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BILD 3 Lecture 14
Community Ecology
52
Biology
Undergraduate 1
11/28/2010

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Term
Biological Community
Definition
an assemblage of populations of various species living close enough for potential interaction
Term
Community Concepts
Definition
Integrated Hypotheses (Clements) and Individualistic Hypotheses (Gleason)
Term
Integrated Hypotheses
Definition
A community is an assemblage of closely linked species, locked into association by mandatory biotic interactions
-Predicts that the presence or absence of particular
species depends on the presence or absence of
other species
-One should see sharp ecotones between distinct
communities with little overlap in the species present in alternative communities
Term
Individualistic Hypotheses
Definition
Proposes that communities are loosely organized associations of independently distributed species with the same abiotic requirements
-Predicts that each species is distributed according to its tolerance ranges for abiotic factors
Term
Populations in a community are potentially linked by
Definition
interspecific interactions
-A community’s interactions include competition, predation, herbivory, symbiosis, and disease
Term
Interspecific competition
Definition
occurs when species compete for a particular resource
Term
Strong competition can lead to
Definition
competitive exclusion
-the local elimination of one of the two competing species
Term
Gause studied competition in laboratory experiments using
Definition
Paramecium species
-Each species, when alone, shows logistic growth to a carrying capacity
-When both species are present, one is driven to extinction by the other
-Conclusion: two species cannot coexist if their niches are too similar
Term
The Competitive Exclusion Principle
Definition
States that two species competing for the same limiting resources cannot coexist in the same place
Term
Ecological Niche
Definition
The ecological niche is the multidimensional space that an organism occupies. The dimensions of the niche include abiotic factors as well as biotic resources and interactions
-Two Types: Fundamental and Realized
Term
Fundamental niche
Definition
is the space occupiable in the absence of biotic interactions
Term
Realized niche
Definition
is the space the organism actually occupies
Term
As a result of competition
Definition
a species' fundamental niche may be different from its realized niche
Term
The Niche concept allows restatement of the
Definition
competitive exclusion principle
-two species cannot coexist in a community if their niches are identical
Term
Ecologically similar species can coexist in a community only if
Definition
there is one or more significant difference in their niches
Term
Resource Partitioning
Definition
the differentiation of niches that enables similar species to coexist in a community
Term
Character Displacement
Definition
-The tendency for characteristics to be more divergent in sympatric populations than in allopatric populations of the same two species
-Evidence of divergence due to competition
Term
Predation
Definition
predator and prey populations can strongly interact (eg. lynx and hare)
-Predation shapes many attributes of both predators and prey:
-Claws, teeth, fangs, stingers, and poison of predators
-crypsis, mimicry, shells, speed, sensory capabilities of prey
Term
Cryptic coloration, or camouflage makes prey
Definition
difficult to spot
Term
Aposematic coloration
Definition
warns predators to stay away from prey
Term
Batesian mimicry
Definition
a palatable or harmless species mimics an unpalatable or harmful model
-ex. hawkmoth larva, green parrot snake
Term
Mullerian mimicry
Definition
two or more unpalatable species resemble each other
Term
Herbivory
Definition
the process in which an herbivore eats parts of a plant
-Has led to the evolution of plant mechanical and chemical defenses and consequent adaptations by herbivores
Term
Parasitism
Definition
one organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process
-ex Cymothoa exigua and the rose snapper; parasite replaces rose snappers tongue to share food
Term
Mutualism (+/+)
Definition
an interspecific interaction that benefits both species
-Mutualisms are systems of mutual exploitation and can break down into interactions that benefit one player at the expense of the other
Term
Ant - acacia mutualism
Definition
-tree provides food, nest sites for ants
-ant provides tree protection from competitors, herbivores
Term
Commensalism (+/0)
Definition
one species benefits and the other is not affected
Term
Two components of Species Diversity
Definition
-number of species
-relative abundance of each species (evenness)
Term
Trophic Structure
Definition
the feeding relationship between organisms in a community
-is a key factor in community dynamics
-food chains, food webs, or trophic pyramids
Term
Food Chains
Definition
link the trophic levels from producers to top carnivores
-usually only a few links long
-in many studies, there is a correlation between productivity and food chain length
Term
Food Webs
Definition
a branching food chain with complex trophic interactions
Term
Certain species have an especially large impact on the structure of entire communities either because
Definition
they are highly abundant or because they play a pivotal role in community dynamics
-dominant and keystone species
Term
Dominant Species
Definition
-Are those species in a community that are most abundant or have the highest biomass
-Exert powerful control over the occurrence and distribution of other species
Term
Keystone Species
Definition
-Are not necessarily abundant in a community
-Exert strong control on a community by their ecological roles, or niches
Term
Ecosystem 'Engineers' (Foundation Species)
Definition
Some organisms exert their influence by causing physical changes in the environment that affect community structure
Term
Some foundation species act as
Definition
facilitators
-have positive effects on the survival and reproduction of some of the other species in the community
Term
2 Models of control that communities can be subjected to
Definition
bottom-up and top-down controls, or both
Term
Bottom-up model
Definition
-Proposes a unidirectional influence from lower to higher trophic levels
-in this case, the presence or absence of abiotic nutrients
determines community structure, including the abundance of primary producers
Term
Top-down model
Definition
-Proposes that control comes from the trophic level
above
-The effects of top down control vary with the length of the food chain
Term
Disturbance
Definition
-Is an event that changes a community
-Removes organisms from a community
-Alters resource availability
-Fire: Is a significant disturbance in most terrestrial ecosystems and is often a necessity in some communities (helps eradicate dead grass)
Term
The large-scale fire in Yellowstone National Park in 1988
Definition
Demonstrated that communities can often respond very rapidly to a massive disturbance
Term
Ecological Succession
Definition
orderly build-up of a community following disturbance and may proceed by any or a combination of tolerance, facilitation, and inhibition
-Diversity might be highest at intermediate rates of disturbance
Term
Primary Succession
Definition
Occurs where no soil exists when succession
begins
-retreating glaciers provide a valuable field-research opportunity on this type of succession
Term
Secondary Succession
Definition
Begins in an area where soil remains after a disturbance
Term
three models of succession
Definition
Facilitation, Inhibition, Tolerance
-Facilitation: Early arriving species may facilitate the appearance of later species by making the environment more favorable
-Inhibition: Early arriving species may inhibit establishment of later species
-Tolerance: Early arriving species have no impact on later arriving species
Term
Intermediate disturbance hypothesis
Definition
-Suggests that moderate levels of disturbance can
foster higher species diversity than low or high
levels of disturbance
-Frequently-disturbed habitats harbor primarily early
successional species
-Rarely-disturbed habitats harbor primarily climax
species
-Intermediate disturbance levels lead to highest levels of diversity
Term
Two Key factors correlated with a community's species diversity
Definition
-geographic location (for instance latitude)
-size
Term
Species richness generally declines along an
Definition
along an equatorial-polar (latitudinal) gradient
-Diversity is usually highest near the equator (tropics) and declines toward the poles
-Many factors may contribute to this pattern including: Greater age of tropical environments (more time for the evolution of species) and Greater Productivity in the tropics due to greater sunlight and water availability
Term
two main climatic factors correlated with biodiversity
Definition
temperature, solar energy input and water availability which are combined in measures of evapotranspiration
-*correlation need not imply causation*
Term
Latitudinal gradients in species richness may have both
Definition
historical and ecological determinants
Term
Species-area curve quantifies the idea that
Definition
All other factors being equal, the larger the geographic area sampled, the greater the number of species
Term
Equilibrium Model of Island Biogeography
Definition
Species richness on islands represents a balance between the rates of immigration and extinction
-explains variation in the species diversity of islands through the effects of island size and distance from source populations.
-Size of island affects both immigration and extinction rates
• Larger islands have higher rates of immigration and lower rates of extinction
-Distance from the source (mainland) affects immigration rates
• Immigration more frequent if island nearer mainland
-ex. Species richness increases with island size in the Galapagos and many other archipelagos
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