Abstract
Compared with species richness, few studies have investigated the patterns and the relationship of phylogenetic and functional structure along elevation gradients. Here, we used general additive models (GAM) to determine the trends of species richness (SR), phylogenetic and functional diversity (PD and FD), phylogenetic structure (NRI), and functional structure (NFRI) of seed plants along the elevation gradient in a tropical mountain of Africa. We measured growth form, fruit type, maximum height, and maximum leaf size of each species, calculated the phylogenetic signal of each trait, and tested the Pearson correlation coefficients between NRI and NFRI of each trait. Our results showed that SR, PD, and FD decrease gradually along the elevation gradient. NRI exhibited a fluctuating pattern along the elevation gradient, while NFRI of the four functional traits showed noticeably different patterns. We concluded that the relationship between phylogenetic and functional structure in different functional traits could be congruent or mismatch along the elevation gradient. Compared with relatively conservative categorical traits (e.g., growth form and fruit type), continuous traits (e.g., height and leaf size) have a random or convergent evolutionary pattern; therefore, they could be more easily affected by the environment and possibly have higher phenotypic plasticity.
Highlights
Understanding the causes of geographic variation in taxonomic diversity, phylogenetic diversity (PD), and functional diversity (FD) is one of the fundamental questions in ecology
We address the following questions: (1) what are the patterns of SR, PD, and FD of seed plants of Mount Kenya along the elevational gradient? (2) How do the phylogenetic structure and the functional structure of the different traits of species assemblages vary along the elevational gradient? and (3) is the relationship of functional and phylogenetic structure congruent or mismatched among convergent or conservatism traits?
Over the entire elevation range of Mount Kenya for the full phylogenetic tree of all the seed plants, the two categorical traits, growth form and fruit type, showed a significant phylogenetic signal, in that the observed number of evolutionary transitions was lower than the randomization of mean evolutionary transitions (Figure 4)
Summary
Understanding the causes of geographic variation in taxonomic diversity (species richness, SR), phylogenetic diversity (PD), and functional diversity (FD) is one of the fundamental questions in ecology. To understand the ecological processes that drive species assembly, numerous researchers have only investigated the phylogenetic structure, overlooking the functional structure of assemblages (Graham et al, 2009; Gómez et al, 2010; Sobral and Cianciaruso, 2016), for they might expect that the phylogenetic structure is a good proxy for functional structure (Cardillo et al, 2008; Graham et al, 2009) This assumption depends on the phylogenetic signal of ecological traits, which can change according to the taxonomic and spatial scale (Losos, 2008; Krasnov et al, 2011). A comparison of the functional and phylogenetic structures of species assemblages can provide a more comprehensive insight into the mechanisms that influence species cooccurrence (Cavender-Bares et al, 2009; Lavergne et al, 2010; Meynard et al, 2011)
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