Below is an example analysis of metacommunity structure following the methods of (Leibold and Mikkelson 2002 and Presley et al. 2010) that is designed to illustrate how to interpret output from the “metacommunity” function in Matlab (available from http://www.tarleton.edu/Faculty/higgins/EMS.htm).
Example output >> [Abs,Apr,MA,SA,Re,Rpr,MR,SR,M,Mpr]= metacommunity(data,1,5,0,1000,1)
Abs = 25
Apr = 1.8764e-004
MA = 53.5800
SA = 7.6517
Re = 940
Rpr = 0.4029
MR = 818.7200
SR = 144.9882
M = 1.0870
Mpr = 0.2909
Interpretation of output In this case, for coherence there were 25 observed embedded absences (Abs), the mean generated by the selected null model was 53.58 (MA) with a standard deviation of 7.65 (SA). This resulted in a p-value (Apr) of 0.0001876. Because the observed number of embedded absences was less than the mean produced by the null model, the metacommunity is significantly positively coherent (with a p-value of .0001876), indicating non-random (and non-checkerboard) structure and that distributions of species are determined by a common latent environmental gradient.
For species turnover, the observed number of replacements (Re) was 940, and the mean (MR) produced by the null model was 818.72 with a standard deviation (SR) of 144.99, resulting in a p-value (Rpr) of 0.403. Because turnover was non-significant but greater than average (i.e. because the observed (940) was greater than the mean produced by the null model (818)), the result is consistent with a non-nested quasi-structure (i.e. quasi-Clementsian, quasi-Gleasonian, or quasi-evenly spaced), which one will depend on boundary clumping results. For combinations of turnover and boundary clumpin that are consistent with each coherent structure, refer to Presley et al. 2010 or the figure of “coherent space” near the bottom of the metacommunity web page (http://hydrodictyon.eeb.uconn.edu/people/willig/Research/metacommunity%20page.html).
For boundary clumping, Morisita's Index was 1.087 and the p-value for the associated Chi-square test was 0.291, indicating that boundary clumping was stochastic (i.e. not significantly different than expected by chance) and that the metacommunity has quasi-Gleasonian structure.
In biological terms, this means that the group of species is responding to the same environmental gradient (positive coherence), that species turnover occurs, but is not strong (which typically occurs because the gradient represented by the group of sites is short compared to the niche breadths of the species), and that the limits of species boundaries occurring in an idiosyncratic fashion (consistent with Gleason's "individualistic hypothesis").