Levels Important to Ecology





Organisms
Populations
Communities
Ecosystems
Biosphere
COMMUNITY AND
POPULATION ECOLOGY
Classification of
Communities



Physical appearance.
forest, grassland, desert, or scrubland.
dominant plant species.
Species diversity.
high diversity (tropical rain forest or coral reef).
low diversity (tundra or boreal coniferous forest).
Niche structure.
how many organisms are in each trophic level.
specialists or generalists.
Physical Appearance and
Biomes
Community Structure and
Diversity
Species present in a
community



Native species--species present since
recorded history began. (oak, hazelnut, ferns)
Invasive species--organisms introduced
accidentally or intentionally by people.
Indicator species--organisms that
responds quickly to environmental
stress.
European Starling
Starling Range Spread
Zebra Mussel
Purple Loosestrife
Giant Hogweed
Attack of the
Giant Hogweed
Indicators of Polluted
Water

Tadpole snails and Tubifex worms thrive in
the low oxygen environments of polluted
streams.
Indicators of Clean Water
Keystone Species


A species that maintains the structure of a
community.
Sea otters, which prevent sea urchins from
destroying kelp “forests.”
Foundation Species

A species that
restores a
community if
the community
is removed.
Competition


Two or more individuals scrambling or
fighting for the same resource.
Can be within the same species or between
species.
Mutualism
Commensalism
Parasitism
Succession



Succession is a generally predictable
change in community composition over
time.
Primary succession—the progression of
species from bare ground to a climax
community. (slow)
Secondary succession—the restoration
of a previously existing community from
a disturbance. (rapid)
Michigan Examples


Succession from open fields to oak-pine forest to
maple-beech forest.
Succession in lakes filling in to form bogs and
then meadows.
Population Terminology




Population size=(births+immigration)(deaths+emigration).
Intrinsic rate of increase called r—related to
birthrate.
Carrying capacity of the environment—number
of individuals the environment can support—
called K.
K also an important part of biological
resistance—all the factors that restrict
population growth.
Age Structure


Many young individuals usually means rapid growth
in the future.
Many older individuals usually means slower growth
in the future.
Exponential Vs. Logistic
Growth


Exponential growth involves ever-increasing rates of
growth; produces J-curve.
Logistic growth starts out like exponential growth,
but slows down as it reaches K; produces S-curve.
r-selected Species
K-selected Species
Comparison of ecological roles
of r- vs. K-selected organisms


Most r-selected organisms are
generalists.
Exception: parasites.
Most K-selected organisms are
specialists.
Exception: humans.
Next up—Climate and Biodiversity
Pages and Figures to Read


Compare and contrast r-selected species
and K-selected species.
- examples of each.
Compare and contrast the characteristics
of natural systems and humandominated systems.
- examples of each.
Human-Dominated vs.
Natural Ecosystems





Human-dominated ecosystems are:
Much “flatter” (fewer trophic levels)
Less diverse.
Have most of primary productivity
directed to human consumption.
Regularly disturbed (plowing,
construction, etc.)