Otterly delicious: Spatiotemporal variation in the diet of a recovering population of Eurasian otters ( Lutra lutra) revealed through DNA metabarcoding and morphological analysis of prey remains

Abstract

Eurasian otters are apex predators of freshwater ecosystems and a recovering species across much of their European range; investigating the dietary variation of this predator over time and space, therefore, provides opportunities to identify changes in freshwater trophic interactions and factors influencing the conservation of otter populations. Here we sampled feces from 300 dead otters across England and Wales between 2007 and 2016, conducting both morphological analyses of prey remains and dietary DNA metabarcoding. Comparison of these methods showed that greater taxonomic resolution and breadth could be achieved using DNA metabarcoding but combining data from both methodologies gave the most comprehensive dietary description. All otter demographics exploited a broad range of taxa and variation likely reflected changes in prey distributions and availability across the landscape. This study provides novel insights into the trophic generalism and adaptability of otters across Britain, which is likely to have aided their recent population recovery, and may increase their resilience to future environmental changes.

Abstract

Our national scale investigation of the trophic ecology of a recovering apex predator over a decade using molecular tools highlights that prey distributions are likely to drive such species recoveries. We show that the trophic interactions of otters vary over spatial, temporal, and biological gradients and that their trophic generalism has likely been a significant factor in their proliferation and future resilience to change. Our data highlight the strength of applying molecular and morphological approaches to dietary analysis in tandem for increased trophic network completeness.