Seed fate of common grassland species along an experimental plant diversity gradient

Background/Question/Methods

Biodiversity is essential for ecosystems that are influenced by environmental changes. With high species richness, ecosystem functions cannot only be stabilized but also optimized. Secondary seed dispersal and post-dispersal predation are important ecosystem functions, which have a major influence on the seed’s fate after the initial dispersal from the mother plant. These processes can transform plant populations and communities and therefore entire ecosystems. However, little is known about the role of biodiversity for seed dispersal, seed predation and the plant-animal interactions they entail.

The aim of this study was to test whether a change in plant diversity influences the rate of seed predation and dispersal and whether a switch between different predator groups takes place under different plant diversity.

We conducted the experiment along an experimental plant diversity gradient, comprising plots from 1 to 60 species mixtures of common grassland species in Jena, Germany. Seed cafeterias were set up as a combination of exclusion experiments with coloured seeds. Traditionally, seeds that are missing from seed cafeterias are classified as predated but this new set-up allowed us to not only identify seed removers but also to distinguish whether seeds were predated or dispersed (if they were discovered away from the seed cafeteria).   

Results/Conclusions

First results show that seed species identity as well as seed remover species are essential for the rate of predation as well as the rate of dispersal. In general, seeds containing starch were predated more frequently than seeds that were not attractive to invertebrates, regardless of plant species diversity. However, at least for slugs, predation rates were much higher in plots with high plant diversity compared to plots with 1 to 8 species mixtures. Mixed modelling revealed that these rates were largely influenced by the number of plant functional types in the plot as well as the density of undergrowth cover.

These results indicate that plant functional diversity can play an important role for the seed fate of different plant species, therefore influencing future plant recruitment and transforming the community.