Overview
This lecture covers ecological succession, the process by which ecosystems recover and change over time after disturbances, focusing on primary and secondary succession, key species roles, and community development stages.
Ecological Succession Basics
- Ecological succession is the gradual process of ecosystem change and development over time after a disturbance.
- Disturbances include events like volcanic eruptions, fires, floods, or human activities.
- Succession occurs in stages, leading to changes in both plant and animal communities.
Types of Succession
- Primary succession starts on bare rock with no soil, often after events like volcanic eruptions or new island formation.
- Pioneer species (lichens, mosses, bacteria, fungi) colonize rock, break it down, and help form soil.
- Succession progresses from pioneer species to grasses, shrubs, shallow-rooted trees (conifers), and eventually to deep-rooted trees (hardwoods).
- Primary succession takes hundreds of years.
- Secondary succession begins with existing soil after disturbances like fires, logging, floods, or tornadoes.
- Follows similar biological progression but is faster because soil is already present.
Successional Stages
- Seral (intermediate) stages are stable, intermediate stages between the beginning and climax community.
- Climax community is the final, stable, and mature community in succession, often including hardwood trees or other long-lived species.
- Animal communities also change in response to plant succession.
Species Roles in Succession
- Pioneer species are the first organisms to colonize barren environments, initiating soil formation.
- Keystone species play a critical role in maintaining ecosystem stability; their removal can alter successional pathways.
- Indicator species reflect the health of an ecosystem; their presence or absence signals environmental conditions (e.g., frogs for water quality, monarch butterflies for habitat health).
Productivity During Succession
- Net primary productivity (NPP) increases during early and intermediate succession as biomass and species richness grow.
- As the climax community is reached, NPP levels off or may slightly decline due to resource limits and community stability.
Examples
- Mount St. Helens eruption (1980) initiated primary succession in areas covered by deep ash.
- Beavers, a keystone species, can trigger secondary succession by flooding land and creating wetlands.
Key Terms & Definitions
- Ecological succession — natural, gradual ecosystem changes over time following disturbance.
- Primary succession — succession starting from bare rock with no soil.
- Secondary succession — succession starting with existing soil after disturbance.
- Pioneer species — first organisms to colonize new or disturbed environments.
- Seral stage — intermediate, stable community in succession.
- Climax community — mature, stable final community in succession.
- Keystone species — species essential for ecosystem stability.
- Indicator species — species that indicate ecosystem health.
Action Items / Next Steps
- Study these key terms and concepts for the upcoming exam.
- Prepare for Unit 3 by reviewing these succession stages and species roles.