Modeling the Expansion of an Introduced Tree Disease |
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Authors: | Fugo Takasu Namiko Yamamoto Kohkichi Kawasaki Katsumi Togashi Yoichi Kishi Nanako Shigesada |
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Institution: | (1) Department of Information and Computer Sciences, Nara Women's University Kita-Uoya Nishimachi, Nara 630-8506, Japan;(2) Department of Knowledge Engineering and Computer Sciences, Doshisha University, Kyo-Tanabe 610-0321, Japan;(3) Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 793-8521, Japan;(4) University Forests, Tokyo University of Agriculture and Technology, Fuchu 183-8509, Japan;(5) Department of Information and Computer Sciences, Nara Women's University Kita-Uoya Nishimachi, Nara, 630-8506, Japan; (e-mail |
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Abstract: | Pine wilt disease is caused by the introduced pinewood nematode, Bursaphelenchus
xylophilus, for which the vector is the pine sawyer beetle, Monochamus alternatus. Native Japanese pines, black pine (Pinus thunbergii) and red pine (P. densiflora), are extremely sensitive to the nematode's infection, and the parasite has been expanding nationwide in the last few decades,
despite intensive control efforts. To understand the parasite's range expansion in Japan, we modeled the dynamics of the pines
and the beetle that disperses the nematode, using an integro-difference equation in a one-dimensional space. Based on field
data collected in Japan, we investigated the dependence of the parasite's rate of range expansion on the eradication rate
of the beetle, the initial pine density, and the beetle dispersal ability. Our model predicts several results. (1) The Allee
Effect operates on beetle reproduction, and consequently the parasite cannot invade a pine stand, once the beetle density
decreases below a threshold. (2) The distribution of the dispersal distance of the beetles critically affects the expansion
rate of the disease. As the fraction of the beetles that travel over long distance increases from zero, the range expansion
accelerates sharply. (3) However, too frequent long-range dispersal results in a failure of the parasite invasion due to the
Allee Effect, suggesting the importance of correctly assessing the beetle's mobility to predict the speed of range expansion
of the parasite. (4) As the eradication rate is increased, the range expansion speed decreases gradually at first and suddenly
drops to zero at a specific value of the eradication rate.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | distribution kernel long-range dispersal nematode infection pine wilt disease range expansion |
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