APES Chapter 8 Notes
Community Ecology: Structure, Species Interactions,
Succession, and Sustainability
General Types of Species
Native species—species that normally live
and thrive in a particular ecosystem
 Non-native, exotic or alien species—
species that migrate into an ecosystem or
are deliberately or accidentally introduced
into an ecosystem humans.

◦ Ex: Africanized Bees, Zebra Mussels, Cane
Toad, Kudzo.
General Types of Species

Indicator species—species that serve as
early warnings that a community or
ecosystem is being damaged.
◦ Birds are excellent indicators because they
are found almost everywhere and respond
very quickly to environmental change.
◦ Some amphibians are also classified as
indicator species.
General Types of Species

Keystone species—species whose roles in
an ecosystem are much more important
than their abundance or biomass would
suggest. They play pivotal roles in the
structure, function, and integrity of an
ecosystem.
◦ Ex: sea otters, wolves, elephants, great white
shark, all pollinators.
Species Interactions:
Competition and Predation

Members of species may be harmed by,
benefit from , or by unaffected by the
interaction.
Competition
 Competition—Two
organisms
compete to obtain the same limited
resource.
◦ Intraspecific—Members of same species
competing for resources.
◦ Interspecific—Members of different species
competing for resources.
 The
more similar the competing
species, the more intense the
competition.
Species compete in two ways:

Interference—one
species limits
another’s access to
some resource by
direct contact, such
as establishing a
territory and
defending it.

Exploitation—occurs
indirectly.
Competing species
have equal access to
a specific resource
but differ in how fast
or efficiently they
exploit it.
Competition

Competitive Exclusion Principle—No two
species can occupy the same ecological
niche in the same place at the same time.
◦ Less fit species may die out or evolve into a
slightly different niche.
Resource Partitioning
Adaptations evolved to reduce or avoid
competition.
 In Resource Partitioning species with
similar needs use similar resources:

◦ 1. at different times (hunting: hawks-day,
owls-night)
◦ 2. in different ways
◦ 3. in different places
Resource Partitioning
Overlapping Niche of
2 species creates
competition
Over time, species
evolve and become
specialized
Fig. 8-9 p. 175; Refer to Fig. 7-13 p. 152 & Fig. 8-10 p. 175
Resource Partitioning
Predation

One species (predator) feeds directly on
another species (prey).
Predation

Predators increase their chances by:
◦
◦
◦
◦
◦
Running fast
Keen eyesight
Hunting in packs
Camouflage
Humans have invented tools (weapons and
traps)
Predation

Prey defend themselves against predators
by:
◦
◦
◦
◦
◦
◦
◦
Run, swim or fly fast
Keen eyesight or sense of smell
Live in herds
Protective shells or spines
Camouflage
Thick bark
Thorns
Predation
◦ Chemicals-poisonous, irritating, foul smelling,
bad tasting
◦ Warning coloration-so predators know they
are poisonous or bad tasting
◦ Mimicry-taking on the appearance of another
organism that may be very poisonous
Symbiotic Relationships

Symbiosis—Close, physical relationship
between two different species. At least one
species derives benefit from the interaction.
◦ Parasitism—One organism (parasite) living in or
on another organism (host), from which it
derives nourishment. Parasite benefits and host
is harmed.
 Ectoparasites—Live on host’s surface.
 Fleas
 Endoparasites—Live inside host.
 Tapeworms
Symbiotic Relationships

Commensalism—One organism benefits,
while the other is unaffected.
◦ Remoras and Sharks

Mutualism—Both species benefit.
Obligatory in many cases as neither can
exist without the other.
◦ Mycorrhizae
Parasitism
Mutualism
Commensilism
Community Structure

4 Characteristics:
◦ 1. Physical appearance: size, stratification, and
distribution of populations.
◦ 2. Species diversity or richness: number of
different species.
◦ 3. Species abundance: number of individuals
of each species.
◦ 4. Niche structure: number of ecological
niches.
Community Structure: Appearance and Species Diversity
Fig. 8-2
p. 166
Stratification
Species diversity
Niche structure
Edge effects
Three Factors Affecting Biodiversity

Latitude(terrestial)- the closer to the equator, the higher
the biodiversity
◦ Highest species diversity in tropics; lowest in polar regions

Ants
Depth(aquatic)- biodiversity increases with depth to
about 2000 m then begins its decrease
Pollution- as levels increase, biodiversity decreases
Birds
25
20
20
15
15
10
10
5
5
Coast
0
0
Fig. 8-3 p. 167
25
Snails
Species diversity

2,000
Deep Sea
4,000
Depth (meters)
0
6,000 0
Tube worms
Coast
2,000
Deep Sea
4,000
Depth (meters)
6,000
Island Biodiversity

© 2004 Brooks/Cole – Thomson Learning
Rate of immigration
or extinction
High
Theory of Island
Biodiversity-the
number of species
found on an island is
determined by:
1. Species immigration
Low
Equilibrium number
Number of species on island
Immigration
(a)
and extinction rates
 Immigration- movement
of organisms into a place
 Emigration- movement
of organisms out of a
place
2. Species extinction
Communities in Transition
Ecological Succession—the gradual
and fairly predictable change in species
composition of a given area over a period
of time.
 Climax community—Stable, longlasting community, primarily determined
by climate.

Succession
 Primary
Succession—Begins with
bare mineral surfaces or water and total
lack of organisms.
 Secondary Succession—Begins with
disturbance of an existing ecosystem.
◦ Much more commonly observed.
Primary Succession

Terrestrial Primary Succession
◦ Pioneer Community: Collection of organisms
able to colonize bare rock
(i.e. lichens, mosses).
◦ Lichens help break down rock, and
accumulate debris helping to form a thin soil
layer.
◦ Soil layer begins to support small life forms.
Terrestrial Primary Succession
Aquatic Primary Succession
Except for oceans, most aquatic systems
are considered temporary.
 All aquatic systems receive inputs of soil
particles and organic matter from
surrounding land.

◦ Gradual filling of shallow bodies of water.
 Roots and stems below water accumulate more
material.
 Wet soil established.
Aquatic Primary Succession
Secondary Succession
Occurs when an existing community is
disturbed or destroyed.
 With most disturbances, most of the soil
remains, and many nutrients necessary for
plant growth may be available for
reestablishment of the previous
ecosystem.

◦ Nearby undamaged communities can serve as
sources of seeds and animals.

Tends to be more rapid than primary
growth.
Terrestrial Secondary Succession
Secondary Succession of a Beaver
Pond
Modern Concepts of Succession and
Climax

As settlers changed “original” ecosystems
to agriculture, climax communities were
destroyed.
◦ Many farms were abandoned, and land began
to experience succession.

Ecologists began to recognize there was
not a fixed, pre-determined community.
◦ Only thing differentiating climax community
from successional community is time scale.