Interactions among populations IV: Ecological networks - mutualists and antagonists Flashcards

1
Q

Species do not exist in isolation but in

A

complex networks of antagonistic (predation, herbivory and parasitism), or mutualistic interactions (e.g. pollination)

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2
Q

Food webs describe

A

antagonistic networks

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3
Q

List some antagonistic networks

A
  • food webs
  • predator-prey
  • parasitoid-host
  • herbivore-plant
  • pathogen-host
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4
Q

List some mutualistic networks

A
  • pollinators and flowers
  • seed dispersers and fruits
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5
Q

Describe linkage networks

A

showing which species interact with which other species

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6
Q

Describe energy flow networks

A

showing the quantity of energy flowing among the species

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7
Q

Describe functional / interaction strength networks

A
  • showing the most important interactions structuring the community
  • require expts
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8
Q

Describe the “small world” property

A

6 degrees of separation

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9
Q

Describe the small world properties of ecological networks

A
  • species from a variety of aquatic and terrestrial ecosystems are on average two links apart
  • > 95% within three links of each other
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10
Q

Why is the small world property of ecological networks important?

A
  • changes to abundance of one species will propagate rapidly
  • dynamics within ecosystems can be highly interconnected
  • biodiversity loss, over-harvesting and species invasions may affect more species than previously thought
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11
Q

What are the advantages of networks

A
  • summarise complexity of community interactions (more realistic than models of a few interacting species)
  • understand community structure (which species occur in a community; why some are rare and some are common)
  • understand community dynamics (what happens if we interfere with ecological communities)
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12
Q

List some network attributes

A
  • number of species in the web, S
  • number of links or connections, L
  • connectance, C: the fraction of possible links in the web that actually occur
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13
Q

Give the equation for connectance

A
  • Actual Links / Possible Links
  • L/[S(S-1)/2]
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14
Q

How can food webs be studied?

A
  • observation: what patterns can be seen in ‘real’ webs?
  • modelling: look at the properties of empirical or computer- generated webs
  • experiment: test food web theory in the laboratory or in the field
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15
Q

Describe observational studies

A

analyse patterns in published networks

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16
Q

Describe artefacts in observational studies

A

– Taxonomic bias
– Lumping
– Omnivory (feeding on more than one trophic level) and ‘rare’ links underestimated
* Newer analyses use ‘purpose built’ webs

17
Q

Give an example of a robust observation

A

most food chains are short (3-4 levels)

18
Q

Describe the energy attenuation hypothesis

A
  • energy is lost at each tropic level (heat, respiration, etc.) due to the 2nd law of thermodynamics
  • eventually there is not enough energy for a further trophic level
19
Q

What are the predictions of the energy attenuation hypothesis

A
  • communities with more efficient energy transfer should have longer food chains (e.g. endotherms v. ectotherms)
  • communities with higher productivity should have longer food chains (at very low productivity they do, but few communities have > 3 or 4 levels)
20
Q

Describe the trophodynamics explanation of short food chains

A
  • chance variations in population size are amplified up the food chain leading to unpredictable dynamics for the top predator
  • food chains are indeed shorter in unpredictable environments
21
Q

Removing species with few trophic connections generally has

A

little effect

22
Q

Robustness increases with

A

connectance

23
Q

complexity (more species and/or more
connections) appears to

A

decrease stability

24
Q

Manipulations can identify

A

‘keystone species’ and ‘indirect effects’

25
Excluding the starfish Pisaster from rocky shores
shifted food web structure and reduced species diversity
26
Community structuring
determine which species occur and their relative abundances
27
List some factors that may structure communities
- indirect interactions - keystone species