Studying Populations

PopulationAll the members of one

species in a particular area

What is the population?

Population A Population B

Both areas have a

population of 9.

Population densityThe number of individuals

in an area of a specific size.

What is the population density?Area A Area B

Population A has a population density of 9/ yard2.

Population B has a population of 9/ foot2.

The areas have the same population but different

population densities.

One yard2

One foot2

Population ◦tells how many organisms there are◦is written as a number 328 burch trees 250,000 people

Population Density ◦Tells how many organisms are in a certain◦is written as a number over an area◦shows how dense, or “smushed together”, the

organisms are. 18 burch trees/ acre 2 people/ meter2

Population vs. Population Density

Direct ObservationCounting all the members

of the population.

Indirect ObservationCounting signs of an organism instead of counting the actual

organism.

SamplingCounting the organism in a

small area and then multiplying to find the larger area.

Mark-and-RecaptureScientists capture animals and mark them.

They go back later and recapture the animals.

Scientists see how many are unmarked and then apply a formula to estimate the total

population.

Limiting factorAn environmental factor

that prevents a population from increasing.

Carrying CapacityThe largest population that

an area can support.

Ecology Terms

An organism’s job or role in the ecosystem.

Includes: what an organism eats, how it obtains food, and

any predators.

Niche

The specific environment that provides the things an organism needs to live, grow, and reproduce; an organism’s

home.A habitat provides food, water, shelter,

living space.

Examples: For fungus=moist earth of the forest floor.For an earthworm=tunnels in garden soil.

Habitat

All the organisms of the same species living in the same

area at the same time.

Examples:All the prairie dogs in a prairie.

All the red oaks of a forest.

Population

All the different populations living in the same area at the

same time.

Example:All the living things (bacteria, protists, fungus, plants, and

animals) in a forest.

Community

A community of living things in an area and their nonliving

environment.

All the living things in a forest, plus the soil, rocks, water, air

temperature, and weather.

Ecosystem

An environmental factor that prevents a population from increasing.

Examples:FoodWaterShelter

Living spaceWeather conditions

Number of predatorsNumber of competitors

Limiting Factor

The largest population that an area can support.

Limiting factors often determine the carrying capacity of an area.

Populations usually stay around the carrying capacity.

Carrying Capacity

The struggle between organisms to survive as they

attempt to use the same limited resources.

Two or more predators that feed on the same prey.

Snakes and hawks compete for mice.

Competition

Often animals can live in the same area and not compete, because they have different

niches. They may eat different foods.

Note:

A relationship between two organisms in which one

organism kills another for food. Also called predation.

Examples:A coyote and a rabbit

A bird and blueberry bush

Predator-Prey Relationship

A close, ongoing relationship between two organisms of

different species that benefits at least one of the organisms.

Note: Predation is not symbiotic, because predator-prey

relationships are quick, not ongoing.

Symbiosis

A symbiotic relationship between two organisms in

which both organisms benefit.

Example:A sea anemone and a clown

fish.

Mutualism

A symbiotic relationship between two organisms in

which one organism benefits and the other organism is

neither helped nor harmed.Example:

A bird builds a nest in a tree.

Commensalism

A symbiotic relationship between two organisms in

which one organism benefits and the other organism is

harmed.

Example:Fleas on a dog

Parasitism

The organism that a parasite (or virus) lives on or in and is harmed in a parasitic relationship.

Host

Parasite The organism that benefits by living on or in

a host in a parasitic relationship.

A behavior or physical characteristic that allows an organism to survive in its environment.

Adaptation