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Chapter 8

BIO120H1 Chapter Notes - Chapter 8: Westerlies, Superorganism, Plant Ecology

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Spencer Barret

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Tuesday, December 6, 2016
Struggle for Existence !
Part VIII: Community ecology, mostly plants
-Early plant ecologists!
used “stands” of vegetation (numerous study sites)!
made lists of plants they found there!
search for informative patterns in data!
argument with colleagues about meaning of patterns!
-Difficulties of plant ecology!
plant communities are pretty resistant to experimentation!
lacks a tradition of experimentation!
-experiments are either undervalued or hard to perform!
-Frederic Clements from Nebraska (~1900)!
pioneer of descriptive study of plant communities!
studied the remaining native prairie vegetation!
later studied other biomes as well!
believed that all sites on Ontario will result in beech-maple forests as a matter of
time (starting product/ influence doesn't matter)!
thought turnover as an autogenic process (recently known as facilitative)!
-one prevalent species changes the environment!
-emphasizes that environment is changed by the species themselves!
-the opposite of this is called “allogenic” (environment is changed by external
forces, NOT biotic community)!
interest: some plant species occurred together more often than one would expect
by chance (pattern association)!
-ex. if you can find American beech in a forest, you’ll probable find sugar maple

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Tuesday, December 6, 2016
-theory: plant association occurs because the species were functionally
dependent on each other!
likened plant community to superorganism!
parts are functionally integrated —> matured the same way as an embryonic
-introducing the term: phytosociology!
tree, shrubs, herbs all have their own particular role!
loved the idea of “succession”; saw it as the same thing as developmental stages of
an organism!
plants will eventually reach stable “climax” stage from unstable “seral” stages!
thought that plant communities can be separated into discrete community types!
-typological thinking: “beech-maple forest” was a category!
explanation for ecological patchiness!
-true vegetation types would be separated by a special type of narrow transition
zone (he called it an ecotone)!
proposal is called organismal, holistic, community-unit, or closed-community
-Henry Gleason (1926)!
differ from Clement’s idea!
provided explanation that didn’t depend on functional interdependencies!
simple idea emphasizing ranges of tolerance!
closely associated species can be found together as they have similar ranges of
tolerance to abiotic factor!
ecological/ sociological “roles” had no influence!
suggested that plant species should be found in wherever there’s suitable soil and
communities are open to any species that can grow in the local climate and soils!
claimed that ecotonal areas of rapid turnover are impossible to recognize!
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