Secondary Dispersal of Wetland Plants by Neotropical Otters

Carnivorous mammals can disperse seeds and other plant propagules through gut passage (endozoochory). Otters are semiaquatic mustelids and opportunistic carnivores that prey on various vertebrates, and their feeding habits can lead to secondary dispersal of plant propagules. However, this secondary dispersal by otters has not previously been investigated. Here, we investigated the internal dispersal of plants by neotropical otters,Lontra longicaudis, in southern Brazil. We collected 31 faecal samples (spraints) from neotropical otters at a Brazilian Ramsar site of the Pampa biome during the wet season of 2022. Intact propagules were separated from each spraint, identified, and their germinability tested where possible. The classes of vertebrate preyed upon in each spraint were identified. We investigated the effects of these prey classes and of spraint mass on the taxonomic richness and abundance of propagules of plants associated with aquatic and/or terrestrial substrates. We recorded 1206 propagules belonging to 33 plant taxa (one charophyte, four pteridophytes, and 28 angiosperms), representing 18 plant families and including 20 strictly aquatic macrophytes. Seeds from six angiosperm taxa were germinated, with a low overall germination rate of 2%. All spraints contained fish, while 10 also contained remains of reptiles, amphibians, and/or mammals. The taxonomic richness of propagules was positively correlated with spraint weight. Propagule abundance depended on both spraint weight and the diversity of prey classes in the spraint. Spraints with three or four prey classes were larger and had the most propagules. Most propagules are likely dispersed by "diploendozoochory" involving ingestion first by prey and then by the otters. Neotropical otters have a wide home range, often travelling several kilometres daily, which can promote plant dispersal by carrying propagules between different habitats. Synthesis: Our results suggest that otters might play an important role in the dispersal of wetland plants, notably aquatic ferns, potentially contributing to the maintenance of these ecosystems. The germination rate, although low, represents opportunities for the successful establishment of some dispersed propagules over longer distances than those provided by otter prey, emphasising the ecological importance of even low-probability dispersal events. This study underlines the potential role of carnivorous mammals in maintaining ecosystem connectivity.