A novel framework of phylogenetic and trait-based community structure
Well known, community assembly processes act on species through a series of phenotypes (or frequently called functional traits) (Chai et al.2019; Laughlin & Messier 2015; Pawar 2015). According to distinct contributions of functional attributes in community assembly, we raised the concepts of “predominant trait” and “assistant trait” to refer major or supporting traits mediating assembly process. Combining prior theoretical efforts (Kraft & Ackerly 2010; Kraft et al. 2007; Cavender-Bares et al. 2004; Webb et al. 2002) and the thought of distinct contributions displayed by traits, we proposed a novel framework of phylogenetic and trait-based structure.
    We built this modified framework on four key assumptions. Firstly, following with prior conceptual work, we assumed that phylogenetic relatedness was a comprehensive proxy of interspecific similarity at multiple ecological niches (Swenson 2013). Secondly, we assumed that functional traits were independent with each other in evolutionary and ecological processes. Because the relationship among phenotypes was extremely complicated and taxon-specified, which was beyond the research scope in this work. Thirdly, we assumed that environmental filtering effect, competitive exclusion and stochastic process are three major processes driving community assembly. Other processes such as mutualism, host-pathogen interactions, plant-insect interactions and negative density-dependence mentioned in (Cavender-Bares et al. 2009) were not involved in this study, but deserved to be considered in future studies. Lastly, we assumed that phylogenetic signal metrics such as Pagel’s lambda (Pagel 1999) and Blomberg’s K (Blomberg et al.2003) could accurately infer the phylogenetic conservatism in functional traits. These assumptions above have also clarified the baselines to apply this framework in interpreting the biodiversity pattern.
    We simulated ecological processes and community structure using virtual species (A~H), phylogeny and traits (phylogenetic conserved traits: T1 and T3; phylogenetic convergent traits: T2 and T4) (Box 1). Two major parameters concerning trait conservatism (phylogenetically conserved or convergent) and trait contribution (predominant or assistant role) were involved in later prediction on phylogenetic and functional dispersion. Given the effects of environmental filtering and competitive exclusion produce opposite imprints on community structure, as a representative, we only simulated the assembly process driven by environmental filtering effect. Following with Kraft and Ackerly (2010), environmental filtering processes were discussed within simple (Fig. 1, scenario A and B) and complex (Fig. 2 scenario C, D and E) habitats, respectively. Besides, we simplified complex habitat with only two microhabitats, which contained independent predominant and assistant traits.
    According to the phylogenetic and functional patterns demonstrated in Fig 1 and 2, the modified framework of phylogenetic and trait-based community structure was summarized in Table 1. Generally, in sample habitat, phylogenetic community dispersion was accordant with the functional dispersion of phylogenetically conserved predominant traits, and opposed to phylogenetically convergent predominant traits. While, dispersion comparison between phylogenetic relatedness and assistant traits in simple habitat became more complicated, which highly depended on the degree of phylogenetic conservatism and inter-trait relationship. In complex habitat, due to multi-directional effect across different microhabitats, phylogenetic and functional dispersion appear complicated and unpredictable.