chapter 20 - lecture

Chapter 20: Succession and Stability

20.1 Community Changes During Succession

• Community changes during succession include:

  • Increases in species diversity

  • Changes in species composition

20.2 Ecosystem Changes During Succession

• Ecosystem changes during succession involve:

  • Increases in biomass

  • Increases in primary production

  • Increases in respiration

  • Improvements in nutrient retention

20.3 Mechanisms That Drive Ecological Succession

• Three main mechanisms:

  • Facilitation

  • Tolerance

  • Inhibition

20.4 Community Stability

• Community stability can arise from:

  • Lack of disturbance

  • Community resistance (ability to maintain structure/function despite disturbances)

  • Community resilience (ability to recover from disturbances)

Introduction to Succession

• Succession is the process of change in plant, animal, and microbial communities following a disturbance or the creation of new substrates.

  • Primary Succession occurs on newly exposed geological substrates.

  • Secondary Succession follows disturbances that do not destroy soil.

• Pioneer Community: First organisms to colonize post-disturbance.

• Climax Community: Stable community that persists until disrupted again.

Research on Succession

Clements vs. Gleason

• Clements: Succession driven by interactions between species, leading to a predictable climax community.

• Gleason: Communities emerge from independent species distributions along environmental gradients, which are less predictable.

Examples of Succession

Primary Succession at Glacier Bay

• Changes studied by Reiners et al. (1971):

  • Total plant species increased with site age.

  • Rapid increase in early years, slowing in later stages.

  • Not all species groups increased uniformly.

Secondary Succession in Temperate Forests

• Studies by Oosting (1942) and Johnston & Odum (1956) demonstrated:

  • Increase in woody plant richness during succession.

  • Correlation between increases in woody plant and bird diversity.

Succession in Stream Communities

• Research by Fisher et al. (1982) found:

  • Rapid succession following floods in Sycamore Creek.

  • Diatoms and algae recolonized after disturbances, with most macroinvertebrates surviving floods as aerial adults.

Ecosystem Changes During Succession

Ecosystem Structure Changes at Glacier Bay

• Study by Chapin et al. (1994):

  • Significant increases in soil depth, organic content, moisture, and nitrogen from pioneer community to spruce stage.

Mechanisms of Succession

Three Models

• Facilitation Model: Pioneer species modify the environment to make it suitable for later species.

• Tolerance Model: Early colonizers do not inhibit species that dominate at climax, which can be present throughout succession.

• Inhibition Model: Early occupants make the habitat less suitable for later arrivals; succession occurs only when space is freed by disturbance.

Community and Ecosystem Stability

Definitions

• Stability: Absence of change; can result from lack of disturbance and involves resistance and resilience.

Park Grass Experiment Findings

• Stability was observed over 150 years, with no new species colonizing, though individual species populations fluctuated significantly.

  • At a broad view, the community remained stable; at a detailed view, it was not stable.

Review Topics

• Introduction to succession, community changes, ecosystem changes, mechanisms of succession, and community stability.