PERSPECTIVES ON ECOLOGY ENERGY FLOW THROUGH ECOSYSTEMS

Transcription

1 PERSPECTIVES ON ECOLOGY ENERGY FLOW THROUGH ECOSYSTEMS

2 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?

3 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

4 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

5 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, CO 2 ) 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

6 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:

7 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

8 Energy flow food = 5 kcal/g (3.8 kcal/g glucose; 9 kcal/g fatty acid)

9 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 )

10 Silver Springs, about 1901

11 Views of Silver Springs today

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13 Gross production: plants/light = 1.2% (about average) IR

14 Respiration, etc (lost to heat) producers: 57% primary consumers: 56% secondary consumers: 84% tertiary consumers: 71% decomposers: 91%

15 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)

16 An energy pyrimid expresses the energy input into each trophic level

17 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

18 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

19 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