Populations & Ecological Succession Chapters 4 & 5

What is a population? A group of organisms of the same species that live in the same area.

3 Major Characteristics of Populations 1) Geographic distribution 2) Density 3) Growth Rate

Geographic Distribution AKA “range” Where the population is located.

Density How closely the individuals live to one another. The lower the density, the more personal space each individual has.

Growth Rate How quickly the size of the population is changing. Can be getting bigger or smaller

What causes changes in population size? Increase in size Births Immigration (In-migration) Decrease in size Death Emigration (Exit – migration)

Common Growth Patterns There are two very common patterns of growth. Exponential Logistic

Exponential Growth “J-shaped” growth Growth starts out slowly, then skyrockets. Occurs only in “perfect” conditions: No disease No predators Unlimited space Unlimited food and water

Logistic Growth “S-shaped” growth Starts out like exponential growth, but eventually levels out. Growth pattern of most real populations.

Carrying capacity (K) The maximum number of individuals of a particular species that the environment can support. Determines the point at which a population stops growing.

Limiting Factors Anything that causes a population to stop growing. Can be: a shortage of food, water, nutrients or shelter.

Density-Dependent Factors Things that only slow/stop population growth when there is a high density. This is because you now have many organisms living close to one another. Disease Predation Parasites Competition (food, water, shelter, mates, etc.)

Density-Independent Factors Things that slow any population’s growth, regardless of density. Natural disasters (tornados, hurricanes, earthquakes, etc.) Seasonal changes (winter freeze) Human activity (Pollution, deforestation, global warming, etc.)