Core and occasional species: A new way forward.

Alvin J Helden

doi:10.1002/ece3.7863

Abstract

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 multimodal 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 also 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 and can help identify multimodality and provide valuable insight into how communities change in time or space.

Highlights

The idea of dividing up communities into species groups, based on their relative abundance or frequency of occurrence, is long standing
Does that mean that the classification of core species by Magurran and Henderson (2003) and by Genner et al (2004) was unreliable? that is theoretically possible, in actuality this appeared not to be the case, as the division of the Bristol Channel fish community was found to be closely aligned to the ecology of the species and their relative abundance (Magurran & Henderson, 2003)
The sequential Simpson's index method resulted in a very similar or identical pattern of deconstruction previously identified for the Bristol Channel (Magurran & Henderson, 2003) and English Channel fish communities (Genner et al, 2004), indicating it is a reliable way of distinguishing core species from occasional

Summary

| INTRODUCTION

The idea of dividing up communities into species groups, based on their relative abundance or frequency of occurrence (persistence), is long standing (e.g., see Winterbottom, 1949). The communities studied have been varied, covering a wide range of taxa (Astudillo-García et al, 2017; Coyle et al, 2013; van der Gast et al, 2011; Genner et al, 2004; Gray et al, 2005; Ulrich & Ollik, 2004; Ulrich & Zalewski, 2006; Umaña et al, 2017) Among these studies, Genner et al (2004) used a modification of Magurran and Henderson's (2003) method to identify core and occasional species of fish in long-term data from the Bristol and English Channels. Does it show the same pattern a species grouping when species are ranked by persistence or by abundance?

| MATERIAL AND METHODS

Findings

| DISCUSSION

| CONCLUSION