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?
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?
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
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?
- 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?
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?
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?
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
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
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?
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?