| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2004: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 2003: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
In this project, we studied the coexistence problem of closely related species during speciation process. During speciation, closely related species may interact with the newly evolving populations. Here the coexistence of newly evolving populations with other closely related species becomes a key factor for the establishment of such populations as a new species. In this project, we investigate three types of coexistence model as a canonical model of such coexistence.
(1)Evolutionary model of chirality in snails
A few land snails often shows left handed coiling, whereas almost all sea snails are right handed. In some species of snails, left handed coiling appears in few (very low density) individuals in many populations ; in others, few populations are left handed. In few species or in some taxonomic group, species and taxa are totally left handed. Here we build a speciation model from right coiling to left coiling. We introduce left and right genes with dominance switch genes. By simula
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tion, we show such speciation from right to left coiling occurs as a rare event. This may explain the single gene speciation by chirality switching in snails. We showed the genetic/philogenetic evidence for such single gene specation.
(2)Lattice ecosystem model of grassland community
We build a lattice space model of two species in a grassland community. We assumed a competitively superior species may invade the inferior species when possible. With this replacement, we show a wide range of coexistence for two species, when coexistence is absolutely impossible when such interactions are not included.
(3)Lattice model of multispecies plankton community
We build a lattice ecosystem of 10 planktonic species. Here we assume a slight difference in growth rates. This growth difference is also dependent on nutritional conditions. In this ecosystem, mathematically only one species (with high growth rates) should exclude all other species. However, we evaluated the coexistence for ten to hundreds thousand generations, assuming this is ecologically feasible scale for generation time. In such ecological time scale, almost all species can coexist without dominant species in lattice space model. In contrast, one species dominate over all other species, when global interactions are assumed (non spatial version of lattice models). Thus we showed that tens of species can coexist during ecological time scale even in a very small lattice ecosystem if local interactions is assumed. Less
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