Do facilitative interactions increase species richness at the entire community level?

Abstract

Summary 1.Although the consequences of facilitation at individual and population levels are well known, the community-level consequences of these processes have received much less attention. In particular, the importance of facilitation in determining richness at the entire community level has seldom been evaluated. 2. In this study, we sampled 11 alpine plant communities along the southern Andes in South America, spanning from tropical (25°S) to sub-antarctic latitudes (55°S). Plant communities were dominated by cushion plants, a particular growth form that acts as a nurse plant for other plant species. Through rarefaction curves, we assessed the effectiveness of community sampling and estimated the number of species present within and outside cushions. Non-metric Multidimensional Scaling ordinations (NMDS) were used to assess differences between the species assemblages growing within and outside cushions. Finally, samples from cushions and open areas were combined in a single matrix accounting for the difference in cover between both microhabitats, and through rarefaction curves we assessed how many more species are added to the community due to the presence of cushions. 3. Samples taken within cushions always contained more species than equivalent samples from open areas. However, the magnitude of this difference varied among communities. NMDS ordination indicated that cushions generate species assemblages structurally different from those found in open areas. Inclusion of samples from cushion and open areas in synthetic analyseswhere differences in cover were accounted for -indicated that the presence of cushions consistently increased species richness at the entire community level. The magnitude of these increases in species richness varied with habitat severity, with lower values at both extremes of the environmental severity gradient. 4. Synthesis. Facilitative interactions with cushion nurse plants along the high Andes of southern South America changed plant assemblage structure and increased species richness at the entire community level, indicating that facilitative interactions are pivotal in maintaining the diversity of these harsh environments.

Characterizing the Interactions Among a Dinoflagellate, Flagellate and Bacteria in the Phycosphere of Alexandrium tamarense (Dinophyta)

“…That is to say, the growth of A. tamarense was controlled by the bacteria and the bacteria were controlled by Ochromonas sp. In general, the results of species interactions are the final outcome of a balance between negative and positive interactions, and consideration of the role played by species interactions in communities could contribute to maintaining community diversity and stability (Mulder et al, 2001;Cardinale et al, 2002;Butterfield, 2009;Cavieres and Badano, 2009). …”

Shrubs as foundation species in a high tropical alpine ecosystem: a multi-scale analysis of plant spatial interactions

“…Cavieres and Badano 2009). They have shown that dominant cushions increased species richness at the site scale even in cases where they did not have a significant local effect on average species richness and diversity .…”

Cluster planting facilitates survival but not growth in early development of restored tropical forest

“…Competition (Dybzinski & Tilman 2007;Weigelt et al 2007) and facilitation (Bruno, Stachowicz, & Bertness 2003;Brooker et al 2008) can act simultaneously and interact in complex ways in structuring communities, and both mechanisms have been reported to explain species coexistence (Cavieres & Badano 2009;Wright 2002). Whereas competition has been proposed to be a major structuring force in less severe environments, facilitation tends to increase in importance in harsh environments (Bertness & Callaway 1994;Callaway et al 2002;Maestre, Callaway, Valladares, & Lortie 2009), where nurse plants (Padilla & Pugnaire 2006) improve environmental conditions for target plants through shading, ameliorating temperature extremes, changing soil properties, and increasing resource availability (Callaway 1995).…”