Ecological role of the Eurasian otter, Lutra lutra (Mustelidae, Carnivora) as a seed dispersal species for riparian vegetation in Iberian fresh waters

Abstract. Endozoochory is a mutualistic interaction between plants and animals. Such a relationship has rarely been examined in the Eurasian otter Lutra lutra. This study aimed to assess the use and electivity of fruit by this carnivore, along with the viability of ingested seeds. Otter spraints and fruit were collected from the River Bullaque (Guadiana River basin, central Spain) in June and September 2018-2019. A high occurrence of fruit (> 40%) was found in spraints during September. Otters ingested fruit in June from only one plant species: Iberian bushweed Flueggea tinctoria (Phyllanthaceae); whereas seeds ingested in September belonged to four plant species: apple mint Mentha suaveolens (Lamiaceae), common hawthorn Crataegus monogyna, dog rose Rosa canina and elmleaf blackberry Rubus ulmifolius (three Rosaceae species). According to the environmental availability, otters displayed avoidance for mint and rose, neutral selection for hawthorn and preference for blackberry. Germination was unsuccessful for mint seeds, whereas germination was the highest for blackberry (37%; 49% for blackbird Turdus merula, a well-known frugivorous species). Otters appear to display an ecological role as seed dispersers for riparian vegetation in Iberian fresh waters. These findings provide insights into this endozoochorous co-evolution between plants and Carnivora.