Theory and Observations of Invasion Processes
Sergei Petrovskii
Shirshov Institute of Oceanology, Russian Academy of Science
Nakhimovsky Prosp. 36, Moscow 117997, Russia
spetrovs@sio.rssi.ru
Horst Malchow
Institute for Environmental Systems Research
Department of Mathematics and Computer Science
Osnabrück University, 49069 Osnabrück, Germany
malchow@uos.de
The problem of biological invasion is an issue of major significance in contemporary ecology. Among many issues related to species invasions, the patterns of spread are of particular interest. The classical models of a mono-species invasion into a homogeneous environment predict, as a typical pattern, a smooth population front propagating with constant speed from the place of the species original introduction. It has often been observed in nature; moreover, sometimes even very simple models can be indeed in a good quantitative agreement with field data. However, it is also at variance with many field observations, particularly, when the speed of invasion appears to be much less or much higher than the value predicted by the classical models. Moreover, in some cases, the population front does not exist at all and spreading takes place due to a different scenario, e.g., via formation and movement of separate patches.
A highly practical and theoretically important question is which environmental and biological factors can affect the pattern of spread and the rate of invasion either speeding up or slowing down spreading of invasive species. The heterogeneity of the environment is apparently one of them although its impact on the species spread is not always as obvious as it may seem to be. Another factor is identified in predation that can slow down or even reverse the invasion [cf. Fagan & Bishop, Amer. Nat. (2000) 155, 238-251]. The Allee effect has recently been shown to possibly affect the whole pattern of spread changing it from population fronts to patchy invasion [Petrovskii et al., Ecol. Lett. (2002) 5, 345-352]. An issue of interest is the interplay of species invasion and other forms of species transport, one but not the only example being given by advection with the wind or water current. The impact of environmental stochasticity may be also important [cf. Lewis & Pacala, J. Math. Biol. (2000) 41, 387-429], although the relative contribution of deterministic and stochastic factors remains still obscure [Malchow et al., Ecol. Mod. (2002) 149, 247-255].
This session will focus on (but will not be limited to) the issues mentioned above. Both rigorous analytical results and results based on numerical simulations are acceptable. We will also welcome presentations based on field data giving more examples of the spread of invasive species that cannot be described by standard models and can stimulate farther development in this field.