Análisis ecológico y genético de interacciones planta-animal en ambientes mediterráneos

Résumé

Mutualisms are widespread in natural ecosystems and play a key role in the maintenance of biodiversity and ecosystem services worldwide. Plant-animal mutualistic interactions such as seed dispersal and pollination are fundamental in the reproductive biology of many plants that rely on animals for the pollination of their flowers, the dispersal of their seeds, or both. The study of the functioning of plant-animal mutualistic interactions can be difficult to achieve through classical ecological techniques (e. g. observational studies). These methods can provide skewed results (e. g. different detectability rate of species), and there are some ecological processes that can not be efficiently addressed through classical methods due to their spatial and/or temporal scale (e. g. long-distance dispersal events). The application of indirect techniques such as genetic tools can help to efficiently monitor these interactions. In that sense, the use of molecular tools (e. g. microsatellites) and their application in ecological studies enlarge our knowledge about plant-animal interactions and their associated processes. This thesis is composed by four chapters in which plant-animal mutualisms are studied from different approaches combining ecological and genetic tools and at different geographical scales. In the first chapter, we used microsatellites to analyse the genetic structure patterns of a fleshy-fruited shrub (Pistacia lentiscus) along its entire distribution range spanning the Mediterranean Basin, and the role of long-distance seed dispersal events in such patterns. We found that the foraging movements of migrant frugivorous birds are congruent with the spatial genetic structure of animal-dispersed plants. Therefore, anthropic disturbances and/or climatic changes that might disrupt the migration routes of frugivorous birds could cascade into genetic consequences for the plant species they feed upon. In the second chapter, we studied the effects of extreme fragmentation on the genetic diversity of remnant populations of a bird dispersed fleshy-fruited shrub (P. lentiscus). We also performed microsatellites analyses, and mist-netting and bird census to address our hypotheses. Results revealed a high genetic diversity and a lack of differentiation between shrub patches of P. lentiscus in the area, probably because of a strong, but rather recent fragmentation, despite an apparently poor contribution of birds to the dispersal of Pistacia seeds. However, the existence of latent impacts cannot be discarded, since at least one of the patches showed signs of inbreeding. In the third chapter, we developed and tested a methodological framework based on the combination of ecological (bird census and camera trapping) and genetic tools (DNA barcoding) to assess the contribution of seed dispersers to old fields restoration. We deployed restoration structures as artificial perches and water troughs to attract birds to abandoned cropfields, and we also provided microenvironments and prevented herbivory to increase seedling survival opportunities. The restoration structures deployed proved to be effective for increasing seed arrival to the study areas. However, a subsequent plant establishment has not been observed so far. The study pointed out to the importance of implementing different techniques, including molecular studies, to characterize and assess avian seed disperser performance. In the last chapter, we investigated the impact of managed bees (honey bee) on pollination networks under a variable degree of land use and beekeeping intensity. We conducted field sampling to build pollination networks, and we analysed land use through geographic information systems and pathogen load on managed and wild bees by PCR-amplification of target DNA of microsporidia (Nosema apis and Nosema ceranae). Results revealed a poor impact of land use on pollination networks and corroborated the impact of honey bees on wild bees also in semiarid ecosystems by promoting the spread of pathogens in the landscape.