Ecology: Communities Ecology: Communities

Interactions Between PopulationsInteractions Between Populations

Properties of CommunitiesProperties of Communities

Interactions Interactions -Competition-Competition -Predation-Predation -Symbiosis-Symbiosis

Change through succession Change through succession

Competition Relates to Niche OverlapCompetition Relates to Niche Overlap

Degree of competition is proportional to Degree of competition is proportional to the overlap in ecological niches of the overlap in ecological niches of competing speciescompeting species

Ecological niche = total way of life of all Ecological niche = total way of life of all members of a speciesmembers of a species

--Habitat--Habitat--Physiological needs such as--Physiological needs such as

temperature, moisture, nutrients temperature, moisture, nutrients--Behavior--Behavior--Interactions with other species--Interactions with other species

One Outcome of Competition: One Outcome of Competition: Competitive ExclusionCompetitive ExclusionGrown inSeparateFlasks

Grown inthe SameFlask

Another Outcome of Competition: Another Outcome of Competition: Resource PartitioningResource Partitioning

Effects of PredationEffects of Predation• Eliminates old and weak individuals Eliminates old and weak individuals

• Regulates numbers of both predators Regulates numbers of both predators and preyand prey

• Coevolution of predator and preyCoevolution of predator and prey

• Regulates diversity of populations in Regulates diversity of populations in communitycommunity

The sea star The sea star PisasterPisasteris a keystone species in is a keystone species in aquatic communities in aquatic communities in the Pacific Northwest.the Pacific Northwest.

SymbiosisSymbiosis

ParasitismParasitism

CommensalismCommensalism

MutualismMutualism

Ecological SuccessionEcological Succession

• Predictable sequence of changes in Predictable sequence of changes in vegetation type over time after a vegetation type over time after a disturbancedisturbance– Primary succession: occurs in barren Primary succession: occurs in barren

environment with no pre-existing ecosystemenvironment with no pre-existing ecosystem– Secondary succession: new community Secondary succession: new community

develops after disturbance of existing develops after disturbance of existing ecosystemecosystem

• Pioneer speciesPioneer speciesclimax communityclimax community

Mount St. HelensMount St. Helensafter 1980 explosionafter 1980 explosion

Same viewSame view20 years later20 years later

Succession in ProgressSuccession in Progress

Primary SuccessionPrimary Succession

Pioneer Pioneer SpeciesSpecies

Climax Climax CommunityCommunity

Succession in a Freshwater PondSuccession in a Freshwater Pond

Secondary SuccessionSecondary Succession

Pioneer Pioneer SpeciesSpecies

Climax Climax CommunityCommunity

• Tolerate environmental extremes Tolerate environmental extremes

• R-selected species predominateR-selected species predominate– High reproductive ratesHigh reproductive rates– Plants with seeds that spread easilyPlants with seeds that spread easily

• Poor competitors in established Poor competitors in established communitiescommunities

•Stable community at endpoint of successionStable community at endpoint of succession

•Suited to specific environmental conditionsSuited to specific environmental conditions

•K-selected species predominateK-selected species predominate

Climax CommunityClimax Community

Pioneer SpeciesPioneer Species

Some Communities Never Some Communities Never Reach the Climax StageReach the Climax Stage

• Grasslands – maintained by disturbances Grasslands – maintained by disturbances (fires & grazing)(fires & grazing)

• Many forests – need fireMany forests – need fire

• Chaparral – needs fire for seed germinationChaparral – needs fire for seed germination

Human Activity Favors Weeds and ShrubsHuman Activity Favors Weeds and Shrubs

Agricultural land is Agricultural land is plowed each seasonplowed each season

Overgrazing of Overgrazing of grasslands ingrasslands inUS SouthwestUS Southwestgave advantage gave advantage to mesquite shrubsto mesquite shrubs

Logging and Logging and forest clearing forest clearing disrupt the disrupt the climax community climax community

Applying Your KnowledgeApplying Your Knowledge

A.A. Which one would occur in a region where Which one would occur in a region where a glacier has receded, leaving a barren a glacier has receded, leaving a barren rock surface? rock surface? (choice 1 or 2)(choice 1 or 2)

B.B. Which category would include a forest of Which category would include a forest of conifer trees? conifer trees? (choice 3 or 4)(choice 3 or 4)

C.C. Which category would include lichens? Which category would include lichens? (choice 3 or 4)(choice 3 or 4)

1.1. Primary SuccessionPrimary Succession2.2. Secondary SuccessionSecondary Succession3.3. Pioneer SpeciesPioneer Species4.4. Climax CommunityClimax Community