Communities

1
Lecture 25

• Chapter 36
• Communities

2
Learning Objectives (p. 1 of 2)

• Explain
• Niche partitioning
• Recite
• The two genera of barnacles in Connells study
• The definition of a community
• Contrast
• Species richness and relative abundance

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Learning Objectives (p. 2 of 2)

• Discuss
• Why commensalism is rare
• Robert Paines study
• Define
• Symbiosis (three kinds)
• Give examples of each
• Keystone predator

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Definition Ecological Niche

• Metaphor if the community a play
• Then all the species are the actors
• Niche an ecological role in the play
• Only one actor per role
• More formally all the resources a species uses

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Niche Partitioning

• Potentially competing species can avoid
  competition
• Specialize upon different resources
• Allows for coexistence of similar species in
  community

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Bats Birds Partition Niches

• Flycatchers and bats both eat flying insects
• Flycatchers forage during day
• Bats forage at night

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Different Hummingbirds Partition Niches

• All hummingbirds drink nectar from flowers
• Species with long beak specialize in long,
  tube-like flowers
• Some have short beak specialize in smaller flowers

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Barnacles Partition Niches

• All barnacles need space on a rock
• Some take higher position
• Some take lower position

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Joseph Connells Study

• Intertidal zone in Scotland
• Barnacles compete for space on rocks
• Two species have niche partitioning

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Connells Study (Contd)

• Two genera of barnacles
• Balanus
• Superior competitor
• Will outcompete, crush other barnacles every time
• Chthamalus
• Loses to Balanus, if its present
• Superior at resisting dessication
• Can live high on rock, where Balanus cant

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Mimicry

• One species imitating another
• In physical appearance
• In behavior
• Usually to avoid predators
• Two types Mullerian Batesian

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Mullerian Mimicry

• Several unpalatable species all resemble one
  another
• Predators learn to avoid all of them

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Batesian Mimicry

• An edible species has appearance of unpalatable
  species
• Predators tricked into leaving the mimic alone
• Relies on mimics being less common than
  unpalatable species (or predators would catch
  on)

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Caution

• Snake on next slide

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Batesian Mimicry

• A caterpillar that looks like a snake!
• Birds will avoid

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Keystone Predator

• A carnivorous species which has a central role in
  its community
• Often times a top-level predator
• Influence much greater than expected simply from
  its abundance

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Robert Paines Study

• Rocky intertidal zone very diverse
• Has many species Starfish, mussels, barnacles,
  limpets, chitons, whelks, sponges, algae
• Starfish eats many of these
• Larger mussels are a favorite item

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Paines Study (Contd)

• Paine removed starfish from some areas
• Left other areas as untreated controls
• Starfish removal resulted in mussels dominating
  entire community!

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Paines Study (Conclusion)

• Take home message predators can help maintain
  diversity
• Highly influential predators are called keystone
  predators

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Symbiosis

• Literally, living together
• Two species, whose life histories are intertwined
• Often live on, next to, or within eachother
• Three basic kinds
• Parasitism
• Commensalism
• Mutualism

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Parasitism

• One species benefits, while another is harmed
• Parasite species that benefits
• Host species that is harmed

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Viruses are Parasites

• Cold, HIV, herpes all benefit from us
• Get place to live
• Use our bodies to copy
• We are the hosts, and we suffer

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Cowbirds are Brood Parasites

• Dont have time to raise young, build nests
• Lay egg in host nest (typically warblers)
• Discards real egg
• Parasite egg looks like host egg
• Baby cowbird will kick hosts chicks out of nest

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Commensalism

• One species benefits
• Other species neither benefits nor suffers
• Very rare in nature

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Cowbirds Cattle

• Cows move through grass, scaring insects
• Cowbirds benefit
• They eat insects
• Get a free ride on cows back
• Question does cow benefit at all?

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Mutualism

• Both species benefit from relationship
• The species are both referred to as symbionts

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Acacia Tree and Ants

• Ants benefit from
• Safe place to live (in thorns)
• Food provided by Acacia tree
• Acacia benefits from
• Its own live in security force

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Another Ant Mutualism

• Leafcutter ants harvest leaves for fungus to use
• Why dont ants just eat the leaves?
• See video for the answer

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Leafcutter Ants
The leafcutter ants grow fungus to be used as
_______. a. fertilizer for their leaf
gardens b. building material within their
colony c. food for their young d. chemical
protection against predators e. all of the
above
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Corals and Algae

• Corals sometimes have algae in their tissues
• Benefits coral polyps receive
• Sugars
• Oxygen
• Benefits algae receive
• Protection
• Carbon dioxide
• Nutrients (nitrogen, phosphorous)

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Counter Example

• Male robin and female robin work together to
  build a nest
• Both benefit from
• Having a place to live
• Sharing parental duties
• What kind of symbiosis is this?

32
Counter Example

• Male robin and female robin work together to
  build a nest
• What kind of symbiosis is this?
• NOT SYMBIOSIS!!!
• Symbiosis only occurs between two different
  species!

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EcoStretch