Communities & Biodiversity
Communities
 Multicelled organism
 Population
 Community
 Ecosystem
 Biosphere
Communities
 An interacting group of
various species in a common
location. For example, a forest
of trees and undergrowth
plants, inhabited by animals
and rooted in soil containing
bacteria and fungi,
constitutes a biological
community.
Communities
 Structure arises from…
 Physical & chemical conditions of habitat
 Availability of food & resources (type, amount, etc.)
 History of habitat & species
 Traits that help species survive in habitat
 Interactions among species
 Physical disturbances
Communities
 Niche— “profession” of a
species that sets it apart
from other species.
 Fundamental niche—
Would happen even in
absence of competitors or
other limiting factors.
 Realized niche—Actual
position taking into
account competition &
limiting factors; can
change over time.
Species Interactions
 Commensalism
 One species helped, other
species not affected
 Bird & tree
 Barnacles & whales
 Remoras & sharks
Species Ineractions
 Mutualism
 Both species benefit
 Ants & aphids
 Pollen & insects
 Sea anemones & fish
 Bacteria & larger organisms
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Horses & cecal bacteria
Termites & hindgut bacteria
Species Interactions
 Parasitism
 One species benefits, other is harmed
 Endoparasite—live inside the host

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Roundworms
Malaria (Plasmodium)
 Ectoparasite—live on the host
 Lice
 Ticks
 Brood parasite—manipulate other
animals to raise young
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Cuckoos
Cowbirds
Cuckoo bees & wasps
Species Interactions
 Parasitism (cont.)
 Drain nutrients from host
 Using resources that host
needs
 Weakened hosts more easily
preyed upon
 Weakened hosts may not be
able to forage
 Hosts may die
Species Interactions
 Predation
 One species kills and
feeds on another species
 Balanced relationship

As prey increases or
decreases, so does predator
Predator-Prey Relationship
 Predation a strong factor in natural selection
 Some modifications in prey make them less likely to be
preyed upon
 Predators also undergo selection to overcome prey’s
defenses
Prey Defenses
 Camouflage
 Blend into surroundings
 Avoid being seen (predator & prey)
Prey Defenses
 Chemical Defense
 Bad-tasting—Monarch butterfly
 Toxic—Poison dart frog,
scorpionfish
 Venomous—Coral snake
 Irritant—Skunk, bombardier
beetle
 Often have bright coloration or
specific behavior as a warning
Prey Defenses
 Mimicry
 Closely resemble dangerous or
unpalatable species
 Predator avoids due to perceived
danger
Prey Defenses
 Physical Defense
 Shell, armor—turtles,
armadillos
 Spines, spikes—porcupines,
hedgehogs, lizards
 Horns, antlers—rhinocerous,
deer
Prey Defenses
 Startle/Surprise Defenses
 Look fearsome or larger
 False eye spots—moths,
caterpillars
 Neck frills—lizards, birds
 “Fluffing” hair or feathers—birds,
mammals
 Vocal displays—hissing
cockroach, cats, growling dogs
Predator Armament
 Camouflage (tiger, leopard)
 Lures (anglerfish, snapping
turtle)
 Heat sensors (pythons, vipers)
 Pack behavior (wolves, lions)
Community Stability
 Communities usually reach stability
 Can be upset by new additions or
subtractions
 Keystone species—species that has
disproportionately large effect relative to
its abundance
 Predators
 Sea star experiment
 Sea stars prey on several species
 Remove sea stars
 Mussels take over, crowd out other species
 Sea otters & sea urchins
Community Stability
 Keystone species (cont.)
 Engineers
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Change the environment through
actions
Grizzly bears—transfer oceanic
nutrients (salmon) to forest
ecosystem
 Up to half of salmon captured
ends up on forest floor
Beavers—transform stream to
pond or swamp
Elephants—destroy trees, make
room for grass
Community Stability
 Introduced species
 Can upset balance
 May not have natural predators
 May not have competition
 Rabbits in Australia

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24 introduced in 1859 for hunting
By 1869 could kill 2,000,000 without
affecting population
Currently over 100 million
Eat native plants, leads to large
erosion
Community Stability
 Introduced species (cont.)
 Zebra mussels
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Native to Russia & Caspian Sea
First detected in Great Lakes in
1988
Suspect were attached to ship
ballast, anchors, chains
Invaded waterways
Kill & outcompete native mussels
Damage boats, harbors, power
plants