Jared Toogood

Epiphytes, Assemble! Epiphytic Fern Distribution Along a Vertical Moisture Gradient

Biodiversity (i.e., species number and relative abundances) in a habitat can be, in part, related to how individual species differ in their abilities to maximize growth rate versus tolerate stress based on their suite of morphological traits.  A fundamental determinant of a plant’s growth rate is its ability to acquire, transport, and utilize water for photosynthesis.  Conversely, a fundamental determinant of a plant’s ability to tolerate drought is its ability to retain water.  As a result, high growth rate in plants is generally associated with low drought tolerance.   In epiphytic communities (plants growing superficially attached to trees), habitats (trees) can vary by: height, trunk diameter, bark texture, bark chemistry, and shading.  Humidity tends to deceases with increasing height along a tree trunk; a gradient along which species may segregate based on their water acquisition versus drought tolerance abilities.  To investigate how the morphological traits of epiphytes influence their vertical distribution along this moisture gradient, I assisted in surveying the epiphytic communities of eighty-eight trees, at three vertical sections (0-1m, 1-2m, and 2-3m) at mid-elevation tropical rainforest in El Yunque National Park, Puerto Rico in 2012.  Specimens of each species encountered in the 2012 survey were collected during May 2013 for anatomical analyses.  For my S3 study, I am investigating anatomical differences among a subset of the species encountered in the 2012 survey, specifically, eighteen pteridophyte (fern and fern allies) species.  Digital photographs of the largest leaf of each plant and of anatomical slides I am currently preparing will be used to make precise measurements.  A species’ water demand will be evaluated based on the size and fractal dimension (complexity) of the leaf, specific leaf area (leaf area divided by its mass), and the stomatal (leaf pore) density.  Slides of the cross-sections of the stem, leaf stalk, and tip of the largest leaf will be measured for traits relating to the ability to supply water (e.g.,  the cross-sectional areas of: xylem (the water-conducting tissue plants), the largest xylary cell) and tolerate drought (e.g., cross-sectional area of sclarified tissue (hard supportive and protective tissue). This data will be analyzed to identify the traits most influential on species distribution and, in the context of the larger study in which my S3 project is embedded, to aid in determining the relative contributions of ecoytpic differentiation and stochasticity on biodiversity in this epiphytic community.

Faculty Mentor: Gary Greer, Biology

Page last modified August 2, 2013