Communities and Ecosystems Change Over Time: Ecological Succession
The types and numbers of species in biological communities and ecosystems change in response to
changing environmental conditions such as fires, volcanic eruptions, climate change, and the clearing of forests to
plant crops. The normally gradual change in species composition in a given area is called ecological succession.
Ecologists recognize two main types of ecological succession, depending on the conditions present at the
beginning of the process. Primary ecological succession involves the gradual establishment of biotic communities
in lifeless areas where there is no soil in a terrestrial ecosystem or no bottom sediment in an aquatic eco-system.
Examples include bare rock exposed by a retreating glacier, newly cooled lava, an abandoned highway or parking
lot, and a newly created shallow pond or reservoir. Primary succession usually takes hundreds to thou-sands of
years because of the need to build up fertile soil or aquatic sediments to provide the nutrients needed to establish
a plant community.
The other, more common type of ecological succession is called secondary eco-logical succession, in which
a series of communities or ecosystems with different species develop in places containing soil or bottom
sediment. This type of succession begins in an area where an ecosystem has been disturbed, removed, or
destroyed, but some soil or bottom sediment remains. Candidates for secondary succession include abandoned
farmland, burned or cut forests, heavily polluted streams, and land that has been flooded. Because some soil or
sediment is present, new vegetation can begin to germinate, usually within a few weeks. It begins with seeds
already in the soil and seeds imported by wind or in the droppings of birds and other animals.
Primary and secondary ecological succession are important natural services that tend to increase
biodiversity, and thus the sustainability of communities and ecosystems, by increasing species richness and
interactions among species. Such interactions in turn enhance sustainability by promoting population control and
by increasing the complexity of food webs. This then enhances the energy flow and nutrient cycling, which are
functional components of biodiversity. As part of the earth's natural capital, both types of succession are
examples of natural ecological restoration. Ecologists have been conducting research to find out more about the
factors involved in ecological succession.
Topic: Ecological Succession
Thesis:
MI’s
Ecological
succession is the
(2+3) There are two types of eco. succession
incremental
that depend on the circumstances when the
change in the
process starts.
makeup of a
species in a
particular location.
(sentence 2,
paragraph 1)
Details
1 – Primary succession
- Creating life in lifeless areas (no soil
on land or no sediment in water)
- Examples: abandoned highway / new
pond
- Takes 100s to 1000s of years
2 – Secondary succession
- More common
- Different species grow in soil or
sediment
- Starts where an ecosystem has been
already but maybe was
destroyed/removed
- Examples: flood land / cut forests
- Begins in weeks – seeds or droppings
(4) Primary and secondary succession are
important in increasing diversity.
Enhance sustainability
Enhance energy flow
Restore ecology to an area
Topic: Disappointment
Thesis:
MI’s
Disappointment
is often met with (2) Depression is one negative response
depression or
to disappointment.
escape instead
of being used for (3) Escape is a second negative response
growth.
to disappointment.
(sentence 4,
paragraph 1)
Details
Yvonne – tries for promotion; fails;
becomes depressed
Kevin – does not get into college; gives
up; escapes with friends and parties
Linda – does not make bball team; gives
up; escapes by getting high
(4) Growing from the experience is a
more positive response to
disappointment
Yvonne – could have looked at options
Kevin – could have looked at other
schools
Linda – could improve skills or choose
another sport