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Geog358LndEco > Reice 1994 - Nonequilibrium determinants > Flashcards

Reice 1994 - Nonequilibrium determinants Flashcards

1
Q

What are the 2 historical approaches to community structure?

A

1 - Community composition determined by environment, which sets range for colonization, reproduction, survival. Taxons results from random colonization and envr variability.
2 - Equilibrium theory

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2
Q

Interspecific

A

Between species interactions

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3
Q

Intraspecific

A

Within species interactions

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4
Q

Equilibrium theory

A
  • Systems in steady-state equilibrium
  • Equilibrium maximizes biodiversity
  • Environment constant
  • Biotic interactions are key determinant
  • Species composition relative abundances stable through time overall
  • Due to biotic interactions among members
  • System returns to original structure after perterbation
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5
Q

What is the key determinant of community structure in equilibrium theory?

A
  • Biotic interactions
  • Community is result of competitive and predator-prey relationships
  • Coexistence and spatial heterogeneity still important for diversity, but still fall w/in equilibrium
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6
Q

Shortcomings of equilibrium theory

A
  • Prediction of interspecific-interactions don’t appear to hold in nature
  • Coexistence of quite similar species and lack of demonstrable effects both of suspected competitors on each other and of predators on their prey distributions
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7
Q

What do non equilibrium theories emphasize?

A
  • Environmental disturbance and spatial heterogeneity as factors that encourage colonization and species diversity
  • Ex. Surge in diversity after fires
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8
Q

What happens to individual organisms with predictable vs. erratic disturbances?

A
  • Predictable = biota adapt

- Erratic = loss of individuals

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9
Q

What concepts do non equilibrium theories include?

A
  • Disturbance theory
  • Patch dynamics
  • Supply-side ecology
  • High diversity and coexistence of species attributed to process of disturbance and recruitment
  • tate, rarely achieved due to frequent disturbance followed by recovery
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10
Q

How is equilibrium viewed in a non equilibrium theory?

A
  • Equilibrium is unusual state, rarely achieved due to frequent disturbance followed by recovery
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11
Q

How does disturbance and patches relate to one another?

A
  • Disturbance creates patches
  • But disturbance is also a product of the patches themselves
  • Underlying control of community structure
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12
Q

What does the underlying physical-chemical environment determine in non-equilibrium theory?

A
  • Determines frequency and magnitude of disturbance
  • Influences time course of recovery
  • Community structure
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13
Q

What does stochastic recruitment in a heterogenous, disturbed, patchy environment result in?

A
  • High overall species diversity
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14
Q

What does disturbance and loss of individuals allow for in an ecosystem?

A
  • Allows for creation of open spaces, recolonization and greater diversity
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15
Q

Environmental crunch

A
  • Fluctuations in environment, temporal variability
  • Affects relative importance of competition in communities over time
  • Scarce resources and competition becomes more important
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16
Q

Features of temporal variability

A
  • Seasonality of rainfall in tropics
  • Temp fluctuations in arctic
  • Temporal variation allows for coexistence of trophically equivalent species, one better under one set of conditions, and vice versa
17
Q

How does coexistence of tropically equivalent species occur?

A
  • Temporal variability resulting in envr fluctuations
  • Leads to fluctuating competitor advantages, perhaps by season
  • Mechanism greatest impact in disturbed ecosystems, ‘ecosystem crunch’
18
Q

Simple definition of disturbance

A

Any relatively discrete event in time that disrupts ecosystems, community, or population structure, and changes resources, availability of substratum, or the physical environment

  • Physical event, not the biotic outcome of the event
  • Physical force that damages natural systems and removes organisms
19
Q

What is the 1st impact of disturbance?

A
  • Removal of organisms
20
Q

What is the relationship of spatial scale with disturbance perception

A
  • Large scales and long temporal scales make disturbances appear normal/predictable
  • Smaller scales and durations lead to a random perception of disturbance
21
Q

Is predation a considered a disturbance?

A
  • No, Even though it removes individuals

- Predation is intrinsic to nature and prey can adapt to it

22
Q

What is the disturbance associated with envr enrichment?

A
  • Addition of nutrients or manure is not the disturbance

- It is the loss of dissolved oxygen that is the disturbance that leads to loss of organisms like fish

23
Q

What is community structure made of?

A
  • Species richness, number of species

- Species evenness, distribution of individuals among species

24
Q

Which level of disturbance leads to maximum species richness?

A
  • Intermediate disturbance (magnitude, intensity, and freq)
  • Some resident species persist along with colonizers
  • Too frequent and dominant competitors reduce and colonizers dominate, = reduced richness
25
Q

Successional sequences after disturbance

A
  • Different disturbances remove different species to different degrees
  • Therefore succession is unique to the community
  • Disturbance is reinitializing step in successional development, restructures whole ecosystem, not just a population process
26
Q

Huston’s model of dynamic equilibrium for community structure

A
  • trade-offs btwn pop growth rates, competitive exclusion rates, and freq of pop reductions
  • Short disturbance interval = poorer competitors persist b/c competitive exclusion doesn’t have enough time to take place, = increased richness
  • Diversity determined not by competition but by influence of the envr on outcome of species interactions
27
Q

What is the return interval of disturbance roughly proportionate to?

A
  • Proportionate to the lifespan of the dominant organisms (space holders) in a system
  • Disturbed frequently relative to life history of dominant species
  • Trees live hundreds of years, freq of fire or wind disturbances is shorter than that
  • Disturbance return interval may be critical for life-history characteristics
28
Q

What does the removal of individuals lead to?

A
  • The opportunity for new species to colonize and change community structure
  • New physical and niche space is created
  • Larger magnitude = more individuals removed = more open space
29
Q

What are the 3 mechanisms of recolonization of newly available niche space after disturbance?

A
  • Regrowth (survivors, trees grow from stubs, coral polyps regenerate)
  • Migration (from adjacent patches)
  • Recruitment (individuals from outside proximate system - wind blown seeds, egg laying)
30
Q

How can patchiness affect disturbance?

A
  • Mitigate or intensify disturbance
  • Patches have differential susceptibility to disturbance
  • Disturbance enhances patchiness, whereby one patch sustains more population loss than other, therefore patches will be differentially open to recolonization
  • Frequency of disturbance is result of physical patchiness of envr
31
Q

How do patches opened by disturbance experience recruitment

A
  • Recruitment pool diversity is varied, in space and time
  • Patches develop distinctly different communities b/c only a portion of pool reaches each patch
  • Patch community consists of random subset of populations available for recruitment
  • Nearby identical patches that receive recruits from same pool may not get same species or diversity
  • Recruits are in right place at right time to move into available space

Geog358LndEco (11 decks)

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