Reice 1994 - Nonequilibrium determinants Flashcards
What are the 2 historical approaches to community structure?
1 - Community composition determined by environment, which sets range for colonization, reproduction, survival. Taxons results from random colonization and envr variability.
2 - Equilibrium theory
Interspecific
Between species interactions
Intraspecific
Within species interactions
Equilibrium theory
- 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
What is the key determinant of community structure in equilibrium theory?
- 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
Shortcomings of equilibrium theory
- 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
What do non equilibrium theories emphasize?
- Environmental disturbance and spatial heterogeneity as factors that encourage colonization and species diversity
- Ex. Surge in diversity after fires
What happens to individual organisms with predictable vs. erratic disturbances?
- Predictable = biota adapt
- Erratic = loss of individuals
What concepts do non equilibrium theories include?
- 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
How is equilibrium viewed in a non equilibrium theory?
- Equilibrium is unusual state, rarely achieved due to frequent disturbance followed by recovery
How does disturbance and patches relate to one another?
- Disturbance creates patches
- But disturbance is also a product of the patches themselves
- Underlying control of community structure
What does the underlying physical-chemical environment determine in non-equilibrium theory?
- Determines frequency and magnitude of disturbance
- Influences time course of recovery
- Community structure
What does stochastic recruitment in a heterogenous, disturbed, patchy environment result in?
- High overall species diversity
What does disturbance and loss of individuals allow for in an ecosystem?
- Allows for creation of open spaces, recolonization and greater diversity
Environmental crunch
- Fluctuations in environment, temporal variability
- Affects relative importance of competition in communities over time
- Scarce resources and competition becomes more important
Features of temporal variability
- 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
How does coexistence of tropically equivalent species occur?
- Temporal variability resulting in envr fluctuations
- Leads to fluctuating competitor advantages, perhaps by season
- Mechanism greatest impact in disturbed ecosystems, ‘ecosystem crunch’
Simple definition of disturbance
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
What is the 1st impact of disturbance?
- Removal of organisms
What is the relationship of spatial scale with disturbance perception
- Large scales and long temporal scales make disturbances appear normal/predictable
- Smaller scales and durations lead to a random perception of disturbance
Is predation a considered a disturbance?
- No, Even though it removes individuals
- Predation is intrinsic to nature and prey can adapt to it
What is the disturbance associated with envr enrichment?
- 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
What is community structure made of?
- Species richness, number of species
- Species evenness, distribution of individuals among species
Which level of disturbance leads to maximum species richness?
- Intermediate disturbance (magnitude, intensity, and freq)
- Some resident species persist along with colonizers
- Too frequent and dominant competitors reduce and colonizers dominate, = reduced richness
