Concept 18.1: Species richness differs among communities due
to variation in regional species pools, abiotic conditions, and species interactions.
Concept 18.2: Resource partitioning among the species in a community does what?
reduces competition and increases species richness.
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.
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.
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.
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.
competing species are more likely to coexist when they use resources in different ways.
To explain how diatom species coexist in nature, he proposed the resource ratio hypothesis—
species coexist by using resources in different proportions.
The theory of resource partitioning assumes that species have
reached a stable population size (carrying capacity) and that resources are limiting
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.
Evidence suggests that positive interactions are more common under
relatively high levels of disturbance, stress, or predation.
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.
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.
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).
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
liquid or gas fuels from plant material (biomass).In the U.S., ethanol is made from corn, while biodiesel is made from soybeans.
the amount of CO2 produced by burning them is matched by the amount taken up by the plants from which they are made.
What was Hutchinson's solution to the paradox of the plankton?
Seasonal changes prevented any one species from competitively excluding the others.
Which of the following statements about lottery models is false?
They have been applied most often to species-poor communities.
Robert MacArthur showed that different species of warblers in New England forests
coexist because they utilize different parts of the same trees.
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
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
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.
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
The ability of a community to remain the same in terms of its structure and function is known as
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.
According to Hutchinson's paradox of the plankton, coexistence of species is likely when
competitive exclusion takes place about as rapidly as environments fluctuate.
Based on the concept of resource partitioning, which of the following attributes of a community would tend to lead to lower species richness?