Community Ecology Chapter 56mmsalemscienceteacher.weebly.com/.../23362738/chapt56_lecture_… · –Monarch butterfly caterpillars feed on milkweed and dogbane families –Monarchs

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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

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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

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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

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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

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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

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9


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.


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

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me

)

75

50

25

0



a.

b.

c.

d.a-d: © Jonathan Losos

• Resource

partitioning

among

sympatric

lizard

species

• Subdivided

niche to

avoid direct

competition

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• 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

(%

)


Predator–Prey

• Predation

– Consuming of one organism by another

• Predation strongly influences prey populations

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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

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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


a. b.a-b: © Lincoln P. Brower

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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

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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

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20Mimicry


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

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• Commensalism benefits one species

and is neutral to the other

– Spanish moss: an epiphyte hangs

from trees

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• 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


• Mutualism benefits both species

– Coevolution: flowering plants and insects

• Ants and acacias

–Acacias provide hollow thorns and food

–Ants provide protection from herbivores

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Mutualism

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Ants of the genus Pseudomyrmex live

within the hollow thorns of certain species

of acacia trees in Latin America


• 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

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• 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

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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


• 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

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• 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

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Infected ant


• 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

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Starfish eat barnacles, allowing other species

to thrive instead of being crowded out by the

explosive population of barnacles

a. b.


a: © F. Stuart Westmorland/Photo Researchers, Inc. b: © Ann Rosenfeld/Animals Animals


• 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

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• 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

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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

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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


• 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

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• 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


• 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

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Succession after a volcanic eruption


b.a.a-b: © Studio Carlo Dani/Animals Animals – Earth Scenes


• 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

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• 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

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44


• Disturbance is common,

rather than exceptional

in many communities

• Understanding the role

that disturbances play in

structuring communities

is an important area of

ecology

Documents

Community Ecology Chapter 56mmsalemscienceteacher.weebly.com/.../23362738/chapt56_lecture_… · –Monarch butterfly caterpillars feed on milkweed and dogbane families –Monarchs