Dominance across montane meadows: Patterns and processes structuring plant communities

Abstract

33 Background. Understanding the underlying factors that determine the relative abundance of 34 plant species is critical to predict both biodiversity and ecosystem function. Biotic and abiotic 35 factors can shape the distribution and the relative abundance of species across natural 36 communities, greatly influencing local biodiversity. 37 Methods. Using a combination of an observational study and a five-year plant removal 38 experiment we: (1) documented how plant diversity and composition of montane meadow 39 assemblages vary along a plant dominance gradient using an observational study; (2) tracked 40 above-and belowground functional traits of co-dominant plant species Potentilla and Festuca 41 along a plant dominance gradient in an observational study; (3) determined whether plant species 42 diversity and composition was directly influenced by commonly occurring species Potentilla and 43 Festuca with the use of a randomized plot design, 5-year plant removal experiment (no removal 44 control, Potentilla removed, Festuca removed, n=10) . 45 Results. We found that subordinate species diversity and compositional dissimilarity were 46 greatest in Potentilla and Festuca co-dominated sites, where neither Potentilla nor Festuca 47 dominated, rather than at sites where either species became dominant. Further, while above-and 48 belowground plant functional traits varied along a dominance gradient, they did so in a way that 49 inconsistently predicted plant species relative abundance. Also, neither variation in plant 50 functional traits of Festuca and Potentilla nor variation in resources and conditions (such as soil 51 nitrogen and temperature) explained our subordinate diversity patterns. Finally, neither Potentilla 52 nor Festuca influenced subordinate diversity or composition when we directly tested for their 53 impacts in a plant removal experiment. 54 Discussion. Taken together, patterns of subordinate diversity and composition were likely driven 55 by abiotic factors rather than biotic interactions. As a result, the role of abiotic factors 56 influencing local-level species interactions can be just as important as biotic interactions 57 themselves in structuring plant communities. 58 Introduction 59 Linkages between species' relative abundance and ecosystem function are important to predict 60 ecosystem resistance and resilience to global change pressures. Dominant species, with high 61 relative abundance (i.e., primary production), have been shown to strongly impact community 62 dynamics and ecosystem function (Whitaker 1972; Wardle et al. 1999;Grime 1977Grime 2001Grime 2006 63 Hooper et al. 2005). In fact, according to Grime's (1998) "mass ratio hypothesis" species with 64 greater primary production exert the main controls for the functioning of ecosystems. Based on 65 this hypothesis, dominant species are considered more important in an ecosystem because of the 66 greater aboveground abundance of biomass or leaf area (e.g., foliar cover) that promotes resource 67 uptake. However, an increasing a...