Scale-dependent responses of pollination and seed dispersal mutualisms in a habitat transformation scenario

Abstract

Transformed habitats are the result of deliberate replacement of native species by an exotic monoculture, involving changes in biotic and abiotic conditions. Despite the fact that transformed habitats are becoming more common and constitute a major biodiversity change driver, little is known about the scale-dependent responses of plant-animal mutualisms. Aiming to test the multiscale responses of pollination and seed dispersal in a habitat transformation scenario, we examined a gradient of native and transformed habitats at three spatial scales (0-50, 50-100 and 100-250m) and focused on a highly specialized mutualistic system composed of a hemiparasitic mistletoe (Tristerix corymbosus) that is almost exclusively pollinated by a hummingbird (Sephanoides sephaniodes) and dispersed by an arboreal marsupial (Dromiciops gliroides). Even though mistletoes were found along the gradient, they were more abundant and more densely aggregated when the transformed habitat was dominant. Disperser and pollinator activity also increased as the transformed habitat becomes dominant, at the scale of 0-50 and 50-100m, respectively. Furthermore, crop size and disperser activity covaried at broad and intermediate scales, whereas recruitment covaried at intermediate and fine scales. Moreover, disperser activity and the number of seedlings were spatially associated, stressing D.gliroides' role in the recruitment of the mistletoe.Synthesis. This highly specialized mutualistic system seems to be responding positively to the habitat structure modifications associated with Eucalyptus plantations. However, the actual costs (e.g. reduced gene flow, increased herbivory) in these transformed habitats are yet to be assessed.