Plant species diversity verses functional trait diversity in tropical human-dominated landscapes.
Mayfield, Margaret1, Ackerly, David1, Daily, Gretchen1, 1 Stanford University, Stanford, CA
ABSTRACT- The conservation value of human-altered landscapes is a problem of increasing importance, as these landscapes become the rule around the world. Most research on this topic focuses on species richness and composition, with little analysis of the ecological or functional differences in surviving floras and faunas. The connection between species diversity and functional diversity has been recognized as important for community function but few studies examine functional diversity from a conservation perspective. In this study we examine the functional diversity of herbaceous and shrubby plant communities, focusing on interaction-traits (i.e. traits potentially involving interactions with animals), such as pollination system and dispersal mechanism. We examine 3 forested (understory, tree-fall gaps and riverbanks) and 3 deforested habitat types (pasture, roadside vegetation, and riverbanks in pasture) in 3 human-dominated landscapes of southern Costa Rica. We ask the questions: Does the loss of species diversity result in similar losses of functional diversity? Are changes in interaction-trait diversity consistent across landscapes? We found that while total native species richness was similar in forested and deforested habitats, only 16-20% of herbaceous and shrubby plant species live in both forested and deforested habitats. However, almost all interaction-traits were found in both forested and deforested habitats. When we examined species composition, we found that forested and deforested habitats were significantly different and that pasture riverbank floras were the most similar to forest floras. These patterns were the same across all three landscapes. When we examined interaction-trait composition, significant differences in trait composition between forested and deforested habitats were observed for only ca. half of the traits examined. The 'trait flora' of roadside vegetation was usually the most similar of the deforested habitats in comparison with forested 'trait floras'. Finally, trait compositional patterns differed markedly between landscapes. We conclude that species richness and composition should not be used to draw inferences about functional and ecological differences in forested and deforested plant communities in tropical human-dominated landscapes.
Key words: conservation, deforestation, functional diversity, herbaceous plants
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