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

Authors

  • Norman W.H. Mason,

    Corresponding author
    1. Landcare Research, Private Bag 3127, Hamilton, New Zealand
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  • Francesco de Bello,

    1. Institute of Botany, Czech Academy of Sciences, Dukelská 135, CZ-379 82 Třeboň, Czech Republic
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  • Jiři Doležal,

    1. Institute of Botany, Czech Academy of Sciences, Dukelská 135, CZ-379 82 Třeboň, Czech Republic
    2. Department of Botany, Faculty of Science, University of South Bohemia, Na Zlaté stoce 1, 370 05 České Budĕjovice, Czech Republic
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  • Jan Lepš

    1. Department of Botany, Faculty of Science, University of South Bohemia, Na Zlaté stoce 1, 370 05 České Budĕjovice, Czech Republic
    2. Biology Centre of Czech Academy of Science, Institute of Entomology, Branišovská 31, 370 05 České Budĕjovice, Czech Republic
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Correspondence author. E-mail: masonn@landcareresearch.co.nz

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.

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