Resistance and Resilience of Lakes to Perturbations

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Resistance and Resilience of Lakes to
Perturbations

• By Chris Oatman

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The degree to which a system is altered when an
environment changes (Knapp 2001)
Resistance
The degree and rate of a systems return to its
previous configuration once the perturbation is
removed (Knapp 2001)
Resilience
Resilience determines the persistence of
relationships within a system and is a measure of
the ability of these systems to absorb change of
state variables, driving variables, and
parameters, and still persist Holling 1975
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Perturbation and Resilience a long-term
whole-lake study of predator extinction and
reintroduction
Mittelbach, Turner, Hall, Rettig and Osenberg,
1995
Research Question What (if any) are the
cascading effects of the removal and
reintroduction of largemouth bass in Wintergreen
Lake?
Methods The researchers found a lake that had
naturally lost its top predator (through anoxic
conditions due to a freezing event). They
collected previous measures of abundance, took
some of their own and then reintroduced the
predator and took more measures of abundance.
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Findings In the absence of largemouth bass,
small planktivorous fish became more abundant and
drove large daphnia populations extinct. Smaller
cladocerans became more predominant and
phytoplankton abundance increased. Largemouth
bass were quick to reestablish with
reintroduction efforts they returned to previous
population levels within 4 years. With their
reintroduction, smaller planktivorous fish were
reduced in population and some were driven
extinct. The larger daphnia returned and
phytoplankton levels were again reduced.
To sum up Two different steady states were
observed. One without largemouth bass and one
with largemouth bass.
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Large Zooplankton
Piscivorous Fish
Plankivorous Fish
Phytoplankton
Small Zooplankton
Large Zooplankton
Piscivorous Fish
Plankivorous Fish
Phytoplankton
Small Zooplankton
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It was also found that all cladoceran species
increased in size with the decrease in
planktivorous fish
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Resistance and Resilience of Alpine Lake Fauna to
Fish Introductions
Knapp, Matthews and Sarnelle, 2001
Research Question To what extent do lake fauna
resist fish invasion. To what extent are lake
fauna resilient to fish invasion.
Methods The researchers compared the faunal
assemblages of alpine lakes in the Sierra Nevada.
All lakes historically contained no fish some
were stocked with fish and among those that were,
some lakes reverted to their fishless condition.
Resistance was assessed by comparing lakes that
never had fish with stocked lakes. Resilience
was assessed by comparing fishless lakes with
stocked-now-fishless lakes.
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Findings Faunal assemblages in the study lakes
had low resistance to fish introductions, but in
general showed high resilience.
Interestingly, they found that it took between 11
and 20 years for lakes that had lost the stocked
fish to return to a lake assemblage similar to
lakes that had never been stocked.
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Although these studies are opposite in the sense
that one shows the removal of a top predator and
the other examines the introduction of one, they
essentially showed identical results, where the
lake assemblage is drastically altered by a
change at the top trophic level (low resistance
to change), but readily reverted back to previous
conditions (or a close approximation) when the
old situation returned at the top trophic level.
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References
Holling, C.S. (1975) Resilience and Stability of
Ecological Systems. Annual Review of Ecology
and Systematics 4, 1-23. Knapp, R. A., Matthews,
K. R., Sarnelle, O. (2001) Resistance and
resilience of alpine lake fauna to fish
introductions. Ecological Monographs 71,
401- 421. Mittelbach, G. G, Turner, A. M., Hall,
D. J., Rettig, J. E., Osenberg, C. W. (1995)
Perturbation and Resilience - a Long-Term,
Whole-Lake Study of Predator Extinction and
Reintroduction 76, 2347-2360.