Environmental fluctuations

1
Environmental fluctuations

• The effect on resource competition

Anneke Procee Supervisors prof. dr. F.J.
Weissing V. Brauer
2
Outline

• Introduction
• Model structure
• Results
• Scenario I two specialists
• Scenario II generalist specialist
• Scenario III multispecies competition
• General Conclusion
• Discussion

3
Introduction

• 1961 Hutchinson
• Paradox of the Plankton
• 1980 Armstrong McGehee
• Coexistence possible when system never approaches
  equilibrium
• 1999 Huisman Weissing
• under specific conditions
• species oscillations and chaos
• coexistence of more species than limiting
  resources

4
This project

• Effects of environmental fluctuations on resource
  competition
• Computer simulations model by Huisman Weissing
  (1999) external factor

5
Intermediate Disturbance Hypothesis (Connel 1978)

• Disturbance large effect on resource competition
• Species diversity maximised under intermediate
  levels of disturbance
• low levels of disturbance system approaches
  equilibrium
• High levels of disturbance species statistically
  the best
• Intermediate levels of disturbance fluctuating
  enough to take turns

6
Temperature

• Environmental fluctuation Temperature
• Temperature differs in period and/or amplitude
• Species influenced in different ways
• First focus on 2 species, later multispecies
  competition

7
Empirical Data Tilman et al (1981)

• Resource competition between 2 species at 4
  different temperatures
• Species Asterionella Synedra
• Outcome independent of starting abundancies

8
Empirical Data Tilman et al (1981)
Temperature may affect competitive abilities
9
Empirical Data Goldman et al (1976)

• Phytoplankton competition between 2 species at
  different temperatures
• Observation
• Some species dominant at both high and low
  temperatures, while other species only at
  intermediate temperatures

Temperature specialists and generalists may exist
10
Research questions

• Goal get an understanding on how temperature
  fluctuations can influence resource competition
• Questions
• Is coexistence possible in a fluctuating
  temperature regime?
• Is coexistence more likely for intermediate
  disturbance (amplitude, frequency regularity)

11
Competition dynamics

• chemostat model
• growth function (Monod)

12
Resource requirement, R

• Equilibrium when
• Species with lowest resource requirement
  outcompetes all other species
• Species with lowest R is best competitor R-rule

(growth equals loss)
13
Temperature regimes

• Regular temperature Random temperature
• Regular random temperature

14
(No Transcript)
15
Results Scenario I

• Competition between high and low temperature
  specialist
• Temperature dependent parameter Halfsaturation
  constant K

16
Results scenario I

• Results between different temperature regimes
  similar
• High temperature specialist inherent advantage
• skewed competitive differences

17
Similar results
Regular temperature regime
Random temperature regime
Regular random temperature regime
18
Skewed competitive differences
19
Results Scenario II.a

• Competition between a temperature generalist and
  a temperature specialist
• Temperature dependent parameter Halfsaturation
  constant K
• Random temperature regime

20
Results Scenario II.a

• Specialist inherent advantage over generalist
• Increasing amplitude of temperature fluctuation
• Generalist able to sustain itself longer
• Decreasing frequency
• Generalist able to sustain itself longer

21
Amplitude
amplitude 6 C
amplitude 2 C
amplitude 10 C
22
Frequency of change
Frequency 1/50
Frequency 1/10
Frequency 1/200
23
Results Scenario II.b

• Competition between a temperature generalist and
  a temperature specialist
• Temperature dependent parameter max. growth rate
  r

24
Results Scenario II.b

• Increasing amplitude of temperature fluctuation
  dominance shifts from specialist to generalist
• Degree of specialization determines dominance
  shift
• No effect of disturbance on competition
• Average growth rate determines dominance

25
Amplitude
amplitude 2 C
amplitude 4 C
amplitude 6 C
26
Degree of specialization
sspec1.0
sspec0.5
sspec1.5
27
Highest average growthrate
28
Results Scenario III

• Multispecies competition
• Increasing amplitude of temperature fluctuation
• Dominance shifts from super specialists to more
  generalists
• No effect of frequency on competition
• Coexistence possible no species rich system
• Only 2 or 3 species left at end simulation
• Coexisting species resemble each other

29
Multispecies competition
specialist
amplitude 2 C
amplitude 4 C
generalist
amplitude 6 C
amplitude 8 C
30
General Conclusion

• In some cases coexistence under intermediate
  disturbance
• General impression competition under external
  fluctuations tends to competitive exclusion
• Conclusion not affected by regime
• Important which parameters affected by
  fluctuations
• Striking differences between halfsaturation
  constant maximum growthrate

31
Discussion

• Species only differ for 1 parameter
• Only 1 resource
• 1 dimensional environment tends to
• competitive exclusion (Metz et al., 1996)