Transcript 1f Unit 10 Ecological Succession

Yellowstone National Park, 1988
Succession is the gradual change in a
community involving species in one stage
being replaced by different species in the
next stage.
• The time involved in succession is on a
scale of tens, hundreds and even
thousands of years.
• Causes:
• Abiotic factors
• Biotic factors
Abiotic factors such as windstorms, droughts and fire can
cause change in a community of plants and animals.
Biotic Factors also change communities over time. Insect
epidemics can kill trees. Overgrazing can selectively
remove species of plants from a forest.
0
5 yrs
The first species to colonize or grow in an area are called pioneer
species. Only pioneer species are able to grow after a major
disturbance in a community due to the lack of soil or nutrients.
Examples: lichens and mosses
Animals begin to inhabit the area. Usually, insects appear first, then
rodents and larger mammals are the last to appear.
0 yrs 5 yrs 15 yrs
Opportunistic species take advantage of the work done by
the pioneer species. Pioneers modify the environment in
such a way that it becomes less suitable for their growth
but more suitable for other species. Opportunists
eventually replace pioneer species. Examples: grasses & weeds
0 yrs 5 yrs 15 yrs
25 yrs
Over time, the decay of pioneer species, grasses and
shrubs adds nutrients to the forest floor allowing more
complex species to grow.
0 yrs 5 yrs 15 yrs
25 yrs
50-80 yrs
The biodiversity of a community continues to increase as it
ages. A variety of plants and animals will inhabit the
area.
0yrs 5yrs 15yrs
25yrs
50-80 yrs
150+
Succession takes hundreds of years before completion. Species
replacement continues until the community is dominated by
competitively superior species. Once the community reaches a
stable state of maturity it is called a climax community.
Timeline
0yrs 5yrs
Pioneer
species
(lichens &
mosses)
15yrs
Grasses and
Small shrubs
Larger
shrubs and
dwarf trees
Biodiversity
25yrs
50-80yrs
Larger Trees
Climax
community
(Mature/stab
le ecosystem)
150+
Two Types of Succession
Primary succession- a change in an environment where soil
never existed before. Examples: recently formed lava
flows or rocks exposed when glaciers melt. Lichens and
mosses (Pioneer species) first grow on the rock then soil
forms from decayed mosses.
Two Types of Succession
Secondary succession also occurs on smaller scales. When
Secondary
successiona changethe
in an
environment
where
one tree falls,
sunlight reaches
forest
floor. This
soil already
includeofareas
destroyed by
brings
many exists.
changes Examples
to this section
the rainforest.
forest fire, clear-cutting, or insect epidemics.