5.3 Populations Exponential growth  Population growth in which the rate of growth in each generation is a multiple of the previous generation. This occurs when resources and conditions are not limiting. Leads to overpopulation.

Populations Exponential growth *Any population has the potential to increase exponentially but conditions are never perfect. Food resources are limited, predation occurs, and abiotic conditions are factors. This limits population growth.

Exponential Growth  Consider a country with 100 people, growing at 7% per year. In 10 years, the population will double to 200 people, in another 10 years it will double again to 400 people, and ten years after that it will double again to 800 people. The following graph shows this exponential population growth.

Carrying Capacity  The number of individuals of a species that can be supported by an ecosystem. In a balanced ecosystem, the carrying capacity of a species is stable. *When an ecosystem reaches the carrying capacity, the population quits growing. This is when the number of deaths equals the number of births.  This is represented in a graph called an S-shaped curve. *Early populations grow exponentially, as system reaches its carrying capacity, population growth starts to slow. Finally population growth stops when carrying capacity is reached.

Carrying Capacity

Limiting Factors   The forces that stop a population’s growth as they reach their carrying capacity.  2 types of limiting factors

1. Density-Dependent Limiting Factors  Affect a population more strongly as the population grows larger  Dependent on population size  3 factors *food and water supply *predation *disease  These populations show an S-shaped growth curve

2. Density-Independent Limiting Factor  ffect a population regardless of size  xample is a hurricane  Affects the same percentage of a population regardless of its size  3 factors *climate *human disturbance *natural disasters   These populations show a boom-and-bust curve. These populations grow exponentially when conditions are favorable and collapse when conditions are bad. Many insect populations follow this pattern.

Human Population   Usually exponential, but not for ever  Due to advances in agriculture, technology, energy development, transportation, and medicine.