Chapter 47 Cloze Notes
Overview: What Is a Community?
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A biological community:
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The various animals and plants surrounding this watering hole are all members of a savanna community in southern
Africa
An example of a community (more
than one population together)
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Concept 53.1: A community’s interactions include _____________________, ______________________,
_______________________ symbiosis, and disease
__________________________ are linked by interspecific interactions
That affect the_________________ and _____________________________ of the species engaged in the
interaction
_____________________________interactions can have differing effects on the populations involved
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Competition
 Interspecific competition occurs when species compete for a particular resource that is in
_______________________supply
 Strong competition can lead to ________________________________ the local elimination of one of the two
competing species
 Competitive Exclusion Principle:
Ecological Niches
 The ecological niche:
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If an organism’s “__________________________” and the habitat it its “______________________”.
An organism’s niche is its ______________________________– how it “fits into” an ecosystem
The ___________________concept allows restatement of the competitive exclusion principle
Two species cannot___________________ in a community if their niches are ________________
However, ecologically similar species can _______________________ in a community--if there are one or more
significant difference in their niches
As a result of competition a species’ _________________________ may be different from its
________________________
Fundamental Niche:
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Realized Niche:
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Resource Partitioning
 __________________________________ is the differentiation of niches that enables similar species to coexist in a
community
Seven species of Anolis lizard
live in close proximity, and
feed on insects and other
small arthropods. However,
competition for food is
reduced because each has a
different perch, thus
occupying a distinct niche
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Character Displacement
 In __________________________ there is a tendency for characteristics to be more divergent in sympatric
populations of two species than in allopatric populations of the same two species
An example is the variation
in beak size between
different population of the
Galapagos finches.
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Predation
 Predation refers to an interaction where one species, the _____________________, kills and eats the other,
the______________________
 Feeding adaptations of predators include_______________________________________________
 Animals also display a great variety of ____________________________________________
 ______________________________ or camouflage makes prey difficult to spot
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___________________________________________warns predators to stay away from prey
In some cases, one prey species may gain significant protection by _______________________________ the
appearance of another
In ___________________mimicry apalatable or harmless species mimics an unpalatable or harmful model
Larva weaves head back
and forth and hisses like
a snake.
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In ______________________________ mimicry two or more unpalatable species resemble each other
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Herbivory
 _____________________________, 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
Parasitism
 In parasitism, one organism, the___________________________ derives its nourishment from another organism, its
___________________, which is harmed in the process
 _____________________ exerts substantial influence on populations and the structure of communities
Three types of parasites
 _____________________________: parasites that live within the body of their host, such as tapeworms and
malarial parasites
 ______________________: parasites that feed on the external surface of host, such as ticks and lice
 _________________________: Insects – usually small wasp-lay eggs on or in living host. The larvae then feed on
the body of the host, eventually killing it.
Disease
 The effects of _________________________ on populations and communities is similar to that of parasites
 Pathogens, disease-causing agents are typically ____________________________________
Mutalism
 Mutualistic symbiosis, or______________ is an interspecific interaction that
_______________________________ species
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Commensalism
 In commensalism one species ____________________ and the other is not _________________
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Commensal interactions have been difficult to document in nature because any close association between
species likely affects __________________________
Interspecific Interactions and Adaptations
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Evidence for ______________________ which involves reciprocal genetic change by interacting populations, is
scarce
 However, generalized___________________________ of organisms to other organisms in their environment is
a fundamental feature of life
 Concept 53.2: Dominant and _______________________________ exert strong controls on community
structure
 In general, a small number of _______________________ in a community exert strong control on that
community’s structure, particularly on the composition, relative abundance, and diversity of its species.
Species Diversity
 The _________________________________________ of a community is the variety of different kinds of
organisms that make up the community
 Has two components:
o _____________________________________ is the total number of different species in the community
o ____________________________________is the proportion each species represents of the total
individuals in the community
 Two different communities can have the same __________________________, but a different
_________________________________
Ecologist would say that
community 1 has greater
species diversity, a measure
that includes both species
richness and relative
abundance
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A _____________________________ with an even species abundance is more diverse than one in which one or
two species are abundant and the remainder rare
Trophic Structure
 __________________________________ is the feeding relationships between organisms in a community
 The transfer of food energy up the trophic levels from its source in plants and other photosynthetic organism
(___________________________) through ____________________________(primary consumers) to
__________________________(secondary and tertiary consumers) is a key factor in community dynamics
Food Chains
 Link the _____________________________levels from producers to top carnivores
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Food Webs
 _____________________________________Is a branching food chain with complex trophic interactions
Example of a
food web
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Food webs can be simplified by ______________________ a portion of a community that interacts very little
with the rest of the community
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Limits on Food Chain Length
 Each food chain in a food web is usually only a few links long (about ________________________________)
 There are two hypotheses that attempt to explain food chain length
 1- The energetic hypothesis suggests that the length of a food chain is limited by the inefficiency of
____________________ along the chain
 Hypothesis predicts that food chains should be relatively longer in habitats of higher
__________________________________
 Generally known as the 10% Law:
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2- The dynamic stability hypothesis proposes that long food chains are __________________ than short ones
___________________ fluctuations at lower trophic levels are magnified at higher levels potentially causing the
local extinction of top predators.
In variable environment, top predators must be able to recover from environmental shocks (such as extreme
winters) that can reduce the ___________________________ all the way up the food chain.
Most of the available data support the energetic hypothesis
Species with a Large Impact
 Certain __________________________ have an especially large impact on the structure of entire communities
either because they are highly abundant or because they play a pivotal role in ___________________________
Dominant Species
 ____________________________ are those species in a community that are most abundant or have the highest
biomass (the total mass of all individuals in a population)
 Exert powerful control over the occurrence and ________________________ of other species
 Example: Sugar maples in North American forest communities has major impact on______________________
factors such as shading and soil, which in turn affect which other species live there
 There is no single explanation for why a species becomes dominant in a community.
 One hypothesis suggests that dominant species are most competitive in ________________________________
 Another hypothesis for dominant species success is that they are most successful at avoiding___________________
Keystone Species
 ___________________________are not necessarily abundant in a community exert strong control on a community
by their ecological roles, or _____________________________
 Field studies of ____________________________ exhibit their role as a keystone species in intertidal communities
A good way to
identify the
keystone species is
to removal
experiment (like
the experiment
here)
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Observation of ______________________________ populations and their predation
Shows the effect
the otters have on
ocean communities
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Ecosystem “Engineers” (Foundation Species)
 Some organisms exert their influence by causing ____________________________ in the environment that affect
community structure
 __________________________________ can transform landscapes on a very large scale
 Some foundation species act as facilitators that have positive effects on the ____________________________ of
some of the other species in the community
Juncus helps prevents
the salt marsh soils
form becoming anoxic
(decrease in oxygen
level) as it transports
oxygen to its below
ground tissue
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Bottom-Up and Top-Down Controls
 The bottom-up model of community organization proposes a unidirectional influence from lower to higher
____________________________________
 In this case, the presence or absence of __________________________ determines community structure, including
the abundance of primary producers
 The _____________________________ of community organization proposes that control comes from the trophic
level above
 In this case, predators control ____________________________ which in turn control primary producers
 Long-term experiment studies have shown that communities can shift periodically from _____________________ to
top-down
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 _______________________ can affect community dynamics
 But through_____________________________ polluted communities can be restored
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Concept 53.3: Disturbance influences species ________________________________________
Decades ago, most ecologists favored the traditional view that communities are in a state of __________________
However, a recent emphasis on change has led to a _________________________model which describes
communities as constantly changing after being buffeted by disturbances
What is Disturbance?
 A disturbance:
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Removes organisms from a ______________________________alters resource availability
__________________________ is a significant disturbance in most terrestrial ecosystems
Is often a necessity in some communities
Sometimes enhances a
community like the
following example
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The intermediate disturbance hypothesis suggests that __________________ of disturbance can foster higher
species __________________ than low levels of disturbance
The large-scale fire in ________________________________________ in 1988 demonstrated that communities can
often respond very rapidly to a massive disturbance
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Human Disturbance
 _____________________ are the most widespread agents of disturbance
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Examples: _________________l development, __________________ and clearing for an urban area
Human disturbance to communities usually reduces ________________________________
Humans also prevent some naturally occurring ________________________ which can be important to
___________________________
Ecological Succession
 Ecological succession:
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____________________________________ occurs where no soil exists when succession begins
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No Soil has ever existed!!!
Example: Volcanic Island that has just formed.
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_________________________________ begins in an area where soil remains after a disturbance
Soil exist!!
Example: Logging, Abandoned farm
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Early-arriving species
May facilitate the appearance of later species by making the environment more ________________
May inhibit establishment of _______________________
May tolerate later species but have _____________________ on their establishment
_____________________________________provide a valuable field-research opportunity on succession
_______________________________________on the moraines in Glacier Bay, Alaska
Follows a predictable pattern of change in _____________________________and soil characteristics
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Concept 53.4: Biogeographic factors affect community diversity
Two key factors correlated with a community’s species diversity are its ___________________________________
and its ___________________
Equatorial-Polar Gradients
 The two key factors in equatorial-polar gradients of species richness are probably __________________________
and________________________________
 Species richness generally declines along an equatorial-polar gradient and is especially great in the _____________
 The greater age of _________________________________________ may account for the greater species richness
Climate (Weather History)
 Climate:
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These factors can be considered together by measuring community rate of ______________________________, the
evaporation of water from soil plus the _______________________
The two main climatic factors correlated with biodiversity are ________________________________ and
___________________________________
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Area Effects
 The species-area curve quantifies the idea that all other factors being equal, the larger the
_______________________ of a community, the _____________________________________________
 A species-area curve of North American ________________________________ supports this idea
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Island Equilibrium Model
 Species richness on islands depends on island size, distance from the ______________________________________
 The _________________________ of island biogeography maintains that species richness on an ecological island
levels off at some dynamic equilibrium point
 Studies of species richness on the Galápagos Islands support the prediction that species richness
__________________with island size
 Concept 53.5: Contrasting views of community structure are the subject of continuing debate two different views on
community structure
 Emerged among ecologists in the 1920s and 1930s, based primarily on observations of
________________________.
Integrated and Individualistic Hypotheses
 The integrated hypothesis of community structure describes a community as an assemblage of ____________
_________________, locked into association by mandatory biotic interactions that cause the community to function
as an integrated view includes the observation that certain species of plants are consistently found together as a
group.
 The individualistic hypothesis of community structure proposes that communities are ___________________
organized associations of independently distributed species with the same abiotic requirements
 The integrated hypothesis predicts that the presence or absence of ____________________________ depends on
the _________________________________ of other species
 The __________________________________ predicts that each species is distributed according to its tolerance
ranges for abiotic factors
 In most actual cases the composition of communities seems to change continuously, with each species more or less
_____________________________________
Rivet and Redundancy Model
 The ________________________________of communities suggests that all species in a community are linked
together in a tight web of interactions
 Also states that the loss of even a _________________________ has strong repercussions for the community
 The redundancy model of communities proposes that if a species is ______________________ from a
____________________, other species will fill the gap
 It is important to keep in mind that community hypotheses and models represent extremes, and that most
communities probably lie somewhere in the _____________________________________