Specialism for larval and adult consumer resources among British butterflies: Implications for conservation

Specialism is a key issue in conserving organisms. Using a new database of consumer resources we investigate specialism among British butterflies. Different measures for the range of sources exploited by adults are compared. As number of nectar sources correlates closely with number of records, new measures of specialism based on the residuals from this relationship are developed as well as a measure generated using a Monte Carlo procedure. Clear evidence for specialism in adult feeding emerges. A number of species depend heavily on alternative substrates to nectar flowers and others on flowers which are also larval host plants. Though many species have varied nectar sources, there is confirmation of the tendency of larval host plant specialists to be adult feeding specialists. Rarity, distribution losses and conservation status are associated with nectar specialism. We suggest that habitat fragmentation and regional extinctions are exacerbating resource (nectar and host plant) specialism. We draw attention to the importance of resource databases; there is clear indication now which nectar plants are more or less suitable for different butterfly species. Nevertheless, despite the current database comprising 10,539 records, it is deficient for 29 species (<50 records each). For conservation, site-specific data obtained according to strict survey protocols are required for determining ecological relationships and to direct site management.