Resilience and Resistance By Dejan Brkic Ecosystem Stability

Resilience and Resistance By Dejan Brkic

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

Resistance www. math. toronto. edu

Resistance: The degree to which a system is altered as a result of a disturbance n Described by Webster et al. (1975) - relationship between degree of nutrient cycling and resistance n Explained further by Loreau (1994) n

Resilience www. nfya. org

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 n Described by Holling (1973) - identifies “resilience” as a property of a system’s stability using real world examples n Back to Loreau (1994)… n Mathematical models of Resistance and Resilience: Harrison (1979) n

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

Alpine Lakes of Sierra Nevada n n n www. lib. utexas. edu 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

Basis of the Study These lakes are perfect for the study of resistance and long-term resilience of the lake communities n The introduction of fish is counted as the disturbance n Resistance and Resilience can be quantified by studying the population densities of all other animals in the community n

Methods Lakes are divided into 3 categories: - Never Stocked (fishless) - Stocked (fish present) - Stocked (fishless) n The presence of fish was determined using a “visual encounter survey” as well as gill nets n

Methods Abundance of amphibians was counted by “visual encounter surveys” of the shoreline n Benthic invertebrates sampled using a D-net sweep of the littoral zone of each lake n Zooplankton were sampled from a float tube by taking vertical sweeps from the deep to the surface n

Measuring Resistance and Resilience Resistance: the comparison of organism abundance between the “never stocked” lakes and the “stocked-fish-present” lakes n Resilience: the comparison of organism abundance between the “never stocked” lakes and the “stocked-fishless” lakes n

Results n Study organisms are divided into the following: - Amphibians - Clinger/Swimmer taxa - Caddisfly taxa - Burrownig/Distasteful taxa - Crustaceans - Rotifers

Amphibians n 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

Amphibians n n n 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

Clinger and Swimmer Taxa n n n 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?

What about Culex? n n 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

Caddisfly Taxa n n n Four of the five caddisfly taxa have reduced abundances in the presence of fish Many seem to have low resilience What about Limnephilus?

What about Limnephilus? n n n 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

Burrowing and Distasteful Taxa n n n 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

Crustaceans n n n 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

Rotifers n n n 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

Conclusions n n n 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

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

Site Description n n n 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)

Purpose To determine the effects of a “keystone” predator on the lower trophic levels of this community over a long time period n 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 n

Largemouth Bass n n www. bhopal. net 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

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

The Zooplankton of Wintergreen Lake n n n 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

Effect on Zooplankton

Effect on Zooplankton

Effect on Zooplankton n n 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

Trophic Cascades n n n 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

Conclusion The system in Wintergreen Lake exhibits high resilience n It returns to its original state rather than an alternative state n Largemouth bass is a keystone predator n The presence or absence of the keystone predator determines the structure of the entire trophic cascade n

Main Points Resistance is a system’s ability to withstand a disturbance n Resistance is low in lakes n Resilience is a measure of a system’s recovery rate after a disturbance n Resilience is high in lakes n This knowledge can be helpful in restoring lake communities that have been damaged by human activity n

References n n n 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.