| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 106 === Functional diversity (FD), the diversity of functionally disparate traits in a community, critically influences ecosystem functioning. FD is a multifaceted concept that includes several key aspects: functional dissimilarity, functional dispersion, functional richness, and functional evenness. While FD was reportedly affected by climate and vegetation productivity in temperate regions, the effects remain to be investigated in the subtropics and different aspects of FD are rarely studied within one community. To help fill the knowledge gaps, we examined how environmental factors (i.e., climate and vegetation productivity) affect different aspects of functional diversity in the subtropics by testing the two hypotheses: 1) Environmental filtering: higher temperature, higher precipitation, and lower CV (coefficient of variation) of precipitation (less harsh environments for functional traits) will lead to higher FD, and 2) Resource availability: higher productivity (a higher resource supplement) will lead to higher FD. Specifically, we calculated the four FD aspects of bird communities in subtropical Taiwan based on the Taiwan Breeding Bird Survey (BBS Taiwan) data (2009 – 2015) and five important bird functional traits. We then investigated the FD pattern along environmental gradients (temperature, precipitation, and vegetation productivity), using linear mixed-effects models. The results generally supported both hypotheses: less harsh environments and higher amount of resources generally led to higher functional diversity (higher functional dissimilarity, dispersion and richness). Although these patterns agreed with those in temperate regions, the subtropical communities in this study showed a quadratic functional richness – temperature relationship, different from the linear functional richness – temperature relationship in temperate regions. This suggests that warming may reduce functional richness more likely in the subtropics than temperate regions. The results also showed that the four functional diversity indices may express different patterns along environmental gradients, suggesting various underlying mechanisms and highlighting a need to consider different indices in functional diversity studies. Based on the results, we urge a more holistic investigation to understand the similarity and difference in functional diversity between temperate and subtropical regions.
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