PopulationsWhy does the US Government

conduct a census every 10 years?

What causes populations to grow?

What contributes to fast or slow growth of a population?

Population – all individuals of a species that live together in 1 place at 1 time

3 key features of populations:1. size – # of individuals – if small, risk extinction (disaster & little genetic variation)

2. density - # of individuals in an area

3. dispersion – how individuals are arranged

Population RangesA species might not be able to expand its

population range because it cannot survive the abiotic conditions found in the expanded region.

PupfishCommon dolphin

Population-Limiting Factors

There are two categories of limiting factors—density-independent factors and density-dependent factors.

Density independent factors – weather, fire, climate, pollution & human alteration of landscape can affect growth

Any factor that does not depend on the # of members in a population

Density-Dependent FactorsAny factor in the environment that

depends on the #of members in a population

Biotic factors Disease Competition Parasites

Growth=more births than deathsExponential growth curve = rate of population growth stays the same

Carrying capacity- the population size an environment can sustain (limiting resources – water, food- density dependent factors)

When a population is below the carrying capacity, the birth rate is high, when the population is at the carrying capacity, the death rate is high

All populations grow exponentially untilsome limiting factor slows the growth.

Carrying capacity is limited by the energy, water, oxygen, and nutrients available.

A population stops increasing when the number of births is less than the number of deaths or when emigration exceeds immigration.

An r-strategist is generally a small organism.Short life span

Produces many offspring

The rate strategy, or r-strategy, is an adaptation for living in an environment where fluctuation in biotic or abiotic factors occur.

A k-strategist is generally a larger organism.Long life span

Produces few offspring

The carrying-capacity strategy, or k-strategy, is an adaptation for living in stable environments.