Projects
PhD project (2007-) Dispersal of aquatic organisms by water birds
The ability of aquatic organisms to establish populations in even the most remote wetlands, far away from all other suitable habitat, already fascinated Darwin 150 years ago. How can these species cross kilometres of dry land? In my PhD project, I investigate the potential role of water birds as dispersal vectors for these aquatic species. Waterbirds are often abundant and fly fast and directed between similar wetlands, and therefore could be ideal dispersal vectors. Since most evidence to date is anecdotal, I currently combine several methods to investigate bird-mediated dispersal of aquatic organisms, with special focus on aquatic invertebrates (freshwater snails).
I perform laboratory experiments to determine the potential dispersal distances of freshwater snails (both in the gut and adhering to the outside of a bird); analyse species distributions to find whether or not aquatic invertebrate occurrence is related to bird movements, and whether or not invertebrate traits are relevant; and analyse microsatellite variability of freshwater snails in relation to potential dispersal vectors. I aim to quantify the importance of (migrating) water birds for the dispersal of aquatic organisms, to understand high biodiversity in remote wetlands, rapid spread of invasive species, and potentially be able to predict the response of aquatic species to human-induced challenges such as habitat fragmentation and climate change.
Msc projects (2005-2007)
An experiment on the foraging behaviour of Mallards in environments with food distributed in contrasting spatial patterns (Netherlands Institute of Ecology, The Netherlands)
We experimentally tested a foraging model that predicts optimal travel distances for animals foraging in a patchy environment with cryptic prey. The model predicts foragers to use spatial pattern to estimate the location of rich patches, of which selectively visiting increases foraging efficiency. We offered three contrasting spatial patterns of cryptic food items to Mallards in an experimental setup, and monitored behavioural differences between the patterns as well as within the patterns over successive days. After a learning period the Mallards started to use the spatial pattern to adjust patch-investment (i.e. search time per patch) rather than patch choice (i.e. travel distance between patches).
* Published as Klaassen, Nolet & van Leeuwen (2007).
Relating gizzard mass and diet of Red Knots using stable isotopes (Groningen University, The Netherlands)
Red Knots (Calidris canutus) can flexibly adjust their gizzard mass to reduce transport costs during migration. Field observations on flocks of Red Knots suggested that birds with small gizzard masses could be digestively constrained. They selected the limited available soft-shelled prey (Crangon, Carcinus), while Knots with larger gizzard masses ingested high amounts of abundant hard-shelled prey (Macoma, Cerastoderma). In this project we investigated these findings on the level of individual Knots rather than group analyses, by using blood stable isotope analysis of C and N. We found a significant difference between isotope ratios of soft-shelled and hard-shelled prey, and predicted to find these same differences between the isotope ratios of Red Knots with small and large gizzard masses, respectively. However, a direct link was impossible due to the time delay between food ingestion and implementation of the isotopes in the blood of the knots, combined with a high gizzard mass flexibility (i.e. very rapid mass changes possible).
However, data did reveal that the knots, that breed on the arctic tundra of Canada and Greenland and fly via a stopover in Iceland in Spring, do not make this stopover in Iceland when they are flying southward in Autumn. Surprisingly, knots arrived at the coasts of northwestern Europe with stable isotope signals of the tundra, adults as well as juveniles. This suggests the knots migration is not necessarily a two-leg process, and that even the juveniles can make cover the distance in one flight.
* Published as Dietz et al (2010).
Mate and site fidelity of Pacific Dunlin breeding at the Yukon-Kuskokwim Delta, Western Alaska (Simon Fraser University, Vancouver, Canada)
We investigate mate fidelity and site tenacity in a breeding Pacific Dunlin (Calidris alpina) population. We ask whether previous reproductive success determines return rates to the breeding sites and/or to the exact previous territory, whether successful breeders are more likely to reunite and failed breeders to divorce, and whether there are possible benefits (for example in terms of increased reproductive success) for one or both of divorcing mates. We test several known hypotheses previously proposed for the high rate of site and mate fidelity generally found in shorebirds.
* MS in preparation
Selected Publications
Van Leeuwen, C. H. A., M. Tollenaar, and M. Klaassen. 2012.
Vector activity and propagule size affect dispersal potential by vertebrates.
Oecologia: 1-9. http://www.springerlink.com/content/avp763673u40230x/
Van Leeuwen, C. H. A., G. Van der Velde, B. Van Lith, and M. Klaassen. 2012.
Experimental quantification of long distance dispersal potential of aquatic snails in the gut of migratory birds.
PLoS One 7:e32292. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0032292
Dietz M.W., Spaans B., Dekinga A., Klaassen M., Korthals H., van Leeuwen C. H. A. and T. Piersma (2010)
Do red knots (Calidris canutus islandica) routinely skip Iceland during southward migration?
Condor 112(1):48-55
Klaassen, R. H. G., Nolet, B. A., Van Leeuwen, C. H. A. (2007)
Prior knowledge about spatial pattern affects patch assessment rather than movement between patches in tactile-feeding mallard.
Journal of Animal Ecology 76(1), 20-29
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