COMMUNITIES AND ECOSYSTEMS
I.
A community is all the organisms inhabiting a particular area
a. COMMUNITY  an assemblage of all the populations of
organisms living close enough together for potential interaction
b. Defining characteristics
i. Diversity
ii. Prevalent forms of vegetation
iii. Response to disturbances
iv. Trophic structure
c. BIODIVERSITY  the variety of different kinds of organisms
that make it up
i. 2 components
1. Species richness  total number of different
species in the community
2. Relative abundance of the different species
d. TROPHIC STRUCTURE  the feeding relationships among
the various species making up the community
II.
Competition may occur when a shared resource is limited
a. INTERSPECIFIC COMPETITION  two different species
competing for the same resource
b. COMPETITIVE EXCLUSION PRINCIPLE  two species, so
similar, that they compete for the same limiting resources
CANNOT coexist in the same place
c. NICHE  a species’ role in its community, or the sum total of
its use of the biotic and abiotic resources of its habitat
d. RESOURCE PARTITIONING  the differentation of niches
that enables similar species to coexist in a community
III.
Predation leads to diverse adaptations in both predator and prey
a. PREDATION  an interaction where one species eats another
b. PREDATOR  the consumer
c. PREY  the food species
d. PARASITISM  a parasite lives on, or in, its host and obtains
its nutrition from the host; may be considered a form of
predation
e. COEVOLUTION  a series of reciprocal adaptations in two
species
f. BATESIAN MIMICRY  a palatable or harmless species
mimics an unpalatable or harmful model
g. MULLERIAN MIMICRY  two unpalatable species that
inhabit the same community mimic each other
IV.
Predation can maintain diversity in a community
a. KEYSTONE SPECIES  a species that exerts strong control
on community structure because of its ecological role, or niche
V.
Symbiotic relationships help structure communities
a. SYMBIOTIC RELATIONSHIPS  an interaction between
two or more species that live together in direct contact
i. PARASITISM
ii. COMMENSALISM  one partner benefits without
significantly affecting the other
iii. MUTUALISM  benefits both partners in the
relationship
VI.
Disturbance is a prominent feature of most communities
a. DISTURBANCE  events such as storms, fire, floods,
droughts, overgrazing, or human activities that damage
biological communities, remove organisms from them, and alter
the availability of resources
b. ECOLOGICAL SUCCESSION  transition in a species
composition in a community
c. PRIMARY SUCCESSION  a community arises in a virtually
lifeless area with no soil
d. SECONDARY SUCCESSION  when a disturbance has
destroyed an existing community but left the soil intact
e. CLIMAX COMMUNITY  a permanent final stage in
succession; mature, stable communities that will persist
indefinitely
VII. Ecologist Frank Gilliam discusses the role of fire in ecosystems
a. Not all fires are bad
b. They help to maintain the appropriate biome that ensures
biological diversity and stability
VIII. Energy flow and chemical cycling are the two fundamental
processes in ecosystems
a. ECOSYSTEM  a biotic community and the abiotic
environment with which it interacts
b. ENERGY FLOW  the passage of energy through the
components of the ecosystem
c. CHEMICAL CYCLING  the circular movement of materials
within the ecosystem
d. *Energy flows in and out, whereas chemicals are recycled
IX.
Trophic structure is a key factor in ecosystem dynamics
a. TROPHIC STRUCTURE  a pattern of feeding relationships
b. FOOD CHAIN  the sequence of food transfer from trophic
level to trophic level
c. PRODUCERS  the trophic level that supports all others,
consists of autotrophs
d. PRIMARY CONSUMERS  herbivores; consume (eat) plants
e. SECONDARY CONSUMERS  tiny carnivores
f. TERTIARY and QUATERNARY CONSUMERS  large
carnivores
g. DETRITIVORES  derive their energy from detritus
i. DETRITUS  dead material produce by all trophic
levels
h. SCAVENGERS vs DECOMPOSERS
i. DECOMPOSERS  the breakdown of organic materials
to inorganic ones
X.
Food chains interconnect, forming food webs
a. FOOD WEB  a network of interconnecting food webs
XI.
Energy supply limits the length of food chains
a. BIOMASS  the amount, or mass, of living organic material in
an ecosystem
b. PRIMARY PRODUCTION  the amount of solar energy
converted to chemical energy (organic compounds) by an
ecosystems autotrophs during a given time period
c. RULE OF 10  only 10 % of energy is passed to next trophic
level
XII. A production pyramid explains why meat is a luxury for humans
a. Humans must eat more meat to obtain the same amount of
energy that can be obtained from an equivalent amount of
plants
XIII. Chemicals are recycles between organic matter and abiotic
reservoirs
a. ABIOTIC RESERVOIRS  the part of the ecosystem where a
chemical accumulates or is stockpiled outside of living
organisms
XIV. Water moves through the biosphere in a global cycle
XV. The carbon cycle depends on photosynthesis and respiration
XVI. The nitrogen cycle relies heavily on bacteria
XVII. The phosphorous cycle depends on the weathering of rock
XVIII.
Ecosystem alteration can upset chemical cycling
XIX. David Schindler talks about the effects of nutrients on freshwater
ecosystems
a. EUTROPHICATION  adding nutrients in ponds and lakes
causes photosynthetic organisms to rapidly multiply
XX. Zoned reserves are an attempt to reverse ecosystem disruption
a. ZONED RESERVES  is an extensive region of land that
includes one or more areas undisturbed by humans