Chapter 2: Populations and Sustainable Ecosystems Section 2.1: Populations and Resources

Changes in Population Size A population is a group of organisms of one species that lives in the same place, at the same time, and can successfully reproduce. Populations increase through births and immigration. Populations decrease through deaths and emigration.

Exponential Growth

Exponential Growth Curve In nature, exponential growth only occurs under certain ideal conditions and for a short period of time.

Limiting Factors Exponential growth is unrealistic in nature. Factors that limit the growth, distribution, or amount of a population in an ecosystem are called limiting factors. As populations grow in size, fewer resources become available. E.g. habitat and food. Predation and competition also regulate population growth.

Carrying Capacity carrying capacity exponential growth Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.

Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.

Population overshoots carrying capacity Number of reindeer Population Crashes Number of reindeer Figure 8.6 Exponential growth, overshoot, and population crash of reindeer introduced to the small Bering Sea island of St. Paul. When 26 reindeer (24 of them female) were introduced in 1910, lichens, mosses, and other food sources were plentiful. By 1935, the herd size had soared to 2,000, overshooting the island’s carrying capacity. This led to a population crash, with the herd size plummeting to only 8 reindeer by 1950. Carrying capacity Year Fig. 8-6, p. 165

Carrying Capacity Click the “Start” button to review the connection between carrying capacity, limiting factors, and equilibrium. Copyright © 2010 McGraw-Hill Ryerson Ltd.

Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Over time species may increase their carrying capacity by developing adaptations. Some species maintain their carrying capacity by migrating to other areas. So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

How Would You Vote? Can we continue to expand the earth's carrying capacity for humans? a. No. Unless humans voluntarily control their population and conserve resources, nature will do it for us. b. Yes. New technologies and strategies will allow us to further delay exceeding the earth's carrying capacity.