• Assemblage of many populations that live in the same place at the same time.
• Variety of scales, can be nested

Studies how groups of species interact and form functional communities

Number of species in each community.

Varies according to geographic range.

• Increasing from polar to temperate, max in tropics.
• Increases by topographical variation.
• Reduced by peninsular effect.

TIME HYPOTHESIS

for latitudinal gradient

Drawback: doesn't work with marine organisms.

Communities diversify (gain species) with time.

Temperate regions younger = less diverse.

Drawback?

AREA HYPOTHESIS

for latitudinal gradient

Drawback: Asia, Tundra, open ocean have low richness by area.

Larger area =  more species: can support larger populations and a range of habitats.

Drawback?

PRODUCTIVITY HYPOTHESIS

for latitudinal gradient

Support: more plants in warm & wet areas.

Drawback: some tropical seas have low productivity but high richness; sub-Antarctic Ocean has high productivity but low richness.

more plants = more production = more species

Support?

Drawback?

INTERMEDIATE-DISTURBANCE HYPOTHESIS

for latitudinal gradient

Support: coral reefs (hurricanes), tropical forests (landslides and treefalls)

Highest number of species with intermediate levels of disturbance.

Disturbance by natural disasters or species interactions i.e. herbivory, predation, parasitism

Support?

Gradual and continuous change in species composition and community structure over time.

Each colonizing species makes the environment a little different.

Each phase of succession = ______

-disturbance might set the community back to earlier ___

FACILITATION

Early colonists may exclude subsequent colonists.

-what gets there first determines later community structure

Species more successful at first

Community of organisms in an area + the abiotic environment affecting that community.

-difficult to give "boundaries"

Primary consumers eat primary producers.

DETRITIVORES

or decomposers

Use light or chemical to gain energy.

Primary producers form the base of the food chain.

Short in most food webs.

# of links beween levels.

Usually less than 6 levels.

Based on laws of physics and chemistry.