OBSERVATIONS ON SPECIES ABUNDANCE DISTRIBUTION IN FLY COLLECTIONS

Reports and methodological considerations relating species abundance distribution (SAD) in different multi-species communities are timely also today. We report detailed observations on SAD in a neutral fly community, sampled on cow pats in the period 2002-2005 in Hungary. The total sample consisted of 93 thousand individuals (faunistic observations were described in a former publication). We discuss among others observations on the change of frequency polygons with increasing sample size and advise further caution concerning the well-known shifting process, focussing on the discussion on 2-moving averaged abundance frequency polygons. We found a sample of about 20 thousand individuals to be yet insufficient and 30 thousand already sufficient to appear a modal abundance class. With larger sample size also a second internal mode was observable. The pool of the singleton and doubleton species was practically inexhaustible by increasing the sample size. A general conclusion is that a collection of the 93 thousand individuals may be yet insufficient to make a final conclusion on the SAD of the fly community sampled. As for observations on the shifting process working by increasing sample size, the shift of the abundance frequency polygon was significantly larger than expected. Remarkably, the shift of abundance class position of the species by increasing sample size in many cases differs significantly from the expected one. We report also other unexpected observations on the development of species abundance polygons by increasing sample size.