Research interests

I study the movement and interactions of plants and animals in freshwater ecosystems. I aim to understand how, why and when organisms move – and how their consequential presence or absence affects other species in aquatic food webs. Freshwater ponds, lakes and rivers are particularly suitable systems in which to study movement because they are often linear (river systems) or isolated by land (ponds and lakes). I combine studies on all tropic levels, including phytoplankton, zooplankton, aquatic invertebrates, aquatic plants, fish and waterbirds. I study how and why organisms move through these challenging landscapes, how they colonize and invade new areas, how interactions among multiple species determine the community assemblies and ultimately structure aquatic food webs and plant community assemblies. I study these questions on both ecological and evolutionary time scales, always with conservation and restoration as a possible application in mind.

Current project  Fieldwork at Marker Wadden

Currently I work as part of a research team that investigates the effects of a large lake restoration project on the lake Markermeer. The aquatic foodweb in this large lake in the Netherlands has been deteriorating over the last decades. To reverse this trend, completely new islands are being constructed in the lake, with the expectation that the addition of heterogeneity will stimulate the food web bottom-up: phytoplankton, zooplankton, macrophytes, fish and (piscivorous) birds. The aim of my research at the Marker Wadden is to determine how the islands may affect the food web in the lake. More information on the project and other team members can be at www.markerwaddenresearch.com.

Fieldwork equipment

Moerasandijvie

 

 

 

 

 

 

 

 

 

 

Main research lines

Dispersal of aquatic organisms by animals - One of my major interests is passive dispersal of aquatic organisms by larger animals, also know as "zoochory". Both aquatic plants and aquatic invertebrates can hitchhike on more mobile waterbirds, fish, large mammals, or even reptiles - using them as transport mechanisms between isolated waterbodies or upstream in rivers. Small organisms can be ingested and egested alive in the faeces of vertebrates (endozoochory), or adhere to the outside of flying, swimming or walking animals (ectozoochory or epizoochory). I study dispersal of aquatic invertebrates and seeds by animals using a combination of lab-experiments and modelling.  European grayling Thymallus thymallus www.caspervanleeuwen.info

Fish ecology - Another one of my major interests is fish movement - which includes their migrations in relation to barriers, habitat selection and the functional roles they play in aquatic food webs. Many fish species use different habitats for overwintering, feeding and spawning - which make connectivity in freshwater systems crucial. Fish movement does not only affect the fish species themselves, but can also facilitate transport of plant seeds (zoochory) or can cause important interaction in the aquatic food web. I study how fish respond to human influences, which includes movemenr restrictions by barriers in rivers (e.g. fragmentation by hydropower dams) and the effects of habitat restoration projects (Marker Wadden) on fish production. Therefore I track individuals by radio-telemetry, analyse long-term capture-mark-recapture datasets and used genetic/genomic analyses to discover if, how and how fast fish are able to cope with changes in their habitat.

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?Dispersal of aquatic organisms by waterbirds www.caspervanleeuwen.info

Bird 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. 

 

Please contact me in case you are interested in collaborating!

Seine fishing in the harbour of Marker Wadden