2.6.5-.7 SUCCESSION
Feb 23, 2016
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