Mistletoe reproductive mutualisms in a West African montane forest
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science (First Class Hons)
In this thesis I investigated the importance of plant-animal mutualisms to the reproductive success of three West African mistletoe species in two genera, Globimetula braunii, Agelanthus brunneus and A. djurensis, in Ngel Nyaki Forest Reserve, Nigeria.
The flowers of all three mistletoes were visited by 3 - 4 species of sunbird. Agelanthus flowers were also visited by honeybees (Apis mellifera) and a small social wasp species (Vespinae). A. mellifera appeared to be robbing nectar from the flowers of A. brunneus. To investigate the relative role of pollinators, I compared flower opening and fruit set amongst bagged, caged, natural, hand-selfed and hand-crossed treatments. The flowers of G. braunii were able to selfopen on average 66% of the time when pollinators were excluded, whereas pollinators were essential to the flower opening mechanism of both Agelanthus spp. Insects were as effective at opening the flowers of Agelanthus spp. as sunbirds. However, flower opening ability did not translate directly into pollination effectiveness, as insect access alone did not result in significantly higher fruit set than that observed under the bagged condition. There was no significant evidence for autonomous selfing within any of the three mistletoes and thus reproduction was almost entirely reliant on 3 – 4 species of sunbird. Hand-pollinations of all three species indicated a high level of self-compatibility, and in one species, G. braunii, pollen limitation was evident (PLI = 0.504).
To investigate dispersal mutualisms amongst the three mistletoe species, fruit ripening and removal were monitored. The fruits of all three mistletoe species appeared to be removed rapidly from plants as they ripened, with few ripe or overripe fruits present on the branches at any time. Dispersal efficiency, or the total proportion of fruit crop removed across the fruiting season, was also very high (>90%) for the Agelanthus spp. but lower in G. braunii, for which almost a third of the total fruit crop was recorded undispersed in fruit nets beneath plants.
Mistletoes are an important component of West African montane forests. Disruption to mistletoe reproductive mutualisms may affect not only mistletoes and their mutualists directly, but also an entire network of species, all linked within a web of interactions. To protect these ecosystems from further degradation, increased community involvement and greater enforcement of laws set out to manage montane forest habitat across the region is essential. Without this support, the future of these ecosystems and the web of interacting species within remains tenuous.