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