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Populations & Limits to Growth Characteristics of a Population Geographic Distribution: area inhabited by a population bacteria: 1 cm3 whale: millions km2 Density: no. of individuals per area Growth Rate Population Growth number of births number of deaths number of individuals that enter/leave a population Populations Grow: births > deaths Populations Shrink: births < deaths Immigration: movement of individuals into the area Emigration: movement of individuals out of an area Young leave to find mates, food shortage Exponential Growth Ideal conditions & unlimited resources individuals in a population reproduce at a constant rate individual number increases slowly but becomes larger and larger until it approaches an infinitely large size Logistic Growth with limited resources, population growth slows or stops after a period of exponential growth produces an S shaped curve Carrying Capacity: the size of the population when the growth rate is 0 Limits to Growth Limiting Factor: a factor that causes population growth to decrease Competition Predation Parasitism and disease Drought and climate extremes Human Disturbances Limits to Growth Density Limiting Factors: depends on the population size Become limiting only when the population density, or size, becomes a certain level Doesn’t affect small, scattered populations Density Limiting Factors Competition: food, water, space, sunlight Predation: population control More individuals living in area, the sooner available resources are used up Between same or different species Sea otters and killer whales Wolves and Moose As the wolves feed upon the moose, the moose population falls which causes the wolf population to fall; the moose population can then rise which rises the wolf population Parasitism and Disease: similar to predators wasp cocoon on a caterpillar Density-Independent Factors affect population regardless of size unusual weather or natural disasters human activities: damming rivers or clearcutting forests crash in population size population may build up or stay small
