How life history affects threat status: Requirements of two Onobrychis-feeding lycaenid butterflies, Polyommatus damon and Polyommatus thersites, in the Czech Republic

Comparisons of related species differing in conservation status may offer insights into causes of species declines. We studied egg-laying patterns and landscape occupancy of two sympatric lycaenidae butterflies inhabiting xeric grasslands, vulnerable Polyommatus thersites and critically endangered Polyommatus [Agrodiaetus] damon, both developing on sainfoin, Onobrychis spp. Females of bivoltine P. thersites oviposit on host plant leaves at a relatively low height (a parts per thousand 20 cm), in both spring (May-June) and summer (July-August) generations. Females of univoltine P. damon (July-September) oviposit to senescing inflorescences, in significantly higher heights (> 30 cm), and the species is hence vulnerable to summer mowing or grazing. On a landscape scale, both species tended to occur at sites with diverse sward management, including temporarily unmanaged patches. In addition, P. damon occurred only in the proximity of other occupied sites. The study documents that grassland management must respect the needs of the most vulnerable species, and because these needs are seldom known, it must maintain a high diversity of conditions within individual sites.