Is it all about the ants? What are the factors influencing the presence of Plebejus argus (the Silver-studded Blue butterfly) on Studland Peninsula?

Abstract

The nationally scarce butterfly, Plebejus argus (silver-studded blue) was identified as a priority species requiring special conservation measures within the UK Biodiversity Action Plan in 1994 and this status was retained by the UK Post 2010 Diversity Framework (2012). The species has undergone a major decline throughout most of its range in the UK and its small populations are particularly vulnerable to local extinction.Current research ascertains that early successional vegetation, with a high abundance of host plants and the presence of the symbiotic Lasius ant species, is vital for the longevity of P. argus colonies which are increasingly threatened by fragmented and isolated habitats. This project forms an investigation into the spatial occurrence of the heathland species, Plebejus a argus across Studland Peninsula, a 350-hectare area of dune, lowland heath, salt marsh, mire and open water habitat on the south-eastern side of Poole Harbour. At present, records from Butterfly Conservation transects document the presence of P. argus at Plateau Heath, on the oldest part of the peninsula, but there is no evidence of populations on the eastern side of the peninsula, despite apparently similar terrestrial components. This study investigates the distribution of P. argus across the peninsula and assesses the factors driving this distribution pattern. Results show a significant, positive association between P. argus with the host plant Erica tetralix (cross-leaved heath), short grass (2-5 cm) and the presence of the black ant Lasius niger, the latter which is distributed primarily on the western side of the peninsula despite the availability of suitable habitat conditions to the east. This research investigates the distribution of six heathland ants found at Studland and considers whether interspecific competition between Lasius niger with the red wood ant, Formica rufa, could be influencing the distribution of this myrmecophilous butterfly.