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Concept 18.1: Species richness differs among communities due
to variation in regional species pools, abiotic conditions, and species interactions.
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Concept 18.2: Resource partitioning among the species in a community does what?
reduces competition and increases species richness.
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Concept 18.3: Nonequilbrium processes such as ------------(3) can do what?
disturbance, stress, and predation can mediate resource availability, thus affecting species interactions and coexistence.
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Distribution and abundance of species in communities is dependent on:
1. Regional species pools and dispersal ability. 2. Abiotic conditions. 3. Species interactions.These factors act as “filters,” which exclude species from (or include species in) particular communities.
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1. The regional species pool provides
an upper limit on the number and types of species that can be present in a community.The importance of dispersal can be seen in cases of non-native species invasions.
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There are two schools of thought on how species coexist in a community:
Equilibrium theory—ecological and evolutionary compromises lead to resource partitioning.Nonequilibrium theory—fluctuating conditions keep dominant species from monopolizing resources.
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Resource partitioning—
competing species are more likely to coexist when they use resources in different ways.
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To explain how diatom species coexist in nature, he proposed the resource ratio hypothesis—
species coexist by using resources in different proportions.
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The theory of resource partitioning assumes that species have
reached a stable population size (carrying capacity) and that resources are limiting
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intermediate disturbance hypothesis
first proposed by Connell (1978):Species diversity should be highest at intermediate levels of disturbance.At low levels of disturbance, competition would determine diversity. At high disturbance levels, many species would not be able to survive.
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Evidence suggests that positive interactions are more common under
relatively high levels of disturbance, stress, or predation.
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At low levels of disturbance,
At intermediate levels,
At high levels,
- At low levels of disturbance, competition reduces diversity.At intermediate levels, species that have positive effects are released from competition and can increase diversity.At high levels, positive
- interactions are common and help to increase diversity.
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The lottery model
emphasizes the role of chance. It assumes that resources are captured at random by recruits from a larger pool of potential colonists.
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A central idea in ecology is that species diversity can control
control certain functions in a community, such as primary productivity, soil fertility, resistance to disturbance, and speed of recovery (resilience).
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A long-standing idea in ecology is that species richness is positively related to
community stability—the tendency of a community to remain the same in structure and function
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biofuels—
liquid or gas fuels from plant material (biomass).In the U.S., ethanol is made from corn, while biodiesel is made from soybeans.
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carbon neutral—
the amount of CO2 produced by burning them is matched by the amount taken up by the plants from which they are made.
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What was Hutchinson's solution to the paradox of the plankton?
Seasonal changes prevented any one species from competitively excluding the others.
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Which of the following statements about lottery models is false?
They have been applied most often to species-poor communities.
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Robert MacArthur showed that different species of warblers in New England forests
coexist because they utilize different parts of the same trees.
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In Sousa's study of succession in intertidal boulder fields in California, disturbance was _______ proportional to the size of the boulders. The highest level of species richness occurred when disturbance was _______.
inversely; at an intermediate level
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According to Hacker and Gaines's extension of the intermediate disturbance hypothesis, mutualisms and other positive interactions should _______ species diversity _______ levels of disturbance.
promote; especially at high
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What is the paradox of the plankton?
There are many more species of phytoplankton in temperate freshwater lakes than would be expected given the limited number of types of resources.
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According to the dynamic equilibrium model, species diversity is highest when disturbance is at _______ levels and competitive displacement is at _______ levels.
low to intermediate; low to intermediate
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The ability of a community to remain the same in terms of its structure and function is known as
stability
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Which of the following is a finding of Sale's studies of fishes in the Great Barrier Reef of Australia?
The pattern of site occupations appeared random.
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According to Hutchinson's paradox of the plankton, coexistence of species is likely when
competitive exclusion takes place about as rapidly as environments fluctuate.
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Based on the concept of resource partitioning, which of the following attributes of a community would tend to lead to lower species richness?
Low specialization of species
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