Niche overlap reveals the effects of competition, disturbance and contrasting assembly processes in experimental grassland communities

Abstract

Summary 1.Understanding the processes by which species sort themselves into communities remains a central puzzle for attempts to maintain biodiversity. It remains unclear whether any single assembly process is generally dominant or whether the influence of contrasting processes varies in a predictable way relative to biotic and abiotic gradients. Abundance-weighted niche overlap between species provides a powerful means of contrasting two major assembly processes -niche complementarity and environmental filtering. 2. We examined mean overlap for four vegetative functional traits, relative to that expected when abundances were randomly allocated to species co-occurring in experimental plots in a wet meadow. This provided a test of whether any single assembly process prevailed for the meadow as a whole and across all traits. The effects of mowing, fertilization and dominant species removal, and associated gradients of Simpson's dominance and biomass on the niche overlap of plots, were also examined. 3. Niche overlap was higher than expected at random for three of the four traits studied (height, leaf and stem dry matter content, leaf C:N ratio). However, niche overlap was lower than expected for specific leaf area. 4. Mowing was the treatment with the greatest effect on both niche overlap and biomass, with overlap significantly lower in the absence of mowing for three of the traits, while biomass was lower in mown plots. For three of the traits there was evidence of a significant decrease in overlap with increasing biomass, but not increasing dominance. None of the significant mowing effects on overlap remained when the effect of biomass had been removed. 5. Synthesis: These results suggest that the importance of niche differences between species in structuring grassland communities should increase with increasing biomass and decrease with disturbance in grassland communities. They also emphasize that contrasting community assembly processes may occur for different niche axes, even within a single community.

Evidence for scale‐ and disturbance‐dependent trait assembly patterns in dry semi‐natural grasslands

“…While a small number of studies have examined the effects of spatial scale on community assembly, a greater number of them have investigated changes in assembly patterns across different disturbance regimes (see, for example, Pausas & Verd 2008;Mason et al 2011;Bernard-Verdier et al 2012;Lalibert e, Norton & Scott 2013). Theoretical predictions and conclusions about the way in which disturbance regimes may influence convergence and divergence patterns vary between studies, depending on the type and intensity of the disturbance regime, but also on the fact that disturbance effects on species coexistence are expected to change across biomes and productivity gradients (Pickett & White 1985;Lalibert e, Norton & Scott 2013).…”

“…It is generally assumed that trait divergence will be stronger under moderately disturbed conditions (Grime 2006) -such as those in traditionally grazed or mown grasslands (Grubb 1986) -where biomass removal should decrease the chance of competitive exclusion of species that bear traits associated with low competitive ability (Mayfield & Levine 2010). However, it has also been observed that a lack of biomass removal in grasslands may enhance niche differentiation and promote functional divergence between species in response to greater competition for light (Mason et al 2011). The abandonment of traditional grassland management may therefore potentially result in either increased divergence or increased convergencedepending on the site conditions.…”

“…Biotic and abiotic effects on community assembly have often been treated as being mutually exclusive (Mason et al 2011;de Bello 2012;G€ otzenberger et al 2012), and their relevance has usually been assessed at a single spatial scale and under specific environmental conditions. However, both effects might operate within plant communities, although they might be detected at different spatial scales and under different environmental conditions (de Bello et al 2009;Kraft & Ackerly 2010).…”

Grass strategies and grassland community responses to environmental drivers: a review

“…The selection and complementarity effects distinguish the effects of very productive and dominant species to the complementarity in resource utilization by different species. Three grassland communities of six grass species across four management treatments (two cut frequencies and two levels of nitrogen fertilization) and throughout 2 years were explored in this study (n=24 for species assembling (Mason et al 2011;Spasojevic and Suding 2012;Gerhold et al 2013;Laliberté et al 2013;Price et al 2014;Carboni et al 2014). For instance, along an environmental severity gradient in productive grassland communities, Maire et al (2012a, see also Bernard-Verdier et al 2012 as another example along a natural soil fertility gradient in Mediterranean rangelands) found that convergence pattern towards high plant stature traits was the predominant force to explain species abundance in fertile and less disturbed habitat.…”

Effects of clipping and fertilizing on the relationship between functional diversity and aboveground net primary productivity in an alpine meadow

“…近年来, 随着全球生物多样性的快速降低, 生 物多样性与生态系统功能的关系成为生态学领域备 受关注的科学问题 (Chapin et al, 2000)。生态系统生 产力是反映生态系统功能的最为综合的指标(如碳 氮循环、枯落物分解、动物采食等) (Chapin et al, 2000;Naeem, 2002) Leibold, 1998;Grime, 2006;Mayfield & Levine, 2010); 二是共存物种间的生态 位分化又会促使性状趋异, 引起FD增加 (Macarthur & Levins, 1967;Navas & Violle, 2009;Mouchet et al, 2010;Mason et al, 2011), FD对施肥的响应取决于 这两种机制的平衡 (Niu et al, 2014 …”