Transcript Community Ecology

Community Ecology
Chapter 54
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Biological Communities
•
A community consists of all the species that
occur together at any particular locality.
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Fundamental and Realized Niches
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An organism’s niche is the total of all ways it
utilizes the resources of its environment.
– fundamental - entire niche potentially
available to an organism
– realized - actual niche utilized by an
organism
Habitat is the place where an organism lives.
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Realized Niche
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Interspecific competition - Occurs when
different species attempt to utilize the same
resource.
– interference - individuals fighting over the
same resource
– exploitative - individuals utilizing shared
resources
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Principle of Competitive Exclusion
The principle of competitive exclusion states
that no two species utilizing the same niche
can coexist indefinitely.
– one will eventually eliminate the other

Gause’s Paramecium experiments
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Detecting Interspecific Competition
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Negative effects of one species on another
do not automatically indicate competition.
– Presence of one species may attract a
predator that consumes both, causing one
species to have a lower population size
than the other.
 must always look at underlying
ecological mechanisms
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Predation and Prey Populations
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Predation occurs when one organism
consumes another.
– provides strong selective pressure on prey
populations
 Any physiologic characteristic or
behavior that would decrease the
probability of capture should be strongly
favored.
 increased fitness
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Plant Defenses Against Herbivores
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Morphological
– thorns, spines, etc.
Chemical
– secondary chemical compounds
Evolutionary response of herbivores
– Certain groups of herbivores are associated
with each group of plants protected by a
particular secondary compound.
 coevolution
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Animal Defenses Against Predators
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Some animals that feed on plants rich in
secondary compounds receive an extra
benefit.
– caterpillars that feed on members of the
milkweed family
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Animal Defenses Against Predators
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Chemical defenses
– poisons and stings
Defensive coloration
– aposematic coloration (warning coloration)
 individuals advertise poisonous nature
– cryptic coloration
 camouflage (blending coloration)
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Mimicry
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Batesian mimicry
–
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Palatable insects resemble brightly colored, distasteful species.
Mullerian mimicry
–
Unrelated protected species resemble one another.
 predators learn more quickly
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Coevolution and Symbiosis
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Coevolution involves long-term mutual
evolution of two or more species.
– predator-prey interactions
– symbiotic relationships
 two or more kinds of organisms live
together in permanent relationships
 commensalism, mutualism, and
parasitism
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Commensalism
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One species in symbiotic relationship
benefits while the other is neither helped or
hurt.
– tropical fish and sea anemones
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Mutualism
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Both species in relationship benefit.
– mutual cooperation
 ants and acacias
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Parasitism
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Parasite benefits while inflicting some form of
harm to the prey.
– ectoparasites
 external parasites - lice
–
endoparasites
 internal parasites
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Interactions Among Ecological Processes
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Keystone species
– Species that have a particularly strong
effect on community composition.
 top predators
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Succession
Succession is the process of ecosystems
changing from a simple to a more complex
structure.
–
–
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primary succession - occurs in bare areas
secondary succession - occurs following disturbance
Succession occurs because species alter
the habitat and available resources in ways
that favor other species.
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An ecosystem includes all the organisms living
in a particular place, and the abiotic
environment in which they interact.
Producers
Autotrophs - capture light energy and manufacture own chemical energy
Consumers
Heterotrophs - must obtain organic molecules from autotrophs
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Trophic Levels - Food Chain
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Primary
producer
Primary
Secondary Tertiary
consumer consumer consumer
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Trophic Levels
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Trophic level refers to the feeding level of an organism.
Organisms from each trophic level constitute a food chain.
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The Energy in Food Chains
Second Law of Thermodynamics
food chains are generally limited to 3 or 4 steps (trophic
levels) ultimately determined by the amount of sunlight
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On average, 10% of the organic matter (energy) transfers
from one trophic level to the next.
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Interactions Among Trophic Levels
Trophic cascading
effect of one trophic level flows down to lower
levels. (top-down effects)
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Bottom-up effects
productivity of an ecosystem is low, herbivore populations
will be too small to support any predators.
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Vegetation
Herbivores
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Productivity
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Interconnected food chains constitute a food web.
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