The Main Points

• Mostly I presented some of my own work with cladoceran assemblages in the lakes, ponds and sloughs of NW Iowa. The central question was "are the assemblages associated in some predictable way with varying combinations of the following environmental variables: Secchi depth, Weed-bed index, seasonality, and maximum depth?"

• The first figure showed the results of a correspondence analysis which was similar to the simple ordination that we discussed in the previous lecture. Two axes extracted much of the variation and patterns or groupings of samples indicated that the
  1. assemblages of the large lakes separated clearly, in all seasons, from those of the smaller lakes, ponds and sloughs.

  2. Sloughs, the shallowest habitats sampled, separated from the small lakes.

  3. While similar in many respects, the "weedy" pothole lakes and the eutrophic "non-weedy" potholes differed in the occurrence of the species associated in their feeding habits with plant surfaces.

• The second figure was the result of a canonical correspondence analysis that showed the relationships of the derived axes (shown in the previous figure) with the four environmental variables (see above). While the analysis of these data are not complete, two conclusions may be drawn:
  1. Amount of rooted aquatic vegetation, seasonality and depth are the independent variables that "regulate" the distribution and abundance of the Cladocera making up the assemblages.

  2. Given a particular set of the independent variables, one may make a reasonable approximation of both the cladoceran group that will be in common with the other bodies of water in the area, and the cladoceran group that is unique to that particular kind of lake.