Abstract
Environmental filtering and niche differentiation are processes proposed to drive community assembly, generating nonrandom patterns in community trait distributions. Despite the substantial intraspecific trait variation present in plant communities, most previous studies of trait-based community assembly have used species mean trait values and therefore not accounted for intraspecific variation. Using a null model approach, I tested for environmental filtering and niche differentiation acting on three key functional traits—vegetative height, specific leaf area (SLA), and leaf dry matter content (LDMC)—in old-field plant communities. I also examined how accounting for intraspecific variation at the among-plot and individual levels affected the detection of nonrandom assembly patterns. Tests using fixed species mean trait values provided evidence of environmental filtering acting on height and SLA and niche differentiation acting on SLA. Including plot-level intraspecific variation increased the strength of these patterns, indicating an important role of intraspecific variation in community assembly. Tests using individual trait data indicated strong environmental filtering acting on all traits, but provided no evidence of niche differentiation, although these signals may have been obscured by the effects of dispersal limitation and spatial aggregation of conspecific individuals. There was also strong evidence of nonrandom assembly of individuals within single species, with the strength of environmental filtering varying among species. This study demonstrates that, while analyses using fixed species mean trait values can provide insights into community assembly processes, accounting for intraspecific variation provides a more complete view of communities and the processes driving their assembly.
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Acknowledgments
I thank Mark Ritchie for advice that improved this research; Jason Fridley, Nathan Kraft, Vincent Jung, C.E. Timothy Paine, and an anonymous reviewer for insightful comments on an earlier version of this manuscript; Maureen Carey for help with trait measurements; and Tom Hughes for providing access to field sites. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship. The data were collected in compliance with current United States laws and with required permission.
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The author declares that he has no conflict of interest.
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Communicated by Bryan Foster.
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Siefert, A. Incorporating intraspecific variation in tests of trait-based community assembly. Oecologia 170, 767–775 (2012). https://doi.org/10.1007/s00442-012-2351-7
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DOI: https://doi.org/10.1007/s00442-012-2351-7