community ecology chapter 56mmsalemscienceteacher.weebly.com/.../23362738/chapt56_lecture_… ·...
TRANSCRIPT
1
Community EcologyChapter 56
Biological Communities
• Community
– Species that occur at any particular locality
– Characterized by
• Species richness
–Number of species present
• Primary productivity
–Amount of energy produced
– Interactions among members govern many
ecological and evolutionary processes
2
3
An African savanna community
Ecological Niche
• Niche: the total of all the ways an
organism uses the resources of its
environment
– Space utilization
– Food consumption
– Temperature range
– Appropriate conditions for mating
– Requirements for moisture and more
4
Ecological Niche
• Interspecific competition
– Occurs when two species attempt to use the same resource and there is not enough resource to satisfy both
• Interference competition
– Physical interactions over access to resources
• Exploitative competition
– Consuming the same resources
5
Ecological Niche
• Fundamental niche
– Entire niche that a species is capable of using,
based on physiological tolerance limits and
resource needs
• Realized niche
– Actual set of environmental conditions, presence
or absence of other species, in which the species
can establish a stable population
• Other causes of niche restriction
– Predator absence or presence
– Absence of pollinators
– Presence of herbivores 6
7
Ecological Niche
J.H. Connell’s classical study of barnacles
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
High tide
Low tide
C.stellatus fundamental and
realized niches are identical when
S.balanoides is removed.
S.balanoides and C.stellatus competing
Chthamalus
Chthamalus
realized niche
Chthamalus
fundamental
niche
Semibalanus
Semibalanus
realized niche
Semibalanus
fundamental
niche
Ecological Niche
• Principle of competitive exclusion
• If two species are competing for a limited
resource, the species that uses the
resource more efficiently will eventually
eliminate the other locally
• G.F. Gause’s classic experiment on
competitive exclusion using three
Paramecium species shows this
principle in action
8
9
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
0
50
100
150
200
40 8 12 16 20 24 40 8 12 16 20 24 40 8 12 16 20 24
a.
Days Days Days
Po
pu
lati
on
Den
sit
y
(me
as
ure
d b
y v
olu
me
)
200
150
100
50
0
40 8 12 16 20 24
Days
Po
pu
lati
on
De
ns
ity
(me
as
ure
d b
y v
olu
me
)
b.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ecological Niche
• Paramecium caudatum and P. bursaria
– Expected same results – one winner
– Both species survived by dividing
resources
• Realized niche did not overlap too much
10
c.
0 20 24161284
Days
Paramecium caudatum
Paramecium aurelia
Paramecium bursaria
Po
pu
lati
on
Den
sit
y
(me
as
ure
d b
y v
olu
me
)
75
50
25
0
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
b.
c.
d.a-d: © Jonathan Losos
• Resource
partitioning
among
sympatric
lizard
species
• Subdivided
niche to
avoid direct
competition
11
• Resource partitioning is often seen in similar species that occupy the same geographic area– Thought to result from the process of natural selection
• Character displacement– Differences in morphology evident between sympatric
species
– May play a role in adaptive radiation12
50
25
0
50
25
0
50
25
07 9 11 13 15
G. fuliginosa
Allopatric
G. fortis
Allopatric
G. fuliginosa
and G. fortis
Sympatric
Finch Beak Depth (mm)
Los Hermanos
Islets
Daphne Major
Island
San Cristóbal and
Floreana Islands
Ind
ivid
ua
ls i
n E
ac
h S
ize
Cla
ss
(%
)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Predator–Prey
• Predation
– Consuming of one organism by another
• Predation strongly influences prey populations
13
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Didinium
Didinium
1200
800
400
0 1 2 3 4 5 6 7
Days
Paramecium
Paramecium
Nu
mb
er
of
Ind
ivid
uals
Predator–Prey
• Prey populations can have explosions and crashes– White-tailed deer in Eastern U.S.
– Introduction of rats, dogs, cats on islands
– New Zealand: Stephen Island wren extinct because of a single cat
• Predation and coevolution
– Predation provides strong selective pressure on
the prey population
– Features that decrease the probability of capture
are strongly favored
– Coevolution race may ensue14
Predator–Prey
15
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
b.a: © Edward S. Ross. b: © Raymond Mendez/Animals Animals
• Plants adapt to predation (herbivory) by evolving mechanisms to defend themselves
– Chemical defenses: secondary compounds
• Oils, chemicals to attract predators to eat the herbivores, poison milky sap, and others
– Herbivores coevolve to continue eating the plants
• Chemical defenses in animals
– Monarch butterfly caterpillars feed on milkweed
and dogbane families
– Monarchs incorporate cardiac glycosides from the
plants for protection from predation
– Butterflies are eaten by birds, but the Monarch
contains the chemical from the milkweed that
makes the birds sick16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. b.a-b: © Lincoln P. Brower
17
Predator–Prey
Poison-dart frogs
of the family
Dendrobatidae
produce toxic
alkaloids in the
mucus that covers
their brightly
colored skin
• Defensive coloration– Insects and other animals that are poisonous use
warning coloration
– Organisms that lack specific chemical defenses are seldom brightly colored
• Camouflage or cryptic coloration help nonpoisonous animals blend with their surroundings
• Camouflaged animals do not usually live together in groups
18
Predator–Prey
• Mimicry allows one species to capitalize on
defensive strategies of another
– Resemble distasteful species that exhibit warning
coloration
– Mimic gains an advantage by looking like the
distasteful model
– Batesian mimicry
• Mimics look like distasteful species
– Müllerian mimicry
• Several unrelated but poisonous species come
to resemble one another
19
20Mimicry
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Heliconius melpomene
Papilio glaucusBattus philenor
a. Batesian mimicry: Pipevine swallowtail butterfly (Battus philenor) is
poisonous; Tiger swallowtail (Papilio glaucus) is a palatable mimic.
Heliconius erato
Heliconius cydnoHeliconius sapho
b. Müllerian mimicry: Two pairs of mimics; all are distasteful.
Species Interactions
• Symbiosis
– 2 or more kinds of organisms interact in more-or-less permanent relationships
– Potential for coevolution
– Three major types of symbiosis
• Commensalism
• Mutualism
• Parasitism
21
Species Interactions
• Commensalism benefits one species
and is neutral to the other
– Spanish moss: an epiphyte hangs
from trees
22
Species Interactions
• When commensalism may
not be commensalism
• Oxpeckers and grazing
animals
– Oxpeckers eat parasites
off of grazers
– Sometimes pick scabs
and drink blood
– Grazers could be
unharmed by the insects
the oxpeckers eat23
Species Interactions
• Mutualism benefits both species
– Coevolution: flowering plants and insects
• Ants and acacias
–Acacias provide hollow thorns and food
–Ants provide protection from herbivores
24
Mutualism
25
Ants of the genus Pseudomyrmex live
within the hollow thorns of certain species
of acacia trees in Latin America
Species Interactions
• Not all ant and acacia relationships are mutualism
– In Kenya, several species of ants live on acacias
• One species clips the acacia branches to prevent other ants from living in the tree
• Clipping branches sterilizes the tree
• A parasitic relationship
26
Species Interactions
• Parasitism benefits one species at the
expense of another
– External parasites
• Ectoparasites: feed on exterior surface of
an organism
• Parasitoids: insects that lay eggs on
living hosts
–Wasp, whose larvae feed on the body
of the host, killing it
27
28
External parasite: the yellow vines are the flowering
plant dodder; it is a parasite that obtains its food from
the host plant it grows on
Species Interactions
• Internal parasites
– Endoparasites live inside the host
– Extreme specialization by the parasite as
to which host it invades
– Structure of the parasite may be simplified
because of where it lives in its host
– Many parasites have complex life cycles
involving more than one host
29
Species Interactions
• Dicrocoelium dendriticum
is a flatworm that lives in
ants as an intermediate
host with cattle as its
definitive host
• To go from the ant to a
cow, it changes the
behavior of the ant
• Causes the ant to climb
to the top of a blade of
grass to be eaten with
the grass
30
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Infected ant
Species Interactions
• Ecological processes have interactive effects
– Predation reduces competition
• Predators choice depends partly on relative abundance of the prey options
• Superior competitors may be reduced in number by predation
• This allows other species to survive when they could have been outcompeted
31
32
Species Interactions
Starfish eat barnacles, allowing other species
to thrive instead of being crowded out by the
explosive population of barnacles
a. b.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a: © F. Stuart Westmorland/Photo Researchers, Inc. b: © Ann Rosenfeld/Animals Animals
Species Interactions
• Parasitism may counter competition
– Parasites may affect sympatric species differently, changing the outcome of interspecific interactions
– Flour beetles and a competition experiment
• Without a parasite: T. castaneum is dominant
• With the parasite: T. confusum is dominant
33
Species Interactions
• Keystone species
– Species whose effects on the composition of communities are greater than one might expect based on their abundance
– Sea star predation on barnacles greatly alters the species richness of the marine community
– Keystone species can manipulate the environment in ways that create new habitats for other species
• Beavers
34
35
Beavers construct dams and transform
flowing streams into ponds, creating new
habitats for many plants and animals
Succession and Disturbance
• Succession
– Communities have a tendency to change
from simple to complex
• Primary succession occurs on bare,
lifeless substrate
–Open water
–Rocks
– Organisms gradually move into an area
and change its nature
36
37
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
50
100
150
200
250
300
Nit
rog
en
Co
nc
en
tra
tio
n
(g/m
2o
f s
urf
ac
e)
b
c
a.
c. d.
Pioneer
Mosses
Invading
Alders
Alder
Thickets
Spruce
Forest
Year 1
Nitrogen
in forest floor
Year 200Year 100
b.
Nitrogen
in mineral soil
b-d: © Tom Bean
Succession and Disturbance
• Secondary succession
– Occurs in areas where an existing community has been disturbed but organisms still remain
• Field left uncultivated
• Forest after a fire
• Succession happens because species alter the habitat and the resources available in ways that favor other species entering the habitat
38
Succession and Disturbance
• Three dynamic concepts in the process
– Tolerance: early successional species are
characterized by r-selected species
tolerant of harsh conditions
– Facilitation: early successional species
introduce local changes in the habitat.
K-selected species replace r-selected
species
– Inhibition: changes in the habitat caused by
one species inhibits the growth of the
original species39
Succession and Disturbance
• Animal species in a community can also
change over time
– Krakatau island
• Volcanic eruption
• Fauna changed in synchrony with the
vegetation
• Changes in animals affect plant
occurrences; pollination, animal
dispersion
40
41
Succession and Disturbance
Succession after a volcanic eruption
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b.a.a-b: © Studio Carlo Dani/Animals Animals – Earth Scenes
Succession and Disturbance
• Communities are constantly changing
as a result of
– Climatic changes
– Species invasions
– Disturbance events
• Nonequilibrium models that emphasize
change rather than stability are used to
study communities and ecosystems
42
Succession and Disturbance
• Intermediate disturbance hypothesis
– Communities experiencing moderate amounts of disturbance will have higher levels of species richness than communities experiencing either little or great amounts of disturbance
• Patches of habitat will exist at different successional stages
• May prevent communities from reaching the final stages of succession
43
44
Succession and Disturbance
• Disturbance is common,
rather than exceptional
in many communities
• Understanding the role
that disturbances play in
structuring communities
is an important area of
ecology