2.6.5-.7 SUCCESSION

Succession is usually described as the orderly succession of communities to a climax community (biome) over time or as a sequence of communities (a sere) with each transitory community as a seral stage.

There are two main types of succession: 1. Primary succession which begins with

bare rock exposed by geologic activity eg. sere: rock -> lichen -> moss -> grass

-> shrub -> trees -> maple-beech -hemlock forest

2. Secondary succession which begins on soil from which a previous community has been removed (by fire, agriculture, etc.)

Secondary succession can proceed much faster because the soil has already been prepared by the previous community

Differences between pioneer and climax communities

Pioneer Community Climax Community

Unfavorable environment favorable environment

biomass increases quickly

biomass is generally stable

energy consumption inefficient

energy consumption efficient

some nutrient loss Nutrient cycling and recycling

r - strategists K - strategists low species diversity, habitat diversity, genetic diversity

high species diversity, habitat diversity, genetic diversity

One thing that limits the carrying capacity, during succession for many organisms, is that the presence of these organisms (themselves) essentially alters the environment (eg. shade, pH, moisture, temperature, chemical composition) sufficiently so that it is no longer suitable for their own offspring to continue.

That is, the populations change the environment so drastically, both biotically and abiotically that it is now more suitable for other populations and less suitable for itself. This leads to the succession of one sere after another until a climax is reached and the changes in the environment are now not so drastic as to produce any further major changes.

Primary Succession

Succession in South Florida

the succession of a pond ecosystem to a meadow over 250 years.

The following charts summarize the major

trends as the ecosystem undergoes succession.

Ecosystem characteristic

Trends in ecological succession

Food chains Simple food chains becoming more complex food webs

Relative Species abundance

Changes rapidly first, changes slower in the later stages.

Total biomass

Increasing

Humus (non-living organic matter)

Increasing

Species diversity

Low diversity in the early stages, then increasing in the intermediate stages and then stabilizing in the final stages as an equilibrium is approached

Productivity

Ecosystem characteristic

Trends in ecological succession

Gross productivity (GP)

Increasing during early stages of primary succession then little or no increase during final stages of secondary succession

Net productivity (NP) Decreasing

Respiration (R) Increasing

Mineral and Nutrient cycles

 

Ecosystem characteristic Trends in ecological succession

Mineral cycles Becomes more self-contained in later stages

Nutrient recycling Increases in later stages