Populations & Limits to Growth

Characteristics of a Population  Geographic Distribution: area inhabited by a population bacteria: 1 cm 3 whale: millions km 2  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 More individuals living in area, the sooner available resources are used up Between same or different species  Predation: population control 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 clear- cutting forests  crash in population size  population may build up or stay small