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Week 4 Discussion Questions
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Departments of Geography & Civil and Environ Engineering, UC Berkeley
Week 4 discussion questions (2/8/13)
1. How can you distinguish between examples of what truly are alternate stable states—i.e., two or more stable point attractors separated by unstable thresholds—and the various other kinds of big changes that systems may exhibit?
2. Can a threshold, a breakpoint between two regimes of a system, be identified before it has been crossed?
3. Why should communities characterized by disturbance be viewed as ever being in a “stable” state? Why not consider them alternative transient states?
4. Using what time scale do we typically consider a community to be stable or resilient? Do we use generation time of focal species? Immigration rates?
5. The extent of historical contingency due to priority effect is difficult to quantify because immigration history is hard to reconstruct for most natural communities. Are lab experiments helpful here? At what point do you need field data at greater scales to test theory?
How well know should be the original conditions of an ecosystem in order to try an ecosystem restoration? How can you decide between an arbitrary, realistic, and original condition goal to restore?
What is the difference between long term transience and natural succession?
In the case that you want to restore a population which needs a minimum number of individual to be successfully restored (e.g.: genetic diversity to avoid inbreeding, or coevolution interactions between plant and specialized pollinators, etc. ) could be the restoration of these ecosystems have alternative stable states considering the relations of denso-dependency between the species ?
In the case of agricultural systems, where you can manage the alternative stable stages, could be more resilient to changes (weeds, insect pest, etc.) the polyculture or monoculture? Which one will develop more alternative stable states under environmental adversity?
In the way to determine the best management (economical/effective) to restore an ecosystem how can you decide if you want to increase the community (plants or animals) that you want to restore, or manage the environmental conditions that will provide a natural succession for self-recovery?
Considering the ecosystems that were historically subject to extreme abiotic regimes, can be a strategy of restoration management the diversification of functional groups?
1. How do alternative states and perturbations to a system differ? How significant must the perturbations or changes in ecosystem states and environmental conditions be to become an alternative state?
2. What type of tests are used to determine whether a degraded system is an alternative and stable equilibrium?
3. How are constraints prioritized (single and multiple constraint)? Would most be considered multiple constraints since interactions and feedbacks to processes are linked?
4. How does the “priority effect” affect variation in community assembly? Why does the probability of stochastic priority effects lead to strong environmental adversity?
When attempting to understand stable states, how is our understanding influenced by time, space and the boundaries of the system? What does it mean to return to a ‘pristine’ state? How do we understand ‘pristine’ state, alternative stable states, and transience vs. stability in the context of (1) a constantly changing base state–for example change arising from shifting climate–as opposed to a static base state and (2) humans as part of the system? Maintenance of a system in the context of ongoing change (climate) would seem to require constant–or at least periodic–intervention to maintain stability. How does this shape the framework of management practices and the factors of a system that are important to understand?
Theory surrounding the causes of alternative stable states is clearly contentious, but understanding dynamics of systems (especially systems in alternative states)is crucial for predicting impacts of management practices. What methodologies are available for validating theory or empirically investigating system dynamics that would give insight on the outcomes of potential management approaches?
So sorry I forgot about these earlier:
1. Fukami and Lee mention that regional diversity can be enhanced when the presence of alternative stable states increases Beta diversity. How are Alpha and Beta diversity impacted by the presence of alternative stable states/are the impacts correlated?
2. How can we utilize paleobiology to determine whether alternative stable states are indeed persistent or transient?
3. Fukami and Lee note that species co-occurrence is more likely to be determined by species response to abiotic conditions than by competition or other interspecific interactions in cases with strong abiotic gradients/disturbances. They predict that communities weakly structured with environmental adversity are more likely than communities abiotically/disturbance-structured to exhibit alternative stable states. Do these abiotically/disturbance-driven states imply a cyclical or lasting disturbance, or can such disturbances be unpredictable/transient in this model?
4. What other interspecific interactions beyond competition tend to characterize ecosystems and move them toward the short-term transient states/successional pathways in Didham and Watts?
5. What stochastic priority effects dominate in community assembly?
1. The authors point out the importance of the scale of observation in determining whether a coummunity is abiotically or biotically driven (413). However, at large enough scales, every ecosystem is abiotically driven. Is the key, then, to first identify the scale of a restoration intervention (usually dictated by politics, land ownership, or resources) and then determine whether biotic or abiotic drivers are more important at that scale?
2. What is meant by “transient states” and how can they be distinguished from alternative stable states?
3. Many degraded ecosystems characterized by invasive species exhibit low diversity. Are these systems also examples of systems where “traits of species are markedly under-dispersed”? (414).