1. Succession and Stability
Chapter 20
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2. Outline
Concept 20.1 Community changes during succession include increases in species diversity and changes in species composition.
Concept 20.1 Review
Concept 20.2 Ecosystem changes during succession include increases in biomass, primary production ,respiration, and nutrient retention.
Concept 20.2 Review
Concept 20.3 Mechanisms that drive ecological succession include facilitation, tolerance, and inhibition.
Concept 20.3 Review
Concept 20.4 Community stability may be due to lack of disturbance or community resistance or resilience in the face of disturbance.
Concept 20.4 Review
Investigating the Evidence 20: Variation Around the Median
Applications: Using Repeat Photography to Detect Long-Term Change
Summary
Key Terms
Review Questions

3. Introduction
Succession: Gradual change in plant and animal communities in an area following disturbance.
Primary succession on newly exposed geological substrates.
Secondary succession following disturbance that does not destroy soil.
Climax Community: Late successional community that remains stable until disrupted by disturbance.

4. 20.1 Community Changes During Succession
Reiners et al. studied changes in plant diversity during succession.
Total number of plant species increased with plot age.
Species richness increased rapidly in early years of succession and more slowly during later stages.
Not all groups increased in density throughout succession.

5. Primary Succession at Glacier Bay

6. Secondary Succession in Temperate Forests
Oosting found number of woody plant species increased during secondary succession at Piedmont Plateau.
Johnston and Odum found increase in bird diversity across successional sequence closely paralleled increase in woody plant diversity observed by Oosting.

7. Succession in Stream Communities
Fisher studied rapid succession in Sycamore Creek, AZ.
Evaporation nearly equals precipitation - flows generally low and intermittent.
Subject to flash floods.
Observed rapid changes in diversity and composition of algae and invertebrates.
Invertebrates found refuge because many adults in aerial stage.
Re-colonized after flooding.

8. 20.2 Ecosystem Changes During Succession
Chapin documented substantial changes in ecosystem structure during succession at Glacier Bay.
Total soil depth and depth of all major soil horizons show significant increase from pioneer community.
In addition, organic content, moisture, and N concentrations all increased.
Physical and biological systems are inseparable.

9. Ecosystem Changes During Succession

10. Four Million Years of Ecosystem Change
Chronosequences such as that found at Glacier Bay are limited.
Hawaiian Islands have formed over hot spots on the Pacific tectonic plate, forming an island chain varying greatly in age.
Hedin et al. found differing patterns of nutrient distribution across the chronosequence.

11. Recovery of Nutrient Retention Following Disturbance
Bormann and Likens found felling trees in Hubbard Brook substantially increased nutrient losses.
Herbicide used to suppress regrowth.
When application stopped, succession proceeded, nutrient losses decreased, and primary production increased.
Vegetation can’t account for all nutrient loss.
Reduced nutrient amounts in ecosystem.

12. Recovery of Nutrient Retention Following Disturbance

13. Model of Ecosystem Recovery
Biomass Accumulation Model
Reorganization (10-20 yrs)
Forest loses biomass and nutrients.
Aggradation (100+ yrs)
Ecosystem reaches peak biomass.
Transition
Biomass declines from peak.
Steady-State
Biomass fluctuates around mean.

14. 20.3 Mechanisms of Succession
Clements
Facilitation
Connell and Slayter
Tolerance
Inhibition

15. Mechanisms of Succession

16. Facilitation
Proposes many species may attempt to colonize newly available space.
Only certain species will establish.
Colonizers “Pioneer Species” modify environment so it becomes less suitable for themselves and more suitable for species of later successional stages.

17. Tolerance
Initial stages of colonization are not limited to pioneer species.
Early successional species do not facilitate later successional species.

18. Inhibition
Early occupants of an area modify the environment in a way that makes it less suitable for both early and late successional species.
Early arrivals inhibit colonization by later arrivals.
Assures late successional species dominate an area because they live a long time and resist damage by physical and biological factors.

19. Successional Mechanisms in Rocky Intertidal Zone
Sousa investigated mechanisms behind succession of algae and barnacles in intertidal boulder fields.
If the inhibition model is in effect, early successional species should be more vulnerable to mortality.
Results showed early successional species had lowest survivorship and were more vulnerable to herbivores.

20. 20.4 Community and Ecosystem Stability
Stability: Absence of change.
Resistance: Ability to maintain structure and function in face of potential disturbance.
Resilience: Ability to recover from disturbance.

21. Park Grass Experiment
Hertfordshire, England
Studied effects of fertilizer treatments.
Continued for 150 years.
Silverton investigated ecosystem stability.
Used community composition variability as measure of stability.
Represented composition as proportion of community consisting of each plant form.

22. Park Grass Experiment
Dodd showed that although community stability is present, populations of individual species can change substantially.
Stability depends on resolution an area is investigated at.

23. Desert Stream Stability
Valett studied interaction between surface and subsurface waters.
Flash floods devastated biotic community.
Spatial relationships of zones stable.
Geomorphology of landscape.

24. Review
Introduction
Community Changes During Succession
Primary Succession
Secondary Succession
Ecosystem Changes During Succession
Disturbance
Ecosystem Recovery
Mechanisms of Succession
Community and Ecosystem Stability