The diversity and conservation of plant reproductive and dispersal functional traits in human-dominated tropical landscapes

Human-altered landscapes dominate the planet, yet little is known about their capacity to sustain plant functional diversity. Most conservation-orientated studies of such landscapes focus on species diversity, whereas less attention is given to functional traits and their conservation. We examine the functional diversity of herbaceous and shrubby plant communities in three forest habitats (understorey, tree-fall gaps and riverbanks) and three deforested habitats (pasture, roadside vegetation and pasture riverbanks), each replicated in three human-dominated landscapes in southern Costa Rica. We focus on six categorical traits related to forest regeneration, reproduction and dispersal: pollination mechanism, dispersal mechanism, growth form, fruit type, fruit size and seed size. We compared trait state richness and composition of each trait in forested and deforested habitats and how three pollination states (bat, bird and bee pollination) and three dispersal states (fur, bird and monkey dispersal) of conservation interest were distributed across these landscapes. Only one trait state was missing from forest, and none was missing from deforested habitats. Understorey and pasture were consistently trait state poor. Forested and deforested plots differed in trait state composition for all traits. Pasture riverbanks and road verges were compositionally similar to forest riverbanks and tree-fall gaps, for multiple traits. There were more compositional similarities between forested and deforested habitat types when abundance of individuals with a trait state was used as the basis for similarity measures than when the number of species with each trait state was used. Bat-, bird- and bee-pollinated plants and plants with bird- and monkey-dispersed fruits were most common in forest and pasture riverbanks whereas species with fur-dispersed seeds were more common in all deforested habitats. Functional diversity patterns were inconsistent across habitat types and locations but overall functional similarity was high between forested and deforested communities. Patterns of functional diversity were far more variable between habitats and landscapes than the consistent patterns found previously for species diversity.