Density-dependent pre-dispersal seed predation

The Janzen–Connell model predicts that common species suffer high seed predation from specialized natural enemies as a function of distance from parent trees, and consequently as a function of conspecific density, whereas the predator satiation hypothesis predicts that seed attack is reduced due to predator satiation at high seed densities. Pre-dispersal predation by insects was studied while seeds are still on parent trees, which represents a frequently overlooked stage in which seed predation occurs.

Hypotheses and predictions about the probability of seed survival or predation as a function of the density of seeds, seedlings or adult trees.
Hypotheses and predictions about the probability of seed survival or predation as a function of the density of seeds, seedlings or adult trees. (A) Positive density-dependent mortality (modified, the Janzen–Connell model), which predicts that individual plant performance (e.g. survival, growth and recruitment) decreased with increasing conspecific density (Wright, 2002). (B) Negative density-dependent seed predation (the predator satiation hypothesis), which predicts reduced seed predation but increased seed survival when seed density is high enough to satiate seed predators at the tree or population scale (Silvertown, 1980; Kelly, 1994). See Xiao et al. for details.

By quantifying pre-dispersal seed predation from ten Quercus serrata populations over two years according to three insect groups, Xiao et al. found that the overall population trend of negative density-dependent, pre-dispersal seed predation due to predator satiation limited the occurrence of Janzen-Connell effects on individual trees.

Reference

Xiao, Z., Mi, X., Holyoak, M., Xie, W., Cao, K., Yang, X., … Krebs, C. J. (2016). Seed–predator satiation and Janzen–Connell effects vary with spatial scales for seed-feeding insects. Annals of Botany, 119(1), 109–116. https://doi.org/10.1093/aob/mcw224