CHAPTER 3: CHAPTER 3: COMMUNITIES + BIOMESCOMMUNITIES + BIOMES

3-1: COMMUNITIES3-1: COMMUNITIES

P.65-69P.65-69

Life in a CommunityLife in a Community• Types of things found in your lawn:

– Weeds– Insects– Earthworms– Grubs– Soil– Fungi– Bacteria

Life in a CommunityLife in a Community• How do all these things survive?

– The various combination of biotic + abiotic factors

Limiting FactorsLimiting Factors• Any biotic or abiotic factor that restricts the

existence, numbers, reproduction, or distribution of organisms

• Such as:– Availability of food + water– Predators– Temperature

Common Limiting FactorsCommon Limiting Factors

• Sunlight• Climate• Temperature• Water• Nutrients/Food• Fire• Soil Chemistry• Space• Other Organisms

Limiting FactorsLimiting Factors• Factors that limit one population in a

community may also have an indirectindirect effect on another population

• Example:– Lack of water

• Affects growth of grass• Affects # seeds produced• Affects # mice• Affects # hawks

Ranges of ToleranceRanges of Tolerance• Tolerance

– The ability of an organism to withstand fluctuations in biotic + abiotic environmental factors (“EXTREMES”)

– Represented by a GRAPH

Succession: Changes over TimeSuccession: Changes over Time

• SuccessionSuccession– The orderly, natural changes and species

replacements that take place in the communities of an ecosystem

– Occurs in STAGES– Difficult to observe because it can take

decades or centuries for communities to succeed

Primary SuccessionPrimary Succession• The colonization of barren land by

communities of organisms– Takes place on land where there are no

LIVING ORGANISMS– Example:

• Volcano

Primary SuccessionPrimary Succession• Pioneer speciesPioneer species

– First species to appear on new, barren land– Example:

• Lichen – group of small organisms

Primary Succession – the Primary Succession – the process…process…

• Pioneer species dies….

• Provides 1st stage of soil….

• New soil develops……

• Small weedy plants develop…

• New organisms move in…

• Area grows in size….

Primary SuccessionPrimary Succession• After some time, primary succession slows

down and becomes stable

• Climax community– Mature, stable community with little or no

change– Change is dynamic – balances out– May last for hundreds of years

Primary Succession StagesPrimary Succession Stages

Secondary SuccessionSecondary Succession• Sequence of changes that takes place

after an existing community is severely disrupted in some way– i.e. A natural disaster

• Community of organisms inhabiting an area gradually changes

• Occurs in areas that previously contained LIFE + land still contains soil

Secondary SuccessionSecondary Succession• May take less time to reach climax

community

• Example:– Yellowstone National Park (1988)

Secondary Succession StagesSecondary Succession Stages