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Community Ecology: Structure,
Species Interactions, Succession,
and Sustainability
G. Tyler Miller’s
Living in the Environment
13th Edition
Chapter 8
Dr. Richard Clements
Chattanooga State Technical Community College
Modified by Charlotte Kirkpatrick
Key Concepts
Community structure
Roles of species
Species interactions
Changes in ecosystems
Stability of ecosystems
Community Structure (Spatial
Distribution): Four Characteristics
Physical Appearance: Stratification,
relative sizes and distribution of its population
and species
Species diversity (richness): Number of
different species in a community
Species abundance: Number of individuals
of each species
Niche structure: number of ecological
niches, how they resemble or differ from each
other and how they interact (species interactions)
Community Structure: Appearance
and Species Diversity
The types, relative sizes, and stratification of plant species
in various terrestrial communities or ecosystems (also seen
in aquatic systems)
Fig. 8-2
p. 166
Physical Structures
• Physical structure within an ecosystem or community
can vary.
• Usually see large vegetative patches (mosaic) of
differing size in large ecosystems or communities.
• Leads to sharp edges as seen in forest and open field
or wider more diverse ecotones.
• Result of the differences in physical structure and
properties at ecotones can lead to an edge effect.
Biodiversity: factors that affect
species diversity
Latitude: diversity
Ants
Birds
decreases with increase in
latitude
Depth: diversity increase
with depth to 2000m and
decreases until the sea bottom
where species diversity is high
Fig. 8-3 and 8-4 p. 167
Biodiversity: factors that affect
species diversity
Pollution: in aquatic
Terrestrial
ecosystems:
diversity
tends to increase with
increasing solar radiation,
increasing precipitation,
decreasing elevation, and
pronounced seasonal
variations
Number of diatom species
systems diversity decreases
with increase in pollution.
Unpolluted
stream
Polluted
stream
Number of individuals per diatom species
Island Diversity
• Two factors effect isolated ecosystem (such as
an island) diversity: size and degree of
isolation (distance from mainland)
– Theory of Island Biogeography by Robert MacArthur, Edward
O. Wilson: balance between two factors
» The rate at which new species immigrate and the rate at
which species become extinct on the island
Theory of Island Biogeography
Also see fig. 8-7 pg. 169
General Types of Species
 Native: species that normally live in and thrive in a
particular ecosystem
 Non-native (exotic or alien): organisms that
migrate into an ecosystem or are accidentally or
deliberately introduced into an ecosystem Zebra mussel page
 Indicator: Species that serve as early warnings
of damage to a community or an ecosystem.
Amphibians ( see connections p. 170-171)
General Types of Species (cont.)
 Keystone: role in ecosystem of species which is
actually more influential than numbers or biomass
suggests.
 These organism play a pivotal role in the structure and
function of ecosystem because they have strong
interaction with other species that affect their health and
survival, and process material out of proportion to their
numbers or biomass.
 Critical roles: pollination, dispersion of seeds, habitat
modification, predation, improve ability of plants to
absorb nutrients and water, and efficient recycling.
 Loss of keystone species can lead to population crashes
and extinctions of other species i.e. domino effect.
Species Interactions: Competition
 Intraspecific competition: within a species
for resources and territoriality.
 Interspecific competition: between different
species for limited resources (niche overlap)
Competing species must:
Migrate to another area
Shift its feeding habits or behavior through
evolution and natural selection
Suffer a sharp decline in population
Extinction
Species Interactions: Competition
 Interference competition: one species
influences another’s access to some resource
regardless of its abundance. Ex. hummingbird
 Exploitation competition: Two competing
species have roughly equal access but differ in how
fast or efficiently they exploit it.
Species Interactions: Competition
 Competitive exclusion principle: by Gauss
describes how one species eliminates another in an area
through competition for limited resources.
High
High
Paramecium
aurelia
Relative population density
Relative population density
Paramecium
aurelia
Paramecium
caudatum
Paramecium
caudatum
Low
Low
0
2
4
6
8
10
12
14
16
18
2
4
6
10
8
12
14
16
18
Days
Days
Each species grown alone
0
Figure 8-8 (1)
Page 174
Slide 13
Both species grown together
Figure 8-8 (2)
Page 174
Slide 14
Resource Partitioning
Resource
partitioning: a method
to reduce competition,
dividing up the resource so
that species with similar
needs use them at different
times, in different ways, or in
different places.
Fig. 8-9 p. 175; Refer to Fig. 7-13 p. 152 & Fig. 8-10 p. 175
Species Interactions: Predation
Predator: feeds directly on all or part of a
living organism
Prey: organism fed on.
 Predator-prey relationship: One
organism is clearly harmed. However at the
population level there are benefits: improve access
to food, and improve the genetic stock.
Prey acquisition: herbivores vs. carnivores
(pursue or ambush)
Predator Avoidance: speed, highly
developed senses,protective coverings
Predator Avoidance by Prey
Span worm
camouflage
Poison dart frog
Chemical warfare
Warning coloration
Wandering leaf insect
camouflage
Viceroy butterfly mimics
monarch butterfly
mimicry
Bombardier beetle
Chemical warfare
Hind wings of io moth
resemble eyes of a
much larger animal
Foul-tasting monarch
butterfly
Warning coloration
When touched, the
snake caterpillar
changes shape to look
like the head of a snake
Deceptive looks Deceptive behavior
Figure 8-11
Page 177
Slide 18
Symbiotic Relationships
• Symbiosis is a relationship in which species
live together in an intimate association.
• There are three types:
– Parasitism (special form of predation)
– Mutualism
– Commensalism
Symbiotic Species Interactions:
Parasitism
Parasite: organisms that feeds on another by
living in or on another living organism. Parasite
benefits.
Host: Organism that a parasite feeds on and lives
in or on. Host is harmed. (rarely killed)
Endoparasites: parasites found inside the host
organisms body. Ex.tapeworms,disease causing
microorganisms.
Ectoparasites: organisms found outside the
host organisms body. Ex. Fleas, ticks, mosquitoes
Symbiotic Species Interactions:
Mutualism
Reproductive mutualism: pollination
Nutritional mutualism
Nutritional/protection mutualism
Fig. 8-12 p. 179
Symbiotic Species Interactions:
Commensalism
 Indirect: i.e., small
plants growing in
shade of larger plants
(redwood sorrel)
 Direct: i.e., epiphytes
(orchids and
bromeliads), remoras
Fig. 8-13 p. 180
Ecological Succession:
Communities in Transition
Primary succession
Secondary succession
Pioneer species
Successional species
Primary Succession
Fig. 8-14 p. 180
Secondary Succession
Fig. 8-15 p. 181
Succession and Wildlife
Fig. 8-16 p. 182
The Rate of Succession
Facilitation: one set of species makes an area
suitable for species with different nich
requirements.
Inhibition: early species hinder the
establishment and growth of other species.
Inhibiting species must be removed for
succession to continue
Tolerance: late successional species are
largely unaffected by plants at earlier stages of
succession
Refer to Table 8-1 p. 182
Ecological Stability and Sustainability
Disturbance: can be catastrophic or gradual;
human caused or natural. May convert a
particular stage of succession to an earlier one.
Refer to Table 8-2 p. 193
Climax community: end product of
succession; stable and predictable community
dominated by a few long-loved plant species and
in balance with its environment. Known as
balance of nature.
 This is not actually the case due to several
unpredictable small and medium-sized
disturbances.
Ecological Stability and Sustainability
Inertia (or persistence): ability of a living
system to resist being disturbed or altered.
Constancy: the ability of a living system such
as as population to keep its numbers within the
limits imposed by available resources.
Resilience: the ability of a living system to
bounce back after an external or internal
disturbance that is not too drastic.
Precautionary principle
Species Diversity and
Ecosystem Stability
• Many believe that the more diverse the ecosystem
the more stable.
• This is not completely supported. And is difficult
to determine
• Generally we find that the more species diversity
has higher net primary productivity, and more
resilient, yet population of individual species can
fluctuate.
• Some level of biodiversity is needed in various
ecosystem to provide insurance against
catastrophe. Yet, how much biodiversity is needed
for this stability.
Species Diversity and
Ecosystem Stability
• Many ecologists disagree on how to define
stability and diversity.
• Does an ecosystem need both inertia and
high resilience to be stable?
• Ex. Rain forests vs. grasslands.
• Another difficulty is that populations,
communities, and ecosystems are rarely if
ever at equilibrium.
• Instead nature is in a continuing state of
disturbance, fluctuation, and change
Precautionary Principle
• Why should we protect our natural systems
and biodiversity if it doesn’t lead to
increased stability and if nature is mostly
unpredictable?
• Precautionary principle: when evidence
indicates that an activity can harm human
health or the environment, we should take
precautionary measures to prevent harm
even if some of the cause and effect
relationships have not been fully established
scientifically.