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Evolutionary and ecological dynamics in fluctuating environments

Confirmed keynote speakers for this session:

Michael Assaf (The Hebrew University of Jerusalem, IL):  "Rare events in interacting populations: the role of environmental noise and spatial heterogeneity".

Systems containing a discrete population of interacting agents dwell most of the time in the vicinity of some attractor, undergoing small random excursions around it, while large deviations from the typical behavior are extremely rare. Yet, it is precisely these extreme, rare events, giving rise e.g. to population extinction, switching between cellular phenotypic states, or fixation and loss of biodiversity, which may be of key practical importance. In most cases, dynamics of such systems are studied within the so-called well-mixed framework, while accounting for demographic noise only. In other words, in the usual setting, spatial degrees of freedom as well as environmental (or extrinsic) noise, are often omitted. In this talk I will review two extensions of this scenario. In the first, the effect of adding extrinsic noise on the frequency of rare events will be studied, as function of the external noise parameters (magnitude, correlation time and statistics). In the second extension, I will consider a population residing on a heterogeneous network, and show how rare events are influenced by the complex spatial topology of individuals. To this end, I will present analytical and numerical techniques that enable the accurate and efficient analysis of large deviations in such complex, many-body problems.

Stefan Klumpp (University of Göttingen, DE): "Heterogeneous populations in temporally or spatially fluctuating environments".

The fitness of microbes is given by the rate of their proliferation in growth-promoting conditions and the success of their strategies for survival under stress conditions.  Cells living in fluctuating environments need to evolve strategies to combine proliferation and stress tolerance. One common such strategy is phenotypic heterogeneity with phenotypic switching rates adapted to characteristic times of the fluctuating environment. I will discuss several aspects of such heterogeneous populations from a theoretical point of view, specifically the question whether heterogeneity is always beneficial, and how heterogeneity can be beneficial for populations spreading in space if the growth and survival conditions are variable in space. As an outlook I may also touch upon the interplay of population dynamics and mechanics in the case of bacterial colonies and biofilms.