Transcript Lecture Powerpoint Here

Community Structure
and Biodiversity
Chapter 40
Ecosystems

Ecosystems vary in size.
 They
can be as small as a puddle or as
large as the Earth itself.
 Any group of living and nonliving things
interacting with each other can be
considered as an ecosystem.

Within each ecosystem, there are
habitats
 These
may also vary in size.
 A habitat is the place where a population
lives. - Turlock habitat
 A population is a group of living organisms
of the same kind living in the same place at
the same time. Turlock humans
 All the different populations interact and
form a community. City of Turlock
The community of living things interacts
with the non-living world around it to
form the ecosystem.
 The habitat must supply the needs of
organisms, such as food, water,
temperature, oxygen, and minerals.
 If the population's needs are not met, it
will move to a better habitat.
 Two different populations can not
occupy the same niche at the same
time, however.

Community

All the populations that live together in
a habitat

Habitat is the type of place where
individuals of a species typically live

Type of habitat shapes a community’s
structure
Factors Shaping
Community Structure

Climate and topography

Available foods and resources

Adaptations of species in community

Species interactions

Arrival and disappearance of species

Physical disturbances
Niche
Sum of activities and relationships in
which a species engages to secure and
use resources necessary for survival
and reproduction
Realized &
Fundamental Niches - What???

Fundamental niche
 Theoretical
niche occupied in the absence
of any competing species

Realized niche
 Niche

a species actually occupies
Realized niche is some fraction of the
fundamental niche
Species Interactions

Most interactions are neutral; have no effect
on either species

Commensalism helps one species and has
no effect on the other

Mutualism helps both species
Species Interactions

Interspecific competition has a negative
effect on both species

Predation and parasitism both benefit
one species at a cost to another
Symbiosis

Living together for at least some part of
the life cycle

Commensalism, mutualism, and
parasitism are forms of symbiosis
Mutualism

Both species benefit

Many examples in nature

Some mutualisms are obligatory;
partners depend upon each other
Example: Mycorrhizae

Obligatory mutualism between fungus
and plant root

Fungus supplies mineral ions to root

Root supplies sugars to fungus
Example: Yucca and Yucca Moth

Example of an obligatory mutualism

Each species of yucca is pollinated only
by one species of moth

Moth larvae can grow only in that one
species of yucca
Competition

Interspecific - between species

Intraspecific - between members of the
same species

Intraspecific competition is most intense
Forms of Competition

Competitors may have equal access to
a resource; compete to exploit resource
more effectively

One competitor may be able to control
access to a resource, to exclude others
Competitive Exclusion Principle
When two species compete for identical
resources, one will be more successful
and will eventually eliminate the other
Competitive Exclusion Expt.
Protists - living together
Paramecium caudatum
Paramecium aurelia
Resource Partitioning

Apparent competitors
may actually have
slightly different niches

Species may use
resources in a different
way or time

Minimizes competition
and allows coexistence
Predation

Predators are animals that feed on other
living organisms

Predators are free-living; they do not
take up residence on their prey
Coevolution

Natural selection promotes traits that
help prey escape predation

It also promotes traits that make
predators more successful at capturing
prey
Variation in Cycles

An association in predator and prey
abundance does not always indicate a
cause and effect relationship

Variations in food supply and additional
predators may also influence changes
in prey abundance
Species Interactions
• Canadian lynx
(dashed lines)
versus
snowshoe hares
(solid line)
Prey Defenses

Camouflage

Warning coloration

Mimicry
Predator Responses

Any adaptation that protects prey may
select for predators that can overcome
that adaptation

Prey adaptations include stealth,
camouflage, and ways to avoid
chemical repellents
Parasitism

Parasites drain nutrients from their
hosts and live on or in their bodies

Natural selection favors parasites
that do not kill their host too quickly
Types of Parasites

Microparasites

Macroparasites

Social parasites

Parasitoids
Biological Controls
Parasites and parasitoids are
commercially raised and release in
target areas as biological controls
 An alternative to pesticides
 Must be carefully managed to not upset
natural balances

Study: Cowbirds

Brown-headed cowbirds evolved in the Great
Plains region of the U.S., living as
commensalists with bison
 As they migrated along with the bison, the
cowbirds learned to lay eggs in the nests of
other birds
 Cowbird hatchlings push the “host” bird eggs
out of the nest
 Today, cowbirds parasitize some 15 species
of birds
End
Succession
Change in the composition of different
of species over time
Pioneer Species

Species that colonize barren habitats - first come,
first served!

Lichens, small plants with brief life cycles

Improve conditions for other species who then
replace them

lose out to better adapted species

who themselves lost out to even better adapted species.
Types of Succession

Primary succession new environments

Secondary succession communities were destroyed or
displaced

Following hurricanes

After the tsunami
Climax Community
Eventually we arrive at the climax community

Stable array of species that persists relatively
unchanged over time

Succession does not always move
predictably toward a specific climax
community; other stable communities may
persist

Multiple outcomes.
Cyclic Changes
DYNAMIC and STABLE
 Cyclic, nondirectional changes also
shape community structure
 Tree
falls cause local patchiness in tropical
forests
 Fires
periodically destroy underbrush in
sequoia forests
Community Instability
REMEMBER

Disturbances can cause a
community to change in ways that
persist even if the change is
reversed
Keystone Species

A species that can dictate community
structure

Removal of a keystone species can
cause drastic changes in a community;
can increase or decrease diversity…
Lubchenco Experiment
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Periwinkles promote or limit diversity in different habitats
Tidepools
Rocks exposed at high tide
Species Introductions

Introduction of a nonindigenous species can
decimate a community

Just recently Hawaii has introduces Sea Stars to
control sea weed

WHY? There are;

No natural enemies or controls

Can outcompete native species
Exotic Species

Species that has left its home natural
range and become established elsewhere

Becomes part of its new community

Can have beneficial, neutral, or harmful
effects on a community…
Kudzu in Georgia
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Kudzu in Georgia
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
Imported for erosion control

No natural herbivores, pathogens, or
competitors

Grows over landscapes and cannot be
dug up or burned out
 May
turn out to have some commercial use
for humans
Caulerpa taxifolia
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Caulerpa taxifolia
Researchers developed a hybrid, sterile
strain of this green alga - for fish tanks.
 Somehow it was released into the wild,
where it reproduces asexually - down
the drain!!!
 Thrives in varying conditions and emits
a toxin that poisons invertebrates and
fishes
 Illegal to import the “aquarium” strain
into the U.S.

Rabbits in Australia
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
Rabbits were introduced for food and
hunting

Without predators, their numbers
soared

Attempts at control using fences or
viruses have thus far been unsuccessful
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Biodiversity

The sum of all species occupying a
specified area during a specified
interval, past and present
Diversity by Latitude

Diversity of most groups is greatest
in tropics; declines toward poles
 a)
ant species
 b) breeding birds
Why Are Tropical Species Rich?

Resources are plentiful and reliable

Species diversity is self-reinforcing

Rates of speciation are highest in the
tropics
Surtsey: Volcanic Island
Primary succession
Distance Effect

The farther an island is from a
mainland, the fewer species. WHY?

Closer islands receive more immigrants

Species that reach islands far from
mainland are adapted for long-distance
dispersal and can move on
Distance Effect
Endangered Species

A species that is extremely vulnerable to
extinction
 Habitat loss is putting major pressure on
more than 90 percent of the endemic species
that now face extinction
Conservation Biology
Is a systematic survey of the full range
of biological diversity
 Entails efforts to decipher biodiversity’s
evolutionary and ecological origins
 Attempt to identify methods of
maintaining and using biodiversity in
ways that can benefit the human
population

 Only
real way to save the local ecosystem
Sampling of Current Species Diversity
Areas at Risk
Preserving Biodiversity
Requires identifying and protecting
regions that support the highest levels
of biodiversity
 It is possible to protect a habitat and still
withdraw resources in a sustainable
fashion - but based on human nature it
is a risky practice!
