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