Phylogenetic composition and structure of tree communities shed light on historical processes influencing tropical rainforest diversity

Abstract

The Neotropics, Afrotropics and Madagascar have different histories which have influenced their respective patterns of diversity. Based on current knowledge of these histories, we developed the following predictions about the phylogenetic structure and composition of rainforest tree communities: (Hypothesis 1) isolation of Gondwanan biotas generated differences in phylogenetic composition among biogeographical regions; (H2) major Cenozoic extinction events led to lack of phylogenetic structure in Afrotropical and Malagasy communities; (H3) greater angiosperm diversification in the Neotropics led to greater phylogenetic clustering there than elsewhere; (H4) phylogenetic overdispersion is expected near the Andes due to the co‐occurrence of magnoliids tracking conserved habitat preferences and recently diversified eudicot lineages. Using abundance data of tropical rainforest tree species from 94 communities in the Neotropics, Afrotropics and Madagascar, we computed net relatedness index (NRI) to assess local phylogenetic structure, i.e. phylogenetic clustering vs. overdispersion relative to regional species pools, and principal coordinates of phylogenetic structure (PCPS) to assess variation in phylogenetic composition across communities. We observed significant differences in phylogenetic composition among biogeographical regions (agreement with H1). Overall phylogenetic structure did not differ among biogeographical regions, but results indicated variation from Andes to Amazon. We found widespread phylogenetic randomness in most Afrotropical and all Malagasy communities (agreement with H2). Most of central Amazonian communities were phylogenetically random, although some communities presented phylogenetic clustering (partial agreement with H3). We observed phylogenetic overdispersion near the Andes (agreement with H4). We were able to identify how differences in lineage composition are related to local phylogenetic co‐occurrences across biogeographical regions that have been undergoing different climatic and orographic histories during the past 100 Myr. We observed imprints of the history following Gondwana breakup on phylobetadiversity and local phylogenetic structure of rainforest tree communities in the Neotropics, Afrotropics and Madagascar.

Seed‐dispersal networks are more specialized in the Neotropics than in the Afrotropics

“…Interestingly, our findings for seed‐dispersal networks are consistent with a cross‐continental study on avian plant–pollinator networks that found a higher degree of specialization in Neotropical than in Paleotropical plant–bird networks (Zanata et al, ). The high diversity of angiosperms in Neotropical ecosystems (Carlucci et al, ) may, thus, generally foster the potential for niche differentiation among mutualists in the Neotropics.…”

“…Within the tropics, species diversity and taxonomic composition of plants and animals vary substantially, owing to differences in evolutionary and historical legacies among biogeographical regions (Carlucci et al, ; Jansson & Davies, ). For example, the Afrotropics and Neotropics differ in their evolutionary history, owing to major extinction events in the Afrotropics and greater diversification of angiosperms in the Neotropics (Carlucci et al, ). Consequently, Neotropical ecosystems comprise a higher diversity of fleshy‐fruited plants (Terborgh et al, ), avian frugivores (Fleming et al, ; Kissling et al, ) and small mammals (De Vivo & Carmignotto, ).…”

Using phylogenetic clade composition to understand biogeographical variation in functional traits

“…While it has been extensively used to investigate variation in phylogenetic composition across communities and to discover the underlying causes (e.g., Carlucci et al 2016), the complex relationships between clade composition, trait variation, and environmental variables still needs to be investigated to enhance understanding of how phylogeny affects CWM at the assemblage level. Evaluating clades with distinct levels of phy- logenetic signal and geographical clade composition across space will be essential for clarifying the expected predictions under this framework.…”

“…After performing a principal coordinates analysis (PCoA) on matrix P, the PCPS (eigenvectors from the PCoA) were obtained (Duarte 2011). This method has been used successfully to understand metacommunity structure and phylobetadiversity (Brum et al 2012, Gianuca et al 2013, Loyola et al 2013, Duarte et al 2014, Carlucci et al 2016, but seldom explored with the purpose of understanding mean trait variation (Pillar and Duarte 2010). Each PCPS expresses a fraction of phylogenetic lineage distribution across metacommunities.…”

Anthropogenic threats can have cascading homogenizing effects on the phylogenetic and functional diversity of tropical ecosystems

“…This separation indicates the presence of broad environmental filtering coupled with more local effects of competition. Tropical rainforests have been shown to promote the coexistence of diverse organisms (Valladares et al 2015), and phylogenetic overdispersion has been reported in angiosperm tree communities in the tropics of Africa and Madagascar (Carlucci et al 2017).…”