Pollinator networks, alien species and the conservation of rare plants:Trinia glaucaas a case study

Abstract

1 Despite the essential role of pollination in the maintenance of many rare plant species, conservation management plans rarely consider the service of pollination. 2 This study identifies the main pollinators of a rare English plant species, Trinia glauca (Apiaceae), and provides recommendations for its conservation. A community-level approach is used, whereby a visitation network is constructed to identify the direct and indirect links between T. glauca and other members of the plant-visitor community. 3 A field experiment that excluded the main visitor species from female T. glauca showed that ants were the main pollinators of T. glauca. The network revealed that over the field season, 33% of the ants’ visits to flowers were to alien plants, with Cotoneaster horizontalis making a particularly high contribution (58%) during the T. glauca flowering period. 4 The removal of alien plants is a part of the conservation management of T. glauca, and we simulated the likely consequences of this form of habitat management on T. glauca pollination, any effects being mediated by shared pollinators. Although positive or neutral effects are possible, a negative effect is also possible, whereby the removal of alien plants leads to a crash in ant populations, potentially reducing pollinator visits to T. glauca by up to 85·2%. 5 Synthesis and applications. Conserving the pollinators of rare plants is essential if their conservation is to be sustainable in the long term. Our data indicate that T. glauca is pollinated by ants and demonstrate that ants can also feed on alien plants, particularly during the flowering season of this rare plant. We suggest that management measures involving the removal of alien plants should consider the possible negative impacts on rare plants through changes in pollinator populations. In this case, a staged removal is likely to prove the best conservation approach, allowing the pollinators’ response to be assessed before any serious negative effects occur.