Chapter #16 – Community Structure
(pg. 334 – 348)
Chapter #16 – Community Structure
(pg. 334 – 348)
16.1 –
16.2 –
16.3 –
16.4 –
16.5 –
16.6 –
16.7 –
16.8 –
16.9 –
The Number of Species and Their Relative Abundance Define
Diversity.
Numerical Supremacy Defines Dominance.
Keystone Species Have an Influence on Community Structure
Disproportionate to Their Numbers.
Food Webs Describe Species Interactions.
Species Within a Community Can Be Classified into Functional
Groups.
Communities Have a Definitive Physical Structure.
Zonation is Spatial Change in Community Structure.
Defining Boundaries Between Communities Is Often Difficult.
Two Contrasting Views of the Community.
Ecological “Lines of Dependency”
Individual to Individual
Species A
Species B
Species C
Species D
Territory, Home Range, Density
Abundance, Distribution
Species to Species
Predator-Prey
Compete (?) for access to essential resources
Species to Abiotic (non-living) Components
Soil, Topography, Weather
Chapter #16 – Community Structure
(pg. 334 – 348)
The group of species that occupy a given
area, interaction either directly or indirectly is
called a community.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.1 –
The Number of Species and Their Relative Abundance Define
Diversity.
Perhaps the simplest and easiest measure of community
structure is a count of the number of species that occur within the
community: species richness.
The percentage or rank
abundance of the species in a
community is called Relative
Abundance.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.1 –
The Number of Species and Their Relative Abundance Define
Diversity.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.1 –
The Number of Species and Their Relative Abundance Define
Diversity.
Simpson’s Index (D)
measures the
diversity and
dominance of species
in a community.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.2 –
Numerical Supremacy Defines Dominance.
When a single or
few species
predominate
within a
community, these
organisms are
referred to as
dominants.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.3 –
Keystone Species Have an Influence on Community Structure
Disproportionate to Their Numbers.
A species that has a disproportionate impact/effect
on the community relative to its abundance is
referred to as a keystone species.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.3 –
Keystone Species Have an Influence on Community Structure
Disproportionate to Their Numbers.
Creel, S. 2005. Elk Alter Habitat Selection as an Antipredator
Response to Wolves. Ecology 86(12):3387-3397.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.4 –
Food Webs Describe Species Interactions.
Each circle represents a species, each
line represents a “link”, or connection to
another species.
A – Autotrophs, H – Herbivores,
C – Carnivores, P - Predator
Chapter #16 – Community Structure
(pg. 334 – 348)
16.5 –
Species Within a Community Can Be Classified into Functional
Groups.
Guilds: another approach to grouping organisms that
derive their food energy in a similar manner. As defined,
guilds typically represent strong species interactions.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.6 –
Communities Have a Definitive Physical Structure.
Factors: in terrestrial communities, vegetation is the principle factor
governing community structure. In aquatic communities, vegetation
and the physical nature of the water (depth, temperature, flow rate,
salinity, pH, light availability) are used to define the community.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.7 –
Zonation Is Spatial Change in Community Structure.
Zonation: the changes in the physical and biological
structures of communities as one moves across the
landscape. Zonation also involves changes associated with
scale.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.7 –
Zonation Is Spatial Change in Community Structure.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.7 –
Zonation Is Spatial Change in Community Structure.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.8 –
Defining Boundaries
Between Communities Is
Often Difficult.
Chapter #16 – Community Structure
(pg. 334 – 348)
16.9 –
Two Contrasting Views of the Community.
Frederic Clements
The Organismic concept of communities
Species similar evolutionary and climatic
histories. “Succession”
Chapter #16 – Community Structure
(pg. 334 – 348)
16.9 –
Two Contrasting Views of the Community.
H. A. Gleason
The Individualistic concept of communities
Species similarities in their tolerances
and requirements, not evolutionary
history. “Gradual Change”
Chapter #16 – Community Structure
(pg. 334 – 348)
– The Ecological Niche Defines the Place and
Role of Each Species in Its Ecosystem
– Adaptations Reduce the Overlap of
Ecological Niches Among Coexisting Species
– Helps Control Population Size and
Distribution
Chapter #16 – Community Structure
(pg. 334 – 348)
Ecological Niche (fundamental and realized)
The total requirements
of a species for all
resources and physical
conditions determine
where it can live and
how abundant it can be
at any one place within
its range.
Chapter #16 – Community Structure
(pg. 334 – 348)
Ecological Niche
• Encompasses all aspects of a species’ way of
life, including
– Physical home or habitat.
– Physical and chemical environmental factors
necessary for survival.
– How the species acquires its energy and
materials.
– All the other species with which it interacts.
Chapter #16 – Community Structure
(pg. 334 – 348)
Resource Partitioning – Coexistence
Gause's Principle: no two species can coexist on
the same limiting resource.
Species avoid competition
by partitioning
resources and
habitats among
themselves.
Chapter #16 – Community Structure
(pg. 334 – 348)
Resource Partitioning
Does not desiccate
at high tide
Desiccates at
low tide.
Competition
Chapter #16 – Community Structure
(pg. 334 – 348)
Reducing Niche Overlap
• When species with
largely overlapping
niches are allowed
to compete, their
niches may focus
on a different part of
the resource spectrum.
– Example: North American Warbler Species.
Chapter #16 – Community Structure
(pg. 334 – 348)
Species – Area Curve
In general, the larger
the area, the greater
the number of
species.