Community Dynamics — Chapter 18

What causes the changing nature of community structure across a landscape?

Shifting distribution of populations in response to changing environmental conditions and species interactions.

What is succession?

The gradual and directional change in community structure through time.

What is a sere?

A sequence of communities from early to late successional stages.

What is a seral stage?

Each distinct community stage in a sere, with its own species and structure.

What characterizes early successional (pioneer) species?

High growth rates, small size, high dispersal, high per capita population growth.

What characterizes late successional species?

Low dispersal, slower growth, larger size, long-lived.

What is primary succession?

Succession on a site that has never supported a community (rock, dunes, glacial till).

What is secondary succession?

Succession on previously occupied sites after disturbance (e.g., old fields, forests after clear-cutting).

What did H.C. Cowles study?

Succession in sand dunes.

What did Sousa study?

Succession in rocky intertidal algal communities.

What is autogenic environmental change?

Changes caused directly by organisms (e.g., shading by plants).

What is allogenic environmental change?

Changes caused by physical processes (e.g., glacial retreat, sediment deposition).

Example of autogenic soil change?

Increased organic matter and nitrogen during succession.

What are chronosequences?

Groups of sites used to study succession by comparing different ages.

How does diversity change during succession?

Usually increases early, peaks mid-succession, then may decline.

What determines the rate of species displacement in succession?

Growth rates of competing species and environmental conditions.

What is the intermediate disturbance hypothesis?

Species diversity is highest at intermediate levels of disturbance

What is succession in heterotrophic communities?

Decomposition of logs, carcasses, or droppings by fungi/invertebrates.

How does plant succession influence heterotrophs?

Changes in structure create new habitats as vegetation becomes more complex.

What is paleoecology?

Study of ancient organisms and environments (often via pollen records).

Example of allogenic succession caused by long-term change?

Post-glacial colonization following the retreat of the Laurentian ice sheet.

What did Clements believe about communities?

Communities act like “super-organisms” with interdependent species.

What did Gleason propose about community structure?

The individualistic/continuum concept — species respond independently to environment.

What is zonation?

Spatial variation in community structure across a landscape.

What does resetting the clock mean in succession?

Disturbance restarts the successional process.

What determines seaward expansion of marshlands?

Silt deposition lowering water depth over time.

What is the pattern of phytoplankton succession typically linked to?

Seasonal changes in temperature, nutrients, and light.

What drives species colonization and replacement in succession?

Species interactions, dispersal abilities, competition, and environmental tolerances.

In old-field succession, what species typically dominates first?

Annual crabgrass.

What eventually replaces pine stands in old-field succession?

Shade-tolerant hardwood species.