Oral Paper

         Ecology

Seed mucilage as a defense against granivory is influenced by substrate characters

Presenting Author
Madison Stessman
Description
Many seeds are consumed by granivores despite numerous adaptations to avoid detection or exploitation. The efficacy of defensive traits can be influenced by the environment. Therefore, understanding the mechanisms by which environmental factors modify defensive efficacy can be important for understanding this important context-dependency that may lead to patterns of plant distribution and recruitment. Seed mucilage is a sticky coating that binds wetted seeds to the substrate; this attachment has been previously demonstrated to lessens exploitation by granivores. Seed mucilage as a defense has been recognized for decades, though rarely investigated. Here, we investigated whether the environment alters this seed defense by addressing two questions: 1) Does substrate particle size affect attachment strength? And 2) Does a change in particle size lead to changes in mortality due to granivores? In the field experiment, ants removed more seeds from finer substrates. Across that same range of grit, seeds took less force to dislodge when mucilage-bound to fine sandpaper than when bound to coarser sandpaper; however, an investigation across a wider range of grits demonstrated nonlinearities occurred for many species. Small differences in substrate grit lead to differential mortality in mucilaginous seeds due to alterations in attachment strength, suggesting that the defensive efficacy of this trait differs across microsites. We propose several mechanistic hypotheses behind these somewhat idiosyncratic relationships. This work paves the way for a more integrative look at mucilaginous seeds. Seed mucilage is a widespread trait that is easily-studied and has important demographic implications. It represents an ideal system to examine dispersal, germination, and granivory to gain a more holistic view of seed ecology.