Editor's Choice

Journal of Ecology, Volume 96, Issue 3 (May 2008)


From the papers in another compelling issue of Journal of Ecology, I’ve chosen the paper by Alfonso Valiente-Banuet and Miguel Verdu, entitled Temporal shifts from facilitation to competition occur between closely related taxa as my Editor’s Choice. This paper continues the discussion raised in Journal of Ecology about a number of contentious issues related to the importance of plant interactions in communities. Briefly, Valiente-Banuet and Verdu use phylogenetic relatedness of co-occurring plants to suggest shifting interactions among plants from facilitation to competition as plants mature from seedlings to adults.

The study is based upon field data collected on the spatial association of 102 woody species in three semiarid columnar cacti-dominated communities in Mexico. Saplings and seedlings of species growing either beneath canopies or in open areas were counted, allowing the authors to recognize pairs of nurse plants and seedlings (representing facilitation) and work out whether these facilitation-pairs persisted as spatially associated adults of both species (indicating continued facilitation) or were lost (resulting from competitive exclusion). They then used independent phylogenetic data to calculate the mean phylogenetic distance (MPD) between both sets of pairs of species.

Mean phylogenetic distance or phylogenetic relatedness was used as a proxy measure of competition (closely related species indicating competition). Comparisons of MPDs were made against a null model indicating no change in MPD between nurse plant – seedling species pairs and sapling - sapling plant species pairs. The analysis showed 53% of facilitation remained with time as plants matured, whereas 47% shifted to competition. Thus, species interactions were shifting from facilitation to competition.

A number of years ago Harvey et al (1995) suggested that ecologists should be phylogenetically challenged in their thinking about the structure of plant communities. Ecologists are increasingly taking this idea on board, yet the issue remains controversial. Competition arising among closely related species has been implicated in explaining high levels of monophyly among island taxa (Silvertown 2005, but see alternate views in Saunders & Gibson 2005, and Herben et al 2005). The nature of plant-plant interactions, particularly facilitation, along stress-gradients is an unresolved question (see lively discussion in Lortie & Callaway 2006, Maestre et al 2005, 2006). Brooker et al (2008) discuss these and other issues in their recent review which considers facilitative interactions to have a central role in determining the structure of plant communities, and that the role of facilitation should now be regarded as just as important as competition has been considered in the past.

These issues aside, Valiente-Banuet and Verdu have shown that we need not view competition-facilitation as an either-or in time or space, but rather as end points of the continuum of interactions in which plants are involved throughout the course of their lives. In their Mexican desert system at least, it appears that facilitation dominates species interactions early on (being 2-3 times more frequent than negative interactions) as nurse plants allow seedlings to grow and vegetation clumps to develop, but that competitive interactions become more important as plants mature. However, the significant number of facilitative interactions among distantly related taxa that do remain among adult plants suggests the need for future mechanistic studies to provide an explanation. Valiente-Banuet and Verdu suggest that the mechanisms allowing facilitation among adult plants may be related to functional complementarity in the belowground soil community. We look forward to seeing this idea addressed and hope to see the results of new research in this direction in the pages of Journal of Ecology in the future.

We hope you will enjoy reading the latest research from Journal of Ecology. If you have any comments about our published output we would be pleased to hear them. Please write to the Managing Editor.

David Gibson
Editor, Journal of Ecology 

References

      Alfonso Valiente-Banuet and Miguel Verdú. (2008)

Temporal shifts from facilitation to competition occur between closely related taxa

      . Journal of Ecology, DOI: 10.1111/j.1365-2745.2008.01357.x.



      Brooker, R.W., F. T. Maestre, R. M. Callaway, C. L. Lortie, L. Cavieres, G. Kunstler, P. Liancourt, K. Tielbörger, J. M. J. Travis, F. Anthelme, C. Armas, L. Coll, E. Corcket, S. Delzon, E. Forey, Z. Kikvidze, J. Olofsson, F. I. Pugnaire, C. L. Quiroz, P. Saccone, K. Schiffers, M. Seifan, B. Touzard & Michalet, R. (2008)

Facilitation in plant communities: the past, the present and the future

      . Journal of Ecology, 96, 18–34.



      Harvey, P.H., A.F. Read, & Nee, S. (1995) Why ecologists need to be phylogenetically challenged. Journal of Ecology, 83, 535-536.



      Herben, T., Suda, J. & Munclinger, P. (2005) The ghost of hybridization past: Niche pre-emption is not the only explanation of apparent monophyly in island endemics. Journal of Ecology, 93, 572– 575.



      Lortie, C.J. & Callaway, R.M. (2006) Meta-analysis and rejection of the stress-gradient hypothesis? Analytical recommendations. Journal of Ecology, 94, 7–16.



      Maestre, F.T., Valladares, F. & Reynolds, J.F. (2005) Is the change of plant-plant interactions with abiotic stress predictable? A meta-analysis of field results in arid environments. Journal of Ecology, 93, 748−757.



      Maestre, F.T., Valladares, F. & Reynolds, J.F. (2006) The stress-gradient hypothesis does not fit all relationships between plant-plant interactions and abiotic stress: Further insights from arid environments. Journal of Ecology, 94, 17–22.



      Saunders, N.E. & Gibson, D.J. (2005) Breeding system, branching processes, hybrid swarm theory, and the hump-back diversity relationship as additional explanations for apparent monophyly in the Macaronesian island flora. Journal of Ecology, 93, 649-652.



      Silvertown, J. (2004) The ghost of competition past in the phylogeny of island endemic plants. Journal of Ecology, 92, 168– 173.



    Silvertown, J. Francisco-Ortega, & Carine, J.M. (2005) The monophyly of island radiations: an evaluation of niche pre-emption and some alternative explanations. Journal of Ecology, 93, 653–657.