Ecological Gradients Influencing Waterbird Communities in Black Water Lakes in the Anavilhanas Archipelago, Central Amazonia

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 variables	Qualitative				Quantitative
	Pillai-Trace	F	DF	P	Pillai-Trace	F	DF	P
Lake shape*	0.075	1.115	3; 41	0.354	0.034	0.483	3; 41	0.696
Lake depth	0.056	0.716	3; 36	0.549	0.239	3.779	3; 36	0.019
Lake productivity
Nitrogen	0.005	0.058	3; 36	0.981	0.100	1.335	3; 36	0.278
Phosphorus	0.091	1.199	3; 36	0.324	0.146	2.047	3; 36	0.125
Water transparency	0.216	3.306	3; 36	0.002	0.109	1.464	3; 36	0.240
Distance to river margins	0.274	4.534	3; 36	0.009	0.325	5.768	3; 36	0.003
Distance to nearest lake	0.329	5.883	3; 36	0.002	0.257	4.159	3; 36	0.013
Habitat richness*	0.394	8.890	3; 41	0.0001	0.598	20.334	3; 41	0.0001

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