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Harvard Forest Symposium Abstract 2014

  • Title: Testing mechanisms of species coexistence in a Costa Rican wet tropical forest with long term observations of woody seedling dynamics
  • Primary Author: Sydne Record (Bryn Mawr College)
  • Additional Authors: Andrew Finley (Michigan State University); Richard Kobe (Michigan State University)
  • Abstract:

    Elucidating the processes that allow for species coexistence is central to understanding patterns of biodiversity and a key goal of community ecology. In hyperdiverse wet tropical forest communities, two potential mechanisms that could allow for such species rich communities are negative density dependence and niche based resource partitioning (e.g., resources such as irradiance and soil nutrients). Here we test how these mechanisms influence seedling mortality using a long term study on tropical woody species at La Selva Biological Station in Costa Rica. Every six weeks from March 2000 to June 2013, we monitored woody seedling dynamics in five transects each 200 m in length across a soil resource gradient. We estimated separate age-specific survival and mortality rates for 68 species of woody seedlings using a hierarchical Bayesian capture-recapture/recovery model, which addresses missing data issues stemming from observation error (i.e., unknown times of birth and death). In these models, we included the following predictors: average lifetime irradiance, average lifetime conspecific density, total soil nitrogen, soil phosphate, and the sum of base cations in the soil (potassium, magnesium, and calcium). Resource based limitation of total nitrogen, phosphate, and irradiance had the largest effects on survivorship and mortality of those species showing significant responses to the predictors in the models. One quarter of the species had survival and mortality rates that were influenced by two or more predictors suggesting that multiple mutually compatible mechanisms of coexistence may explain recruitment dynamics in this wet tropical forest. Species with smaller average seedling sizes, which correlated with smaller seed sizes (i.e., lower stored energy reserves prior to germination), had more variable mortality rates. These results stress the importance of resource based niche limitation in structuring wet tropical forest communities.

  • Research Category: Biodiversity Studies, Ecological Informatics and Modelling, Physiological Ecology, Population Dynamics, and Species Interactions