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Chapter 37
Communities and Ecosystems
Introduction: Hungry Hippos
A.)
All communities and ecosystems have certain features in
common
B.)
Each type of ecosystem has its own unique structure and
dynamics
C.)
Human activities can disrupt the balance of ecosystems
COMMUNITY STRUCTURE
AND DYNAMICS
37.1 A community includes all the organisms inhabiting a
particular area
A.)
B.)
Biological community
– An assemblage of populations living close enough together for potential
interaction
– Described by its species composition
Boundaries of the community vary with research questions
– Can be a pond
– Can be the intestinal microbes of a pond organism
37.2 Interspecific interactions are fundamental to community
structure
A.)
B.)
Interspecific interactions
– Relationships with other species in the community
Interspecific competition
– Two different species compete for the same limited resource
–
–
Squirrels and black bears
Compete for acorns
37.3 Competition may occur when a shared resource is limited
A.)
Ecological niche
– Sum of an organism’s use of biotic and abiotic resources
– Interspecific competition occurs when the niches of two populations
overlap
B.) Competition lowers the carrying capacity of competing
populations
C.)
Interspecific competition between orange-crowned warbler and
Virginia’s warbler
37.4 Mutualism benefits both partners
A.)
Reef-building corals require mutualism
– Photosynthetic dinoflagellates
– Live in the cells of each coral polyp
– Produce sugars used by the polyps
– Provide at least half of the energy used by the coral animals
37.5 EVOLUTION CONNECTION: Predation leads to diverse
adaptations in prey species
A.)
Predation benefits the predator but kills the prey
B.)
Prey adapt using protective strategies
– Camouflage
– Mechanical defenses
– Chemical defenses
37.6 EVOLUTION CONNECTION: Herbivory leads to
diverse adaptations in plants
A.)
B.)
C.)
Herbivory is not usually fatal
– Plants must expend energy to replace the loss
Plants have numerous defenses against herbivores
– Spines and thorns
– Chemical toxins
Herbivores and plants undergo coevolution
– A change in one species acts as a new selective force on another
– Poison-resistant caterpillars seem to be a strong selective force for Passiflora
plants
37.7 Parasites and pathogens can affect community
composition
A.)
A parasite lives on or in a host from which it obtains
nourishment
– Internal parasites include nematodes and tapeworms
– External parasites include mosquitoes and ticks
B.)
C.)
D.)
Pathogens are disease-causing parasites
– Pathogens can be bacteria, viruses, fungi, or protists
Non-native pathogens can have rapid and dramatic impacts
– American chestnut devastated by chestnut blight protist
– A fungus-like pathogen currently causing sudden oak death on the West
Coast
Non-native pathogens can cause a decline of the ecosystem
37.8 Trophic structure is a key factor in community dynamics
A.)
B.)
C.)
Trophic structure
– A pattern of feeding relationships consisting of several different levels
Food chain
– Sequence of food transfer up the trophic levels
Producers
– Support all other trophic levels
– Autotrophs
–
D.)
Consumers
– Heterotrophs
–
–
–
–
E.)
Photosynthetic producers
– Plants on land
– Cyanobacteria in water
Primary consumers
Secondary consumers
Tertiary consumers
Quaternary consumers
Detritivores and decomposers
– Derive energy from dead matter and wastes
37.9 Food chains interconnect, forming food webs
A.)
Food web
– A network of interconnecting food chains
37.10 Species diversity includes relative abundance and species
richness
A.)
Species diversity defined by two components
– Species richness
– Relative abundance
B.)
Plant species diversity in a community affects the animals
C.)
Species diversity has consequences for pathogens
37.11 Keystone species have a disproportionate impact on
diversity
A.)
Keystone species
– A species whose impact on its community is larger than its biomass or
abundance indicates
– Occupies a niche that holds the rest of its community in place
37.12 Disturbance is a prominent feature of most communities
A.)
Disturbances
– Events that damage biological communities
– Storms, fire, floods, droughts, overgrazing, or human activity
– The types, frequency, and severity of disturbances vary from community
to community
B.)
Communities change drastically following a severe disturbance
C.)
Ecological succession
– Colonization by a variety of species
– A success of change gradually replaces other species
D.)
E.)
Primary succession
– Begins in a virtually lifeless area with no soil
Secondary succession
– When a disturbance destroyed an existing community but left the soil
intact
37.13 CONNECTION: Invasive species can devastate
communities
A.)
Introduction of rabbits in Australia
ECOSYSTEM STRUCTURE
AND DYNAMICS
37.14 Ecosystem ecology emphasizes energy flow and chemical
cycling
A.)
B.)
Ecosystem
– All the organisms in a community as well as the abiotic environment
Components of ecosystems
– Energy flow
– Passage of energy through the ecosystem
– Chemical cycling
– Transfer of materials within the ecosystem
C.)
A terrarium has the components of an ecosystem
37.15 Primary production sets the energy budget for
ecosystems
A.)
Primary production
– The amount of solar energy converted to chemical energy
– Carried out by producers
– Produces biomass
– Amount of living organic material in an ecosystem
B.)
Primary production of different ecosystems
37.16 Energy supply limits the length of food chains
A.)
A pyramid of production
– Illustrates the cumulative loss of energy transfer in a food chain
37.17 CONNECTION: A production pyramid explains why
meat is a luxury for humans
A.)
The dynamics of energy flow apply to the human population
37.18 Chemicals are cycled between organic matter and abiotic
reservoirs
A.)
B.)
C.)
D.)
Ecosystems are supplied with a continual influx of energy
– Sun
– Earth’s interior
Life also depends on the recycling of chemicals
– Organisms acquire chemicals as nutrients and lose chemicals as waste
products
Biogeochemical cycles
– Cycle chemicals between organisms and the Earth
– Can be local or global
Decomposers play a central role in biogeochemical cycles
37.19 The carbon cycle depends on photosynthesis and
respiration
A.)
Carbon is the major ingredient of all organic molecules
B.)
The return of CO2 to the atmosphere by respiration closely
balances its removal by photosynthesis
C.)
The carbon cycle is affected by burning wood and fossil fuels
37.20 The phosphorus cycle depends on the weathering of rock
A.) Organisms require phosphorus for nucleic acids, phospholipids,
and ATP
– Plants absorb phosphate ions in the soil and build them into organic
compounds
– Phosphates are returned to the soil by decomposers
– Phosphate levels in aquatic ecosystems are typically low enough to be a
limiting factor
37.21 The nitrogen cycle depends on bacteria
A.) Nitrogen is an essential component of proteins and nucleic
acids
B.)
C.)
Nitrogen has two abiotic reservoirs
– Air
– Soil
Nitrogen fixation converts N2 to nitrogen used by plants
– Carried out by some bacteria and cyanobacteria
37.22 CONNECTION: Ecosystem alteration can upset
chemical cycling
A.)
B.)
Chemical cycling in an ecosystem depends on
– The web of feeding
– Relationships between plants, animals, and detritivores
– Geologic processes
Altering an environment can cause severe losses in chemical
cycling
– Erosion
– Acid rain
37.23 TALKING ABOUT SCIENCE: David Schindler talks
about the effects of nutrients on freshwater ecosystems
A.)
Major changes in terrestrial ecosystems disrupt chemical cycling
B.)
These changes can increase nutrients in aquatic ecosystems
– Algal and cyanobacteria blooms
– Eutrophication
C.)
The most serious current threats
– Acid precipitation
– Changes in land use
– Climate warming
You should now be able to
§ Describe the characteristics of a community
§ Explain how interspecific interactions affect the dynamics of
populations
§ Describe the trophic structure of a community
§ Explain how species diversity is measured
§ Describe the role of environmental disturbance on ecological
succession
§ Explain energy and nutrient cycling in ecosystems