Succession is the gradual process of change in the composition and function of biological communities over a period of time.
The process reflects the results of the continuing competition among species with different adaptations for obtaining food, light, space, protection, and other resources.
Successive communities that appear in the process are referred to as seral stages. One community causes changes in the physical environment that allow another community to become established.
Primary succession occurs in a barren habitat where no significant biological community has ever been established. (e.g. sand dunes, rock outcrops, after volcanic eruptions, newly deposited alluvial soil, exposed glacial till)
Secondary succession occurs in an area where an existing biological community has been disturbed or destroyed. (fills, spoil banks, railroad grades, road sides, abandoned fields, or after a forest fire)
Most aquatic succession (as in a stream, pond or lake) will be primary succession since you start with a hole or depression in the ground that fills with water.
(Note: to have secondary succession you would almost have to look at cleaning up a human-caused problem. For example, decontaminating the water in an existing lake or stream and allowing organisms to re-populate would be an example of secondary succession in a water body.)
The first species to colonize an area where no community is established are pioneer species.
Pioneer Plants: These are weeds! They are usually r-selected species, with short life cycles, fast-growing, with lots of seeds.)
Pioneer Animals: crickets, grasshoppers, spiders, and other arthropods.
The process of succession proceeds toward a relatively stable community referred to as the climax community. A climax community is usually very diverse, with a well-developed spatial structure and complex food chains.
Factors affecting the nature of Climax Communities:
Climate is a major influence and includes the long term patterns of temperature, precipitation, and light. Biomes such as tropical rainforest, desert, etc. represent climax communities that are the result of climate.
Soil factors (edaphic factors) including texture, moisture and availability of nutrients account for variation over a smaller region, such as from place to place in Leon County or the State of Florida.
Regularly occurring natural events, such as fire, or human intervention (mowing, etc.) may keep succession from reaching the climax community and hold it at a subclimax level.
Local Examples (of ecosystems maintained at “subclimax” levels by recurring fires):
· Long Leaf Pine forests
· The Everglades
Changes in ecosystem structure and function during succession (General Trends)
· The number of species in successive communities generally increases (diversity increases).
· Energy flow is simple (a few food chains) in early stages and becomes more complex as succession proceeds. (The food web becomes well developed and more complex.)
· Net productivity is higher in early stages of succession as a lot of energy is converted to new growth. As succession proceeds more and more energy is used for respiration and net productivity declines.
· In late stages (climax community) gross production and respiration are both high and net productivity approaches zero.
· Inorganic nutrients (nitrates, phosphates, etc.) become increasingly locked up in biotic components as succession proceeds and the storages in soil and other abiotic components decrease.
· Mineral cycling becomes more efficient moving quickly through abiotic storage components. For example, tropical rainforest soils are nutrient poor. Nutrients cycle rapidly and most are locked up in biomass.