Populations

As you may recall….

Populations - the # of individuals of 1 species living in the same ecosystem

Many populations in nature find a point of balance.

The number of individuals a community can hold is called the Carrying Capacity

Populations Change Naturally

Four factors that determine population size:

(i) Natality (# of births / year)

Populations Change Naturally

Four factors that determine population size:

(ii) Mortality (# deaths / year)

Populations Change NaturallyFour factors that determine population

size: (iii) Immigration (# of individuals moving

into an area)

Populations Change Naturally

Four factors that determine population size:

(iv) Emigration (# of individuals moving away from an area)

Populations Change Naturally

•In open ecosystems, all 4 factors affect populations

Population Growth = Births + Immigration - Deaths - Emigration

Abiotic factors Affecting Populations• Every species is able to survive in a range of tolerance in the environment. Populations are largest when conditions are optimal. (usually in a midpoint between an upper and lower limits)

eg. Daphnia live in a temperature range 10°C - 45°C

Key Terrestrial Ecosystem Factors • light availability • water availability • nutrients availability • temperature availability

Key Aquatic Ecosystem Factors • light availability • nutrients availability • temperature availability • salinity • acidity

Biotic factors Affecting Populations• Given optimal abiotic factors, biotic factors will determine a species success

eg. Daphnia provide food to many species

Key Biotic factors • Predation/Parasitism • competition • Commensalism • Mutualism