How Populations Grow & Limits to Growth

Population Growth What is a population? A group of organisms that all belong to the same species and live in a given area

Populations can change by: Immigration – individuals moving into a population Increase or decrease? Emigration – individuals moving out of a population Increase or decrease Birth rate Death rate

Population Growth Two Types: Exponential Growth Logistic Growth

Exponential Growth Exponential Growth occurs when organisms are provided with ideal conditions for growth and reproduction If nothing stops population from growing, it grows faster and faster

Exponential Growth

Logistic Growth Population begins to grow exponentially Growth of population slows down Growth levels out due to deathrate and birthrate equalizing (steady state)

Logistic Curve Carrying capacity Number of Mice Time (hours)

Quick Think #1 What are the four factors that can affect a change in population? What are the causes of these factors?

What do you think would cause the growth of a population to decrease? LIMITING FACTORS! Factors that cause the growth of a population to decrease Density-dependent factors Density-independent factors

Density Dependent Factors Affected by other populations Strongest when population is large and dense Four Common Types: Competition Parasitism Predation Disease

Density Independent Factors Not affected by population Common examples: Unusual weather Natural disasters Seasonal cycles Human interference

Figure 5-7 Wolf and Moose Populations on Isle Royale Section 5-2 60 2400 50 2000 40 1600 30 1200 20 800 10 400 1955 1960 1965 1970 1975 1980 1985 1990 1995 Moose Wolves Go to Section:

Quick Think #2 What is the difference between density dependent factors and density independent factors? Name one density-dependent and one density-independent factor.