Download Define the term trophic level. - science-b

AP Environmental
Science
Mr. Grant
Lesson 31
Ecological
Communities
© 2011 Pearson Education, Inc.
Objectives:
• Define the term trophic level.
• Characterize feeding relationships and energy flow, using
them to construct trophic levels and food webs.
• Distinguish characteristics of a keystone species.
• Characterize disturbance, succession, and notions of
community change.
• Perceive and predict the potential impacts of invasive
species in communities.
• Explain the goals and the methods of restoration ecology.
© 2011 Pearson Education, Inc.
Define the term trophic level.
Trophic Level: Rank in the feeding hierarchy of a food
chain. Organisms at higher trophic levels consume those
at lower trophic levels.
© 2011 Pearson Education, Inc.
Characterize feeding relationships and
energy flow, using them to construct trophic
levels and food webs.
• Energy is transferred among trophic levels in food
chains.
• Lower trophic levels generally contain more energy,
biomass, and individuals.
• Food webs illustrate feeding relationships and energy
flow among species in a community.
© 2011 Pearson Education, Inc.
Ecological Communities
 Community = an assemblage of populations of
organisms living in the same place at the same time
 Members interact with each other
 Interactions determine the structure, function, and
species composition of the community
 Community ecologists are people interested in:
 Which species coexist, and how species relate to one
another
 How communities change, and why patterns exist
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Energy passes among trophic levels
 One of the most important species interactions
involves who eats whom.
 Matter and energy move through the community
 Trophic level = rank in the feeding hierarchy
 Producers (autotrophs)
 Consumers
 Detritivores and decomposers
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Producers
 Producers, or autotrophs (“self-feeders”) =
organisms that capture solar energy for
photosynthesis to produce sugars
 Green plants
 Cyanobacteria
 Algae
 Chemosynthetic bacteria use the geothermal energy
in hot springs or deep-sea vents to produce their
food
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Consumers
 Primary consumers = second trophic level
 Organisms that consume producers
 Herbivores consume plants
 Deer, grasshoppers
 Secondary consumers = third trophic level
 Organisms that prey on primary consumers
 Carnivores consume meat
 Wolves, rodents (that eat insects)
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Consumers
 Tertiary consumers = fourth trophic level
 Predators at the highest trophic level
 Consume secondary consumers
 Are also carnivores
 Hawks, owls
 Omnivores = consumers that eat both producers
(plants) and consumers (animals)
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Detritivores and decomposers
 Organisms that consume nonliving organic matter
enrich soils and/or recycle nutrients found in dead
organisms
 Detritivores = scavenge waste products or dead
bodies
 Millipedes, soil insects
 Decomposers = break down leaf litter and other
nonliving material into simpler chemicals that can be
used by plants
 Fungi, bacteria
 Enhance topsoil and recycle nutrients
© 2014 Pearson Education, Inc.
Energy, biomass, and numbers decrease at
higher trophic levels
 Most energy organisms use is lost as waste heat
through cellular respiration
 Less and less energy is available in each successive
trophic level
 Each level contains only about 10% of the energy of
the trophic level below it
 There are also far fewer organisms and less
biomass (mass of living matter) at each higher
trophic level
A human vegetarian’s ecological footprint is smaller
than a meat-eater’s footprint
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Food webs show feeding relationships and
energy flow
 Food chain = a linear series of feeding relationships
 Food web = a visual map of feeding relationships
and energy flow
 Includes many different organisms at all various
levels
 Greatly simplified; leaves out most species
 Contains many food chains
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Distinguish characteristics of a keystone
species.
• Keystone species exert impacts on communities that are
far out of proportion to their abundance.
• Top predators are frequently considered keystone
species, but other types of organisms also exert strong
effect on communities.
© 2011 Pearson Education, Inc.
Some organisms play outsized roles in
communities
 Community dynamics are complex
 Species interactions differ in strength
 Keystone species = a species that has a strong or
wide-reaching impact far out of proportion to its
abundance
 Removal of a keystone species has substantial
ripple effects
 Significantly alters the food web
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Some organisms play outsized roles in
communities
 Trophic cascade = a phenomenon in which
predators at high trophic levels indirectly affect
populations at low trophic levels
 Predators keep species at intermediate trophic levels
in check, allowing growth of species at a lower level
 Extermination of wolves led to increased deer
populations, which overgrazed vegetation and
changed forest structure
 “Ecosystem engineers” physically modify the
environment
 Beaver dams, prairie dogs, ants, zebra mussels
© 2014 Pearson Education, Inc.
Characterize disturbance, succession, and
notions of community change.
• Disturbances are varied, and communities respond to disturbance
in different ways.
• Succession describes a typical pattern of community change
through time.
• Primary succession begins with an area devoid of life.
Secondary succession begins with an area that has been severely
disturbed but where remnants of the original community remain.
• Ecologist today view succession as being less predictable and
deterministic than they did in the past.
• If a disturbance is severe enough, communities may undergo
phase shifts involving irreversible change – or novel
communities may form.
© 2011 Pearson Education, Inc.
Communities respond to disturbance in various
ways
 Disturbance = event that causes rapid changes in
the environment that alters the community or
ecosystem
 Tree falling, opening space in a forest
 Removal of keystone species, spread of invasive
species
 Natural disturbances like tornadoes, hurricanes
 Human impacts cause major community changes
 Some species become adapted to disturbance
 Plants growing in fire-prone regions may have seeds
that require fire to germinate
© 2014 Pearson Education, Inc.
Communities respond to disturbance in various
ways
 Communities have different ways of maintaining
themselves when disturbed
 Resistance = when a community of organisms resists
change and remains stable despite the disturbance
 Resilience = when a community changes in response
to a disturbance, but later returns to its original state
 A disturbed community may never return to its
original state
© 2014 Pearson Education, Inc.
Succession follows severe disturbance
 Succession = the predictable series of changes in a
community following a disturbance
 Primary succession = disturbance removes all
vegetation and soil life
 Community is built from scratch
 Glaciers, drying lakes, volcanic lava
 Pioneer species = the first species to arrive in a
primary succession area (e.g., lichens, mosses)
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Succession follows severe disturbance
 Secondary succession = a disturbance
dramatically alters, but does not destroy, all local
organisms
 The remaining organisms and soil form “building
blocks” that help shape the process of succession
 Fires, hurricanes, farming, logging
 Climax community = community that remains in
place with few changes until another disturbance
restarts succession
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Communities may undergo shifts
 The dynamics of community change are more variable
and less predictable than thought
 Competition may inhibit progression to another stage
 Chance factors also affect movement between stages
 Climax community may not be based on climate alone
 Phase (regime) shift = occurs when the overall
character of the community fundamentally changes
 Some crucial threshold is passed, a keystone species is
lost, or an exotic species invades
 Human activity may be creating novel or no-analog
communities that are new mixtures of species that
have not been seen before in nature
© 2014 Pearson Education, Inc.
Perceive and predict the potential impacts
of invasive species in communities.
• People have introduced countless species to new areas.
Some of these no-native species may become invasive
if they do not encounter limiting factors on their
population growth.
• Invasive species such as the zebra mussel have altered
the composition, structure, and function of
communities.
• We can respond to invasive species with prevention,
control, and education measures.
© 2011 Pearson Education, Inc.
Invasive species pose new threats to
community stability
 Invasive species = non-native (exotic) organisms
that spread widely and become dominant in a
community
 Introduced species = species that were deliberately
or accidentally brought from elsewhere
 Growth-limiting factors (predators, disease,
competitors, etc.) are removed or absent
 Have major ecological effects
 Chestnut blight from Asia wiped out American
chestnut trees
 Some species help people (e.g., European
honeybees)
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Zebra Mussels…
There are two sides to the story. Eutrophication has plagued the Great Lakes for decades. But by
filtering phytoplankton and other suspended material from the water column, the nonnative zebra
mussel has helped clean up Lake Erie and other parts of the Great Lakes, the Hudson River, and
many more aquatic environments. These mussels are much more efficient at filtration than their
native counterparts. Many birds feed on them, and the mussels’ excrement provides habitat for a
food chain anchoring a great diversity of species. Biologists credit the zebra mussel with
restoring native grasses and fishes. Were it native, the zebra mussel would be hailed as a savior,
not reviled as a scourge.
EXCERPT FROM
Whole Earth Discipline
Stewart Brand
Category: Nature
We can respond to invasive species through
control, eradication, or prevention
 Techniques to control invasive species
 Removing them manually
 Applying toxic chemicals
 Introducing native predators or diseases
 Stressing them with heat, sound, electricity, carbon
dioxide, or ultraviolet light
 Control and eradication are hard and expensive
 Understanding the biology of invasive species can
help predict where they will be a problem
Prevention, rather than control, is the best policy
© 2014 Pearson Education, Inc.
Explain the goals and the methods of
restoration ecology.
• Restoration ecology is the science of restoring
communities to a previous, more functional or more
“natural” condition, variously defined as before human
or before recent industrial impact.
• The growing practice of restoration ecology, informed
by the science of restoration ecology, helps us restore
ecological systems.
© 2011 Pearson Education, Inc.
Altered communities can be restored
 Humans have dramatically changed ecological
systems
 Severely degraded systems cease to function
 Ecological restoration = efforts to restore
communities
 Restoration is informed by restoration ecology =
the science of restoring an area to an earlier
condition to restore the system’s functionality (e.g.,
filtering of water by a wetland)
 It is difficult, time-consuming, and expensive
 It is best to protect natural systems from degradation
in the first place
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Altered communities can be restored
 Prairie restoration involves replanting native species,
controlling invasive species
 Nearly all tallgrass prairie was converted to
agriculture by the 19th century
 The world’s largest project is the Florida Everglades
 Flood control and irrigation removed water
 Populations of wading birds dropped 90–95%
 It will take 30 years and billions of dollars to restore
natural water flow
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.