Populations &

1. Populations & Limits to Growth

2. 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

3. 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

4. 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

5. 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

6. Limits to Growth • Limiting Factor: a factor that causes population growth to decrease • Competition • Predation • Parasitism and disease • Drought and climate extremes • Human Disturbances

7. 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

8. 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

9. 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