Abstract
Numerous interactions between plants and animals vary in their outcome between antagonism and mutualism, but it proved to be difficult to quantify their final outcome. Interactions between plants and scatterhoarding animals provide a prime example of this phenomenon. Scatterhoarders consume large quantities of seeds (potentially reducing plant establishment), yet also disperse seeds and bury them in shallow caches (potentially improving recruitment). However, it has been rarely determined which role prevails for particular plant species.
We experimentally evaluated the benefits of rodent seed dispersal in two model oak species (sessile oak Quercus petraea, and red oak Q. rubra) and used a heuristic mathematical model to place the interactions at the antagonism-mutualism continuum.
Our results indicate that during the period of the study, interactions between scatterhoarding rodents and both focal oaks were antagonistic. Even though acorn burial increased the likelihood of seedling establishment, this effect was not strong enough to compensate for the costs of seed predation. Furthermore, we found no evidence that the short-distance transportation that is usually provided by small mammals benefits early oak recruitment.
Even relatively large improvements in seedling establishment after seed burial do not necessarily render the plant-scatterhoarder interaction mutualistic. Our study is the first to separate and directly quantify two most important services provided to plants by their rodent partners: seed transportation away from parent plants and seed burial in topsoil. It also demonstrates how readily accessible field data can be used to gauge the outcomes in plant-granivore conditional mutualisms.