Download perspectives on ecology energy flow through

PERSPECTIVES ON ECOLOGY
ENERGY FLOW THROUGH
ECOSYSTEMS
Ecology: study of interactions among organisms and between
organisms and the non-living environment
Some of the most important and topical questions concern ecology:
How will the greenhouse effect change the world?
Will an “ecological disaster” (fire, volcano, oil spill) permanently
change a community?
How will introduction of genetically engineered crops affect a
community?
How best can we maintain genetic diversity in a world crowded
with humans?
Can we send people into space (or to the planets) for long
periods?
What is the effect of long-term use of antibiotics?
Levels of study--approaches to key concepts
individuals and their adaptations to environment--physiological ecology
populations: interbreeding group of organisms-- population biology
life histories --strategies for reproduction and survival
population growth kinetics
communities and ecosystems: interacting populations and non-living
environment in defined space--community ecology, ecosystem ecology
material cycles and energy flow
predation
competition
community structure--biodiversity
ecological succession --predictable changes in communities
biomes: collection of communities with similar structures and
environments
The place of humans in the environment
ECOSYSTEMS: ENERGY FLOW
How do living organisms depend on their environment, and viceversa?
This is the sort of question considered in "ecosystem ecology."
Defining an ecosystem: all interacting populations (species,
organisms) plus physical influences in one contiguous area
specific definitions depend on the ecosystem under study:
arbitrary choice of investigator: define boundaries
(best ones are easy to see, have measurable interior)
things to be measured:
biotic factors: all species (plants, animals, etc.)
abiotic factors: light, temp, humidity, topography, rainfall, wind
speed, wind direction, soil composition, etc.
inputs, outputs: some biotic, some abiotic
Ecosystem structure
trophic levels ("trophic" = feeding) describe structure of an
ecosystem: significant because they indicate where, how organisms
get their materials and energy
Producers: plants, photosynthesizers (some bacteria)
("produce" bioorganic material from light energy, CO2)
Primary consumers: herbivores, eat plants to obtain their
energy, organic compounds
Secondary consumers: carnivores, eat herbivores to obtain
their energy, organic compounds
Tertiary consumers: carnivores eating carnivores
Decomposers: simple organisms (bacteria, fungi) that break
down dead material for energy, organic compounds
Food chains (who eats whom) show organization, specifics of trophic levels
e.g.,
grass-->rabbit-->fox-->cougar
algae-->fish-->fish (trout)-->heron
Food web shows interrelated food chains:
Generalized food web:
1) some ecosystems are not self-supporting (have no
producers) and depend on imported food (e.g., benthic ocean
floor ecosystems): this analysis may still be useful, with
measured import substituting for producers;
2) in some aquatic ecosystems, bacteria are links in the food
web, absorbing dissolved organic material secreted by
producers (and others) and being eaten by zooplankton
Energy flow
food = energy @ 5 kcal/g (3.8 kcal/g glucose; 9 kcal/g fatty acid)
Example of energy flow: Silver Springs, Florida
Eelgrass (Sagittaria) community in fresh water mineral springs, studied
by
Odum
Boundaries: river banks, upper 3/4 miles
Stability: resort owners with glass bottom boats say "no change"
Biotic components:
Producers: blue green algae and eelgrass
Primary consumers: insects, turtles, snails, some fish
Secondary consumers: catfish, stumpknocker
Tertiary consumers: bass, gar
Decomposers: bacteria, crayfish
Inputs: light, nutrient input (bread “import”)
Outputs: fish collection, outflow of stream (“export”)
Silver Springs, about 1901
Views of Silver Springs today
Gross production: plants/light = 1.2% (about average)
IR
Respiration, etc (lost to heat)
producers: 57%
primary consumers: 56%
secondary consumers: 84%
tertiary consumers: 71%
decomposers: 91%
Passed to consumers by:
producers: 14%
primary consumers: 11%
secondary consumers: 5.5%
(Generally: 5-30%: in deciduous forest, most energy
flows from producers to decomposers, in marine
systems, more flows through consumers)
An “energy pyrimid” expresses the energy input into each trophic level
Ecosystem analysis can also be used to follow the course of materials, for instance,
carbon:
As with energy,
photosynthesis injects
carbon into the biotic
part of the ecosystem;
respiration returns it
to the abiotic environment
On a global basis, materials cycle through the ecosystem (rather than pass
through, as energy)--I.e., there is conservation of materials, although not
necessarily at one place and one time
Summary
•Ecosystems consist of biotic and abiotic components
•Energy flows through trophic levels of an ecosystem
and on a global basis is gained from the sun through
photosynthesis and lost to space through respiration and
radiation
•Materials cycle through trophic levels