Lecture 19: Community Dynamics (Equilibrium)

1
Lecture 19 Community Dynamics (Equilibrium)

• EEES 3050

2
Community Change

• What determines distribution of species?
• Dispersal, habitat, other species, abiotic
  factors
• What determines the abundance of a population?
• Extrinsic and intrinsic factors.
• Now, what factors determine the structure and
  dynamics of a community?
• Past 2 lectures Defined the structure of a
  community and succession.

3
Equilibrium vs. non-equilibrium

• Equilibrium
• Define communities in which species abundances
  remain constant or stable over time.
• Nature is in a state of balance.
• Non-equilibrium
• Define communities in which species abundances
  do not remain constant. Abundances continually
  change.

4
Concept of Stability

• Stability
• Constant composition or abundance
• Consistent pattern in fluctuations
• Elements of stability
• response
• resistance
• resilience
• elasticity
• amplitude
• recovery

5
Response
Type of change.
6
Resilience Resistance
7
Resilience Resistance

• speed of recovery vs minimize displacement

8
Recovery

• Nature of rebound

9
Local vs. Global Stability
10
Equilibrium vs. non-equilibrium what controls
these types of system?
Equilibrium Non-equilibrim
Species interactions? Competition Species independence
What is limiting? Resources Abiotic factors
Density impacts? Dependent Independent
Stochastic impacts? Few Large
11
Equilibrium vs. non-equilibrium what controls
these types of system?
Equilibrium Non-equilibrim
Species interactions? Competition Species independence
What is limiting? Resources Abiotic factors
Density impacts? Dependent Independent
Stochastic impacts? Few Large
12
Equilibrium systems

• Some history
• Food chains and trophic levels
• Brief intro to
• Functional roles and guilds
• Keystone species
• Dominant species
• Science Paper

13
Again some history

• Clements-gtHutchinson -gt MacArthur
• Development of Classical Competition theory
• Population growth deterministic
• Homogeneous environment
• Competition is only significant biological
  interaction
• Coexistence requires a stable equilibrium point.
• Why is this theory limited?
• Other biological interactions are important.
• Such as predation
• Space/location is important
• Environments are rarely homogenous.

14
Equilibrium systems

• Again
• Rarely find such an ideal system.
• Despite that, there are general patterns of
  relationships that exist.
• See Science paper.

15
Food Chain

• How does energy flow through an aquatic system?
• Plants produce
• phytoplankton
• Herbivores eat
• zooplankton
• Carnivores
• small fish
• Bigger carnivore
• walleye eats small fish
• Even Bigger carnivore
• I eat walleye!

16
Food chain? Or web?
17
(No Transcript)
18
Food webs quickly become complex

• Simplify with trophic levels
• Producers
• green plants
• Primary consumers
• herbivores
• Secondary consumers
• Carnivores, insect parasitoids
• Tertiary consumers
• Higher carnivores.

19
(No Transcript)
20
Quantifying food webs

• Connectance
• actual interactions/potential interactions.
• Food chain lengths
• The number of lengths from top predator to
  basal species.

21
Quantifying food webs

• Possible connections?
• 7 x 7 49
• Actual connections
• 10
• Connectance 10/49 0.2
• Chain lengths
• V1 4,3
• V2 3

22
Example Food webs in 50 lakes

• Observations
• 50 lakes have different of species and
  different food webs.
• The webs with more species have more links.
• Hypothesis
• Connectance will increase/decrease/remain
  constant across lakes.
• Results

23
(No Transcript)
24
Chain links are usually short, why?

• Energetic hypothesis
• Transfer of energy through consumption is not
  efficient.
• 10
• Stability hypothesis
• Long chains would be weak.

25
Guilds

• Guilds or functional groups
• Define groups of species exploiting a common
  resource base in a similar fashion.
• A subdivision of trophic levels
• Examples?

26
(No Transcript)
27
Importance of single species

• Activities dominate community
• Remember dunes
• Succession was passed through specific species.
• Keystone species
• Effects much larger than would be predicted from
  their abundance.
• Dominant species
• Recognized by numerical abundance

28
(No Transcript)
29
Impacts of Biodiversity Loss on Ocean Ecosystem
Service.

• Science Nov. 3 2006
• By B. Worm et al.

30
Introduction

• Read Introduction
• Topics from lectures?
• Biodiversity, species richness, stability,
  experiments to natural systems, exploitation
  (harvesting)
• Species richness may enhance ecosystem
  productivity and stability.
• Hard to go from experiments to large-scale.
• Marine systems are rapidly losing populations,
  species, functional groups.
• What is role of biodiversity at the ecosystem
  level?

31
Experiments

• Read Experiments Section
• What did they do?
• Meta analysis?
• Examined published data.
• Compared response of several different factors
  between systems with low and high diversity.

32
(No Transcript)
33
(No Transcript)
34
Experiments

• Results
• Diversity enhanced production
• Diversity enhanced stability.
• Linked to resistance to disturbance
• Linked to enhanced recovery.

35
Coastal Ecosystems

• Read Coastal Ecosystems section
• What did they do?
• Examined 12 coastal and estuarine ecosystems.
• Examined 30 to 80 species in each system.

36
(No Transcript)
37
(No Transcript)
38
Coastal Ecosystems

• Results
• Percent of collapsed taxa has increased since
  industrialization.
• Loss of biodiversity is associated with loss of
  ecosystem services.
• Suggests increasing risks for coastal
  inhabitants.
• Experimental results supported at regional scale!

39
Large marine ecosystems

• Read next section
• What did they do?
• Analyzed relationships between biodiversity and
  ecosystem services.
• Used global catch database from U.N. FAO
• Examine 64 Large marine ecosystems.
• Definition a collapse occurs when catches drop
  below 10 of the recorded maximum.

40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
Large marine ecosystems

• Results
• Proportion of collapsed fisheries declined with
  increasing species richness.
• Productivity increase with richness
• Recovery increased with richness

44
Marine reserves and fishery closures

• Read Marine Reserves section.
• What did they do?
• Have marine reserves and fishery closures
  reversed the decline of biodiversity at these
  locations?
• Examined 44 protected reserves.

45
(No Transcript)
46
Marine reserves and fishery closures

• Results
• Reserves and fishery closures have resulted in
• Increased richness
• Higher catch and catch per unit effort
• Higher resistance
• Lower variability
• Higher

47
Conclusions

• Read Conclusions
• If things dont change
• Collapse of all fisheries by 2048.
• No dichotomy between conservation and economic
  development.
• No evidence of redundancy (supports rivet)
• Buffering provided by high species diversity
  generates insurance value.

48
Seminar

• Tonight Lake Erie Center
• "Thinking Sustainingly  What Would That Be
  Like?.
• Charles V. Blatz, Department of Philosophy,
  University of Toledo.
• Thursday November 8, 700 PM
• Friday 330
• Dennis Ojima Colorado State University