When mutant individuals with a changed trait are successful, they will increase in numbers and thus start affecting population dynamics, resource availability, the prevalence of parasites, the intensity of interspecific competition, community structure, and so on. Together, these effects will cause a feedback because ecological parameters will, in general, affect the traits that are favoured. More on this can be found in the introduction to my thesis.
Such eco-evolutionary feedback loops will be particularly intense in systems with interacting populations: adaptation and counteradaptation often have population dynamical consequences. A good example is the evolution of virulence. If avirulent parasites are common, host density increases and, with it, the force of infection. But so does the intensity of within-host competition, which favours more virulent parasites. Ecological effects will modify or sometimes even revert selection pressure on virulence.
How spatial dynamics affect evolution (and vice versa) is still poorly understood. When a mutant invades a 'viscous' system it typically does so in the form of an expanding cluster of relatives. Ultimately it is therefore the characteristics of these clusters that determine whether the invasion will be successful. On other words, the unit of selection in a viscous systems is a cluster of relatives rather than the individual (which amounts to a re-discovery of Hamilton's kin selection principle). Correlation dynamics modeling provides new mathematical tools to study the effect of space on ecological interactions.
Traditionally, ecology recognizes three broad kinds of interactions among organisms: competitive interactions, exploiter-victim interactions (i.e., predators and prey, host and parasites) and mutualistic interactions. Upon closer scrutiny, however, interactions between individuals often appear to be mixtures. For example, certain parasites may, under certain conditions, benefit their hosts. Under what conditions does the common interest prevail over the private interests of the partners? If we understand better under what conditions (if ever) parasites will become full-blown mutualists, we obtain much-needed insight in many evolutionary transitions, ranging from the appearance of eucaryotes to the evolution of sociality.
When an organism communicates, it does so to increase its fitness. If it can gain from misleading the recipient, it will therefore give false information. The recipient of the signal is selected to judge the signal with respect to its 'credibility'. Recipients can enforce credibility by only `believing' signals that are costly, so costly that senders cannot afford cheating. But sometimes sender and receiver do have a sufficient common interest, however, so that both benefit from the exchange of accurate information. But what will happen if sender and receiver have only partially overlapping interests?
Since Darwin and Hamilton it has become obviously clear that harmony in colonies of social insects is due to the relatedness of colony members. Why, then, do we sometimes observe queens that mate with multiple males or even unrelated queens that share a nest? Either of these processes diminishes relatedness and increases the potential for conflict. One of the hypotheses that has been proposed to explain this phenomenon is that heterogeneous colonies are more resistant to parasitism. This is an interesting hypothesis, but it is not at all immediately clear whether it works if it is taken into account that such heterogeneous colonies are likely to have more parasites able to infect them.
At a different level again, it has become clear that parasite evolution can be strongly affected by within-host competition among strains. What is not often realised (and certainly not in the simplest mathematical models) is that these interactions are often mediated by the immune system. Does within-host competition still lead to increased virulence or, as has been suggested recently, to reduced virulence instead?
A selection: Maurice W. Sabelis (University of Amsterdam), Vincent Jansen (Royal Holloway College, London), Sylvain Gandon (Montpellier), Madeleine Beekman (University of Sydney).