Research interests

Casper van LeeuwenI am interested in dispersal and migration of plants and animals. Freshwater ponds, lakes and rivers are particularly suitable study systems in which to investigate movement of individuals and species, because they are often linear (river systems) or isolated by land (ponds and lakes). I study how organisms move through these challenging landscapes, how they colonize or invade new areas, how interactions among multiple arriving species determine the structure of the new community, and how dispersal affects (meta-)populations. How does movement, or restriction of movement, affect individual life history strategies, population structures, and whole communities? I study these questions on both ecological and evolutionary time scales.

Current projects 

Currently I work on my Marie S-Curie project at the Netherlands Institute of Ecology with Dr. Liesbeth Bakker, investigating seed dispersal by large mammals, fish and waterbirds. By studying the digestion of seeds in detail, my project will inform on the potential of different plant seeds to use animals as dispersal vectors. I also still actively collaborate with Dr. Jon Museth from the Norwegian Institute for Nature Research) and Prof. Asbjørn Vøllestad from the University of Oslo on connectivity in Norwegian fish populations. 

Main research lines

European grayling migration riverDispersal of aquatic organisms by animals - One of my major interests is passive dispersal of aquatic organisms by larger animals, i.e. zoochory. Both aquatic plants and aquatic invertebrates are known to hitchhike on more mobile waterbirds, fish, large mammals, or even reptiles, using them as transportation mechanisms between isolated water bodies or upstream in rivers. Smaller organisms can be ingested and excreted alive in the faeces of vertebrates (endozoochory), or cling to the outside of flying, swimming or walking animals (ectozoochory). I study dispersal of aquatic invertebrates and seeds by animals. 

Fish migration - Another one of my major interests is fish migration. Many fish species use different habitats for overwintering, feeding and spawning. Connectivity in freshwater systems, allowing migration between different habitats, is crucial. I study fish movement to unravel how individual fish, fish populations and whole communities may respond to restriction of movement by barriers increasingly constructed by humans in rivers (e.g. hydropower dams and weirs). Despite mitigation measures such as fishways (or fish ladders) to enable fish to pass barriers, (migratory) life history strategies of fish are still influenced by river fragmentation. I tracked individuals by radio telemetry, analysed long-term capture-mark-recapture datasets of fishway passages, and used genetic/genomic analyses to discover if, how and how fast fish are able to cope with increased river fragmentation.

European grayling Thymallus thymallus

Restoration of plant communities - Plants in and on the shores of wetlands often produce seeds that are buoyant and disperse by drifting to new suitable habitat. Where these seeds germinate depends on many factors, but first of all on where the seeds drift by water and where there are suitable conditions to germinate. Hydrochory, i.e. the dispersal of seeds by water, is therefore an important dispersal process worldwide. I am interested in the influence of water level fluctuations, shore morphology and plant traits on hydrochory. How do dispersal, estalishment and species interactions together shape plant community assemblies? And if plants are unable to colonize new habitat by themselves, which species should we deliberately introduce to restore pristine wetland habitats?

Bird migration ecology - Many bird species annually migrate over long-distances between breeding and overwintering sites. During these migrations they need to make many decisions, which starts with when to leave for migration with how much fuel, how to store the fuel (physiological adaptations) and where to potentially acquire more food along the way. Upon arrival on breeding sites they again face multiple decisions, including where to nest, with whom, and when to leave for migration again. I study waterfowl and shorebirds to answer a subset of these questions, as birds are know to make some of the most spectacular long distance migrations in the world.  


Scientific collaborations

Dispersal of aquatic organisms by waterbirds

My key collaborators include:
Liesbeth Bakker, Wageningen, The Netherlands
Andy Green, Seville, Spain
Sarah Jamieson, Peterborough, Canada
Niels Jepsen, Silkeborg, Denmark
Erik Kleyheeg, Radolfzell, Germany
Jon Museth, Lillehammer, Norway
Bart Nolet, Wageningen, The Netherlands
Bart Pollux, Wageningen, The Netherlands
Merel Soons, Utrecht, The Netherlands
Asbjørn Vøllestad, Oslo, Norway


Please contact me in case you are interested in collaborating!