Population Ecology continued Interactions between two populations

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Population EcologycontinuedInteractions between
two populations

• Lecture 14

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Symbiosis

• The term symbiosis (from Greek) literally means
  living together
• Describes close and often long-term interactions
  between different species

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Symbiosis

• Can be applied to a various relationships may be
  categorized as being
• Mutualistic
• Commensal
• Parasitic

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Mutualism

• Lichens
• Pollination (plant-pollinator interactions)
• Clown fish and anemone

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Commensalism

• One species benefits from the presence of the
  second species but the second species is
  unaffected by the first species
• Cattle Egrets following water buffalo
• Marsh wrens nesting in cattails

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Parasitism

• One species benefits and the other is negatively
  affected
• Lamprey (ectoparasite)
• Tapeworms (endoparasite)

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Parasitiods

• Lay there eggs in larvae of other insects and
  once the eggs hatch the parasitiod larvae eat the
  host larva
• Many wasps and flies are parasitoids of other
  insects (especially moths and butterflies)
• Often used in biological control

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Ammensalism

• One species negatively effects another but the
  first species is unaffected by the interactions
• Many plants that produce metabolic by products
  that negatively effect other plants
• Black ash, Black walnut

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Neutralism

• Both species are unaffected
• Tarantulas and cacti

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Symbioses

• Can be obligatory or facultative (Mullarian
  mimicry)

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Competition

• Both populations can have a negative effect on
  the other
• Both species require the same resources which are
  available in limited supply
• Resources used by one species reduce what is
  available for the other
• May reduce survival, reproductive output

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Predation

• One population can benefit at the expense of the
  other
• Classical examples are those in which one animal
  the predator kills and consumes the other (lion
  and antelope)

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Predation

• In some ways parasites, parasitoids and
  herbivores represent special cases of predation
  in which the predators consume only part of
  their prey and leave enough behind so that the
  prey continue living

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Predation Competition

• Importance of predation and competition has been
  debated for decades
• Two hypotheses for population control
• Top down control
• Bottom up Control

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Bottom up (competition for resources controls
populations)
Walleye
Perch
Snails
Primary Production
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Top down control (populations controlled by
predators)
Walleye
Perch
Snails
Primary Production