Apparent competition in canopy trees determined by pathogen transmission rather than susceptibility

• Published in: Ecology (Durham) 2010-02, Vol.91 (2), p.327-333
• Main Authors: Cobb, Richard C., Meentemeyer, Ross K., Rizzo, David M.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; apparent competition; Biological and medical sciences; community epidemiology; Coniferous forests; disease ecology; Disease susceptibility; Disease transmission; Ecological competition; Ecology; emerging infectious disease; Epidemiology; Forest ecology; forest pathogens; Forestry; Forests; Fundamental and applied biological sciences. Psychology; General aspects; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Host-Pathogen Interactions; Infections; Lithocarpus densiflorus; Mortality; Pathogens; Phytophthora; Phytophthora - physiology; Phytophthora ramorum; Plant diseases; Plant Diseases - microbiology; Plant pathology; Quercus spp; Sequoia sempervirens; sudden oak death; Time Factors; Trees; Trees - microbiology; Umbellularia californica
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/09-0680.1

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.