Resilience and Resistance

1. Resilience and Resistance By Dejan Brkic

2. Ecosystem Stability • Stability: The degree to which an ecosystem is affected by a disturbance and that system’s ability to return to its original state • Why is this important? - maintains community structure - predict effects of disturbances - provides solutions to common problems • Aspects of stability: Resistance and Resilience

3. Resistance www.math.toronto.edu

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)

5. Resilience www.nfya.org

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)

7. Resistance and Resilience of Alpine Lake Fauna to Fish Introductions Roland A. Knapp, Kathleen R. Matthews, and Orlando Sarnelle (2001) www.randisco.com

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 www.lib.utexas.edu

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 www.cwsd.org

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

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?

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 www.emporia.edu

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?

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

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 Gary G. Matthews, Andrew M. Turner, Donald J. Hall, Jessica E. Rettig, and Craig W. Osenberg (1995) www.kbs.msu.edu

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 www.bhopal.net

28. The Fish of Wintergreen Lake Fish abundances were determined by mark-recapture techniques. Note that after bass reintroduction, the abundances of all planktivorous fish declined

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 Daphnia www.uni-koeln.de Bosmina www.esf.edu

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.