Research interests

Section Population Biology

The research group Population Biology is managed by one Full Professor in Population Biology (Prof. Sabelis) and one part-time Full Professor (parttime Associate Professor) in Theoretical Ecology (Prof. De Roos). They provide guidance to one full time Assistant Professor (Dr Boerlijst), two part-time Assistant Professors (Dr Egas, Dr Janssen) and the technical staff. Postdocs and PhD projects are mostly financed through external funding, e.g, from the Netherlands Organisation for Scientific Research (NWO-ALW open competition, NWO-VENI-fellowships program, NWO-Evolution & Behaviour program), the Science and Technology Foundation (STW), The Tropical Science Foundation (WOTRO), the European Union (EC-FAIR, Marie Curie) and through projects financed by other institutes (Plant Research International, PRI; Netherlands Institute for Sea Research, NIOZ) and organisations (AIDS-fund, NUFFIC, CNPQ-Brazil, CAPES-Brazil, PRAXIS-Portugal).

Mission

The mission of the subprogram Population Biology is (1) to develop a theoretical basis for understanding how population structure, be it genetic, physiological, social, spatial or trophic, influences the persistence and extinction of populations and communities of organisms and (2) to test the hypotheses emerging from these models in biotic systems amenable to experimental manipulation. The emphasis is on understanding the emergence of multiple stable states, both in population density and composition, and feedback processes between natural selection, life history development, social and mutualistic processes, dispersal and population dynamics.

Research

To fulfill this mission, a team of theoretical and experimental ecologists develops testable hypotheses and creative to design experiments that can serve as an anvil to accept or reject these hypotheses. The experimental systems are partly in-house, such as arthropod communities on plants, and partly accessible through collaboration with research groups elsewhere (zooplankton and fish communities in lakes and pathogens of medical/veterinary/agricultural importance). The main research lines are:

(1) Physiologically-structured population models and food-web dynamics (de Roos)

Existing theory on the dynamics and structure of biological communities is mostly based on mathematical models that ignore differences between individual organisms. In addition, complex, interspecific interactions have received little attention. The aim is to address these shortcomings and to develop ecological theory, firmly based on species life histories and its consequences for complex interactions in the food web. Complex community interactions include size- or stage-dependent foraging and mortality rates, ontogenetic diet and habitat shifts, juvenile bottlenecks, cannibalism, stage- or size-dependent dispersal and intraguild predation. These are investigated in the context of systems involving planktivorous and piscivorous fish, where individual performance (feeding, growth, reproduction and mortality) strongly depends on body size. Hence, the population size-structure is pivotal to the dynamics of this system. To combine theory and experimental tests collaboration with fish ecologists and mathematicians has been established.

(2) Evolutionary Epidemiology (Boerlijst)

Evolutionary processes affect the dynamics of infectious diseases due to the short generation times of pathogens. Major questions are: How do parasites evolve to escape from the host's immune system, or become resistant against e.g. antibiotics? Which selective forces shape the virulence (i.e. the “parasite induced” loss of host fitness) of infectious agents?  Under which conditions will pathogens evolve towards decreased virulence?  Developing successful remedies against the evolution of new types of pathogens requires a detailed understanding of the pathogen's evolutionary dynamics.  Applying this knowledge to manipulate (and typically decrease) the virulence of pathogens has become known as "virulence management". This concept is potentially important not only for public health but also for agricultural and veterinary epidemiology. Experimental tests are developed in collaboration with microbiologists, parasitologists and epidemiologists.

(3) Ecological and evolutionary dynamics in food webs involving arthropods on plants (Janssen, Sabelis)

Herbivores can induce plants to emit chemical signals that act as an SOS to predators (see early publications by Sabelis and Dicke). This phenomenon has probably evolved, because it is in the interest of the plant to get rid of herbivores and it is in that of predators to find herbivores as prey. However, conflicts of interest arise when plants ‘cry wolf’ in advance of attack by herbivores and so that the responding ‘bodyguards’ get no prey in return. This will affect the signals plants evolve, because predominance of honest signallers creates opportunities for invasion by dishonest signallers and vice versa. This process of frequency-dependent change gives rise to cycles in the composition of signal traits in the plant population and the chemical languages in plant-predator communication may not be stable. Whether such dynamical changes occur and how these will influence the long-term dynamics of tritrophic systems, are major questions for future theoretical and empirical research. It provides a novel framework for showing that conflicts of interest are inherent to communication and learning processes, alter natural selection processes, promote polymorphisms and add new features to the dynamical repertoire of tritrophic systems. This requires collaboration between molecular plant biologists, environmental chemists, neurobiologists, ecologists and mathematical biologists.

(4) Adaptive dynamics of host race formation and speciation (Egas, Sabelis)

Theoretical advances in population genetics theory and adaptive dynamics have paved the way for a new theory on sympatric speciation. This theory hinges on a number of assumptions (separation of ecological and evolutionary time scales; adaptive learning, adaptive food choice and adaptive mate choice) and generates some pertinent and novel predictions on the conditions and manifestations of evolutionary branching in populations. Plant-feeding mites represent an ideal system for experimental analysis of evolutionary branching and adaptive behaviour. It has been shown that these mites rapidly and repeatedly undergo host race formation in glasshouses harbouring tomatoes and cucumbers as host plants. Molecular tools (micro-satellites) and QTL-approaches are being developed as an aid to measure invasion fitness, the genetic make-up of mite populations and the genetic architecture of adaptations to host plants.

(5) Adaptive dynamics of indirect reciprocity and altruistic punishment in human networks (Egas, Sabelis)

The rise and fall of networks of cooperative individuals in human and animal societies are likely to play an important role in the emergence of social population structure and dynamics. Recent experiments show that humans have an inordinate fondness to punish non-altruists (albeit at low costs to the punisher; altruistic punishment) and to incorporate individuals in their interaction network when they have a good reputation of cooperating with others (indirect reciprocity). Realistic manifestations of ‘altruistic punishment’ are to be expected in the way humans manage networks of interactions with others. To understand network dynamics and its evolution, adaptive dynamics may offer new clues for hypotheses, whereas experiments with humans offer relatively good prospects by making good use of the internet and of game settings developed in experimental economy. To initiate research in this direction collaboration has been established between evolutionary ecologists, mathematical biologists, evolutionary psychologists and experimental economists.

(6) AppliedPopulation Biology (de Roos, Boerlijst, Janssen, Egas, Sabelis)

Identifying fundamental questions in applied problems of societal relevance is an art cultivated in the Population Biology group. This has led to a suite of research projects on (1) vaccination strategies, (2) virulence management, (3) fisheries-induced changes in life history and population states, (4) management of grazers to maintain ecosystem states, (5) species conservation strategies, (6) impact of toxins on food chains, (7) biological pest control in glasshouses (tomato, cucumber, sweet pepper), orchards (apple, pear) and field crops (cassava, strawberry, coconut, tulips, lilies, freesia), by selecting candidate control agents and by implementing knowledge on how plants promote the performance of the enemies of their enemies.

 

Training and education

The above research program enables  the Population Biology group to participate in the Bachelor program of Biology (Biomathematics, Ecology, Evolutionary Ecology, Theoretical Biology and Adaptive Dynamics (3 rd year), Medical Biology (Epidemiology) and Psychobiology (Evolution and Behaviour) and to provide an MSc program Ecological and Evolutionary Dynamics. (since September 2003; 6 MSc students per year). In addition, the group participates in two other M.Sc. programs (Frontiers in Plant Science(SILS) and Chemicals in Ecosystems (IBED)) and organizes courses in Population Dynamics, Community Dynamics and Adaptive Dynamics at the PhD level in the framework of the national graduate school Functional Ecology.

Website of the Section Population Biology