UNIT 3 ECOLOGY
1. Populations (Section 5-1)
Population size-the number of individuals it contains. (Difficult to measure)
Population Density- measures how crowded a population is. (number of individuals per unit of area of volume)
Dispersion-is the spatial distribution of individuals within the population.
Clumped- clustered together (ex. turtles)
Even- usually result from social interactions (individuals getting as far away from each other as possible)
Random-usually results from seed dispersal (trees in a forest.)
Human Population Growth
Hunter-Gatherer Lifestyle- human life about 10,000-12,000 years ago. Humans lived in groups and hunted to gether food
Populations grew slowly-high mortality rate among infants and young children.
Agricultural Revolution- the dramatic change in lifestyle of humans.
Humans discovered how to domesticate animals and cultivate plants for food.
Human population increased rapidly.
The Population Explosion- See graph below
Developed Countries- about 20% of the world’s population lives in developed countries. (U.S., Japan, Germany France, UK, etc.) Population growth rates are low.
Developing Countries- includes most countries in Asia, all Central America, South America, Africa. Populations are growing very rapidly.
2. Population Regulation (Section 5-2)
A. Density-Independent factors- weather, floods, and fires. Reduce the population by the same proportion, regardless of the population’s size.
B. Density-Dependent factors-resource limitations, such as shortages of food or nesting sites-triggered by an increasing population density.
C. Population Fluctuations- example- Lynx and Snowshoe Hare
The hare has a very regular cycle
When hare population increases, more food is available for the Lynx.
Then the Lynx population increases.
D. Small Populations (due to human causes, weather disturbances, or other factors) may lead to inbreeding.
Offspring of related individuals come from a small gene pool.
They are more susceptible to disease and have a short life span.
This impacts the population’s ability to evolve in the future.
3. Population Dynamics (Section 5-3)
All populations change in size and composition over time.
Birth Rate-the number of births occurring in a period of time.
Death Rate- number of deaths in a period of time.
Life Expectancy-how long on average an individual is expected to live.
Age Structure- the distribution of individuals among different ages in a population.
Survivorship Curves- the graph of a species’ mortality-rate data.
Population Growth Rate- the amount by which a population’s size changes in a given time.
The growth rate depends on:
Birth rate
Death rate
Emigration – is the movement of individuals out of the population.
Immigration- is the movement of individuals into a population.