Small-step invasion research.

Recent invasion research can be categorized broadly into two types: studies of the spatial spread, and those of the biological impact the invader has on the native biota. The first type is the most factual, and the second the most theoretical. So far, however, it is difficult to connect the two, implying that neither the spatial spread nor the species interactions can be explained in terms of each other. Recent models, analysing spatial spread, progress steadily by making small steps.