Predation. One species benefits, the other incurs a cost; also herbivory & parasitism. Important in adaptive evolution: predator and prey adaptations. Orcinus orca calls. Phoca vitulina response (most common prey). Predator (usually silent).
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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
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)
R. W. Baird
Plant defenses against herbivory.
Also important in shaping communities.
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.
Also important in adaptive evolution
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?
Competition, Predation, Mutualism, Commensalism
[Coevolution: reciprocal evolutionary change in interacting species, ending in some degree of specialization.]
Dominant and Keystone Species
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.
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.
For example, sugar maple and impact on shading and soil and thus forest community.
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.
Keystone species. thus forest community. 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.
Top-down model of regulation of community structure thus forest community.
Prog. Ser. 2005
Oikos 2004 predators
Disturbance- predatorsData 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.
Mount St. Helens predators
Despite the importance of natural disturbances, humans are the greatest agents of disturbance.
Ecological succession- predators 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- predators Occurs where an existing community has been cleared by some disturbance that leaves the soil intact.
One year later