Environmental conditions and biotic interactions acting together promote phylogenetic randomness in semi-arid plant communities: new methods help to avoid misleading conclusions
Article first published online: 26 MAR 2012
© 2012 International Association for Vegetation Science
Journal of Vegetation Science
Volume 23, Issue 5, pages 822–836, October 2012
How to Cite
Soliveres, S., Torices, R., Maestre, F. T. (2012), Environmental conditions and biotic interactions acting together promote phylogenetic randomness in semi-arid plant communities: new methods help to avoid misleading conclusions. Journal of Vegetation Science, 23: 822–836. doi: 10.1111/j.1654-1103.2012.01410.x
- Issue published online: 4 SEP 2012
- Article first published online: 26 MAR 2012
- Manuscript Accepted: 17 FEB 2012
- Manuscript Received: 13 JUN 2011
- Fundación Biodiversidad and CINTRA S.A. RT
- Spanish Ministerio de Educación. Grant Number: BVA 2010-0375
- European Research Council under the European Community's Seventh Framework Programme. Grant Numbers: FP7/2007-2013, 242658
- Environmental filtering;
- Habitat differentiation;
- Niche expansion;
- Phylogenetic structure;
- Plant–plant interactions
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?
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.
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).
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.
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.