1997 Fiscal Year Final Research Report Summary
Mathematical Study of Spatial Spread of Biological Invasion
| Project/Area Number |
08640804
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
生態
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| Research Institution | Nara Women's University |
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Principal Investigator |
SHIGESADA Nanako Nara Women's University Department of Science, Professor, 理学部, 教授 (70025443)
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| Co-Investigator(Kenkyū-buntansha) |
FUGO Takasu Nara Women's University Department of Science, lecturer, 理学部, 講師 (70263423)
KAWASAKI Kohkichi Doshisha University Department of Knowledge Engineering and Comupter Sciences, P, 工学部, 教授 (10150799)
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| Project Period (FY) |
1996 – 1997
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| Keywords | biological invasion / rate of spread / stratified diffusion / long-distance dispersal / fragmentation / environmental disturbance / pine wilt disease / マツ枯れ |
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| Research Abstract |
1. An epidemic of pine wilt disease has been spreading in wide areas of Japan for several decades. The disease is caused by the pinewood nematode, Bursaphelenchus xylophilus, which the pine sawyer, Monochamus alternatus, as vector. We present a mathematical model to describe the host-parasite interaction between pines and pine sawyers carrying nematodes based on detailed data on the population dynamics of pine sawyers and the incidence of pine wilt disease at a study site located on the northwest coast of Japan. By analyzing the model we simulate the temporal change in the incidence of the disease and predict how the epidemic could be controlled by eradication of the pine sawyer. The main results are : 1) There is a minimum threshold of the initial pine density for successful invasion of the disease. However, even if the pine density exceeds the minimum threshold, the disease fails in invasion due to the Allee effect of the pine sawyer when its density is very low. 2) The minimum threshold density increases disproportionately with increase in the eradication rate. 3) The probability for a healthy tree to escape from infection until the epidemic dies out decreases sharply with increase in the initial pine density, when the eradication rate is low.
2. We analyzed the range expansion of an invading species and derived the conditions for persistence of a species two kinds of fragmented environments :
(1) an environment segmented into belts, with favorable and unfavorable patches arranged alterately.
(2) an environment segmented in both horizontal and vertical axs, with square-shaped favorable patches regularly distributed within the unfavorable environment.
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