Visitor diversity and pollinator specialization in Mediterranean Legumes

Papilionaceous flowers present functional traits commonly associated to the so-called “bee-syndrome”. Despite this evolutionary specialization, many legume species are visited by a large number of insect species. In a sample of seven perennial Mediterranean legumes we focus on the ecological aspects of plant-pollinator interactions. Our aim is to compare the degree of specialization of pollination systems among species showing similar floral traits associated with bee pollination. In particular we ask the following questions: (1) Do all flower visitors act as pollinators? (2) Are pollinators equally important? and (3) Is there any relationship between the degree of specialization of plant-pollinator system and plant fitness? We describe the spectrum of visitors and identify the potential pollinators by observing insects’ behaviour on flowers. The diversity of each population’s insect assemblage (flower visitors and potential pollinators) is calculated in order to estimate to which degree pollination systems are specialized. The importance value (PI) for main taxa of potential pollinators is computed considering both quality and quantity components of the pollination service: insect fidelity and relative abundance. Pollinator assemblages show different values of importance and dominance, revealing various degrees of plant-pollinator specificity. Visitors’ and pollinators’ diversity is negatively correlated with fruiting success, while there is a positive relation between maximum pollinator importance value and fruit set, suggesting the tendency towards a positive relationship between pollinator specificity and reproductive success.