Species abundance distribution model for real periphyton samples

The recognition of abundance distribution of periphyton species is important both from theoretical ecological aspect, and from the view of the water monitoring practice. The periphyton species showed exponential distribution, but the rare species have an excess above the expected value. The distribution of the rare species can be hardly investigated by classical statistical methods, because the expected value and the standard deviation are in the same order of magnitude. The distribution function was modelled by computer. This software can generate a multitude by the resultant of two different types of distribution functions, and take random samples from it, according to the valid sampling standard. The artificial samples were compared to the real ones by different methods. The distribution of rare species was found to be uniform in the periphyton.