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Community Ecology
A Community Includes All Life in an Area
Niche: “JOB”
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The sum total of all the ways as organism
utilizes the resources of its environment
Such as: space utilization, food
consumption, temperature range, moisture
requirements, etc.
Fundamental niche – entire niche a species
is CAPABLE of using
Realized niche – actual niche a species
occupies
NOTE:
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Niche is NOT the same as habitat
HABITAT – a physical place
NICHE – pattern of living
The niche of a lion – predator
Turkey vulture – scavenger
Cacti – drought tolerant species
Biotic Interaction
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Competition
Predation
Symbiosis
Competition
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Interspecific competition – two different
species attempt to utilize the same resource
Intraspecific competition – two members of
the same species fighting for same resource
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Organisms may occupy more than one niche
Gauses’ Rule: No two organisms may
occupy the same niche for very long when
resources are LIMITING
“Survival of the fittest” – the stronger will
force the weaker out of the habitat or
contribute to its demise
This is known as the Competitive Exclusion
Principle
Resource Partitioning
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The reduction of competition of resources
between species by “subdividing the niche”
Warblers: (5) species that fed on insects of
spruce trees
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One species fed on insects near branch tips
One fed on dense foliage
One fed on bases of tree branches
One on the tree top
One on the tree bottom
Each bird fed on different insects by
feeding at different levels of the
spruce tree – different niches
 Sympatric species – differentiation of
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populations into different species within
the same geographical areas
(brown/green anole)
 Partition resources by feeding in different
portions of the habitat, utilizing different
foods, feeding at different times
 Believed to be driven by natural
selection
Allopatric Populations
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The differentiation of geographically
isolated populations into distinct
species
Predators
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Consuming of one organism by another
Predators (or lack of) can often have large effects
on prey populations
Eastern Coast
- population explosions of white-tailed deer –
strip the habitat of all edible plant life
Western Coast
- sea otters hunted to near extinction – sea
urchin populations exploded (otters eat urchins)
Predation
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Prey ↑ = Predator ↑
Prey ↓ = Predator ↓
Predator ↑ =
Predator ↑ = Prey ↓
How Would Evolution Apply?
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Evolution – change in a species over time
Adaptation – species becomes better suited
for survival
Natural selection - “survival of the fittest”
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PREDATOR – strong selective pressure on prey
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Only the strongest, quickest prey survive – prey evolve
defensive adaptations
Also only the strongest, fastest predators will survive
Plant Defenses against Herbivores
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Morphological defenses – thorns, spines,
prickles, and plant hairs
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Chemical defenses – toxic to most herbivores
or disturb their metabolism (mustard,
cabbage, watercress, radish, and
horseradish, the same taste we enjoy!)
Animal Defenses against Predators
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Defensive Coloration –
Cryptic coloration – color that blends with the
surroundings and thus hides the individual from
predators *usually do not live together in
groups*
Warning coloration – showy coloration that
shows they are poisonous
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Chemical Defenses –
Poisons and Stings
Mimicry – looking like a harmful
organism
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Batesian Mimicry – palatable insects having
coloration of a distasteful insect
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Monarch and viceroy butterflys
Mullerian Mimicry – the resemblance of
dangerous, unpalatable, or poisonous
species (even unrelated species) to one
another so that they become more easily
recognized by potential predators
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Brightly colored species of poison dart frogs
Coevolution
long-term mutual evolution of members of
biological communities
Ex. Predator-Prey interactions
Flowers and pollinators
A Type of Co-evolution
Symbiotic relationships – two or more kinds of
organisms live together in elaborate and
permanent relationships
Example:
Fungi and roots of plants – fungi and expedite
the plants’ absorption of nutrients and the
plants in turn provide the fungi with
carbohydrates
Kinds of Symbiosis
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Commensalism
Mutualism
Parasitism
Saprophitism
Commensalism
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One species benefits while the other neither
benefits nor is harmed
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Example:
Epiphytes on trees (epiphytes – plants that
live on other plants)
Vermiliads and orchids in rain forest
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Mutualism
Both participating species benefit
Example:
Cattle egret on back of cow
Parasitism
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One species benefits but the other is harmed
Ex. Tapeworm in dog
Tick on human
3 Types of Parasites
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External – parasites that feed on the exterior
surface ex. Lice
Internal – parasites that feed on the interior
*not bacteria of fungi*
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Brood – ex. Birds lay eggs in nests of other
species
Keystone Species
Species that have a particularly strong effects
on the composition of communities
Examples:
Dung beetle
Beavers
Succession
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Change in which one ecosystem is
replaced by another
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ex. Pond becoming a forest, field
becoming a marsh
Primary Succession
where there has been no life
previously
 Occurs on bare, lifeless substrate
when organisms gradually move into
an area and change its nature
 Ex. sand dune, lava, bare rock
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Secondary Succession
where life has existed previously
 a wooded area is cleared and left
alone, plants will slowly reclaim the
area
 ex. After a forest fire, a fallow field
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Why Succession Happens
 Species
alter the habitat and
the resources available in it in
ways that favor other species.