Developing Sufficient Understanding to Predict Response to Perturbation

1
HOW WILL POPULATIONS OF SURFPERCH BE
AFFECTED BY HARVESTING GIANT KELP?
Developing Sufficient Understanding to
Predict Response to Perturbation
2
LOGICAL PROCEDURE

• How does Removal of Giant Kelp Alter
  Environmental Conditions Important to
  Surfperch?

• How do Altered Environmental Conditions
  Affect Per Capita Birth / Death Rates of
  Surfperch?

3. Develop Predictions
4. Develop Alternatives
3
Effect of Giant Kelp on Environmental
Conditions
Kelp Reduces Light Reaching Bottom
Removal of Kelp will Increase Light Reaching
Bottom
4
Effect of Giant Kelp on Environmental
Conditions
Under Kelp, Turf Dominates in Low Light
Increasing Light will Enhance Foliose Algae,
Harm Turf
5
Effect of Altered Environmental Conditions on
Per Capita Birth / Death Rates
FOR STRIPED SURFPERCH

• Gelidium will Increase, Increasing Food
  Supply for Striped Surfperch

• Increased Food Supply will Increase Birth
  and/or Decrease Death Rate

PREDICTION STRIPED SURFPERCH POPULATION WILL
INCREASE WHEN KELP IS REMOVED
6
Effect of Altered Environmental Conditions on
Per Capita Birth / Death Rates
FOR BLACK SURFPERCH

• Turf will Decrease, Decreasing Food Supply
  to Black Surfperch

• Decreased Food Supply will Decrease Birth
  and/or Increase Death Rate

PREDICTION BLACK SURFPERCH POPULATION WILL
DECREASE WHEN KELP IS REMOVED
7
HYPOTHESIS 1 (SHORTHAND)
GELIDIUM
KELP
LIGHT
TURF
STRIPED SURFPERCH
BIRTH
GELIDIUM
FOOD
POPULATION
DEATH
BLACK SURFPERCH
BIRTH
POPULATION
TURF
FOOD
DEATH
8
Develop Alternative(s)
Alteration of Environmental Condition
Newly Settled Kelp Bass in Fronds of Giant
Kelp
Kelp Bass Primarily Settle to Giant Kelp
9
The More Kelp, The More Kelp Bass
10
Importance to Surfperch
Adult Kelp Bass are Piscivores
Consume Baby Surfperch
11
Effect of Altered Environmental Conditions
on Per Capita Birth / Death Rates
FOR BOTH SURFPERCH SPECIES
Removal of Kelp Reduces Abundance of Kelp
Bass Predators
Reduced Predators Decrease Death Rate
Prediction Both Striped Black Surfperch
Populations will Increase when Kelp is
Removed
12
HYPOTHESIS 2 (SHORTHAND)
SETTLEMENT OF KELP BASS
KELP BASS POPULATION
KELP
PREDATION ON BABY SURFPERCH
SURFPERCH DEATH RATE
POPULATION SIZES OF BOTH BLACK SURFPERCH AND
STRIPED SURFPERCH
13
Next StepAnalyze Predictions

• How do Predictions from Alternative
  Hypotheses Differ?

• What Must Hold True if Hypothesis is
  Correct?

Helps Identify the Research Needed to
Distinguish Among Alternative Hypotheses
14
Life History Attributes of Marine Species

• Some Species have DEMOGRAPHICALLY CLOSED
  Populations (e.g., Surfperch)

Factors that Affect Abundance Dynamics all
Occur Within Local Population (No
Migration)
15
Life History Attributes of Marine Species

• Most Species have DEMOGRAPHICALLY OPEN
  Populations because of DISPERSING LARVAE

Abundance Dynamics Depend on Local Events
AND Events outside of Local Population
Means Impacts can be Dispersed (Effect on
Fecundity Expressed Downstream)
16
Surfperch Example Illustrates that Species
Do Not Occur in A Vacuum
Species Interact with One Another
Abundance Dynamics must be considered in
the Context of the Community in which a
Species is Embedded
Consumer - Resource Interactions One
Important Feature
17
A Simple Food Chain
PREDATION
PREDATION
HERBIVORY
PRIMARY PRODUCERS
18
A Simple 3 Trophic Level Food Web
PREDATOR
GRAZER 1
GRAZER 2
ALGAE
19
Large Number of Interactions Possible

• DIRECT INTERACTION
• INTERFERENCE COMPETITION

-
GRAZER 1
GRAZER 2
-
20

• INDIRECT INTERACTION
• EXPLOITATION (OR RESOURCE) COMPETITION

-
GRAZER 1
GRAZER 2
-
-
-


ALGAE
21

• INDIRECT INTERACTION
• PREDATOR - MEDIATED APPARENT COMPETITION

PREDATOR

-
-

-
GRAZER 1
GRAZER 2
-
MUTUALISM ( , ) ALSO POSSIBLE IN THIS FOOD WEB
22
Real Systems have many more Interacting
Populations
Challenge to Understand How Such Systems
Might Respond to Disturbance
Explore Simple 3 Trophic Level System to
Consider Effects from Addition of Fertilizer
in Farmland Runoff
23
3 Trophic Level Aquatic System STUDIED BY
CRAIG OSENBERG (FORMER UCSB UNDERGRAD
POST-DOC)
SUNFISH
-

? FISH BIRTH RATE
? SNAIL DEATH RATE
SNAILS
-

? SNAIL BIRTH RATE
? ALGAL DEATH RATE
MICROALGAE
BOTTOM - UP or TOP-DOWN CONTROL?

? ALGAL BIRTH RATE
NUTRIENTS
24
THE STUDY ORGANISMS
25
Approach Field Experiment - Develop
Graphical Model

• Osenberg Manipulated 2 Aspects
• Primary Productivity of Microalgae
• Predation on Snails (grazers) by Sunfish

EXPERIMENTAL DESIGN PRODUCTIVITY
FERTILIZED UNFERTILIZED
ABSENT SUNFISH PRESENT
? ?
? ?
26
Initial Conditions (Prior to Manipulation)
0.1
FERT NO FERT PREDS ?
? NO PREDS ? ?
T 0
0.01
?
?
?
MICROALGAL BIOMASS (mg/mm2)
?
?
?
?
?
0.001
10
100
GRAZER BIOMASS (mg/sample)
27
Final Conditions
T 95 Days
0.1
FERT NO FERT PREDS ?
? NO PREDS ? ?
?
?
0.01
MICROALGAL BIOMASS (mg/mm2)
?
?
?
?
?
?
0.001
10
100
GRAZER BIOMASS (mg/sample)
28
Effects of Productivity Predation
Unfertilized
Fertilized
INCREASED SNAIL RECRUITMENT?
? INCREASED PREDATION
INCREASED ? PRODUCTION
MICROALGAL BIOMASS
dG/dt dM/dt 0
GRAZER BIOMASS
29
Food Web Theory Productivity Trophic
Structure (HSS)
1 LEVEL SYSTEM
PRIMARY PRODUCERS
EQUILIBRIUM BIOMASS
POTENTIAL PRIMARY PRODUCTIVITY
30
Food Web Theory Productivity Trophic
Structure (HSS)
2 LEVEL SYSTEM
HERBIVORES
PRIMARY PRODUCERS
EQUILIBRIUM BIOMASS
POTENTIAL PRIMARY PRODUCTIVITY
31
Food Web Theory Productivity Trophic
Structure (HSS)
3 LEVEL SYSTEM
PRIMARY CARNIVORES
HERBIVORES
PRIMARY PRODUCERS
EQUILIBRIUM BIOMASS
POTENTIAL PRIMARY PRODUCTIVITY
32
Food Web Theory Productivity Trophic
Structure (HSS)
4 LEVEL SYSTEM
SECONDARY CARNIVORES
PRIMARY CARNIVORES
HERBIVORES
PRIMARY PRODUCERS
EQUILIBRIUM BIOMASS
POTENTIAL PRIMARY PRODUCTIVITY