Lecture 12 Community Interactions

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Lecture 12 Community Interactions
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• Types of Interactions Within A Community
• Competition
• Predation
• Symbiosis two (or more) kinds of organisms live
  together in close association
• Three kinds
• Mutualism Both participating species benefit
• Commensalism One species benefits and the other
  neither benefits nor is harmed
• Parasitism One species benefits while the other
  is harmed

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• Competition is the struggle of two organisms to
  use the same resource ie. share same niche
• any use .. of a resource by one species
  reducing its availability to another species
• Interspecific competition between species
• Intraspecific competition within species
• Outcome varies
• One species may be eliminated
• Both may persist but at decreased population
  levels
• Niche is divided
• Fundamental niche
• Realized niche

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• Interspecific competition and relatedness
• Darwin greater competition between related spp.
• Many exceptions convergence/food in webs
• Species of intertidal
• Species feeding on krill
• Species feeding on inverts of forest litter

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• Competitive Exclusion
• In the 1930s, G.F. Gause studied interspecific
  competition among three species of Paramecium
• P. aurelia P. caudatum P. bursaria
• All three grew well alone in culture tubes

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• However, P. caudatum declined to extinction when
  grown with P. aurelia

• The two shared the same realized niche and P.
  aurelia was better competitor

• Gause formulated the principle of competitive
  exclusion
• No two species with the same niche can coexist
• What parameter (think about evolutionary
  processes) results in survival of one species, to
  the exclusion of another (or others)?
• Is one competitor always eliminated from the
  habitat?

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• P. caudatum and P. bursaria were able to coexist

• The two have different realized niches and thus
  avoid competition

• Gauses principle of competitive exclusion can be
  restated
• No two species can occupy the same niche
  indefinitely
• When niches overlap, two outcomes are possible
• Competitive exclusion or resource partitioning

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Resource Partitioning

• Persistent competition is rare in natural
  communities
• Either one species drives the other to extinction
• Or natural selection reduces the competition
  between them

• Five species of warblers subdivided a niche to
  avoid direct competition with one another

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• Asymmetric Competition
• Results in division of niche ? realized niche of
  each
• Determined by competion/competator
• each exists in microhabitat
• Connell study of interspecific competition
  between Chthamalus stellatus and Balanus
  balanides

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• Mutualism
• Interactions between individuals of different
  species that benefit both partners.
• Facultative Mutualism occurs when a species can
  live without its mutualistic partner.
• Obligate Mutualism occurs when a species is
  dependent on a mutualistic relationship.

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• Animal Animal Mutualism

• Ants and Aphids

• Aphids provide the ants with food in the form of
  continuously excreted honeydew

• Ants transport the aphids and protect them from
  predators

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Ants and Bullshorn Acacia

• Herbivores attempting to forage on accacia plants
  occupied by accacia ants are met by a large
  number of fast, agile, highly-aggressive
  defenders.
• Ant Benefits
• Thorns provide living space.
• Foliar nectaries provide sugar.
• Beltian bodies are a source of oils and protein.

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• Mycorrhizae
• Plant Fungus mutualistic relationship
• Fungus benefits from carbohydrate nutrition
  provided by plant
• Plant benefit
• Fungus provides increased access to water and
  soil nutrients
• In many cases plants cannot effectively become
  established without mycorrhizal association

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Plant Performance and Mycorrhizal Fungi

• Two most common types of mycorrhizae
• Arbuscular mycorrhizal fungi (AMF)
• Produces arbuscules - site of exchange between
  plants and fungi, hyphae - fungal filaments, and
  vesicles - energy storage organs.
• Ectomycorrhizae (ECM)
• Forms mantle around roots - important in
  increasing plant access to phosphorus and other
  immobile nutrients.

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• Animals and Evolution of Flowering Plants
  Mutualism and Coevolution
• Two levels
• Movement of male gametophyte plant (pollen)
• Wind random, not efficient
• Coevolution with pollinators
• Movement of pollen more reliable
• Dispersal
• Heavy seed reserves for developing plant
• Efficient dispersal relies on mechanical
  transport by animals

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• Parasitic Relationships
• Host
• Parasite types
• Based on size
• Microparasite
• Macroparasite
• parasitioids
• Based on living within or on outside of host
• Ectoparasite
• Endoparasite
• Relationship with Host
• Obligate parasites
• Facultative parasites

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• Parasite Life Cycle
• may involve multiple hosts
• Definitive host supports maturation of parasite
• Intermediate host harbor developmental phase(s)
• Sometimes several
• Vector
• Alternate hosts
• Reservoir host(s) alternate hosts

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• Parasite Impacts on Host
• Balanced host-parasite relationship tolerant
• Host survives often with less vigor
• Parasite multiplies
• Balance altered
• High host mortality
• Possibly decreased parasite multiplication
• Reduced host fitness
• Altered host behavior

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• Brood parasitism
• common in birds within species non-obligate
• Obligate brood parasites
• Cuckoo
• Cowbird
• Host species react by ejecting eggs of parasite
  from next
• May be severely affected if behaviors not evolved
• Kirklands warbler

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