BIOL 1140


Requirements for the Maintenance of an Ecosystem

An ecosystem will be self-sustaining if three conditions exist:

  1. a constant source of energy
  2. a living system capable of incorporating that energy and converting it into organic molecules
  3. a means of recycling the organic molecules and inorganic nutrients
It therefore follows that the overall stability of an ecosystem is maintained by three major mechanisms:
  1. controlling the rate of energy flow through the system
  2. controlling the rate of chemical cycling within the system
  3. maintaining a diversity of species and food webs so that
    the stability of the system is not seriously affected by
    the loss of some species or food web links
The living portion of the ecosystem exhibits a characteristic species
structure: a few species represented by large populations (DOMINANTS)
and many species represented by small populations.

Species diversity contributes to community HOMEOSTASIS (dynamic equilibrium or balance) - the presence of many different kinds of organisms provide a reservoir (gene pool) of adaptive types able to withstand many change in the physical environment.

The distribution of species into various HABITATS results from the interaction of their genetically controlled physiological tolerance limits and natural selective forces (including humans) represented by the environment.

Nitrogen Sources in Water [Notes]
AMMONIA Occurrence - Ammonia is a product of the microbiological decay of plant and animal protein. In turn it can be used directly to produce plant protein. Many fertilizers contain ammonia. Significance - The presence of ammonia nitrogen in raw surface waters might indicate domestic pollution. Its presence in waters used for drinking purposes may require the addition of large amounts of chlorine in order to produce a free chlorine residual. The chlorine will first react with all the ammonia present to form chloramines before it can exert its full bactericidal effect. NITRITE Occurrence - Nitrite nitrogen occurs in waters as an intermediate stage in the biological decomposition of organic nitrogen. Nitrite forming bacteria convert ammonia under aerobic (aerated) conditions to nitrites. The bacterial reduction of nitrates can also produce nitrites under anaerobic (oxygen-free) conditions. Nitrite is often used as a corrosion inhibitor in industrial process water. Significance - Nitrites are usually not found in surface waters to a great extent. The presence of large quantities indicates a source of wastewater pollution. NITRATE Occurrence - Nitrate forming bacteria convert nitrites, under aerobic conditions, to nitrates. During electrical storms, large amounts of atmospheric nitrogen are oxidized to form nitrates. Finally, nitrates can be found in fertilizers. Significance - Nitrates in water usually indicate the presence of wastes in the final stages of biological stabilization or the presence of run-off water from heavily fertilized fields. Nitrate rich effluents discharging into receiving waters can, under proper environmental conditions degrade stream quality by encouring excessive algal growth. Drinking water containing excessive amounts of nitrates can cause infant methemoglobinemia (a substance formed in red blood cells that makes them useless as carriers of oxygen.) Source of information: U.S. Department of the Interior ----------------------------------------------------------------- N2 atmospheric nitrogen NH3 ammonia NH4+ ammonium ion - never found uncombined in nature NO2- nitrite NO3- nitrate


Ecological Succession may be defined in terms of the following parameters:
  1. it is an orderly process of COMMUNITY development; it normally proceeds in a predictable, orderly direction; it represents the gradual replacement of populations by others that are better adapted to the conditions
  2. it results from modification of the physical environment by the populations that interact to make up the community thus, succession is community controlled; the physical factors of the environment and climate determine the pattern and the rate of change; the climate and immediate environment often set the limit as to how far development can proceed
  3. the end result of succession is a stabilized ecosystem which is in balance with the climate and environment of the area; under these conditions the maximum number of organisms (biomass) and their symbiotic (nutritional) interactions are balanced or maintained with the energy available to the system
Thus, the "strategy" of succession as a short term process is very much like the strategy of long-term evolutionary development of the biosphere. It results in HOMEOSTATIC balance of organisms with the physical environment WITH THE BENEFIT of achieving a means of effectively dealing with the constant changes or perturbations presented by the environment.

As an example of these changes and their effects:

    A. Effects upon SOIL

  1. Moderation of drainage (deficient or excessive to regular)
  2. Addition of organic matter as organism die
  3. Improvement of structure (compaction or loosening)
  4. Tapping or release of buried or bound elements

    B. Effects upon VEGETATION

  5. Increase of coverage or biomass
  6. Progressive utilization of layers above and below the soil line
  7. Progressive increase of shade

    C. Effects upon MICROCLIMATE (Ground Level)

  8. Attenuation or moderation of temperature extremes
  9. Reduction of temperature and humidity fluctuations
  10. Decrease of evaporation, at least near soil surfaces