stu ch 15 communities [read-only]
TRANSCRIPT
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Community Ecology
Chapter 15
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Community ecology
• A community is
• Interspecific interactions
– classified according to effect on population concerned
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Interspecific interactions• Competition: -/-
• Mutualism: +/+
• Predation/herbivory: +/-
• Parasite/pathogen: +/-
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Each organism has a niche
• Ecological niche: a multidimensional description of a species; its way of living
• The more similar 2 niches are, the more intense the competition for resources
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When niches overlap• Competitive exclusion
• OR• Resource partitioning
• Both of these result in a reduction or removal of competition
• Competition seems to be indirect, not head-to-head; both species trying for same resource, one is just a bit better at getting it
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When niches overlap
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Key properties to a community
• Prevalent vegetation• Species diversity• Response to disturbance
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Vegetation & species diversity
• The more diverse the vegetation, the more diverse the population of animal species
• The more diverse the community, the more resistant it is to the negative effect of pathogens
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Diversity defined by 2 components
• Species richness
• Relative abundance
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Species richness & relative abundance together
determine community diversity
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Keystone species impact diversity• A keystone species greatly
influences which other species are present
• If a keystone species is removed from community, the composition changes drastically
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Community response to disturbance
• What is a disturbance?
• Not always negative; small scale disturbances can contribute to species diversity
• Succession is the change in species composition over time following a disturbance
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Primary succession• Starts in lifeless area without even soil
– 1st life forms are autotrophic bacteria– photosynthetic mosses & lichen– grasses & shrubs– small trees– larger, longer-living species that eventually
become prevalent vegetation• Primary succession can take 100s or 1000s
of years
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Primary succession
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Primary succession
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Secondary succession
• Occurs when disturbance destroyed existing community but left soil intact
• 1st grasses & shrubs followed by larger vegetation. . . – because animals depend on plants, animal
community goes through succession too; ex. diversity of birds increases as trees replace shrubs
• Secondary succession can happen in decades or even a few years
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Secondary succession
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More about succession• Succession can lead to a climax community
– the specific species in a climax community is dependent on the temperature & rainfall
• The most diverse communities are at some intermittent step of succession
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Summary• Community ecology is the study of
interspecies interactions• Interactions can be classified as beneficial or
harmful• Interactions shape the community structure• The presence or absence of some species
play a larger role in the community structure than others (keystone species)
• How communities respond to disturbance help define the community
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Predation• An interaction where one species eats
another, including herbivory– the predator benefits; the prey or plant don’t
• One of the most important forces shaping the composition & abundance of species in a community
• Defenses against predation– physical– behavioral
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Physical prey defenses• Mechanical defenses
– spines, quills, armor, claws, etc.
• Chemical toxins– make prey poisonous or
unpalatable– used by many plants;
can be harmful to one species and harmless to another
– some animals also use this defense
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Physical prey defenses, cont.
• Warning coloration– danger! poisonous!
& mimics
• Camouflage– patterns of
coloration that allow an organism to blend into its environment
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Behavioral prey defenses• Hiding or escaping
– requires vigilance to avoid predators– safety in numbers
• Alarm calling– many species, especially birds &
mammals, warn others of danger• Fighting back
– some species mob the predator– spitting, vomiting, eliminating waste,
dropping tails, eviscerating, etc.
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Parasitism• Parasitism: a symbiotic relationship where one
species benefits (the parasite) & one is harmed (the host)
• Two types of parasites– ectoparasites live outside the host’s body
• lice, leeches, ticks, fleas– endoparasites live inside the host’s body
• tapeworms, roundworms, Plasmodium
• Different from other forms of predation – the parasite is much smaller then the host – parasites stay in contact with the host for long periods
of time, weakening the host as it uses the host’s resources
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Positive interspecies interactions
• Mutualism: everyone benefits– both species gain & neither is
harmed– common in virtually every
community• honeybees & flowers; cleaner fish &
the “dirty” fish
• Commensalism: one species benefits & the other neither benefits or is harmed– cattle egrets & livestock