Identifying the effects of multiple stressors on ecological processes influencing recovery of zoopla

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(No Transcript)
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Zooplankton
Ceratium
Cyclops
Daphnia
Keratella
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Clearwater Lake zooplankton richness time series
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Clearwater Lake has the zooplankton community
recovered?
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pH increase in 3 groups of Killarney Park lakes
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Has zooplankton community composition recovered?
Mean CA axis I score of the groups
Never acid
No longer acid
Still acid
Holt Yan (in press)
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Recovery patterns from Acid Rain 2000 the Japan
conference

• Both liming and long-term monitoring studies
  indicate that ecological recovery can and is
  occurring, but
• It is generally incomplete, and
• rates vary among species, and among lake and
  river systems.
• Hence, there are promising case studies, but we
  cannot yet make general predictions about rates
  or endpoints of ecological recovery from
  acidification

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Why is generalization not yet possible?

• We have no widely accepted framework (set of
  models) identifying the key steps and processes
  influencing ecological recovery from
  acidification
• There are many phenomena which may confound
  recovery and the factors are system- and
  species-specific

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An ecological recovery frameworkand its use in
identifying the effects of confounding factors on
recovery processes - a zooplankton example
by

• Norman Yan, Shelley Arnott, Bill Keller, Anurani
  Persaud, Carrie Holt, John Gunn, Jocelyne
  Heneberry, Peter Dillon and Robert Girard

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A framework for studying ecological recovery from
acidification
Monitor alkalinity/pH, or predict them using BGC
models
Choose species Design recovery targets
Identify lethal acid thresholds
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Is water quality OK for the species?
Are colonists available?
Y
N
Y
Are s gt minimum viable population size?
Run dispersal model
N
Y
Are there confounding factors?
N
Y
Run population growth models compare with
recovery targets
Modify population growth models
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Implications of this framework

• Recovery is, a root, a species-level phenomenon
• Recovery bottlenecks may occur at different
  stages in different water bodies and for
  different species
• Confounding factors act at particular points in
  the process
• In theory, general predictions about recovery are
  possible
• Hysteresis can be handled
• The models need not be built from scratch, but
  they must all be parameterized with new research

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Objectives of the talkTo identify the impact of
several confounding factors within this framework

• Loss of colonists due to drought/acid
  interactions (Arnott et al).
• Unexpected mortality from UVR (Persaud and Yan)
• Loss of essential elements (Ca) lowering growth
  (Keller, Hessen, Alstad)
• The impact of unexpected predators (Yan)

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1. Drought/acid interactions and the potential
loss of colonists
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Swan Lakes Re-acidification
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10
5
0
Keller et al. (1992) Yan et al. (1996) Arnott et
al. (2001)
-4
-8
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Arnott et al. (2001)
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Drought
Exposed littoral sediments
Acidification
Warmer, brighter, water with O2
Drying freezing of resting eggs
Increased Emergence of Resting Stages
Arnott Yan in press
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Does drying littoral sediments trigger emergence
events?
Arnott Yan in press
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What does Arnotts work teach us?

• Drought that leads to re-acidification may derail
  ecological recovery
• The effects may be long-term if the drought
  triggers emergence of animals into inhospitable
  waters, and if the sedimented reservoirs of
  resting eggs are depleted in consequence.
• The size of these reservoirs, and their role in
  recovery is not currently known.
• Recovery cant be predicted from pH alone. We
  need to know if colonists are available

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2 Unexpected mortality from UV radiationPart of
A. Persauds MSc research
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Larval Chaoborus were held in three light
treatments at four depths in Ruth Roy Lake on 5
occasions in the summer, 2001
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Can UV radiation alter Chaoborus survival?
survival of instar III larvae in a 2-day
incubation under clear skies at 4 depths
Quartz - UVRVisible light
OP3- Visible light only
Dark controls
(Persaud, MSc in prep)
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Why might this matter?
Clearwater Lake
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What does Persauds work teach us?

• Mortality rates of at least one species may be
  increased by UV penetration in clear-water lakes
• These mortality rates may, on occasion, be so
  high as to prevent recovery despite colonist
  arrival
• We may have to consider the impacts of UV
  radiation as a modifier of rates of ecological
  recovery from acidification in some lakes.

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3. Unexpected potential importance of changes in
Ca (Keller, Hessen, Alstad)
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Reductions in Ca in Sudbury-area lakes (Keller
et al. 2001)
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Ca (ueq/L)
100
50
0
1999
1997
1995
1993
1991
1989
1987
1985
1983
1981
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Why might this matter?
From Yan et al. (1989)
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Recruitment of calcified taxa may fall at low
Ca eg. egg production in D. magna (Hessen et
al. 2000)
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3. What does Keller, Hessen and Alstads work
teach us

• That falling Cas may alter birth rates and
  longevity of Ca-rich taxa. There are a lot of
  such taxa in softwaters.

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4. Might predators alter recovery rates? - the
Bythotrephes example
photo by B. ONeill
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Long term changes in richness in Dorset lakes
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Harp Lake - reductions in summer Cladoceran
richness
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Is the zooplankton of Harp Lake now unusual?
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4. What does the Harp Lake invasion teach us?

• Invading species may force us to alter recovery
  targets
• invading predators may alter recovery pathways
  and trajectories by altering death rates or,
  indirectly, birth rates of prey taxa
• Bythotrephes has invaded Killarney Park

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Conclusions

• We can develop a framework of the process of
  ecological recovery from acidification, for the
  moment, as a research organizing tool, but
  perhaps ultimately as a predictive tool
• Research suggested by the framework complements,
  but cannot replace long-term and large-scale
  monitoring efforts
• The framework can help elucidate which recovery
  processes are affected by particular confounding
  factors

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Where confounding factors operate?
The stage of recovery
The confounding variable

• Is water quality OK?
• Are colonists available?
• What are birth and death rates of colonists?
• What are the recovery targets?

• Drought-induced acidification
• Ca declines
• Drought
• UV radiation, Ca declines, and unusual predators
• unusual predators