Populations Unit 2: Ecology

Populations Population—a group of individuals of the same species that live in the same area.

Characteristics 3 characteristics of a population: Geographic Distribution Density Growth Rate

Geographic Distribution Geographic Distribution is often determined by availability of resources.

Population Density Population Density— the number of individuals per unit of area.

Factors Affecting Population Size Number of births Number of deaths Immigration and Emigration

Migration Immigration—movement of individuals into an area that has an existing population Emigration—movement of individuals out of a population

Types of Growth Exponential Logistic

Exponential Growth Exponential Growth—(also called J curve) occurs when population grows at a constant rate.

Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially. Exponential growth does not continue in natural populations for long because resources are limited.

Logistic Growth Logistic Growth— (also called S curve) occurs when a population’s growth slows or stops following a period of exponential growth.

Carrying Capacity The maximum number of organisms of a particular species that can be supported by the environment. If the population is larger than the carrying capacity, the death rate may rise.

Resources Renewable Resources—a resource that can regenerate quickly and that is replaceable. Examples: sunlight, trees, etc… Nonrenewable Resources—a resource that cannot be replenished by natural processes. Example: fossil fuels

Limiting Factors Limiting Factor—a factor that causes population growth to decrease. Most of the time the limiting factor is a resource in insufficient supply.

Limiting Factors Density-dependent limiting factor factor that only limits growth of a population when the population density reaches a certain level (overcrowded). Examples: competition, predation, parasitism, and disease

Limiting Factors Density-independent limiting factors these limit growth regardless of the population size. Examples: unusual weather, natural disasters, seasonal cycles, and human activities