Ch 54 - Community Ecology

What is a biological community?

An assemblage of populations of various species living close enough for potential interaction

What are interspecific interactions?

Relationships between species in a community

What is competition?

-/- interaction
Occurs when species compete for a resource that limits survival and reproduction
- Resources must be in short supply for competition to occur

What is competitive exclusion?

Local elimination of a competing species

What is an ecological niche?

The sum of an organism's use of biotic and abiotic resources
- Ecological role

What is resource partitioning?

Differentiation of ecological niches, enabling similar species to coexist in a community

What is a species' fundamental niche?

The niche potentially occupied by that species

What is a species' realized niche?

The niche actually occupied by that species

What is character displacement?

A tenancy for characteristics to be more divergent in sympatric populations of 2 species than in allopatric populations of the same 2 species

What is exploitation?

Any +/- interaction in which one species benefits by feeding on the other species

What are the 3 kinds of exploitative interactions?

- Predation
- Herbivory
- Parasitism

What is predation?

A +/- interaction in which one species, the predator, kills and eats the other, the prey

What is aposematic coloration?

Bright warning coloration on animals with effective chemical defenses

What is cryptic coloration?


What is Batesian mimicry?

When a palatable or harmless species mimics an unpalatable or harmful model

What is Mullerian mimicry?

When 2+ unpalatable species resemble each other

What is herbivory?

+/- interaction in which a herbivore eats parts of a plant or alga

Are most herbivores vertebrates or invertebrates?


What defenses to plants have against herbivores?

They may produce toxic or distasteful chemicals or mechanical defenses, such as spines or thorns

What is parasitism?

A +/- interaction in which one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process

What are endoparasites?

Parasites that live within the body of their host

What are ectoparasites?

Parasites that live on the external surface of a host

What is mutualism?

+/+ interaction that is a common interspecific interaction that benefits both species
- Both species incur costs, but the benefits to each partner exceed the costs

What is commensalism?

+/0 interaction in which one species benefits and the other is neither harmed nor helped
- Some interactions that are typically commensal may at times be mutualistic

Positive interactions can have (significant/insignificant) influence on the structure of ecological communities


Two-species interactions are classified by the impact each species has on the other. Thus, a competitive interaction is one where the populations of each species are negatively impacted by the presence of the other species, usually because each species us

Avoiding direct competition

Which of the following best describes resource partitioning?
A. 2 species can co-evolve to share identical niches
B. Competitive exclusion results in the success of the superior species
C. A climax community is reached when no new niches are available

D. Slight variations in niche allow similar species to coexist

What is one difference between the fundamental niche and the realized niche?

Individuals will be found only in the realized niche

How might an ecologist test whether a species is occupying all of its fundamental niche or only a portion of it?

Observe if the species expands its range after the removal of a competitor

If 2 species are close competitors and one species is experimentally removed from the community, the remaining species would be expected to...

Expand its realized niche

The common spiny mouse and the golden spiny mouse can occupy essentially the same ecological niche in Rocky Habitats of the Middle East and China. They accomplish this by...

Temporal niche partitioning

Character displacement...
A. Can be observed in sympatric populations of 2 species
B. Is usually observed in allopatric populations of 2 species
C. Is usually observed for 2 species living in widely separated habitats
D. Is the result of niche partitionin

A. Can be observed in sympatric populations of 2 species

An obligate mutualism is an interaction in which at least one species cannot survive without the presence of the other species; a facultative mutualism is an interaction that benefits both species but is not required by either species. One reason facultat

E. In an obligate mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct

What are 2 fundamental features of community structure?

- Species diversity
- Feeding relationships

What is species diversity?

The variety of organisms that make up the community

What 2 components make up species diversity?

- Species richness
- Relative abundance

What is species richness?

The number of different species in a community

What is relative abundance?

The proportion each species represents of all individuals in the community

What are 4 advantages of communities with higher diversity?

- More productive; produce more biomass
- More stable in their productivity
- Better able to withstand and recover from environmental stresses
- More resistant to invasive species

What is trophic structure?

The feeding relationships between organisms in a community

What are food chains?

Link trophic levels from producers to top carnivores

What are trophic levels?

The position an organism occupies in a food chain

What is a food web?

A group of food chains linked together forming complex trophic interactions

What is the energetic hypothesis?

Suggests that length of each food chain is limited by inefficient energy transfer

How much of the energy stored in organic matter at each tropic level is converted to organic matter at the next trophic level?


What are dominant species?

Those that are most abundant or have the highest biomass

Why might invasive species become dominant?

They lack natural predators or parasites

How could you discover the impact of a dominant species?

Remove it from the community

What are keystone species?

Exert strong control on a community by their ecological roles, or niches
- Not usually abundant, unlike dominant species

What are ecosystem engineers?

Foundation species"
- Cause physical changes in the environment that affect community structure

What is the bottom-up model?

Proposes a unidirectional influence from lower to higher trophic levels

What is the top-down model?

AKA trophic cascade model
- Proposes that control comes from the trophic level above

What is biomanipulation?

Can help restore polluted communities

What view was supported by F. E. Clements?

- Plant communities had only one state of equilibrium, a climax community, controlled by climate
- Suggested that biotic interactions caused species in a climax community to function as a superorganism

What did A. G. Tansley argue?

Variation in abiotic conditions created many possible stable communities within a region

How did H. A. Gleason view communities?

Viewed communities as chance assemblages of species with similar abiotic requirements

What is a disturbance?

An event that changes a community, removes organisms from it, and alters resource availability

What is the nonequilibrium model?

Describes communities as constantly changing after disturbance

What 2 natural events are significant sources of disturbance in many ecosystems?

Storms and fires

What is the intermediate disturbance hypothesis?

Moderate levels of disturbance can foster greater diversity than either high or low levels

What do high levels of disturbance exclude?

Slow-growing species

What do low levels of disturbances allow?

Allow dominant species to exclude less competitive species

What is ecological succession?

The sequence of changes in community composition following a disturbance

What is primary succession?

Occurs where no soil exists when succession begins

What provides a valuable field-research opportunity for observing primary succession?

Retreating glaciers

What is succession the result of?

Changes induced by vegetation

What is secondary succession?

Begins in an area where soil (and a legacy) remains after a disturbance

What has the greatest impact on biological communities worldwide?


What are 2 key biogeographic factors that affect the species diversity of biological communities?

Latitude and area

Where is species richness especially great?


What are 2 key factors affecting latitudinal gradients of species richness

Evolutionary history and climate

Why might tropical environments have greater species richness?

There has been more time for speciation to occur

What are 2 main climatic factors correlated with biodiversity in terrestrial communities?

- Sunlight
- Precipitation

What is evapotranspiration?

The evaporation of water from soil plus transpiration of water from plants

What idea does the species-area curve quantify?

A larger geographic area has more species

What is the island equilibrium model?

Species richness on islands represents a balance between immigration of new species and extinction of established species

In the island equilibrium model, what are immigration and extinction affected by?

- Island size
- Distance from mainland

As the number of species on an island increases, what happens to immigration and extinction?

- Immigration decreases
- Extinction increases

(Smaller/Larger) islands have lower immigration rates and higher extinction rates


Islands (closer to/farther from) the mainland have higher immigration rates and lower extinction rates

closer to

How are zoonotic pathogens transferred?

From humans to other animals

Disturbance is an important component of succession because it

tends to promote early successional stages

Disturbance is hypothesized to be the most beneficial in terms of increasing biodiversity at

moderate levels

A unidirectional influence on biomass from lower to higher trophic levels is called

a bottom-up model

Some birds follow moving swarms of army ants in the tropics. As the ants march along the forest floor hunting insects and small vertebrates, birds follow and pick off any insects or small vertebrates that fly or jump out of the way of the ants. This situa


Which of the following defines mutualism?
A. -/-
B. +/-
C. +/+
D. +/0
E. 0/0

C. +/+

Plants growing beneath and completely dependent upon the shade and dim light provided by the canopy of tall trees is an example of which kind of species interaction?