Grassland Hemiptera and Coleoptera collected from Teagasc Grange, Ireland between 2002 and 2005

Various methods have been used to divide communities into core species and
occasional or satellite species. Some methods are somewhat arbitrary and
there is evidence that many communities are more multi-modal than bimodal.
They also tend to rely on having multiple years of data. A completely
novel method is presented that not only has no requirement for long-term
datasets but can divide communities into multiple groups. It is based on
probability a species is present, calculated using Simpson's index
and the sequential removal of species from the data. The sequential
Simpson’s index method was applied to species data from a grassland insect
community. It was also applied to eleven other datasets that had been
divided into core and occasional species in previously published studies.
The new method was found not only to be consistent with previous
core-occasional assessments but was able to identify multimodality in
species-abundance distributions. Although ideally used with a measure of
persistence (frequency of occurrence) to rank species, community structure
is consistently described even with only species abundance data. The
method can be applied to short or long-term datasets, help identify
multimodality and provide a valuable insight into how communities change
in time or space.