Facilitation and competition in the desert: saguaro cactus and Palo Verde trees

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Final Presentation

GROUP 4 PRESENTATION

Group

Abrego, Nerea; University of the Basque Country, Dept. Plant Biology and Ecology, Spain
Contreras, Susana; Universidad de los Andes, Dept. Biomedical Engineering, Colombia
Gonçalves, Guilherme Casas; University of São Paulo, Mathematics Institute, Brazil
Medeiros, Lucas Paoliello de; University of São Paulo, Ecology Department, Brazil
De Alencar Rocha, Maria Cecilia de Lima e Sá, Federal Uni. Bahia, Biology Institute, Brazil
Rattis, Ludmila; University of Campinas, Graduate School of Ecology, Brazil

Assistants

Bruno Pace
Vitor Rios

Assignment

Facilitation

Facilitation is an interaction between species that benefits at least one of the participants in the interaction and causes harm to neither ¹⁾. This project concerns interactions between two different plant species in an arid environment. An example of facilitation between plants is connected to the idea of nurse plants. Nurse plants are those that facilitate the growth and development of other plant species beneath their canopy because they offer benign microhabitats that are more favorable for seed germination and/or seedling recruitment than their surrounding environment ²⁾.

Saguaros and Palo Alto

In the Sonora Desert the saguaro cactus (Carnegiea gigantea) is commonly associated with canopies of trees (ex: Palo Alto), that function as nurse plants providing shelter for the cactus seedlings and young saguaro cacti. However, the nature of the interaction between saguaros and Palo Alto trees can change as the cactus grows: the larger cacti compete with the Palo Alto trees, and it has been established that the presence of saguaros contributes to Palo ALto mortality. The interaction switches from positive to negative.

Project

You should take as your starting point the paper by J.R. McAuliffe, ³⁾. You will find a description of a particular system and references to previous studies. The initial idea is to propose a model for the population dynamics of saguaros (sometimes called sahuaros) and Palo Altos.

One of the possible next steps is to consider what happens when the external conditions vary, leading to abiotic stress variations. Abiotic stress can be water availably, temperature conditions, etc. We expect that the larger the abiotic stress, the more positive the saguaro-palo alto interaction will be. Intuitively, when conditions are harsh for saguaro seedlings, the effects of the nurse plants become more important . You can find some references on this in C. Smit et alli⁴⁾.

Further Reference

A general reference on facilitation and competition between plants is

Ragan M. Callaway and Lawrence R. Walker, Competition and facilitation: a synthetic approach to interaction in plant communities, Ecology 78:1958-1965 (1997). Available at http://www.esajournals.org/doi/abs/10.1890/0012-9658%281997%29078%5B1958%3ACAFASA%5D2.0.CO%3B2

Notes

¹⁾

Adapted from Encyclopedia of Theoretical Ecology (A. Hastings and J. L. Gross, editors, Univ. California Press, 2012)

²⁾

Adapted from H. Ren, L. Yang, and N. Liu, Progress in Natural Science, 18, pp 137-142, 2008.

³⁾

Sahuaro-nurse tree associations in the Sonoran Desert: competitive effects of sahuaros, Oecologia 64, pp. 319-321 (1984), available at http://link.springer.com/article/10.1007%2FBF00379128

⁴⁾

Nurse plants, tree saplings and grazing pressure: change in facilitation along a biotic environmental gradient, Oecologia 52, pp. 265-273 (2007), which you can find at http://www.unifr.ch/ecology/groupmueller/assets/files/Publications/2007/Smit2007.pdf . This paper is actually on biotic stress, but you can find references on abiotic factors in the introduction.

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