Phylogenetic and functional trait‐based community assembly within Pacific Cyrtandra (Gesneriaceae): Evidence for clustering at multiple spatial scales

Abstract

Tropical rainforest communities are often characterized by a small number of species‐rich genera that contribute disproportionately to the alpha diversity in these habitats. In the Pacific Basin, there are nearly 200 species of Cyrtandra, most of which are white‐flowered woody shrubs that are single‐island endemics. Within these island communities, multiple Cyrtandra species are commonly observed to occur sympatrically in wet forest understories, forming swarms of what appear to be ecologically similar taxa. The aim of this study was to determine whether species of these plants are randomly assembled with respect to phylogenetic relatedness and traits that are ecologically relevant. I examined assembly patterns across three Pacific archipelagoes using a combination of 10 functional traits and a well‐resolved phylogeny comprising 34 species of Cyrtandra. Coexisting species were found to be more closely related and more phenotypically similar than would be expected by chance. This pattern was observed at both regional (island) and local (site) spatial scales. The retention of phylogenetic signal in floral traits and the strong influence of these traits on the observed degree of phylogenetic clustering may indicate that generalist insect pollinators act as a biotic filter on oceanic islands, driving selection for similar floral morphology among closely related species of Pacific Cyrtandra. Phylogenetic signal was also detected in leaf size, which contributed to niche clustering at both spatial scales. Coupled with a propensity for long‐distance dispersal, and the restricted distribution of Cyrtandra to rainforest understories, this finding suggests that environmental filtering along this trait axis may be more important than dispersal limitation in determining species assemblages. This study supports the theory that plant species are not randomly assembled, and instead, that niche‐based processes structure biodiversity at regional and local spatial scales in diverse congeneric species assemblages.

Deciduous forests hold conservation value for birds within South Andaman Island, India

“…However, empirical evidence for intra-island community assembly is relatively scarce. A study on plants found evidence for clustering due to habitat filtering within islands (Johnson 2023), while dispersal limitation and stochasticity likely led to overdispersion of intra-island microbial communities (Wang et al 2020). On the contrary, our study detects no signals of community-wide functional and phylogenetic clustering or overdispersion of forest birds between contrasting habitats on the same island (Figure 3c).…”

Slowing taxon cycle can explain biodiversity patterns on islands: Insights into the biogeography of the tropical South Pacific from molecular data

“…The potential for radiations to fill available niche space has been well documented (e.g., Gillespie, 2004). Incorporating ecological traits with denser phylogenetic sampling across different scales would allow testing of this hypothesis (Cerca et al, 2023;Johnson, 2023).…”