Projecting consequences of global warming for the functional diversity of fleshy-fruited plants and frugivorous birds along a tropical elevational gradient

Aim Species in ecological communities are linked by biotic interactions. It is therefore important to simultaneously study the impacts of global warming on interdependent taxa from different trophic levels. Here, we quantify current and potential future associations of functional diversity (based on multiple traits) and functional identity (based on individual traits) between interacting taxa using projection models under climate change. Location A tropical elevational gradient (500-3,500 m a.s.l.) in the Manu biosphere reserve, south-east Peru. Methods We investigated different scenarios of how species' elevational ranges might change under climate change based on projected future increases in mean annual temperature and current associations of species' elevational ranges with temperature. We computed the functional diversity and identity of current and potential future plant and bird communities based on morphological traits that have been shown to be important for plant-frugivore interactions. Finally, we tested for changes in the associations between projected functional diversity and identity of future plant and bird communities. Results Projected functional diversity of plants and birds decreased under range contraction and range shift scenarios at low elevations. At mid- and high elevations, functional diversity of both species groups increased most strongly under range expansion. Correspondence between plant and bird functional diversity was weakest under range contraction, while it remained strong under range expansion and shift. Similarly, the correspondence of projected plant and bird functional identity was weakest under a range contraction scenario. Main conclusions Our findings suggest that a scenario in which species are dispersal-limited and sensitive to increasing temperatures is likely to cause a functional mismatch between plant and bird communities along this tropical elevational gradient. This implies that certain functional types of plants could miss avian seed dispersers in the future. Our approach of studying functional diversity of interacting taxa could be more widely applied to identify potential future mismatches between trophic levels.