Comment on "Functional Traits and Niche-Based Tree Community Assembly in an Amazonian Forest"
Jeffrey K. Lake* and
Annette Ostling
Department of Ecology and Evolutionary Biology, University of Michigan, Kraus Natural Sciences Building, 830 North University, Ann Arbor, MI 48109, USA.
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Fig. 1. Representation of the effect of sampling from intraspecific variability. (A) Hypothetical plot-level trait distributions of three species with a perfectly overdispersed, normally distributed trait, with means of 90, 100, and 110, respectively, and a SD of 10. (B) An example within-quadrat trait distribution that results when we sample one "real" individual from the distribution for each species instead of assuming that individual follows the species means, as Kraft et al. did. The height of the bars represents the number of occurrences, which is one for each species. (C) The resulting distribution of SD of nearest-neighbor distances (SD of NN) across 100 quadrats created in this way. The values of SD of NN if species means were used as Kraft et al. did is 0. Hence, intraspecific variation causes the SD of NN to go up on average. It will have this effect on both the observed and null model SD of NN. However the effect on the null model SD of NN will be extremely small because the species are so tightly packed in trait space at the plot level that traits sampled from species near one another in trait space become essentially interchangeable. The net result is that the observed SD of NN goes up, whereas the null SD of NN remains approximately the same, when intraspecific variation is accounted for, and the evidence for niche differentiation gets weaker.
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