Abstract Detail

Biogeography

Brown, Herrick [1], Wethey, David [2].

Toward Developing a Species Distribution Model for Gordonia lasianthus Using Empirical Evidence from Seed-Drop Trials and Some Discussion on the Variation in the Rotational Movement Patterns of the Winged Seeds.

Initial results from a Species Distribution Model (SDM) designed to study the potential effects of predicted climate change on a tree species that is endemic to the southeastern United States indicated areas of favorable environmental conditions that seemed far outside the current range of the species. This led to speculation regarding dispersal mechanisms and ‘migration’ rates. In order to include these biotic variables we developed an agent-based model that incorporates data from seed-drop trials as acted upon by observed and predicted wind speed, direction and humidity in addition to other environmental parameters. Gordonia lasianthus produces a dehiscent capsule with five locules each containing 4 winged seeds (20 seeds per fruit). Mature capsules dehisce along five vertical sutures and when dry the apices of each carpel may spread apart as much as 1cm. We noticed after collecting recently matured fruit that when placed in an air-tight vial over night the relative humidity rose in the vial to a point sufficient to produce a small amount of condensation; the moisture apparently escaping from the still-green pedicel. The increase in available atmospheric moisture was apparently absorbed by the dry tissue in the carpels which caused the distance between their apices to contract about 0.5cm. Therefore, our model includes a term that acts negatively upon seed dispersal during periods of high humidity. Wing-loading was calculated based on surface area results from analysis tools in ImageJ. Although there was no significant difference in the size of the seeds, variation in seed morphology was noteworthy. Seeds were then dropped from 3m in an indoor, wind-less room using a video camera with a high frame rate. On slow motion playback, the speed at which the seed traveled was measured when it reached terminal velocity. Significant differences in fall rates were observed among three fall patterns. While the wing apparently evolved to slow the fall rate and thus increase potential for horizontal dispersal distance, subtle variation in wing-loading, seed weight and wing morphology evidently produce either rotation around a vertical axis, rotation around a horizontal axis, or zero rotation. Seeds exhibiting the lattermost pattern fell significantly faster than others.

1 - A. C. Moore Herbarium (USCH), Department of Biological Sciences, University of South Carolina, Columbia, SC, 29208, USA
2 - Department of Biological Sciences, University of South Carolina, Columbia, SC, 29208, USA

Keywords:
Gordonia lasianthus
Species Distribution Model
Agent Based Model
climate change
Seed dispersal
Anemochory.

Presentation Type: Oral Paper
Session: 43, Biogeography III
Location: 205/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 2:00 PM
Number: 43003
Abstract ID:900
Candidate for Awards:None