Forest tree neighborhoods are structured more by negative conspecific density dependence than by interactions among closely related species

Abstract

Interactions among neighbors influence the structure of communities of sessile organisms. Closely related species tend to share habitat and resource requirements and to interact with the same mutualists and natural enemies so that the strength of interspecific interactions tends to decrease with evolutionary divergence time. Nevertheless, the degree to which such phylogenetically related ecological interactions structure plant communities remains unclear. Using data from five large mapped forest plots combined with a DNA barcode mega‐phylogeny, we employed an individual‐based approach to assess the collective effects of focal tree size on neighborhood phylogenetic relatedness. Abundance‐weighted average divergence time for all neighbors (ADT_all) and for heterospecific neighbors only (ADT_hetero) were calculated for each individual of canopy tree species. Within local neighborhoods, we found phylogenetic composition changed with focal tree size. Specifically, significant increases in ADT_all with focal tree size were evident at all sites. In contrast, there was no significant change in ADT_hetero with tree size in four of the five sites for both sapling‐sized and all neighbors, even at the smallest neighbourhood scale (0–5 m), suggesting a limited role for phylogeny‐dependent interactions. However, there were inverse relationships between focal tree size and the proportion of heterospecific neighbors belonging to closely related species at some sites, providing evidence for negative phylogenetic density dependence. Overall, our results indicate that negative interaction with conspecifics had a much greater impact on neighborhood assemblages than interactions among closely related species and could contribute to community structure and diversity maintenance in different forest communities.

Host plant phylogeny and abundance predict root‐associated fungal community composition and diversity of mutualists and pathogens

“…Thus, our results contribute to a growing body of evidence showing that pathogen communities show host preference, as required for them to drive CNDD (Bagchi et al, ; Mangan et al, ; Sarmiento et al, ). Furthermore, the fact that closely related host species shared more similar pathogen communities than distantly related host species is consistent with the possibility that RAF drive phylogenetic Janzen–Connell effects: which would serve to increase plant phylogenetic diversity (Liu et al, , Chen et al, , but see Lebrija‐Trejos, Wright, Hernández, & Reich, , Zhu et al, ). However, future studies will need to address the degree to which overlap in pathogen community composition predicts the strength of interspecific plant–soil feedback in order to contextualize results from this study.…”

Intra‐specific relatedness, spatial clustering and reduced demographic performance in tropical rainforest trees

“…Chen et al . ). However, there is little prior evidence showing that the degree of relatedness between a focal individual and its conspecific neighbours has an impact on growth rates.…”

“…Chen et al . ). This result is even found when functional traits or phylogenetic relationships are used to scale the similarity of heterospecific individuals to the focal individual (e.g.…”

Neighborhood effects explain increasing asynchronous seedling survival in a subtropical forest

“…For sessile organisms like trees, individuals interact most intensely with immediate physical neighbors (Janzen , Connell , Terborgh , Chen et al. ). A comparison between mixed models with and without neighborhood effects reveals that seedling survival depends on feature of the neighborhood (Table ).…”

“…These results reinforce the idea that environmentmediated changes in local biotic interactions are essential to account for when forecasting forest community shifts in a changing world. For sessile organisms like trees, individuals interact most intensely with immediate physical neighbors (Janzen 1970, Connell 1971, Terborgh 2012, Chen et al 2018. A comparison between mixed models with and without neighborhood effects reveals that seedling survival depends on feature of the neighborhood (Table 1).…”