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Predation. One species benefits, the other incurs a cost; also herbivory &
parasitism. Important in adaptive evolution: predator and prey adaptations.
Orcinus orca calls
pages 1178-1179
Phoca vitulina response (most common prey)
Predator (usually silent)
Changes in number
of seals visible at the
surface
Distance of nearest
seal to playback
source
Familiar non-predator (frequently vocal)
Unfamiliar non-predator (frequently vocal)
Nature 2002
Plant defenses
against herbivory.
Also important in
shaping communities.
R. W. Baird
K. Starks
Mutualism. Both species benefit from the interaction. Some are obligatory:
both species cannot persist without the other; others are facultative: the
association is nonessential. Overlooked as a mechanism in community
structure; it may be more significant than either competition or predation.
F
Bill
H. bihai
M
H. caribaea
Flower
H. bihai
H. bihai
H. caribaea
Inflorescence
St. Lucia
H. bihai
Inflorescence
Dominica
pages 1180-1181
Also important in
adaptive evolution
Science 2003
H. caribaea H. caribaea
SOME questions from February 17th
1- When determining human population growth, do the only
consider natural death or all causes?
2- In the barnacle example, are you saying that Balanus is better
suited to the environment and that if desiccation was not a problem
at the higher water level, they would force out the Chthamalus?
3- Assuming two species occupy the same ecological niche, why
couldn’t they both co-exist assuming they were equally fit?
Species Interactions
Competition, Predation, Mutualism, Commensalism
[Coevolution: reciprocal evolutionary change in interacting species,
ending in some degree of specialization.]
Trophic Structure
Dominant and Keystone Species
Community Control
COMMUNITY STRUCTURE
TROPHIC STRUCTURE
Feeding relationships
between organisms.
Describe species
interactions.
Food chain- Transfer of
food energy all the way
until decomposers.
Trophic levels- Links in
the food chain. Usually
four or five.
Food web- Branching
and interconnected
food chains.
page 1181
Fig. 53.10
ANTARCTIC FOOD WEB
page 1182
Fig. 53.11
FOOD WEB TUESDAY LAKE, MI
Fish
Zooplankton
Phytoplankton
Proc. Natl. Acad. Sci. 18 Feb 2003
What limits the length of a food chain?
Energetic hypothesis. Inefficiency of
energy transfer along the chain limits
the number of levels.
Dynamic stability hypothesis. Long
food chains are less stable than
short food chains.
Productivity in holes on tree trunks
Fig. 53.13
page 1183
Species that control community structure
Dominant species. Have the highest abundance or highest biomass
(sum weight of all individuals).
Exert control over the
distribution and abundance
of other species.
For example, sugar maple
and impact on shading and
soil and thus forest
community.
pages 1183-1184
treeguide.com
Keystone species. Exert strong control on community structure by their
ecological roles (niches). They are not particularly abundant.
For example, Pisaster ochraceous (ochre sea star) and
Mytilus californianus (mussel).
Keystone in wave-exposed sites,
not so in wave-protected sites due
to low food supply and sand burial.
pages 1184-1185
Fig. 53.14
Top-down model of regulation of community structure
pages 1185-1186
western Alaska
Science 1998
Examples of
changes in
community
structure regulated
by predators
Bioscience 2005
Bottom-up
model of
regulation of
community
structure
Mar. Ecol.
Prog. Ser. 2005
pages 1185-1186
Oikos 2004
Disturbance- Data suggest that the norm for most communities IS
disturbance and nonequilibrium (constantly changing), rather than
stability and equilibrium (species composition relatively constant).
Disturbances are events that damage communities, remove species
and alter resource availability.
pages 1186-1188
Fig. 53.17
Mount St. Helens
1980
1978
ÙSFS
1981
Despite the importance of natural disturbances,
humans are the greatest agents of disturbance.
1999
Ecological succession- Transitions in species composition over
ecological time.
Primary succession- Begins in a virtually lifeless area where soil has
yet not formed (new volcanic island or rubble left by retreating glaciers).
Glacier Bay, Alaska
Spruce butting in: 80-200 yrs.
Alder, cottonwoods: 30-80 yrs.
Spruce and hemlock: 200-300 yrs.
Secondary succession- Occurs where an existing community has been
cleared by some disturbance that leaves the soil intact.
Secondary succession- Occurs where an existing community has been
cleared by some disturbance that leaves the soil intact.
One year later
Yellowstone