Spatial patterns in insect community composition in coldwater springs

The insects living in 27 coldwater springs in southern Ontario, Canada were analyzed using several permutation and ordination methods, in order to detect patterns in the composition of their communities. These patterns were compared against simulations using artificial landscapes. A Moving Window Mantel Correlogram indicated the presence of both a strong local spatial aggregation and a global trend toward higher dissimilarity of sites with increasing geographical distance, especially beyond 50 km. Ordination plots showed a clear global gradient from a southern group of springs to a northern group (likely related to temperature and pH), which dominated the global, total, and local plots in both a SCA (Spatial CA) and a SPCA (Spatial PCA) analysis. However, the results of the local analysis differed markedly between the two methods: while the local plot for the SCA analysis indicated considerable variation among sites belonging to the same spatial group (thought to be related to discharge and random colonization episodes) and showed a pattern that was different from both the global and total analysis plots, the local SPCA plot showed little within-group variation and resembled the global and total plots.