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    Author(s): Richard Cobb; Ross Meentemeyer; David Rizzo
    Date: 2010
    Source: Ecology 91(2): 327-333
    Publication Series: Scientific Journal (JRNL)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (218.45 KB)


    Epidemiological theory predicts that asymmetric transmission, susceptibility, and mortality within a community will drive pathogen and disease dynamics. These epidemiological asymmetries can result in apparent competition, where a highly infectious host reduces the abundance of less infectious or more susceptible members in a community via a shared pathogen. We show that the exotic pathogen Phytophthora ramorum and resulting disease, sudden oak death, cause apparent competition among canopy trees and that transmission differences among canopy trees drives patterns of disease severity in California coast redwood forests. P. ramorum ranges in its ability to infect, sporulate on, and cause mortality of infected hosts. A path analysis showed that the most prolific inoculum producer, California bay laurel (Umbellularia californica), had a greater impact on the mortality rate of tanoak (Lithocarpus densiflorus) than did other inoculum-supporting species. In stands experiencing high tanoak mortality, lack of negative impacts by P. ramorum on bay laurel may increase bay laurel density and subsequently result in positive feedback on pathogen populations. This study demonstrates the degree to which invasive, generalist pathogens can cause rapid changes in forest canopy composition and that differences in transmission can be more important than susceptibility in driving patterns of apparent competition.

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    Cobb, Richard C. ; Meentemeyer, Ross K.; Rizzo, David M. 2010. Apparent competition in canopy trees determined by pathogen transmission rather than susceptibility. Ecology, 91(2), 2010, pp. 327–333


    apparent competition, community epidemiology, disease ecology, emerging infectious disease, forest pathogens, Lithocarpus densiflorus, Phytophthora ramorum, Quercus spp., Sequoia sempervirens, sudden oak death, Umbellularia californica.

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