November 2017: "We have reason to believe that species in a state of nature are limited in their ranges by the competition of other organic beings quite as much as, or more than, by adaptation to particular climates". Such wrote Darwin one and a half century ago. He was right -- see our new paper on climate change in a food-web context in Proc. Roy Soc. L. B (post print here) We show that species interactions — competition and predation — are more important processes than the increasing temperatures: apparently warm-adapted species are equally likely to be affected by climate change than cold-adapted species. Therefore, unfortunately, the effects of climate change cannot be predicted by the direct effects of temperature alone. In most cases we must account for changes in competitors and predators, which are much harder to predict.
Figure: The development of food-webs under climate change. Each dot represents a species and the colour shows its preferred temperature. The solid circles are species that are established in the food-web, and the lines represents their strength of interaction. As the temperature in the environment increases, some species may go extinct, or new species may invade (only in the left panel). Consequently, the structure of the food- web changes.
September 2017: Doctor defence "Fish and fisheries - the size- and trait-based approach" is now online: https://www.youtube.com/watch?v=OJXArL3TNg4
April 2017: Try the new version of the size spectrum fish community calculator here. The new version is written in R and includes 5 calibrated ecosystems.
November 2016: “What checks the natural tendency of each species to increase in numbers is most obscure”. Such wrote Charles Darwin one and a half century ago in “Origin of Species”. The statement is still true: empirical knowledge about density dependent regulation of animal populations is exceedingly difficult to obtain and interpret. In the new paper “When in life does density dependence occur in fish populations?” published in Fish and Fisheries, we develop the missing theoretic understanding about density dependent regulation in fish populations. Why care? We show that a correct understanding of density dependence is crucial for a central instrument in Maximum Sustainable Yield fisheries management – the minimum landing size regulations – that are used to avoid landing young fish by fisheries. See the paper in Fish and Fisheries here or download a preprint.
Fisheries yield vs. minimum landing size limit for four types of density-dependent regulation (thick lines) compared to the classic stock-recruitment theory that are used today (thin black dashed line). Fisheries yield is maximized with a size limit around size at maturation (vertical dotted line) only when density-dependent regulation occurs early.
July 2016: Sharks vs telests: How does the life-history strategy differ between elasmobranchs (sharks, rays etc) and teleosts (bony fish)? With respect to the size of their offspring, one difference is striking: elasmobranchs make offspring that is roughly a factor 100 (in weight) smaller than the adults, while most teleosts make offspring that is around 1 mg, independent of the adult size (see figure). We show that the difference in the offspring size strategy is unrelated to whether offspring is live or eggs, and there are no significant differences between growth, mortality etc. of elasmobranchs and teleosts. How, then, can evolution maintain these two very different offspring size strategies among very similar groups of organisms? In a recent paper in Journal of Theoretical Biology we develop an evolutionary model to show how the two offspring size strategies can co-exists evolutionary — in technical terms, we can say that there exists two local evolutionary stable states. The difference between the two strategies boils down to a difference in density-dependent control in the populations: if newly hatched offspring compete with one another, the evolutionary stable strategy is one where offspring size proportional to the adult size (the elasmobranch strategy), while if early life is devoid of density-dependent competition, the strategy with small offspring independent of adult size emerges.
Offspring size as a function of adult size. Open symbols are teleosts; closed are elasmobranchs.
See archive for older news.
I am currently involved in the courses:
- 25303 Mathematical biology
- 25304 Differential equations in biology
- 25314 Computational Marine Ecological Modelling
- 25803 Ocean Life Meeting Series
Send me a mail if you are interested in any of these courses.
I want to understand how life in the ocean is organised, why marine organisms look and act the way they do, and how marine ecosystems react to perturbations like fishing, species removals/invasions or climate change. More specifically I work on:
- Trait-based models of life in the ocean. See http://www.oceanlifecentre.dk
- Size-structured models of marine ecosystems. See the community calculator and the single-species calculator.
- Fisheries induced evolution. See the evolutionary calculator.
Previously I have worked with sand ripples under surface waves and barchan dunes in deserts.
I have a number of possible student projects available for students related to the impact of fishing and climate change on marine and fresh water ecosystems. The projects ranges from applied projects on specific ecosystems to abstract theoretical topics. Send me an email if you are interested in learning more.
Students and post docs:
- Camila Maria Serra Pompei (PhD student)
- Rob van Gemert (PhD student)
- Daniel van Denderen (post doc)
- Trondúr Kragesteen (PhD student)
- Subhendu Chakraborty (post doc)
- Kasia Kenitz (post doc)
- Nis Sand Jacobsen, Ph.D. student. With Henrik Gislason.
- Alexandros Kokkalis, Ph.D. student. With Uffe Thygesen and Anders Nielsen.
- Julie Sainmont, Ph.D. student. Main supervisor: Andy Visser.
- Karin Olsson, Ph.D. student. Main supervisor: Henrik Gislason
- Christina Frisk, Ph.D. student. Co-supervised by Gerd Kraus.
- Nuria Calduch Verdiel, Ph.D. student. With James Vaupel, Max Planck Institute for Demographic Research, Rostock; and Brian MacKenzie. Thesis: Protecting the larger fish: an ecological, economical and evolutionary analysis using a demographic model.
- Lai Zhang, Ph.D. student. Thesis: Mathematical model of ecology and evolution
- Martin Hartvig (aka Martin Pedersen), Ph.D. student. Main supervisor: Per Lundberg, Lund University. Thesis: Food web ecology.
- Matthieu Gerard, under-graduate student: "Turing structure in a size-structured ecosystem model". Together with Uffe H. Thygesen and Michael Pedersen (MAT, DTU).
Ken Haste Andersen - firstname.lastname@example.org - +45 35 883399
National Institute of Aquatic Resources, AQUA
Technical University of Denmark
DK-2800 Kgs. Lyngby