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Project Amazonia: Characterization - Biotic - Fauna

Fauna are defined as being the animal life of a region or geological period, and they are essential to the survival of the rainforest8. Animals serve an integral role in the ecosystem of the rainforest, as they interact with all parts of the ecosystem, such as the flora, soil, air, and water systems.  They contribute to the various nutrient cycles, the energy cycle, and act as ambassadors for the jungle to humanity.        

With approximately 500 species of mammals, 1600 species of birds, and 1 million species of insects in a 2.5 million square mile area, the Amazon rainforest is considered one of the most biologically diverse places on the planet1,2.  To ensure the health of the rainforest, we must preserve the health of the fauna. Because of the diversity of animal species and the constant discoveries of yet more species, it is impossible to characterize the Amazon's fauna by listing all the species.  However, it is possible to break the fauna of the Amazon into different categories and know that each category is necessary for the survival of others.  Soil health has been defined the ability to function as a vital living system, that is the capacity of soil to sustain biological productivity, promote air and water quality, and maintain plant, animal, and human health4.  Similarly, the health of fauna can be defined as their ability to exist as a vital living system and sustain biological productivity.  This idea can be further generalized to the entire ecosystem.   Accordingly, a health ecosystem can be described as stable and sustainable. However, the health of an ecosystem is nearly impossible to measure directly.  Instead, proxies or bioindicators are employed9.  Thus, as bioindicators, fauna can be very important to monitoring the health of the Amazon Basin rainforest.           

There are still many important questions to be resolved.  For instance, what is the relationship between species and ecosystem health?  Since one cannot investigate all species, which are the most important species?  Ecological theorists have proposed answers to the former question.  Lawton (1994) tried to explain an interesting facet of the relationship between biodiversity, and ecological ability to function properly.  If all species are present and relationships unaffected, then one can be sure that ecological functions are constant.  However, the presence of all functions does not require the presence of all species.  He proposed 3 models to explain this relationship:

  1. Redundant species hypothesis - With a decrease of biodiversity, ecosystem functions are unaffected until the point where only a few key species remain. If one of these species is lost, the system collapses.
  2. Rivet hypothesis - With a decrease of biodiversity, ecosystem function will decrease proportionally.  This represents a direct correlation between the two.
  3. Idiosyncratic hypothesis - There is no relationship between biodiversity and ecosystem functions.

There is some evidence for the redundant species hypothesis.  For example, the effect of heavy metal contamination on soil respiration is the death of fungi in a gradient surrounding the source of the metals.  However, respiration and therefore species proliferation, was only affected by high metal concentrations near the source7.  Although there is a general consensus that functional redundancy plays a role, there is little evidence to support any of Lawton's hypotheses9.


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3: Costanza, R. Norton BG and Haskell BD (eds) (1992) Ecosystem Health. Island Press, Washington, D.C

4: Doran JW and Safley, M. (1997) Defining and assessing soil health and sustainable productivity.  In: Pankhurst CE, Doube BM and Bupta VVSR (eds) Biological Indicators of Soil Health (pp 1-28).  CAB Inernational, Wallingford.

5: Lawton, JH (1994) What do species do in ecosystems? Oikos 71: 367-374.

6: Naeem S, and Li S (1997) Biodiversity enhances ecosystem reliability. Nature 390: 507-509.

7: Nordgren A, Baath E and Soderstrom B (1983) Microfungi and microbial activity along a heavy metal gradient.  Applied and Evironmental Microbiology. 45:

8: The Oxford Dictionary of Natural History.  Oxford
University Press, Oxford, 1985.

9: van Straalen, Nico M (2002) Assessment of soil contamination - a functional perspective. Biodegeneration. 13: 41-52.