: as time goes on, population increases exponentially. 2. Logistic growth: ______________________________________ Population grows rapidly until some factor ________ limits growth _____________ a. When does population growth slow or stop? 1. Birthrate – Down 2. Immigration – Down 3. Death rate – Up 4. Emigration – Up b. Example: Any animal population in nature. c. Shape of graph: S-shaped d. Graph example: Notice: as time goes on, population increases then hits a limit and levels off. This limit is the carrying capacity for that population. e. Carrying capacity: Maximum number of individuals that an area can support. Limiting factor: something that causes population growth to decrease. VS A. Density-dependent limiting factors: When population is high these take effect. 1. Competition: Organisms compete for food, water, space, sunlight, and other essentials. Example: Birds and mice both eat seeds. Effect on Evolution: Both species are put under pressure to change in ways that decrease competition. Remember Competitive Exclusion Principle! 2. Predation: One organism eats another. Example: Lynx eats rabbit. Predator: Lynx Prey: Rabbit Effect on Evolution: Prey species (rabbit) evolves defenses (speed, camouflage), predators evolve counter-defenses (eyesight). Parasitism: Organisms live in and on a host organism. Examples: Ticks, fleas, leeches, tapeworms. B. Density-independent limiting factors: Not related to population size. 1. random events: Unusual weather, natural disasters: volcanoes, hurricanes, floods, ice age Density-independent limiting factors: Not related to population size. 2. human disturbances – such as damming rivers and clear-cutting forests. Lava Flow Number of predators Spread of disease Especially cold winter Toxic chemical spill into a stream Another species competing for same resource Diverting river for irrigation Beetles that attack trees