Table 1: Results of the multiple linear models performed to test the effect of lake shape, physicochemical properties—depth, water transparency, and productivity (nitrogen and phosphorus concentration)—isolation (distance to river margin and distance to nearest lake), and habitat richness provided by marginal vegetation, on the qualitative and quantitative composition of the communities of aquatic birds. The first figures in the DF columns are the degrees of freedom of the treatment; the second, those of lakes. The analyses were performed on scores resultant from nonmetric multidimensional scaling (NMDS). See Section 2 for details.

Ecological variablesQualitativeQuantitative
Pillai-TraceFDFPPillai-TraceFDFP

Lake shape*0.0751.1153; 410.3540.0340.4833; 410.696
Lake depth0.0560.7163; 360.5490.2393.7793; 360.019
Lake productivity
 Nitrogen0.0050.0583; 360.9810.1001.3353; 360.278
 Phosphorus0.0911.1993; 360.3240.1462.0473; 360.125
Water transparency0.2163.3063; 360.0020.1091.4643; 360.240
Distance to river margins0.2744.5343; 360.0090.3255.7683; 360.003
Distance to nearest lake0.3295.8833; 360.0020.2574.1593; 360.013
Habitat richness*0.3948.8903; 410.00010.59820.3343; 410.0001

*Lake shape and habitat richness were significantly correlated to other variables, and therefore analyzed in separate models (see Section 3 and also Figure 7).