Predation Ecology of Marine Fishes

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PredationEcology of Marine Fishes
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Consumer vs. Resource Control

• Resource Control (Bottom-up regulation)
• Productivity and equilibrium abundance dictated
  by availability of (prey) resources
• Consumer Control (Top-Down regulation)
• Productivity and equilibrium abundance dictated
  by predation
• These are context dependent and not mutually
  exclusive
• At some point, all populations are dictated by
  resources

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What does consumer and resource control look like

• Ideal way to look at this is through changes in
  population size as correlated with Resources (R)
  and Consumers (C)

Low Population Size
High Population Size
DN/Dt
0
DN/Dt
0
Resource Supply
Resource Supply
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Consumer Control
Strong Consumer Control
Weak Consumer Control
DN/Dt
DN/Dt
0
0
Consumer Abundance
Consumer Abundance
Why weak consumer control?
Predation is not a major source of
mortality Predation is distributed among many
species (so little response to any single
species) Mortality is steady across a range of
consumer abundances Resources primarily constrain
populations (density dependent response)
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What is usually done is simpler
Correlation w/ predator abundance Correlation w/
resource density
Population Size
Consumer Abundance
Potential for consumer control mirage when both
predator and prey are responding to same
environmental cues
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Evidence for Resource Control NE Pacific and
Fish Production
Ware and Thompson, 2005. Nature 308 1280-1284
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Correlations with Fish Yield
Yield not standardized by species or trophic level
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Concept the Functional Response

• Functional Response relates consumers
  per-capita feeding rate to prey availability
• Originally only considered prey availability
• Consumer density also affects the functional
  response

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The Functional Response The Predators
Perspective
Type I
Type II Saturating
Predator Consumption Rate
Type III Switching
Prey Abundance
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The Functional Response The Preys Perspective
Type II Saturating
Type III Switching
Prey Mortality Rate (fraction of prey consumed)
Type I
Prey Abundance
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The Functional Response The Preys Perspective
Type I, II and III
Prey Mortality Rate (fraction of prey consumed)
Predator Abundance
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There seems to be a widespread opinion that
functional responses are an old topic that was
thoroughly studied decades ago. However, this is
certainly not the case for field
measurements. ...ecologists know pitifully
little about the functional response. Abrams
and Ginzburg 2000
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Alternative Functional Response Models
The Preys Perspective
Predator-Independent
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Derivation of Predator-Independent Models
Prey (N)
Predator (P)
IF P and N are homogenously distributed AND under
go Brownian movement, THEN Total Prey Consumed
aNP
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Derivation of Predator-Independent Models
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Actual Consumption Rate 0
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Alternative Functional Response Models
The Preys Perspective
Predator Independent
Ratio-Dependent
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Pelagic Food Web of The Baltic Sea
Cod
Herring
Sprat
Monoporeia affinis
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Population Dynamics in the Baltic Sea
ICES 2000
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An Empirical Functional Response Model Hassell
and Varley, 1969
Mortality Rate aPq
q2
q1
Mp
q0.1
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Estimates of Predator Dependence
For young sprat predation mortality highly
sensitive to cod abundance For young herring
predation mortality moderately sensitive to cod
abundance These results are consistent with
observed population dynamics
Essington and Hansson 2004. CJFAS 61 2215-2226
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Predation across life history stages

• Because of size-structured predation,
  small-bodied fishes are more vulnerable to
  predation than larger bodied
• In general, estimates of mortality rate suggest
  that mortality declines with increasing size
• Both suggest that predation is most important for
  earlier (e.g. juvenile) life stages

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Magnitude and importance of predation

• Egg and larvae predation mortality
• Predation is the major source of egg mortality
• Information on larval stages not as clear
• Most larvae die through interactions of
  starvation and predation
• Does this affect population dynamics??

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Magnitude and importance of predation
2. Juvenile predation mortality
Tsou and Collie, 2001. Predation mediated
recruitment on Georges Bank. ICES J. Mar. Sci.
58 994-1001
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Multi-Species Virtual Population Analysis
Age-3
fisheries catches
Age-2
other mortality
Age-1
Age-0
Explicitly account for interannual variation in
predation mortality
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Magnitude and importance of predation
2. Juvenile predation mortality Predation
mortality is typically large and variable.
Tsou and Collie, 2001. Predation mediated
recruitment on Georges Bank. ICES J. Mar. Sci.
58 994-1001