Multi‐species competition experiments with peatland bryophytes

Abstract

Question Species interactions are one of the processes determining composition of plant communities. We used the community density series method to study competition in a multi‐species community of bryophytes common in calcareous fens. The succession of mires is driven by Sphagnum species, which are supposedly superior to brown mosses in competition for resources and space, but little is known about the environmental conditions in which brown mosses can prevail when subject to neighbour interactions. How are interactions among peatland bryophytes affected by the environment? Location Field and garden experiments near Uppsala in mid‐eastern Sweden. Methods To examine the effects of environment on competition and competitive hierarchies we assembled multi‐species communities of ten bryophyte species from shoot fragments (brown mosses and Sphagnum species) at two densities and grew them on three types of peat (representing poor, intermediate and rich fens) under dry or wet conditions in a garden experiment and along pH and wetness gradients in the field. Results A multivariate analysis of the garden experiment showed that community composition was affected by peat type and wetness and their interactions. The brown mosses performed better in wet and rich fens, the Sphagnum species in drier and poorer fens. The Sphagnum species were overall the best competitors. Conclusions The experiments demonstrated contrasting responses of brown mosses and Sphagnum to properties of the microhabitat. Sphagnum species were generally less affected by competition than the brown mosses. Sphagnum species were competitive in habitats typically dominated by brown mosses and even responded positively to crowding. This can explain why Sphagnum can invade calcareous fens. In contrast, brown mosses performed poorly in habitats more typical of Sphagnum species.

Species‐pair associations, null models, and tests of mechanisms structuring ecological communities

“…Many laboratory‐ and field‐based experimental studies have inferred competition as the mechanism driving changes in the abundance or occurrence of one species as a function of the abundance or occurrence of another (Connell , Goldberg and Barton , Udd et al. ), but contrary to expectations, we found that species within a group of potential competitors were consistently aggregated (Fig. ).…”

“…Competition has often been regarded as the dominant species interaction and among the most important mechanisms driving community structure (Elton 1946, Diamond 1975, Meyer and Kalko 2008; however, this assumption has often lacked appropriate quantitative testing Simberloff 1979, Englund et al 2009). Many laboratory-and field-based experimental studies have inferred competition as the mechanism driving changes in the abundance or occurrence of one species as a function of the abundance or occurrence of another (Connell 1983, Goldberg and Barton 1992, Udd et al 2016, but contrary to expectations, we found that species within a group of potential competitors were consistently aggregated (Fig. 3) Fig.…”

Tolerance of fen mosses to submergence, and the influence on moss community composition and ecosystem resilience

“…Similar interactions have been observed in multi‐species experiments where Sphagnum spp. were out‐competed by true mosses in wet rich fens (Udd et al., ) and A. palustre was competitively excluded in mature communities (Li & Vitt, ). In boreal rich fens, T. nitens is one of the most abundant and has the widest habitat niche breadth among true peatland moss species (Gignac, ; Vitt, Wieder, Scott, & Faller, ).…”

Bryophyte community assembly on young land uplift islands – Dispersal and habitat filtering assessed using species traits

“…However, there is mixed evidence for biotic filtering due to interspecific bryophyte competition, with studies showing that competitive exclusion may (e.g. Li & Vitt, 1995;Udd, Sundberg, & Rydin, 2016) or may not (e.g. Mälson & Rydin, 2009;Økland, 1994) affect species occurrences.…”