Hydrological stability and otter trophic diversity: a scale- insensitive pattern?

Two recent works related otter (Lutra lutra, L., 1758) trophic patterns over large areas with the stability of aquatic ecosystems. Higher levels of instability lead to a reduced availability and/or predictability of fish, and consequently to a decrease of fish consumption by otters. The aim of the present study is to test these macrogeographical patterns in otter diet at regional and local-scale approaches. We analysed otter diet in Mediterranean streams in south-western Iberian Peninsula where clear hydrological stability gradients (related to drainage area or distance to the sea) could be defined. Hydrological stability was directly related to fish consumption and inversely to otter diet diversity in terms of occurrence and biomass, both at regional and local-scale approaches. The level of stability of aquatic ecosystems appears as a critical indirect factor modulating otter diet, through its effects on fish populations. The resulting trophic patterns are maintained from local to macrogeographical scales.