Vertical stratification of plant-animal interactions and their impact on pollination and seed dispersal within a single Neotropical plant species

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Plant-animal interactions in tropical rainforests are crucial for pollen and seed dispersal, and thus, for gene flow within plant populations. Recent studies indicate that these interactions are vertically stratified: species assemblages and the frequencies of their interactions differ among forest strata, which in turn might impact pollen and seed dispersal, and thereby gene flow. So far, most studies on pollination and seed dispersal focused on plant species that provide nectar and fruit resources in only one of the strata. In our study, we aim to investigate a plant species that flowers from ground level up to the canopy. We seek to study the animal assemblages involved in pollination and seed dispersal across forest strata as well as the impact of these interactions on pollination and seed dispersal, and thus, on gene flow. If interactions differed between strata, this would strongly support the existence of a vertical stratification of pollinator and/or seed dispersal assemblages independently of the available resources. Marcgravia longifolia is a Neotropical liana species that provides nectar and fruit resources from the forest floor to the canopy for a large number of nectarivorous and frugivorous vertebrate species, and thereby embodies the perfect study species for our purposes. First, we seek to obtain a detailed picture of the assemblages of nectarivores and frugivores that interact with M. longifolia across strata. We will systematically assess visitation rates with video cameras and complement this with focal observation of diurnal frugivores and with mist netting of nectarivorous and frugivorous bats that visit the liana inflorescences at night. Second, we will investigate whether quality and quantity of nectar and fruits vary along the vertical gradient and whether this correlates to shifts in frugivore and nectarivore assemblages. Third, we want to study in detail pollination and seed dispersal interactions and their impact on gene flow. To study seed dispersal, we will determine fruit removal rates across forest strata, approximate dispersal distances by behavioral observations of a subset of frugivores (tamarins and Phyllostomid bats). Further, we will use microsatellite markers to determine outcrossing rates and pollen and seed dispersal distances. Finally we will examine spatial genetic structure within the Marcgravia longifolia population to obtain an overall estimate for intra-population gene flow.