Vanishing meadows — Quantitative analysis of factors driving population declines of endangered butterflies

Abstract

There is a growing number of alarming reports indicating serious declines in biodiversity of invertebrates, mostly manifested through loss of local populations and abundances, and prognosing their regional extinctions. Proper defining of threats is crucial for the effective conservation of endangered species and valuable habitats. Nevertheless, while typically such threats are broadly recognized, their long-term quantitative assessments are rarely available. The aim of this study was to identify and quantify the main drivers of population dynamics and habitat loss of two endangered butterfly species of the genus Phengaris within an extensive semi-urban landscape with 70 initial habitat patches. Over two decades of the study, almost half of the habitat patches remained abandoned, whereas a quarter was directly destroyed through conversion to build-up areas. The latter process was most harmful to butterfly numbers, although it occurred only outside Natura 2000 protected sites. Besides, afforestation works, even if rare, caused significant declines in local populations of the investigated butterflies. Similarly, the meadow abandonment led to decrease in butterfly numbers and their local extinctions due to habitat loss. Meadows were threatened mostly by direct human destruction. The habitat area decreased nearly by 15 %, of which ca. 2/3 suffered direct destruction by built-up, especially in most recent years. As meadows are one of globally threatened terrestrial biodiversity hotspots, and meadow abandonment is partially reversible, there is an urgent need to implement conservation-oriented management of remaining fragments as an effective tool ensuring the persistence of these habitats and their species communities.