Community Interactions Community An assemblage of all the populations interacting in an area
Populations are affected by: Available living space habitat Resource Availability niche Species interactions Symbiosis living together commensalism mutualism parasitism Competition Predation Coevolution
Available Living Space Habitat an organism s mailing address the type of place where the individuals normally live
Resource Availability Niche an organism s profession (role) in the community
Species Interactions Symbiosis Living together for at least some part of the life cycle Most interactions are neutral; they have no effect on either species Commensalism Mutualism Parasitism
Commensalism One species benefits and has no effect on the other
Mutualism Both species benefit Some are obligatory; partners depend upon each other (coevolution) Yucca plants and yucca moth Mycorrhizal fungi and plants Anemone fish and anemone
Mutualism Protection
photograph Alex Wild 2004
Mutualism Birds get food, help plant disperse seeds
Mutualism Pollination
Yucca and Yucca Moth Example of an obligatory mutualism Each species of yucca is pollinated only by one species of moth Moth larvae can grow only in that one species of yucca
Yucca Moth Yucca Plant Obligate Mutualism
Mycorrhizae Obligatory mutualism between fungus and plant root Fungus supplies mineral ions to root Root supplies sugars to fungus
Parasitism Parasites draw nutrients from hosts live on or in host body Vectors Convey a parasite from host to host Parasitoids Develop inside another species Consume and kill host
Protozoan - flagellate Micro Parasites bacteria fungus
Macro parasites tick flea
Macro parasite lamprey
Parasites
Parasites as biological controls Some parasites and parasitoids are used as biological controls Adapted to specific host and habitat Good at locating host High population growth rate Offspring disperse
Biological Controls Wasp and aphid
Social Parasite Brown-headed cowbird
Competition Interspecific: among different species Exploitative competition Interference competition Intraspecific: between members of the same species Intraspecific competition is most intense Territoriality Allelopathy Some species have eliminated ways of avoiding competition: Resource partitioning
Interspecific Competition
Intraspecific Competition
Intraspecific Competition Territoriality
Intraspecific Competition Allelopathy (sibling harming) Eucalyptus oils harm young saplings of same species. Can also affect other species
Forms of Competition Exploitative competition Species have equal access to resource; compete to exploit resource Interference competition One species prevents another from using resource usually through aggressive behavior
Interference Competition
Competitive Exclusion Principle When two species compete for identical resources, one will be more successful and will eventually eliminate the other
Gause s Experiment Species grown together Paramecium caudatum Paramecium aurelia
Resource Partitioning Apparent competitors may have slightly different niches May use resources in a different way or time Minimizes competition and allows coexistence
Predation Predators animals that feed on other living organisms free-living do not reside on their prey Carnivores and omnivores
Predator Prey Relationships: Canada Lynx and the Showshoe Hare Species are limited by the number of available prey In some cases predators limit a prey species
Coevolution Two or more species exert selection pressure on each other Prey defenses evolve Predator responses to prey evolve
Prey Defenses Camouflage Warning coloration Mimicry
Camouflage
Warning Coloration & Mimicry
Predator Responses Predators counter prey defenses with new adaptations stealth camouflage avoidance of chemical repellents
Predator Responses
Community Dynamics Factors affecting changes in community structure Intermediate Disturbance Hypothesis Community Instability (Alternate stable states) Keystone Species Exotic (introduced species) Ecological Succession Primary Secondary
Species Diversity Species diversity Variety, Abundance of Species in a Particular Place Species richness: The number of different species in a given area Species evenness: Comparative number of individuals
Variations in Species Richness and Species Evenness Higher richness and evenness lower richness and evenness Fig. 4-12, p. 93
Species Diversity: Diversity varies with geographical location The most species-rich communities Tropical rain forests Coral reefs Ocean bottom zone Large tropical lakes
# seaweed species log # seaweed species Species are not assembled randomly in nature. Physical stress Species richness 5 4 3 2 1 0 Nov-75 May-76 Oct-76 May-77 Low Mid High Disturbance level (Sousa 1979 Ecology) 15 10 5 0 Herbivory 0 100 200 300 Herbivore Density (snails/m 2 ) (Lubchenco 1978 Am Nat) 1.00 0.75 0.50 0.25 Nitrogen availability 0.0 0.2 0.4 0.6 0.8 1.0 log ammonium loading (micromol/l/h) (Bracken & Nielsen 2004 Ecology)
Intermediate Disturbance Hypothesis Ecological Community stability is an uneasy balance Areas with moderate levels of disturbance have greater species diversity
Community Instability Disturbances can cause a community to change in ways that persist even if the change is reversed. In some cases these are considered alternate stable states
Keystone Species A species that has a disproportionately large effect on community structure Removal of a keystone species can cause drastic changes in a community can increase or decrease diversity
sea star community 15 species coexist - 1 sea star is removed 8 remain in community
Keystone species exert an important regulating effect on other species in a community. Populations are limited by competition for resources Fig. 53.14 Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
If Keystone Species are removed, community structure is greatly affected.
Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Over time, one array of species is replaced by another Ecological Succession
Types of Succession Primary succession: new environments Begins with foundation species Ends with climax community Secondary succession: communities destroyed or displaced May not have foundation species Also ends with climax community
Climax Community Stable array of species that does not change over time In a particular habitat, succession produces the same climax community
Most communities are disturbed by events like fire, weather, or human activities
Marine communities are subject to disturbance by tropical storms. Fig. 53.17
Volcanic Island Succession Foundation Species Climax Community
Glacial Succession
Primary succession begins in a new or lifeless area where soil has not yet formed. Lake Succession
Sand Dune Succession
Secondary succession occurs where an existing community has been cleared, but the soil is left intact. Relatively rapid succession Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Secondary Succession: Disturbed Habitats Along Roadsides Abandoned Fields
Cyclic Replacement Fire Damage Disease Damage Sudden Oak Death Storm Damage
Cyclic Replacement: Fire Climax Chaparral fire adapted plant community
Giant Sequoia High intensity crown fire destroys forest No fire no seedlings, growth of white fir Low intensity allows Giant Sequoia to re-seed Medium intensity kills competing fir trees