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• Community
Ecology
-Types of Species
-Species Interactions
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General Types of Species
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Examining roles of various species in
ecosystems:
• Native species = a species that, other than as a
result of an introduction, historically occurred or
currently occurs in an ecosystem (Indigenous)
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• Invasive species = an alien species whose
introduction does or is likely to cause economic or
environmental harm or harm to human health. (non
native species, exotic, introduced etc.)
Some characteristics of Invasive
Species:
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• High rate of reproduction
• “pioneer species”
• High dispersal rates
• Tolerant of a wide range
of conditions
• Generalist
• Impact on native
ecosystems
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– Invasive species impact 3050% of the species
currently listed as
Threatened or Endangered
under the U.S Federal
Endangered Species Act.
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– (Second only to habitat
destruction.)
Examples of Non-natives (Invasive)
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• Non-native herbivores, like gypsy moth,
directly affect the flow of energy captured
by plants from the sun.
• Non-native earthworms can dramatically
increase decomposition in soils.
• Non-native bee species (killer bees)
• Rats (Sandy Cay)
• Cane Frog (Tortola)
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Keystone species
….play pivotal roles in the structure,
function, and integrity of an ecosystem…
affect the health and survival of other
species.
 Their strong interactions with other
species, and the fact that they process
material out of proportion to their numbers
makes them a Keystone Species.
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Keystone Species
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Critical roles Include:
 Pollination
of flowering plant species by bees,
hummingbirds, bats
 Dispersion of seeds by fruit eating animals
 Predation by top carnivores to control the populations
of various species
 Habitat modifications: bats and birds regenerate
deforested area by depositing plant seeds in their
droppings
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Loss of keystone species can lead to pop.
Crashes and extinction of species that depend
on it for certain services.
Indicator Species
 Can be described as species that serve as
early warnings that a community or an
ecosystem is being damaged or not stable.
One example would be:
 Apex species (top carnivores or top
predators)
 Are always the first to be affected by any change
in their ecosystems and therefore, how their
numbers indicate the health of the ecosystem
Birds as Indicator Species
 Birds are excellent bioindicators because
they are found almost everywhere, and
they respond quickly to environmental
change.
 Migratory paths
 Habitat loss and fragmentation
Amphibians
The indicators for Tropical
Caribbean eco-region
(Marine)
 Species: All Sharks
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Blacktip shark Carcharhinus limbatus
Blacktip reef shark Carcharhinus melanopterus
Blue shark Prionace glauca
Bull shark Carcharhinus leucas
Caribbean reef shark Carcharhinus perezi
Great hammerhead shark Sphyrna mokarran Carcharhinus perezi
Grey reef shark Carcharhinus amblyrhynchos
Lemon Shark Negaprion brevirostris
Nurse shark Ginglymostoma cirratum
Tiger shark Galeocerdo cuvier
Whale shark – Vulnerable Rhincodon typus
Species: All Marine
Turtles
 Most experts recognize seven species of marine
turtles: the green, hawksbill, loggerhead, Kemp's ridley,
olive ridley, leatherback, and flatback. All but one - the
flatback - can be found in the Latin American and
Caribbean region, and all are threatened by extinction.
Community structure
• Community~ an assemblage of
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populations living close enough
together for potential interaction
• Richness (number of species) &
abundance…….
• Species diversity
• Hypotheses:
•Individualistic~ chance
assemblage with similar abiotic
requirements
•Interactive~ assemblage
locked into association by mandatory
biotic interactions
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Species Interactions: Predation
 Predator: feeds directly on all or part of a living
organism
 Prey: organism fed on.
 Predator-prey relationship: One organism is clearly
harmed. However at the population level there are benefits:
improve access to food, and improve the genetic stock.
 Prey acquisition: herbivores vs. carnivores (pursue or
ambush)
 Predator Avoidance: speed, highly developed
senses,protective coverings
Predator Avoidance by Prey
Span worm
camouflage
Poison dart frog
Chemical warfare
Warning coloration
Wandering leaf insect
camouflage
Viceroy butterfly mimics
monarch butterfly
mimicry
Bombardier beetle
Chemical warfare
Hind wings of io moth
resemble eyes of a
much larger animal
Foul-tasting monarch
butterfly
Warning coloration
When touched, the
snake caterpillar
changes shape to look
like the head of a snake
Deceptive looks Deceptive behavior
Figure 8-11
Page 177
Slide 18
Predation defense
• Cryptic (camouflage) coloration
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Aposematic
(warning)
coloration
• Mimicry~ superficial resemblance to
another species
√ Batesian~ palatable/ harmless species
mimics an unpalatable/ harmful model
√ Mullerian~ 2 or more unpalatable,
aposematically colored species resemble each
other
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Symbiotic Relationships
 Symbiosis is a relationship in which
species live together in an intimate
association.
 There are three types:
 Parasitism (special form of predation)
 Mutualism
 Commensalism
Interactions
 Interspecific
(interactions between
populations of different
species within a community):
Symbiotic Species Interactions:
Mutualism
Reproductive mutualism: pollination
Nutritional mutualism
Nutritional/protection mutualism
Fig. 8-12 p. 179
Symbiotic Species Interactions:
Commensalism
 Indirect: i.e., small
plants growing in
shade of larger plants
(redwood sorrel)
 Direct: i.e., epiphytes
(orchids and
bromeliads), remoras
Fig. 8-13 p. 180
Symbiotic Species Interactions: Parasitism
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Parasite:
organisms that feeds on another by
living in or on another living organism. Parasite
benefits.
Host: Organism that a parasite feeds on and lives
in or on. Host is harmed. (rarely killed)
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Endoparasites: parasites found inside the host
organisms body. Ex.tapeworms,disease causing
microorganisms.
Ectoparasites: organisms found outside the
host organisms body. Ex. Fleas, ticks, mosquitoes
Species Interactions:
Competition
 Intraspecific competition: within a
species for resources and territoriality.
 Interspecific competition: between
different species for limited resources
(niche overlap)
Competing species must:
Migrate to another area
Shift its feeding habits or behavior
through evolution and natural selection
Suffer a sharp decline in population
Extinction
Species Interactions: Competition
 Interference competition:
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One species influences another’s access to
some resource regardless of its
abundance. Ex. hummingbird
 Exploitation competition:
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Two competing species have roughly equal
access but differ in how fast or efficiently
they exploit it.
Competition: a closer look
 Competitive exclusion principle: by
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Gauss describes how one species eliminates
another in an area through competition for
limited resources.
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High
Relative population density
Paramecium
aurelia
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Paramecium
caudatum
Low
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Days
Both species grown together
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Figure 8-8 (2)
Page 174
Slide 14
Competition evidence
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• Resource
partitioning
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sympatric species consume slightly
different foods or use other
resources in slightly different ways
• Character displacement~
sympatric species tend to diverge in
those characteristics that overlap
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Ex: Anolis lizard sp. perching sites in the
Dominican Republic
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Ex: Darwin’s finch beak size on the
Galapagos Islands
Resource partitioning
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Resource Partitioning
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Resource
partitioning: a method
to reduce competition,
dividing up the resource so
that species with similar
needs use them at different
times, in different ways, or in
different places.
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Fig. 8-9 p. 175; Refer to Fig. 7-13 p. 152 & Fig. 8-10 p. 175
The Niche
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• Ecological niche~ the sum total of
an organism’s use of biotic and abiotic
resources in its environment; its “ecological
role”
√ fundamental~ the set of
resources a population is theoretically
capable of using under ideal conditions
√ realized~ the resources a
population actually uses
• Thus, 2 species cannot coexist in
a community if their niches are
identical
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Ex: Barnacle sp. on the coast of Scotland