Download Ch. 6Community Ecology - DVUSDEnvironmentalScience

Chapter 6
Community Ecology,
Population Ecology, and
Stability
Chapter Overview Questions
 What
determines the number of species in a
community?
 How can we classify species according to
their roles in a community?
 How do species interact with one another?
 How do communities respond to changes in
environmental conditions?
 Does high species biodiversity increase the
stability and sustainability of a community?
Core Case Study:
Why Should We Care about the
American Alligator?
 Hunters
wiped out
population to the
point of near
extinction.
 Alligators have
important ecological
role.
Core Case Study:
Why Should We Care about the
American Alligator?
 Dig

deep depressions (gator holes).
Hold water during dry spells, serve as refuges
for aquatic life.
 Build


nesting mounds.
provide nesting and feeding sites for birds.
Keeps areas of open water free of vegetation.
 Alligators

are a keystone species:
Help maintain the structure and function of the
communities where it is found.
COMMUNITY STRUCTURE AND
SPECIES DIVERSITY
 Biological
communities differ in their structure
and physical appearance.
Species Diversity and Niche
Structure: Different Species Playing
Different Roles
 Biological
communities differ in the types and
numbers of species they contain and the
ecological roles those species play.

Species diversity: the number of different
species it contains (species richness) combined
with the abundance of individuals within each of
those species (species evenness).
Species Diversity and Niche Structure
 Niche
structure: how many potential
ecological niches occur, how they resemble
or differ, and how the species occupying
different niches interact.
 Geographic location: species diversity is
highest in the tropics and declines as we
move from the equator toward the poles.
TYPES OF SPECIES
 Native,
nonnative, indicator, keystone, and
foundation species play different ecological
roles in communities.
1. Native: those that normally live and thrive in a
particular community.
2. Nonnative species: those that migrate,
deliberately or accidentally introduced into a
community.
3. Indicator Species:
Biological Smoke Alarms
 Species
that serve as early warnings of
damage to a community or an ecosystem.

Presence or absence of trout species because
they are sensitive to temperature and oxygen
levels.
4. Keystone Species: Major Players
 Keystone
species help determine the types
and numbers of other species in a
community thereby helping to sustain it.
Foundation Species:
Other Major Players
 Expansion
of keystone species category.
 Foundation species can create and enhance
habitats that can benefit other species in a
community.

Elephants push over, break, or uproot trees,
creating forest openings promoting grass growth
for other species to utilize.
Case Study p. 108-109:
Why are Amphibians Vanishing?
 Frogs
serve as indicator species because
different parts of their life cycles can be easily
disturbed.
Case Study:
Why are Amphibians Vanishing?
 Habitat
loss and fragmentation.
 Prolonged drought.
 Pollution.
 Increases in ultraviolet radiation.
 Parasites.
 Viral and Fungal diseases.
 Overhunting.
 Natural immigration or deliberate introduction
of nonnative predators and competitors.
SPECIES INTERACTIONS:
COMPETITION AND PREDATION
How can species avoid competition or
predation?


Species can interact through competition,
predation, parasitism, mutualism, and
commensalism.
Some species evolve adaptations that allow
them to reduce or avoid competition for
resources with other species (resource
partitioning).
Resource Partitioning
 Each
species minimizes
competition with the others
for food by spending at
least half its feeding time
in a distinct portion of the
spruce tree and by
consuming somewhat
different insect species.
Niche Specialization
 Niches
become
separated to
avoid competition
for resources.
SPECIES
INTERACTIONS:
PREDATION
 Some
prey escape
their predators or
have outer
protection, some
are camouflaged,
and some use
chemicals to repel
predators.
(a) Span worm - camouflage
(b) Wandering leaf insect - camouflage
(c) Bombardier beetle – chemical warfare
(d) Foul-tasting monarch butterfly
(e) Poison dart frog
(f) Viceroy butterfly mimics
monarch butterfly – mimicry
(g) Hind wings of Io moth
resemble eyes of a much
larger animal.
(h) When touched, snake
caterpillar changes shape
to look like head of snake.
SPECIES INTERACTIONS:
PARASITISM, MUTUALISM, AND
COMMENSALIM
 Parasitism
occurs when one species feeds
on part of another organism.
 In mutualism, two species interact in a way
that benefits both.
 Commensalism is an interaction that
benefits one species but has little, if any,
effect on the other species.
Parasites: Sponging Off of Others
 Although
parasites can harm their hosts, they
can promote community biodiversity.



Some parasites live in host (micororganisms,
tapeworms).
Some parasites live outside host (fleas, ticks,
mistletoe plants, sea lampreys).
Some have little contact with host (dump-nesting
birds like cowbirds, some duck species)
Mutualism: Win-Win Relationship
 Two
species
can interact in
ways that
benefit both of
them.
(a) Oxpeckers and black rhinoceros
(b) Clownfish and sea anemone
(c) Mycorrhizal fungi on juniper seedlings
in normal soil
(d) Lack of mycorrhizal fungi on juniper seedlings
in sterilized soil
Commensalism: Using without Harming
 Some
species
interact in a way
that helps one
species but has
little or no effect
on the other.
ECOLOGICAL SUCCESSION:
COMMUNITIES IN TRANSITION
 New
environmental conditions allow one
group of species in a community to replace
other groups.
 Ecological succession: the gradual change
in species composition of a given area


Primary succession: the gradual establishment
of biotic communities in lifeless areas where
there is no soil or sediment.
Secondary succession: series of communities
develop in places containing soil or sediment.
Primary Succession:
Starting from Scratch
 Primary
succession
begins with an
essentially
lifeless are
where there is
no soil in a
terrestrial
ecosystem
Primary Succession
Lichens on rocks
Shrubs and grasses grow
in cracks created by lichen
Each stage accumulates soil and organic material
that facilitates the growth of the next stage
Pre-eruption
Volcanic Eruptions
Mt. St. Helen’s
Pyroclastic Flow area
1981
1985
1995
2004
25 years after eruption
In the blast area
1978
1981
1985
2004
Secondary Succession:
Starting Over with Some Help
 Secondary
succession
begins in an
area where
the natural
community
has been
disturbed.
ECOLOGICAL STABILITY AND
SUSTAINABILITY
 Having
many different species appears to
increase the sustainability of many
communities.
 Human activities are disrupting ecosystem
services that support and sustain all life and
all economies.
Changes in Population Size:
Entrances and Exits
 Populations
increase through births and
immigration
 Populations
emigration
decrease through deaths and
Age Structure: Young Populations
Can Grow Fast
 How
fast a population grows or declines
depends on its age structure.



Prereproductive age: not mature enough to
reproduce.
Reproductive age: those capable of
reproduction.
Postreproductive age: those too old to
reproduce.
Limits on Population Growth:
Biotic Potential vs. Environmental
Resistance
 No
population can increase its size
indefinitely.


The intrinsic rate of increase (r) is the rate at
which a population would grow if it had unlimited
resources.
Carrying capacity (K): the maximum population
of a given species that a particular habitat can
sustain indefinitely without degrading the habitat.
Exponential and Logistic Population
Growth: J-Curves and S-Curves
 Populations
grow rapidly with
ample
resources, but
as resources
become limited,
its growth rate
slows and levels
off.
Exponential and Logistic Population
Growth: J-Curves and S-Curves
 As
a population
levels off, it
often fluctuates
slightly above
and below the
carrying
capacity.
S-Curve
Exceeding Carrying Capacity: Move,
Switch Habits, or Decline in Size
 Members
of
populations which
exceed their
resources will die
unless they adapt or
move to an area with
more resources.
Exceeding Carrying Capacity: Move,
Switch Habits, or Decline in Size
 Switch
Habits: Over time species may
increase their carrying capacity by developing
adaptations.
 Move: Some species maintain their carrying
capacity by migrating to other areas.
 So far, technological, social, and other
cultural changes have extended the earth’s
carrying capacity for humans.
Population Density and Population
Change: Effects of Crowding
 Population
density: the number of individuals
in a population found in a particular area or
volume.

A population’s density can affect how rapidly it
can grow or decline.
• e.g. biotic factors like disease

Some population control factors are not affected
by population density.
• e.g. abiotic factors like weather
REPRODUCTIVE PATTERNS
 Some
species reproduce without having sex
(asexual).

Offspring are exact genetic copies (clones).
 Others



reproduce by having sex (sexual).
Genetic material is mixture of two individuals.
Disadvantages: males do not give birth, increase
chance of genetic errors and defects, courtship
and mating rituals can be costly.
Major advantages: genetic diversity, offspring
protection.
Sexual Reproduction: Courtship
 Courtship
rituals
consume time and
energy, can transmit
disease, and can
inflict injury on males
of some species as
they compete for
sexual partners.
Reproductive Patterns:
Opportunists and Competitors
 Large
number of
smaller offspring with
little parental care (rselected species).
 Fewer, larger
offspring with higher
invested parental
care (K-selected
species).
Reproductive Patterns
 r-selected
species tend to be opportunists
while K-selected species tend to be
competitors.
Cockroach
r-Selected Species
Dandelion
Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental
conditions
High population growth rate (r)
Population size fluctuates wildly above and below
carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species
K-Selected Species
Elephant
Saguaro
Fewer, larger offspring
High parental care and protection
of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental
conditions
Lower population growth rate (r)
Population size fairly stable and usually close to
carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
Case Study: Exploding White-Tailed
Deer Populations in the United States
 Since
the 1930s the white-tailed deer
population has exploded in the United States.

Nearly extinct prior to their protection in 1920’s.
 Today
25-30 million white-tailed deer in U.S.
pose human interaction problems.


Deer-vehicle collisions (1.5 million per year).
Transmit disease (Lyme disease in deer ticks).