Environmental conditions and biotic interactions acting together promote phylogenetic randomness in semi-arid plant communities: New methods help to avoid misleading conclusions

Santiago Soliveres*, Rubén Torices, Fernando T. Maestre

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


Questions: Molecular phylogenies are increasingly used to better understand the mechanisms structuring natural communities. The prevalent theory is that environmental factors and biotic interactions promote the phylogenetic clustering and over-dispersion of plant communities, respectively. However, both environmental filtering and biotic interactions are very likely to interact in most natural communities, jointly affecting community phylogenetic structure. How do environmental filters and biotic interactions jointly affect the phylogenetic structure of plant communities across environmental gradients? Location: Eleven Stipa tenacissima L. grasslands located along an environmental gradient from central to southeast Spain, covering the core of the distribution area of this vegetation type in Europe. Methods: We jointly evaluated the effects of environmental conditions and plant-plant interactions on the phylogenetic structure - measured with the mean phylogenetic distance index - of the studied communities. As an indicator of environmental conditions, we used a PCA ordination including eight climatic variables. Different metrics were used to measure the following processes: (1) competition/facilitation shifts at the entire community level (species combination index), and (2) the effect of microclimatic amelioration provided by the two most important nurse plants on neighbour composition (similarity indices and comparison of the phylogenetic pattern between canopy patches and bare ground areas). Results: Biotic interactions and, to a less extent, environmental conditions affected the phylogenetic pattern of the studied communities. While positive plant-plant interactions (both at community level and the scale of individual nurse plants) increased phylogenetic overdispersion, higher rainfall increased phylogenetic clustering. The opposing effects of environmental conditions and biotic interactions could be the main cause of the overall random phylogenetic structure found in most of these communities. Conclusions: Our results illustrate, for the first time, how an overall random phylogenetic pattern may not only be promoted by the lack of influence of either environmental filtering or biotic interactions, but rather by their joint and opposing effects. They caution about making inferences on the underlying mechanisms shaping plant communities from the sole use of their phylogenetic pattern. We also provide a comprehensive set of easy-to-measure tools to avoid misleading conclusions when interpreting phylogenetic structure data obtained from observational studies. We jointly evaluated environmental conditions and interactions among plants, at the community and patch scales, as drivers of the phylogenetic structure of semi-arid steppes. The opposed effects and the interactions between them (facilitation increased phylodiversity while higher rainfall decreased both phylodiversity and the degree of microhabitat amelioration provided by nurse plants) caused random phylogenetic structures in most studied communities.

Original languageEnglish (US)
Pages (from-to)822-836
Number of pages15
JournalJournal of Vegetation Science
Issue number5
StatePublished - Oct 2012


  • Competition
  • Diversity
  • Environmental filtering
  • Facilitation
  • Habitat differentiation
  • Mediterranean
  • Niche expansion
  • Phylogenetic structure
  • Plant-plant interactions

ASJC Scopus subject areas

  • Ecology
  • Plant Science


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