Evidence for assembly rules: limiting similarity within a saltmarsh

Abstract

Summary1. We sought evidence for limiting similarity, a basic aspect of community structure, in three zones of a saltmarsh. Sampling was conducted at three spatial scales (grains), from a single point up to the scale of several square metres. Twenty-three functional traits, related to the structure of the shoot and root systems and to nutrient status, were measured on each species present, separately in each community. 2. Patterns of association between plant species were compared with those expected under a null model, to assess whether plants with similar functional traits tended to coexist or to separate, i.e. whether there was environmental filtering or limiting similarity. A patch null model was used, a type that tends to be conservative but that avoids spurious evidence of limiting similarity caused by environmental pseudoreplication. One overall and four univariate test statistics were calculated, to capture possible patterns in trait space whilst minimising the problem of multiple testing. 3. In the Shrub community, overall evidence for even spacing of co-occurring species in functionaltrait space, the pattern expected from the theory of limiting similarity, was seen at the area scale. In univariate tests in that community, there was evidence for even spacing in leaf lobation and leaf succulence, especially at small scales. 4. In the Rush community, there was significant evidence for limiting similarity in several traits, especially those related to canopy interactions, but also in some root characteristics. However, clustering in other traits, presumably owing to microenvironmental filtering, reduced overall tests for limiting similarity to 'marginal significance' (0.1 > P > 0.05). 5. In the species-poor and salt-stressed Salt turf, significant departures from the null model were sporadic and not consistent, although chlorophyll characters and leaf nitrogen concentration tended to be clustered. 6. Synthesis: There was evidence for niche limitation in two of the communities -Rush and Shrubapparently based on canopy interactions in both cases and perhaps also root interactions in the latter community. Limiting similarity can be an important force in community assembly. However, in situations when it cannot be demonstrated, we do not know whether trait-based competition is absent or whether its signal is overwhelmed by other processes.

How to design trait-based analyses of community assembly mechanisms: Insights and guidelines from a literature review

“…Similarly, species abundance reflects whether species are more or less successful competitors, leading to limiting similarity and competitive dominance patterns depending on the limiting resource(s) (Cingolani et al, 2007). Indeed, biotic interactions are generally studied with abundance data Wilson and Stubbs, 2012), as also observed in our literature review in which limiting similarity and competitive dominance were more frequently detected using abundance than presence-absence data (Götzenberger et al, 2016; Fig. 3A).…”

Seedling recruitment factors in low‐diversity Hawaiian wet forest: towards global comparisons among tropical forests

“…Pianka's O measures the relative frequency of shared microhabitat utilization by species pairs; values range from 0 (no overlap) to 1 (total overlap). This approach is commonly used for analysis of habitat use by animals (e.g., Glen andDickman 2008, Hadi et al 2012) and may also be effectively applied to vegetation, as the index behaves similarly to other commonly used niche overlap measures (Potts et al 2004, Rö dder and Engler 2011, Wilson and Stubbs 2012. Habitat association and niche overlap analyses were conducted for the six species found in at least four of the seedling plots.…”

Non-Native Plants Disrupt Dual Promotion of Native Alpha and Beta Diversity

“…Treatment symbols are as in Fig. 1 arrival may have led to variation in the degree of habitat modification by this species, causing different species to establish in different plots according to their ecological traits (Stubbs and Wilson 2004;Holdaway and Sparrow 2006;Wilson and Stubbs 2012) and ultimately increasing beta diversity more than expected from random assembly (Fukami et al 2005;Lanta and Lepš 2009;Chase 2010). This biotic increase in beta diversity occurred without compromising enhancement of alpha diversity by immigration.…”