MBI Videos
Sergei Petrovskii
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Sergei PetrovskiiBiological invasion admittedly consists of a few distinctly different stages such as exotic species introduction, establishment and geographical spread. Each of the stages has its own specific mechanisms and implications, which require application of specific research approaches. In my talk, I focus on the challenges arising during the stage of the geographical spread. A well-developed theory based on diffusion-reaction equations predicts a simple pattern of alien species spread consisting of a continuous traveling boundary or 'population front' separating the invaded and non-invaded regions. A propagating population front has been a paradigm of the invasive species spread for several decades. However, it also appears to be at odds with some observations. In some cases, the spread takes place through formation of a distinct patchy spatial structure without any continuous boundary. Perhaps the most well known and well studied example of this 'patchy invasion' is the gypsy moth spread in the USA; e.g. see www.fs.fed.us/ne/morgantown/4557/gmoth/atlas/#defoliation
In order to address this problem theoretically, I first re-examine the current views on possible mechanisms of the patchy spread and argue that the importance of the stratified diffusion may be significantly overestimated. Second, I will revisit the traditional diffusion-reaction framework and show that the patchy spread is, in fact, its inherent property in case the invasive species is affected by predation or an infectious disease and its growth is damped by the strong Allee effect. The patchy spread described by a diffusion-reaction model appears to be a scenario of alien species invasion "at the edge of extinction" and this can have important implications for the management and control of the invasive species. I will then show that patchy spread is not an exclusive property of the diffusion-reaction systems but can be observed as well in a completely different type of model such as a coupled map lattice which is capable of taking into account environmental heterogeneity. Finally, I will argue that these theoretical results taken together with the evidence from field data may result in a paradigm shift: A typical pattern of exotic species spread is a patchy invasion rather than the continuous population front propagation. -
Sergei PetrovskiiSustainability of agroecosystems: insights from the multiscale insect pest monitoring
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Sergei PetrovskiiA conventional view of the spatial spread of invasive species dating back to the works by Fisher (1937) and Kolmogorov et al. (1937) is that it occurs via the propagation of a travelling population front. In a realistic 2D system, such a front normally separates the invaded area behind the front from the uninvaded areas in front of the front. This view has eventually been challenged by discovering an alternative scenario called “patchy invasion� where the spread takes place via the spatial dynamics of separate patches of high population density with a very low density between them, and a continuous population front does not exist at any time. Patchy invasion was studied theoretically in much detail using diffusion-reaction models. However, diffusion-reaction models have many limitations; in particular, they almost completely ignore long-distance dispersal. In this talk, I will present some new results showing that patchy invasion can occur as well when long-distance dispersal is taken into account. Mathematically, the system is described by integral-difference equations with fat-tailed dispersal kernels. I will also show that apparently minor details of kernel parametrization may have a relatively strong effect on the rate of species spread, which evokes the general issues of understanding the uncertainty and the limits of predictability in ecology.