ricklefs_lecture_ppt_ch19 - Rick Relyea Robert Ricklefs The...

The Economy of Nature
7th edition
Lecture PowerPoint
Chapter 19
Community Succession
Rick Relyea · Robert Ricklefs
© 2014 by W. H. Freeman and Company

Chapter 19 concepts
Succession occurs in a community when species replace
each other over time.
Succession can occur through different mechanisms.
Succession does not always produce a single climax
community.
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Defining succession
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To predict how communities respond to environmental disturbances,
we must understand how species composition changes over time.

Observing succession
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Direct observation of changes over
time is the clearest way to record
succession in a community.
Example:
In 1883 a volcanic eruption blew away
three-quarters of the island of Krakatau.
Remaining land was covered with volcanic
ash that obliterated all life.
Researchers began observing the island
after eruption; by 1886 they saw that 26
plant species had colonized the island.
Many early colonizing species were wind-
and sea-dispersed. Later colonizers were
dispersed by animals (e.g., birds and bats).

Observing succession
1
When direct observation of succession is not possible, scientists can
use methods of indirect observation, such as a chronosequence .
Chronosequence: a sequence of communities that exist over time at
a given location.
Example:
Water level in Lake Michigan has fallen since the last glaciation; old sand dunes are
far from the shoreline and new dunes are along the shore edges.
In the 1800s, Henry Cowles studied succession
by examining a chronosequence of dunes.
On younger dunes, he found early successional
species (e.g., grasses); on older dunes, he found
later successional species (e.g., herbs, shrubs).
On the oldest dunes, he found beech, oak,
maple, and hemlock trees.

Observing succession
1
It is possible to look back in time by examining pollen preserved in
layers of lake and pond sediments.
Flowering plants produce pollen grains with distinct sizes and shapes
that travel through the air and land on a lake surface.
The pollen grains sink and become preserved in layers of sediment at
the bottom of the lake.
Researchers can take a sample that penetrates through many layers
of mud on the lake bottom.
Carbon dating can be used to identify the age of the pollen in each
layer, and helps to determine the changes in plant species
composition around the lake over hundreds or thousands of year.

Primary succession
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Primary succession: the development of
communities in habitats that are initially