Soil fertility and flood regime are correlated with phylogenetic structure of Amazonian palm communities

Identifying the processes that generate and maintain biodiversity requires understanding of how evolutionary processes interact with abiotic conditions to structure communities. Edaphic gradients are strongly associated with floristic patterns but, compared with climatic gradients, have received relatively little attention. Muscarella et al. asked:

  1. How does the phylogenetic composition of palm communities vary along edaphic gradients within major habitat types?
  2. To what extent are phylogenetic patterns determined by (a) habitat specialists, (b) small versus large palms, and (c) hyperdiverse genera?
Physiological stress gradients can interact with evolutionary processes to mediate the phylogenetic composition of communities.
Physiological stress gradients can interact with evolutionary processes to mediate the phylogenetic composition of communities. (A) In lowland rain forests of western Amazonia, nutrient limitation and inundation intensity represent two sources of physiological stress in non-inundated ‘uplands’ and seasonally inundated floodplains, respectively. (B) If high levels of abiotic stress select for closely related lineages with traits enabling them to tolerate these conditions, we expect communities in relatively stressful sites to be phylogenetically clustered and communities in relatively favourable conditions to be more phylogenetically even (or ‘over-dispersed’). In this figure, species present in a given location are represented by circles and species absent from a location are represented by crosses. (C) In contrast, if low levels of abiotic stress are associated with diversification rates and evolutionary radiations, we expect communities in relatively favourable sites to be phylogenetically clustered and communities in more stressful conditions to be more phylogenetically even (or ‘over-dispersed’). See main text for additional details.

Overall, Muscarella and colleagues recorded 112 008 individuals belonging to 110 species. Palm communities in non-inundated upland transects (but not floodplain transects) were more phylogenetically clustered in areas of low soil fertility, measured as exchangeable base concentration. In contrast, floodplain transects with more severe flood regimes (as inferred from floristic structure) tended to be phylogenetically clustered. Nearly half of the species recorded (44 %) were upland specialists while 18 % were floodplain specialists. In both habitat types, phylogenetic clustering was largely due to the co-occurrence of small-sized habitat specialists belonging to two hyperdiverse genera (Bactris and Geonoma).

Edaphic conditions are associated with the phylogenetic community structure of palms across western Amazonia, and different factors (specifically, soil fertility and inundation intensity) appear to underlie diversity patterns in non-inundated upland versus floodplain habitats.

Further reading

Muscarella, R., Bacon, C. D., Faurby, S., Antonelli, A., Kristiansen, S. M., Svenning, J.-C., & Balslev, H. (2018). Soil fertility and flood regime are correlated with phylogenetic structure of Amazonian palm communities. Annals of Botany. https://doi.org/10.1093/aob/mcy196