Population extinctions in the Italian diurnal lepidoptera: an analysis of possible causes

In depth studies of patterns of extinction are fundamental to understand species vulnerability, in particular when population extinctions are not driven by habitat loss, but related to subtle changes in habitat quality and are due to ‘unknown causes’. We used a dataset containing over 160,000 non-duplicate individual records of occurrence (referred to 280 butterflies and 43 zygenid moths), and their relative extinction data, to carry out a twofold analysis. We identified ecological preferences that influence extinction probability, and we analysed if all species were equally vulnerable to the same factors. Our analyses revealed that extinctions were non-randomly distributed in space and time, as well as across species. Most of the extinctions were recorded in 1901–1950 and, as expected, populations at their range edges were more prone to become extinct for non-habitat-related causes. Ecological traits were not only unequally distributed between extinction and non-extinction events, but also not all ecological features had the same importance in driving population vulnerability. Hygrophilous and nemoral species were the most likely to experience population losses and the most prone to disappear even when their habitat remained apparently unchanged. Species vulnerability depends on both ecological requirements and threat type: in fact, each species showed a distinct pattern of vulnerability, depending on threats. We concluded that the analysis may be an important step to prevent butterfly declines: species that are strongly suffering due to ‘unknown changes’ are in clear and urgent need of more detailed auto-ecological studies.