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    Author(s): Julian M. Norghauer; Christopher M. Free; R. Matthew Landis; James Grogan; Jay R. Malcolm; Sean C. Thomas
    Date: 2015
    Source: Oikos
    Publication Series: Scientific Journal (JRNL)
    Station: International Institute of Tropical Forestry
    PDF: Download Publication  (907.0 KB)


    The Janzen -- Connell hypothesis proposes that specialized herbivores maintain high numbers of tree species in tropical forests by restricting adult recruitment so that host populations remain at low densities. We tested this prediction for the large timber tree species, Swietenia macrophylla, whose seeds and seedlings are preyed upon by small mammals and a host-specific moth caterpillar Steniscadia poliophaea, respectively. At a primary forest site, experimental seed additions to gaps -- canopy-disturbed areas that enhance seedling growth into saplings -- over three years revealed lower survival and seedling recruitment closer to conspecific trees and in higher basal area neighborhoods, as well as reduced subsequent seedling survival and height growth. When we included these Janzen -- Connell effects in a spatially explicit individual-based population model, the caterpillar’s impact was critical to limiting Swietenia’s adult tree density, with a 10-fold reduction estimated at 300 years. Our research demonstrates the crucial but oft-ignored linkage between Janzen -- Connell effects on offspring and population-level consequences for a long-lived, potentially dominant tree species.

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.


    Norghauer, Julian M.; Free, Christopher M.; Landis, R. Matthew; Grogan, James; Malcolm, Jay R.; Thomas, Sean C. 2015. Herbivores limit the population size of big-leaf mahogany trees in an Amazonian forest. Oikos 125: 137–148.


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    Swietenia macrophylla, Steniscadia poliophaea, seedling growth, seedling survival, herbivores, host populations, tropical forests

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