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Major Objectives
1. Understand basic community ecology
definitions and processes
2. Know the two main hypotheses for why
plant communities have different species
assemblages
3. Know the 5 potential interspecific
interactions between species
4. Know the difference between bottomup and top-down control mechanisms
What is a Community?
A collection of all the populations of
different species that inhabit a particular
area.
Communities differ in SPECIES
RICHNESS and RELATIVE ABUNDANCE
Beaver (Castor canadensis)
Ecosystem
Engineer
Beaver Lodges
Ecosystem
Engineer
keystone species
Pisaster spp. is
a keystone
species
Competitive Exclusion Hypothesis
Two species competing for same limited resource can not exist
Why do plant communities
have different species
assemblages?
Individualistic Hypothesis
A community is the result
of chance because of
species having similar
abiotic requirements
Interactive or "Organismic" Hypothesis
A community is
the result of
closely linked
species locked in
by mandatory
biotic
interactions
Species Interactions
Parasitism
Interspecific
Interaction:
Predation
• Cryptic coloration, or camouflage
Figure 53.5
• Aposematic coloration
– Warns predators to stay away from prey
Batesian Mimicry
– A palatable or harmless species mimics an unpalatable or
harmful model
Frequency-dependent
Batesian mimicry:
David W. Pfennig,
William R. Harcombe
and Karin S. Pfennig
Nature 410, 323(15
March 2001)
The proportion of carnivore attacks on ringed replicas of scarlet kingsnakes (top left; a mimic of eastern coral snakes) and sonoran mountain
kingsnakes (top right; a mimic of western coral snakes) increased with a, latitude (y = - 13.314 + 0.391 x , P < 0.035, R2 = 0.345) and b, elevation
(y = - 0.329 + 0.00032 x, P < 0.014, R2 = 0.310). Horizontal dashed line: proportion of attacks on ringed replicas expected under randomness.
Vertical dashed line: maximum latitude and elevation for coral snakes in North Carolina and Arizona, respectively.
Müllerian mimicry
– Two or more unpalatable species resemble each
other
(a) Cuckoo bee
Figure 53.8a, b
The viceroy (Limenitis sp.; right) and monarch (Danaus sp.)
butterflies look very similar but may differ in their
palatability to avian predators.
(b) Yellow jacket
Interspecific Interaction:
Herbivory
• The process in which an herbivore eats parts
of a plant
Mutualism
Mutualism
Figure 53.9
Commensalism
Competition
Life in the shade
Plants can tell the difference between
the shade of an inanimate object and
the shade of another plant. When a
plant detects competition from
neighboring plants, it initiates a set of
responses, called collectively the
shade avoidance syndrome, that alter
its growth and physiology. A rapid and
transient increase of newly synthesized
auxin via a newly discovered auxin
synthesis pathway allows plants to
elongate and grow toward the sun.
Image: Courtesy of Dr. Jean-Luc
Ferrer, Salk Institute for Biological
Studies
Nuetralism
+
Species "A"
0
-
0
Species "B"
+
+
Parasitism
Predation
Herbivory
Commensalism
Mutualism
Species "A"
0
-
Neutralism
Commensalism
Competition
No interaction
Parasitism
Predation
Herbivory
-
0
No interaction
Species "B"
+
Bottom-Up
Control
Top-Down Control
Trophic
Structure
Feeding
relationship
between
organisms
Major Objectives
1. Understand basic community ecology
definitions and processes
2. Know the two main hypotheses for why
plant communities have different species
assemblages
3. Know the 5 potential interspecific
interactions between species
4. Know the difference between bottomup and top-down control mechanisms