chapter # 16 – community structure (pg. 334 – 348)

Chapter #16 – Community Structure(pg. 334 – 348)


16.1 – The Number of Species and Their Relative Abundance Define Diversity.

16.2 – Numerical Supremacy Defines Dominance.

16.3 – Keystone Species Have an Influence on Community Structure Disproportionate to Their Numbers.

16.4 – Food Webs Describe Species Interactions.

16.5 – Species Within a Community Can Be Classified into Functional Groups.

16.6 – Communities Have a Definitive Physical Structure.

16.7 – Zonation is Spatial Change in Community Structure.

16.8 – Defining Boundaries Between Communities Is Often Difficult.

16.9 – Two Contrasting Views of the Community.

Individual to IndividualTerritory, Home Range, DensityAbundance, Distribution

Species to SpeciesPredator-PreyCompete (?) for access to essential resources

Species to Abiotic (non-living) ComponentsSoil, Topography, Weather

Species A Species B

Species C Species D

Ecological “Lines of Dependency”


The group of species that occupy a given area, interaction either directly or indirectly is called a community.



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 rankabundance of the species in a community is called RelativeAbundance.



Simpson’s Index (D)

measures the diversity and dominance of species in a community.

16.2 – Numerical Supremacy Defines Dominance.


When a single or few

species predominate

within a community,

these organisms

are referred to as

dominants.



A species that has a disproportionate impact/effect on the community relative to its abundance is referred to as a keystone species.



Creel, S. 2005. Elk Alter Habitat Selection as an Antipredator Response to Wolves. Ecology 86(12):3387-3397.


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


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.


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.


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.


16.7 – Zonation Is Spatial Change in Community Structure.


16.8 – Defining Boundaries Between Communities Is Often Difficult.



Frederic Clements The Organismic concept of communities

Species similar evolutionary and climatic histories.

“Succession”



H. A. Gleason The Individualistic concept of communities

Species similarities in their tolerances and requirements,

not evolutionary history. “Gradual Change”

– 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


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.


• 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.

Ecological Niche


Resource Partitioning – CoexistenceGause's Principle: no two species

can coexist on the same limiting resource.Species avoid competitionby partitioningresources andhabitats amongthemselves.



Resource Partitioning

Desiccates atlow tide.

Does not desiccateat high tide

Competition

• When species withlargely overlappingniches are allowedto compete, theirniches may focuson a different part ofthe resource spectrum.

– Example: North American Warbler Species.

Reducing Niche Overlap


Species – Area Curve

In general, the larger the area, the greater the

number of species.


chapter # 16 – community structure (pg. 334 – 348)

Documents

community structurepg

community relative

number of species

keystone species

dominance of species

species richness

group of species

strong species interactions