Environmental factors and distribution of littoral oligochaetes in Pyrenean lakes
Collado, Rut; De Mendoza, Guillermo
Littoral oligochaete populations of 82 representative mountain lakes were sampled throughout the Pyrenees. Forty different oligochaete taxa were collected, and thirty of them were identified to species level. Naididae and Enchytraeidae were found to be dominant in terms of incidence, abundance, and species richness. Measurements of several descriptors relating to the physical and chemical environment, and productivity of each lake, revealed that these two oligochaete groups segregate along the main gradient of environmental variation related to species variance. This environmental gradient was defined by the first ordination axis in a Canonical Correspondence Analysis (CCA), and was mostly related to the variables ‘altitude’, ‘temperature’, ‘fishless’, ‘fine substrate’, and ‘pH’. The segregation patterns observed among the Naididae and the Enchytraeidae mainly occurred relative to the variables ‘temperature’and ‘fine substrate’, and only temperature appeared to explain the observed incidence and abundance patterns found within these two oligochaete groups. Thus, we suggest that temperature, rather than substrate type, is most likely to underlie the observed segregation patterns among the Naididae and the Enchytraeidae. The incidence of the Naididae was positively related to temperature, and this tendency was consistently observed when analysing the frequently observed species within the group, in concordance with the idea that very cold temperatures limit the distribution of the Naididae. In contrast, the abundance of the Enchytraeidae was negatively related to temperature, but this pattern was strongly governed by Cervosvitoviella spp. distribution.