Core and satellite butterfly species on Elba island (Tuscan Archipelago, Italy). A study on persistence based on 120 years of collection data

Records for butterflies on Elba island in the last 120 years have been summarized and examined. I assessed species occurrence for six periods of twenty years by bibliographic, museum and field data. For five periods data appear complete and species assemblage highly concordant. Nonetheless, a certain evolution of Elba butterflies seems to be occurring. Moreover, I assessed the regression between frequency at sources and frequency on islands among species living on Italian islets and used the residuals as a tendency to be less or more common on islands compared to mainland. By a successive regression, I verified that these residuals are actually related to the number of periods each species has been recorded on Elba. Interestingly, the number of record periods is not correlated with species appearance. I concluded that there is a large core of persistent species and a few species that are occasionally reported on Elba. Such satellite species represent butterflies that are less likely to occupy island biotas and may represent endangered populations.