Vissen als verspreiders van plantenzaden

Fish as plant seed dispersers Many plant species rely on animal vectors for dispersal of their seeds. Most well-known seed-dispersing animals are birds and mammals, but also fish are important. Fish can notably contribute to upstream dispersal of seeds of aquatic and riparian plant species, and therefore have an important ecological function. Worldwide, over 275 fish species across all biogeographical regions have been identified as seed dispersers, although there is great interspecific and intraspecific variation in their dispersal capabilities. In the Netherlands, most research has concentrated on dispersal by Cyprinids, for which experiments in aquaria and experiments in the field have shown great potential for dispersal of plant seeds and vegetative plant parts. Fish typically retained seed for 4 to 8 hours, but particularly if fish are actively swimming retention up to 15 h is possible because the activity slows their digestive system. Tracking experiments have shown that fish disperse most seeds within 4 km of the location of ingestion, but that dispersal up to 16 km is possible. To achieve such distances, however, fish movements should not be restricted by fragmentation of their habitat by sluices and weirs. In conclusion, fish can contribute to dispersal of plant seeds, but many aspects remain to be studied. It is important to halt and reverse the ongoing decline of freshwater fish species worldwide, because of their intrinsic value as well as their functions for other organisms in ecosystems. Veel plantensoorten zijn afhankelijk van dieren voor de verspreiding van hun zaden. Bekende voorbeelden zijn bessen die door vogels gegeten worden en graszaden die door grote grazers gegeten worden, waarna de pit uit een bes of een deel van de graszaden het spijsverteringskanaal overleeft. Zo kunnen er vanuit uitwerpselen nieuwe planten ontkiemen, vaak na transport over aanzienlijke afstanden van de moederplant. Verspreiding via dieren voorkomt genetische verarming van plantenpopulaties, het verdwijnen van kleine populaties door toeval en kan soorten de kans geven om verschuivende abiotische omstandigheden te volgen; bijvoorbeeld door klimaatverandering. Behalve verspreiding via vogels en zoogdieren is het misschien minder bekend dat ook vissen zaden verspreiden. Hoe belangrijk is die rol van vissen als zaadverspreiders eigenlijk?