Disentangling the relative contributions of factors determining seed physical defence: A global‐scale data synthesis

Abstract Physical defence investment in seeds varies greatly among plant species and is associated with many potential factors. Exploring the factors explaining the interspecific variation in physical defence has long attracted particular attention in both ecology and evolution studies. However, the relative importance of the factors has not yet been quantitatively evaluated, which may lead to the misunderstanding of the main driver generating such interspecific variation. Here, by compiling a global database of the seed coat ratio (SCR), a proxy of seed physical defence, for 1362 species, we provided the first quantification of the relative explanations of six factors that have been commonly considered to be associated with the interspecific variation in SCR: seed mass, seed desiccation response (desiccation‐sensitive vs. desiccation‐tolerant), seed dormancy (nondormant, physical dormant or other dormant types), growth form (herbaceous vs. woody), fruit type (dry vs. fleshy) and climate (19 bioclimatic variables representing temperature and precipitation). Using partial R 2 calculation that can estimate the reduction in explained variance of a given factor after removing it from a full model containing all the other factors, we disentangled the relative contribution of each factor to explain variation in the SCR. Seed desiccation response was the most important factor associating with SCR variation, followed by seed dormancy, with a partial R 2 lik value of 9.70% and 1.41%, respectively. Plant growth form, seed mass, climate and fruit type showed little power to explain SCR variation, although they are often cited in the literature as potential factors. Our results highlight the important roles of seed desiccation response in shaping interspecific variation in the SCR. These findings provide a detailed interpretation of ecological patterns underlying the physical defence mechanisms and allocation strategies of plant seeds. Read the free Plain Language Summary for this article on the Journal blog.