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Community Ecology
Chapter 20
Symbiosis
• Organisms of different kinds living together
i th
in
the same ecosystem
t
• Any of the following relationships are
considered
id d tto b
be symbiotic:
bi ti
- Predator – prey
- Parasite – host
- Commensalism
- Mutualism
- Pathogen
g - host
Predator – Prey (Predation)
• Lions and zebras, for example
• One hunts and kills,
kills the other gets killed and eaten
Parasite – Host (Parasitism)
• Fleas and dogs for example
• The parasite harms the host
and benefits from the
relationship The host is
relationship.
harmed, but not usually
killed
Pathogen - Host
• A pathogen is a disease-causing
disease causing agent, like a
bacterium or a virus
E.coli
H.I.V.
Mutualism
• A symbiotic relationship where
two organisms are in a
mutually
t ll b
beneficial
fi i l relationship
l ti
hi
• Examples: Lichens are not one
organism but two – an algae
and a fungus living as one.
The algae provides the fungus
with glucose in return for
moisture from the fungus.
Clown Fish are protected from predator
fish by the stinging tentacles of the
anemone. The anemone receives
protection from polyp-eating fish, like
Butterfly Fish
Fish, which the Clown Fish
chases away. The anemone also gets
fertilizer from the feces of the Clown Fish.
Commensalism
• In this relationship, one organism benefits but
the other is neither harmed nor benefited
• Examples: Shark and remora
Predator Adaptations
Natural selection favors the evolution of predator
p
adaptations for finding, capturing, and consuming
prey.
• Rattlesnakes
R ttl
k have
h
an acute
t sense off smell
ll and
d heath t
sensitive pits for detecting warm-bodies prey.
sq irrel
squirrel
•
•
•
•
Sticky webs of spiders
Flesh-cutting
Flesh
cutting teeth of wolves and coyotes
Speed of cheetahs
Striped patterns of tiger’s coat; provides camouflage
in a grassland habitat.
Prey Adaptations
• Some organisms flee
when a predator
approaches
h
• Hiding or resembling an
inedible object
• Deceptive markings; fake
eyes, false heads
• Chemical defenses
Mimicry
One species closely resembles another species.
2 forms:
Batesian mimicry: is a form of mimicry typified by a
situation where a harmless species has evolved to
imitate the warning signals of a harmful species
directed at a common predator.
King snake
Coral snake
Mullerian mimicry: two or more harmful species that
are not closely related, and share one or more
common predators, have come to mimic each
other's warning signals.
Plant Prey Adaptations
• Physical defenses; sharp thorns, spines, sticky hairs,
and tough leaves.
leaves
• Chemical defenses that are poisonous, irritating, or
bad-tasting
• Secondary compounds: chemicals that are often
byproducts of the plants’ metabolism
ex: strychnine (used as a pesticide,
pesticide particularly for
killing small vertebrates such as rodents. Strychnine
causes muscular convulsions and eventually death
through asphyxia or sheer exhaustion)
nicotine
Competition
Organisms
g
may
y compete
p
for things
g such as: food,,
space, sunlight, nutrients, or water.
Patterns In Communities
Disturbances: events that change communities,
remove or destroy organisms from communities, or
alter resource activity.
Stability: the tendency
Stabilit
tendenc of a community
comm nit to maintain
relatively constant conditions.
• Relates to the community’s
y resistance to
disturbance
Succession
Ecological succession: the gradual, sequential
regrowth
g
of a community
y of species
p
in an area.
2 types:
primary succession: the development of a
community in an area that has not supported life
previously such as a bare rock
previously,
rock, sand dune
dune, or an
island formed by volcanic eruption. Soil is not
initially present.
Secondary succession: the sequential replacement of
species that follows disruption of an existing
community.
it Occurs
O
where
h
soil
il is
i already
l d present.
t
Pioneer species: species of organisms that
predominate early in succession.
Climax community: a community that has reached a
generall stable point.
generally
point