Communities Flashcards

1
Q

Whats a community?

A
  • Group of species that occur together in space and time

- Large number of similar species

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2
Q

4 basic processes determine species composition:

A
  1. Selection: Species are outcompeted and go extinct
  2. Drift: Species go extinct through random chance
  3. Dispersal: Species arrive from outside local community
  4. Speciation: New species are created (on very long time scale)
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3
Q

Whats selection? What does persist mean?

A
  • Each species can persist under a particular range of environmental conditions (niche)
  • Persist- having a positive growth rate
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4
Q

Whats niche partitioning? Example?

A
  • Many species can coexist because they occupy different niches in heterogeneous environments 
(= niche partitioning)
  • Forest composition along elevation/moisture gradients in Great Smoky Mountains
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5
Q

Whats a resource utilization niche?

A

-Niche can be defined based on resource use

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6
Q

Whats the principle of competitive exclusion?

A

-Species with lower fitness 
(in a given environment) 
expected to go extinct

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7
Q

Invasibility criterion: do all species have a positive growth rate when rare (and rest of community at equilibrium)?

A

Given finite resources, this means a rare species must have higher fitness (per-capita growth) than community average

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8
Q

How might rarity increase fitness?

A

Less conspecific interference (e.g., defending territory)
Predators switch to other prey
Attract fewer pests/pathogens

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9
Q

Constant environment vs fluctuating environment.

A

Constant environment

  • Niche partitioning
  • Frequency-dependent selection

Fluctuating environment

  • Non-linearities
  • Storage effect
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10
Q

What if environment varies so that each species does best at different times?

A
  • This does not necessarily enable co-existence

- The species that does best on average wins 
(unless particular conditions are met)

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11
Q

When is coexistence possible in communities?

A

1) Species A does best when R is constant
; Species B does best when R fluctuates
 (only possible if responses have relative non-linearity)
2) High density of species A causes R to fluctuate

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12
Q

Whats the storage effect?

A

Co-existence is also possible when:

1) Species have different responses to environment
2) Competition covaries with environmental conditions
3) There is buffered population growth (life history stages that are resistant to competition in bad periods)

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13
Q

What do environment- competitions interactions happen from?

A

Life history stages immune to competition

-Arise from buffered population growth

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14
Q

Whats buffered population growth?

A
  • competition has a smaller effect in bad environments

- e.g., seed bank, dormancy, long-lived adults

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15
Q

How does storage effect work?

A

When one sp does well its growth is reduced by competition more than the other sp.

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16
Q

How does the storage effect give invading sp a fitness advantage?

A

Invaders do very well in good environments. A little worse in bad environments

17
Q

What conditions are needed for the storage effect?

A

1) Different environmental responses- Different year-to-year
 environmental responses
2) Competition co-varies with environment- Covariation between competition and environment
3) Buffered pop growth-competition has a greater effect in good times than bad times

18
Q

When does spatial storage effect occur?

A

When local microhabitats are favourable to different species

19
Q

Conditions producing spatial storage effect

A
  1. Different responses to environment
 - created by local spatial variation (e.g., soil)
  2. Covariance between environment and competition
 - higher pop size on good patches
 - competes more strongly with itself than others
  3. Buffered population growth
 - automatically produced by dispersal among patches
20
Q

Whats a trade off that enables co-existence across space? How does it work?

A

Colonization-competition trade-off
1. Each blue square (“colonizer”) has a chance to colonize any empty cell

  1. Each red square has a (lower) chance to colonize any non-red cell. If that cell is blue, they take it over (“competitor”)
  2. A fraction of all squares are killed off (disturbance)- both species have same mortality rates
  3. Repeat
21
Q

Why is the colonization competition trade off stable?

A

Blue benefits when rare because there are lots of empty cells available

Red benefits when rare because there are lots of non-red cells available

Blue is a “fugitive species” →
persists only by staying on the move

22
Q

How can blue species survive in colonization competition trade off? What would happen if there were no disturbances?

A

-Be on the move
-red would take over as disturbances cause empty habitats for blue
-

23
Q

Whats the dispersal-fecundity trade-off?

A
  • Requires variation in patch density
  • High-fecundity species wins where patches are close together
  • Better disperser wins where patches are far apart
24
Q

Whats the tolerance-fecundity trade-off?

A
  • Requires variation in patch quality
  • Combines aspects of niche partitioning and colonization-competition trade-off
  • Co-existence under a broader range of conditions