Research Interest:
Searching the environmental conditions and mechanisms that determine the realized (observed) biodiversity using theoretical modeling and field observation. Specifically, my interests are on coexistence mechanism among sessile species in competitive relationship.

Main Subjects:
1) Coexistence mechanism between understory and canopy species: the adaptive significance of "trunk inclination", a conspicuous tendency of trees on slopes, is analyzed. Its cost is increasing function of trunk length and the angle of inclination, while the benefit has a critical (optimal) point determined by slope steepness. The trait was clarified to be a privileged strategy of light acquisition for understory species on slopes. Taller species would have less adjustability of trunk inclination to the slope steepness. Population of inferior understory species, inferior in light acquisition, can thus persist under superior canopy species, by inclining trunks on sloping habitat. (at Center for Ecological Research, Kyoto Univ.)

2) Coexistence between outcrossing flowering species of different competitive ability in resource acquisition: In pollen-limited condition, reproductive success becomes a function of conspecific flower rate in simultaneous flowers in the habitat. Assuming the flowering timing as a genetic trait, the major species in a flowering period would exclude the minors from the period through generations. This allows the competitively inferior species to invade and exclude the superior from a temporal period in the habitat if the invading population has sufficient number with high synchrony in flowering timing. Thus the initial condition and sufficient pollen-limitation is essential for inferior species to coexist with superior species in the same habitat. (at Center for Ecological Research, Kyoto Univ.)

3) Coexistence between herbal species with different strategies in trade-off relationship against herbivory: The efficiency of defense and reproduction are function of herbivory pressure and the size of herbivores. If the herbivore is large then reproductive species in the immediate neighbourhood of defended plants may be more likely to persist (associative defense) even at higher grazing pressure. If the herbivore shows a positive numerical response to the average palatability of the habitat, then both plant populations are stabilized and coexistence is promoted because both species obtain a minority advantage through negative feedback caused by herbivory (NERC-Center for Population Biology, Dept. Biological Sciences, Imperial College)

4) Environmental conditions for the sustainability of aquatic populations suffering multiple human-impacts: Incorporating different classes of anthropologic threats in a population model, their relative importance on the population dynamics is clarified. Chemical pollution and habitat loss synergically reduce the recruitment rate of species with free-dispersal stage. Heavy harvesting pressure, by introducing unstable fixed point, might allow chemical to cause catastrophic population extinction whose critical concentration decreases as these threats grow. (at Center for Chemical Risk Management, Advanced Institute for Industrial Science and Technology)