Comparative studies on the population dynamics ofMazus japonicus andM. Miquelii,scrophulariaceae

The population dynamics ofMazus japonicus andM. Miquelii was compared. In contrast with the summer annual growth habit (Vandellia crustacea) and the winter one(Veronica persica), M. japonicus had a “year-long annual growth habit” as the population of this species existed all year-round, notwithstanding that each individual of the population germinated and died within a year. TwoMazus species were sympatric on the levee of a rice paddy field where many other species were thickly grown. Those two species were difficult to propagate there, because their seeds, which were light germinators, could hardly germinate in the shade of other plants, or even if germination was possible, their seedlings may have soon died. However, asM. Miquelii, a perennial species, was able to reproduce by stolon vegetatively, it was a dominant species on the levee. On the contrary, the population density ofM. japonicus was thicker in the abandoned paddy field and an upland field than that ofM. Miquelii, because seeds of the former germinated under a greater variety of temperatures and under conditions of less soil moisture than those of the latter. These observations present an example of the fact that the difference of the reproductive strategy in annual and perennial plants has a striking effect on the population dynamics in the sympatric habitat.