Trophic diversity of the otter (Lutra lutra L.) in temperate and Mediterranean freshwater habitats

Aim: To analyse the geographical patterns in the composition and diversity of otter’s (Lutra lutra, L.) diet and their relationship with climatic characteristics. Location: European freshwater habitats under Mediterranean and temperate climatic regimes. Methods: 37 otter diet studies were reviewed, 21 from temperate and 16 from Mediterranean areas. All studies were based in spraint analysis and their results expressed as relative frequency of occurrence (RFO) of seven main prey categories. Principal Component Analysis (PCA) was performed to extract the main gradients of diet composition. Pearson’s correlation and T-tests were used to assess the relation between diet characteristics (composition, diversity, taxonomic richness) and geographic and climatic variables. Results: A clear latitudinal gradient in trophic diversity and diet composition is observed. Otter diet is more diverse and features more prey classes in southern localities, while the species is more piscivorous towards the north, where it predates upon a higher number of fish families. This pattern is contrasting when temperate and Mediterranean localities of Europe are compared. Mediterranean otters behave as more generalist predators than temperate ones, relying less on fish, and more on crayfish, aquatic invertebrates and reptiles. Main conclusions: Geographical differences in otters feeding ecology in Europe seem to be related with the two contrasted climatic conditions affecting prey populations. The otter can act as a highly specialised piscivorous predator in temperate freshwater ecosystems, which do not suffer a dry season and are comparatively more stable than Mediterranean ones. However, the unpredictable prey availability in Mediterranean areas, affected by strong spatial and temporal water shortages, would favour a diversification of otter diet