The shape is more important than we ever thought: Plant to plant interactions in a high mountain community

Abstract

Plant to plant interactions are probably the most important driver of species coexistence at fine spatial scales, but their detection represents a challenge in Ecology. Spatial point pattern analysis (SPPA) is likely the approach most used to identify them, however, it suffers from some limitations related to the over‐simplification of individuals to points. Here, we propose a new approach called Overlapping Area Analysis (OAA) to test whether the consideration of the shape and orientation of the individuals reveal signs of interactions between species that would remain undetected with SPPA. We used this approach to analyse a fully mapped cryophilic grassland in the Sierra de Guadarrama National Park (Spain), where the crown of each individual plant (i.e. the species canopy) was approximated by a polygon. We then computed and compared the total overlapping area between the canopy of a focal species and that of any other species in the community with the expectations of a null model of random rotation of each plant around its centroid. We complemented the results of our new approach by comparing with that of SPPA of plants’ centroids. Results of OAA showed that up to 41% of species pairs had less canopy overlap than expected, suggesting that many interspecific canopy associations in this plant community were significantly negative at the finest spatial scale. Contrarily, SPPA estimated that 12% of species pairs were positively associated at spatial scales up to 20 cm, confirming the facilitative effect displayed by the main engineer in the community (Festuca curvifolia Lag.) and by some other dominant species. Our new approach quantifying canopy associations provides new insights into the processes guiding community assembly. While the results of SPPA suggested the prevalence of traditional ‘stress gradient hypothesis’ (i.e. prevalence of positive interactions under stressful abiotic conditions), OAA revealed that many interspecific canopy associations were significantly negative. Overall, most facilitated species optimized this positive effect by placing their centroids as close to the benefactor species as their foraging behaviour allowed while avoiding crown overlap. The method proposed is available in a dedicated r‐package that will facilitate its application by other ecologists.

A dimmer shade of pale: revealing the faint signature of local assembly processes on the structure of strongly filtered plant communities

“…Some authors have interpreted the convergence in plant height as a result of cold‐ and resource‐mediated abiotic processes (Pellissier et al 2010, Bernard‐Verdier et al 2012, de Bello et al 2012, Spasojevic and Suding 2012), but none of the environmental variables considered in our independence model seem to account for this convergence. In addition, this alpine community had also lower trait diversity than expected by co‐occurrence processes, indicating a minor role of weaker–competitor exclusion or competitiveness among functionally similar species (Chesson 2000, Pescador et al 2019, Scherrer et al 2019). In any case, other factors not accounted for in the independence model could be also involved in this result.…”

Portfolio effects and functional redundancy contribute to the maintenance of octocoral forests on Caribbean reefs

“…The height of colonies, as well as the vertical distribution of their biomass in branches and polyps, will affect resource acquisition, interactions with other octocorals 70 , and their capacity to form canopies 18 . In terrestrial communities, the sizes and shapes of plants are important predictors of the outcomes of interactions among individuals 71 , 72 and, more generally, the canopy created by assemblages of arborescent organisms can be considered an emergent property of dense stands of organisms (i.e., forests) 35 . The canopy modulates physical environmental features around the constituent organisms, thereby determining conditions within the understory habitat 51 , 62 , 73 , and the capacity of the forest to resist the destructive forces of the medium within which it operates (i.e., winds or the flow of water).…”

Every bit helps: The functional role of individuals in assembling any plant community, from the richest to monospecific ones

“…The so-called plant's eye perspective (sensu Aarssen, 1989;Murrell et al, 2001), centred on the response or effect of individual plants in realized assemblages, leads to evaluating the phenotypic differentiation in each neighbourhood at different scales. For example, recent studies in different speciesrich communities, using brand-new spatial pattern tools, have shown how the taxonomic (e.g., Wiegand et al, 2007;Pescador et al, 2019 for point and shape patterns), phylogenetic (Gusmán et al, 2018) and functional diversity (Chacón-Labella et al, 2016) are non-randomly organized around individuals of different species. Using the same framework, if we measure several functional traits in all individuals, we might be able to assess, for instance, the relative importance of ITV vs BTV in the assembly of neighbourhoods around each individual.…”