Code Appendix: Do Seed Dispersal Strategies Reflect Adaptation to Environmental Variability? Functional Ecology, 2023

This code appendix contains all of the R code and data for the manuscript:

Van Den Elzen, C. L., N. Sigman, and N. C. Emery. 2023. Do Seed Dispersal Strategies Reflect Adaptation to Environmental Variability?. Functional Ecology (Manuscript ID: FE-2022-00850).

Abstract: 

1. Dispersal is one of the primary mechanisms by which organisms adapt to spatial and temporal variation in the environment. Theory predicts that increasing spatiotemporal variation drives selection for offspring dispersal away from their natal habitat and one another. However, due to inherent difficulties in measuring dispersal in plant systems, there are few empirical tests of the extent to which this hypothesis can explain variation in seed dispersal strategies.

2. In this study, we characterized and compared the dispersal patterns of three closely related plant species that segregate across gradients in spatiotemporal variation in seasonal wetlands.

3. We tracked individual seeds as they dispersed in their natural habitats to measure seed dispersal distance (the distance traveled from the maternal plant) and inter-seed spread (distances between dispersed seeds), and to identify the plant traits causing within-species variation in seed dispersal. We also evaluated the seed traits causing within-species variation in seed flight distance and terminal velocity in a wind tunnel and a drop tube, respectively.

4. We found that average seed dispersal distance was lowest in the species that occupies the most spatiotemporally variable habitat, contradicting our predictions; however, inter-seed spread was lowest in the species from the least variable habitat, which aligned with our expectations.

5. The maternal plant and seed traits explaining intraspecific variation in seed dispersal varied among species as well as the method used to measure dispersal potential. Two traits had non-intuitive effects on dispersal, including pappus size, which reduced seed flight distance in two of the focal taxa.

6. Overall, our results indicate that the differences we detected in seed dispersal among three closely related plant taxa can be only partially explained by current patterns of environmental variability in their respective habitats, and that the traits driving within species variation in seed dispersal can evolve rapidly and change with the environmental context in which they are measured.

本代码附录包含下述手稿的全部R代码与相关数据：Van Den Elzen, C. L.、N. Sigman 与 N. C. Emery. 2023. 《种子扩散策略是否反映对环境变异的适应？》（Do Seed Dispersal Strategies Reflect Adaptation to Environmental Variability?），刊载于《功能生态学（Functional Ecology）》，稿件编号：FE-2022-00850。

摘要：
1. 扩散是生物适应环境时空变异（spatiotemporal variation）的核心机制之一。理论预测，时空变异程度的提升会驱动选择作用，促使后代扩散至远离其出生地生境（natal habitat）与其他同胞后代的区域。然而，由于植物系统中扩散行为的测量存在固有难点，目前针对该假说能否解释种子扩散（seed dispersal）策略差异的实证检验仍较为匮乏。
2. 本研究对三种沿季节性湿地时空变异梯度分化的近缘植物物种的扩散模式进行了表征与比较。
3. 我们通过在自然生境中追踪单颗种子的扩散过程，测量了种子扩散距离（即从母株出发的移动距离）与种子间散布距离（inter-seed spread，即扩散后种子间的间距），并鉴定了导致物种内种子扩散差异的植物性状。此外，我们分别在风洞与落管实验中评估了影响种子飞行距离与终端速度的种内性状变异。
4. 研究发现，栖息于时空变异程度最高的生境的物种，其平均种子扩散距离最低，这与我们的预测相悖；但栖息于时空变异程度最低的生境的物种，其种子间散布距离最低，这与我们的预期相符。
5. 解释种子扩散种内变异的母株性状与种子性状，因物种而异，同时也因扩散潜力的测量方法不同而存在差异。有两个性状对扩散的影响与直觉相悖，例如冠毛（pappus），它会降低两个目标类群（focal taxa）的种子飞行距离。
6. 总体而言，本研究结果表明，我们在三种近缘植物类群中检测到的种子扩散差异，仅能部分通过其各自生境当前的环境变异模式加以解释；同时，驱动种内种子扩散变异的性状可快速演化，并随测量时的环境背景发生改变。