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Ecosystem Stability. Stability: The degree to which an ecosystem is affected by a disturbance and that system
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1. Resilience and Resistance By Dejan Brkic
2. Why study stability? – a community requires some form or stability to exist
- knowledge of this stability is essential to predicting the future of communities
- problems caused by humans (such as habitat alteration, invasive species, climate change) can either be solved or prevented
There are seven aspects of stability. Only two are discussed here: Resistance and ResilienceWhy study stability? – a community requires some form or stability to exist
- knowledge of this stability is essential to predicting the future of communities
- problems caused by humans (such as habitat alteration, invasive species, climate change) can either be solved or prevented
There are seven aspects of stability. Only two are discussed here: Resistance and Resilience
3. Resistance A brick wall is representative fo a highly resistant (but not resilient) ecosystemA brick wall is representative fo a highly resistant (but not resilient) ecosystem
4. Resistance Resistance: The degree to which a system is altered as a result of a disturbance
Described by Webster et al. (1975)
- relationship between degree of nutrient cycling and resistance
Explained further by Loreau (1994)
Examples: A brick wall, a forest
In Webster’s work, he determined that the degree of nutrient cycling (i.e. how closed the loops is) increases the stability of the system by increasing resistance.
This work by Webster is not a journal article, but a later journal article by M. Loreau describes this relationshipExamples: A brick wall, a forest
In Webster’s work, he determined that the degree of nutrient cycling (i.e. how closed the loops is) increases the stability of the system by increasing resistance.
This work by Webster is not a journal article, but a later journal article by M. Loreau describes this relationship
5. Resilience
6. Resilience Resilience: the degree to which a system returns to its original state after a disturbance has passed and the rate at which it does so
Described by Holling (1973)
- identifies “resilience” as a property of a system’s stability using real world examples
Back to Loreau (1994)…
Mathematical models of Resistance and Resilience: Harrison (1979)
Example: budworm outbreaks in spruce-fir forests of Eastern Canada-
-The budworms attack mostly mature fir, but leave the spruce and birch intact.
-After the invasion ends, the immature fir quickly regenerate and cause immense crowding
-Prior to this the budworms were extremely rare (thus it is a disturbance)
-The crowding attracts more budworm
-The fir are considered to have extremely high resilience
Loreau – Found that a closed system of nutrient cycling has very low resilience but high stability due to high resistance- low resilience does not mean low stability
Mathematical models: Resistance and Resilience can both be high or low, or can be oppositeExample: budworm outbreaks in spruce-fir forests of Eastern Canada-
-The budworms attack mostly mature fir, but leave the spruce and birch intact.
-After the invasion ends, the immature fir quickly regenerate and cause immense crowding
-Prior to this the budworms were extremely rare (thus it is a disturbance)
-The crowding attracts more budworm
-The fir are considered to have extremely high resilience
Loreau – Found that a closed system of nutrient cycling has very low resilience but high stability due to high resistance- low resilience does not mean low stability
Mathematical models: Resistance and Resilience can both be high or low, or can be opposite
7. Resistance and Resilience of Alpine Lake Fauna to Fish Introductions John Muir Wilderness shown in pictureJohn Muir Wilderness shown in picture
8. Alpine Lakes of Sierra Nevada The research area, which includes the John Muir Wilderness and Kings Canyon National Park contains thousands of alpine lakes (oligotrophic) which were historically fishless
Fish were introduced to these lakes to create recreational fisheries
Some of these lakes still contain fish, some have reverted to being fishless, and some were never stocked to begin with
9. Basis of the Study These lakes are perfect for the study of resistance and long-term resilience of the lake communities
The introduction of fish is counted as the disturbance
Resistance and Resilience can be quantified by studying the population densities of all other animals in the community
10. Methods Lakes are divided into 3 categories:
- Never Stocked (fishless)
- Stocked (fish present)
- Stocked (fishless)
The presence of fish was determined using a “visual encounter survey” as well as gill nets
11. Methods Abundance of amphibians was counted by “visual encounter surveys” of the shoreline
Benthic invertebrates sampled using a D-net sweep of the littoral zone of each lake
Zooplankton were sampled from a float tube by taking vertical sweeps from the deep to the surface
12. Measuring Resistance and Resilience Resistance: the comparison of organism abundance between the “never stocked” lakes and the “stocked-fish-present” lakes
Resilience: the comparison of organism abundance between the “never stocked” lakes and the “stocked-fishless” lakes
13. Results Study organisms are divided into the following:
- Amphibians
- Clinger/Swimmer taxa
- Caddisfly taxa
- Burrownig/Distasteful taxa
- Crustaceans
- Rotifers
14. Amphibians The mountain yellow-legged frog was used as a representative for amphibians as it is the most common amphibian in this area
15. Amphibians The abundance of frogs is significantly lower in lakes containing fish thus they show low resistance
Frogs show some resilience since the abundance of frogs in the “stocked-fishless” lakes is similar to that of the “never-stocked” lakes
Note that frogs were found in very few of the “stocked-fishless” lakes. This is because none of the lakes that have been fishless for less than 10 years contained any frogs. This suggests frogs have a slow recovery time Low resilience attributed to the fact that colonization from other lakes is slow in amphibiansLow resilience attributed to the fact that colonization from other lakes is slow in amphibians
16. Clinger and Swimmer Taxa Five out of the six clinger/swimmer taxa have reduced abundances in lakes containing fish
Of the five, four show high resilience
Why are there discrepancies? What about Culex? Why does agabus have low resilience and corixidae have high resilience? Maybe corixidae have high growth rates in the absence of predators and outcompete agabus
High resilience attributed to flying abilities of adultsWhy does agabus have low resilience and corixidae have high resilience? Maybe corixidae have high growth rates in the absence of predators and outcompete agabus
High resilience attributed to flying abilities of adults
17. What about Culex? Abundance of mosquito larvae is much greater when fish are present
These larvae hide in dense vegetation
Only accessible to invertebrate predators
Fish eliminate these predators
18. Caddisfly Taxa Four of the five caddisfly taxa have reduced abundances in the presence of fish
Many seem to have low resilience
What about Limnephilus? Low resilience attributed to poor dispersal
Low resilience attributed to poor dispersal
19. What about Limnephilus? The abundance is equal in lakes with and without fish
High resistance?
Its case is constructed from organic materials which camouflage well against organic substrates
20. Burrowing and Distasteful Taxa Burrowing/Distasteful taxa are either more abundant in the presence of fish or remain unchanged
Fish eliminate potential predators and competitors
Fish may help in enhancing food availability for oligochaetes
21. Crustaceans Large zooplankton are much less abundant when fish are present
Small zooplankton are unaffected, with the exception of cyclopoids which increased (due to reduction in predators and competitors)
Larger crustaceans show high resilience due to presence of resting eggs
Hesperodiaptomus and Daphnia were completely eliminated in some lakes but managed to make a returnHesperodiaptomus and Daphnia were completely eliminated in some lakes but managed to make a return
22. Rotifers Abundance of rotifers is higher when fish are present
Fish eliminate potential predators
After fish disappearance, rotifer abundance is significantly lower due to the reappearance of predators
23. Conclusions The measurements taken in this study are like looking at a lake at different stages in time from the introduction of a disturbance to many years after the disturbance has passed
Lake communities tend to have very low resistance to invasion, but high resilience after the removal of the invader
This study has high implications on restoration of lake communities, and especially on controlling the decline of amphibians in these communities
24. Perturbation and Resilience: A Long-Term, Whole-Lake Study of Predator Extinction and Reintroduction
25. Site Description Wintergreen Lake is a small shallow lake in southwestern Michigan
Extremely eutrophic
Contains many species of planktivorous fish
Contained the piscivorous largemouth bass until “winterkill” events in 1977 and 1978
Before 1977, zooplankton were dominated by large Daphnia
After the winterkill, most zooplankton were small cladocerans (Bosmina, Ceriodaphnia, Diaphanosoma)
26. Purpose To determine the effects of a “keystone” predator on the lower trophic levels of this community over a long time period
To determine the ability of this community to return to its pre-winterkill state after the reintroduction of largemouth bass over a long time period
27. Largemouth Bass Considered a “keystone” predator in Wintergreen Lake prior to 1977
Effective piscivore
Was completely wiped out in 1978
In 1986, largemouth bass was reintroduced to Wintergreen Lake
28. The Fish of Wintergreen Lake
29. The Zooplankton of Wintergreen Lake The most common zooplankton in Wintergreen are shown
Note the differences in body size of each species
All zooplankton were sampled using vertical net tows
30. Effect on Zooplankton
31. Effect on Zooplankton
32. Effect on Zooplankton After the winterkill, the large Daphnia disappeared
Small cladocerans like Bosmina began to dominate the system
After the reintroduction of bass, Bosmina seemed to disappear
Daphnia reappeared
33. Trophic Cascades The largemouth bass kept the densities of planktivorous fish low
After the removal of the bass, those fish multiplied and began to eliminate larger cladocerans
The loss of the main competitors allowed smaller cladocerans (which probably appeared due to long-lived resting eggs) to multiply
After the reintroduction of bass, planktivorous fish densities fell, allowing large cladocerans to emerge from their resting stages
The increase in competition brought the densities of the smaller cladocerans down
Thus, the system has reverted to its original pre-winterkill state
34. Conclusion The system in Wintergreen Lake exhibits high resilience
It returns to its original state rather than an alternative state
Largemouth bass is a keystone predator
The presence or absence of the keystone predator determines the structure of the entire trophic cascade
35. Main Points Resistance is a system’s ability to withstand a disturbance
Resistance is low in lakes
Resilience is a measure of a system’s recovery rate after a disturbance
Resilience is high in lakes
This knowledge can be helpful in restoring lake communities that have been damaged by human activity
36. References Harrison, G. W. 1979. Stability under environmental stress: resistance, resilience, persistence, and variability. The American Naturalist 113: 659-669.
Holling, C. S. 1973. Resilience and stability of ecological systems. Annual Review of Ecology and Systematics 4: l - 24.
Knapp, Ronald A., Matthews, Kathleen R., and Orlando Sarnelle. 2001. Resistance and resilience of alpine lake fauna to fish introductions. Ecological Monographs 71: 401-421
Loreau, Michael. 1994. Material cycling and the stability of ecosystems. The American Naturalist 143: 508-513.
Mittelbach, Gary G., Turner, Andrew M., Hall, Donald J., Rettig, Jessica E., and Craig W. Osenberg. 1995. Perturbation and resilience: a long-term, whole-lake study of predator extinction and reintroduction. Ecology 76: 2347-2360.
Webster, J. R., J. B. Waide, and B. C. Patten. 1975. Nutrient recycling and the stability of ecosystems. Pages 1-27 in F. G. Howell, J . B. Gentry, and M. H. Smith, eds. Mineral cycling in south-eastern ecosystems. CONF-740513, National Technical Information Service, Springfield, Va.