New study describing how apparent predation occurring between two sympatric oaks influence their recruitment rates was just published in Journal of Ecology.

The Authors (Michał Bogdziewicz, Nathanael Lichti, Rafał Zwolak) wrote a short summary of their work:

Numerous plants are dispersed by scatterhoarding animals such as corvids and rodents. These animals carry away and cache seeds, but the ultimate goal of this activity is seed consumption. Thus, scatterhoarders act both as seed dispersers and predators and the net outcome of plant-scatterhoarder interactions is often influenced by environmental conditions.  As a result, it can be quite variable.

In a study conducted in a temperate Polish forest, we pursued an idea that the fragile balance between seed predator and disperser can be tilted by neighborhoods of the focal seeds. We used seed tracking experiments to test whether seed fates of two oak species (native sessile oak Quercus petraea and invasive red oak Q. rubra) are different when they occur alone or in mixed treatments. We predicted that we will observe a novel class of indirect interactions, called ‘apparent predation’, between the two oaks.

Apparent predation arises when scatterhoarders perceive one seed species to be more useful for storage then others and its presence leads the hoarders to alter their handling of seeds that are less valued for caching. Situation when hoarders can focus on one seed species for caching and on other for consumption is clearly beneficial for the cached species, but detrimental for the consumed ones. Thus, the co-occurring seed species experience opposite effects. This phenomenon has been termed apparent predation because its demographic effects resemble those of a direct, pairwise predatory interaction (the cached seed species “preys” on the consumed species when they occur together).

We found such an interaction in our study system. The presence of acorns of the native oak suppressed dispersal and survival of cached acorns of the invasive oak. Furthermore, the dispersal and survival of the native oak acorns was higher when they were presented together with the invasive species.

We then conducted simulations to examine how this phenomenon can affect patterns of invasion at the landscape level. These showed that apparent predation with native oaks slows down the invasion at its initial stages – when most invasive oaks co-occur with the native ones. Yet, as the invasion progress, the suppressing effect of the native oak is diminishing. This can unexpectedly accelerate the invasion progress.

These results offer a new twist on the old idea of “biotic resistance”, or the innate ability of communities to thwart invasions of alien species. Our study demonstrates that this ability can result from apparent predation of native plants on invasive ones. However, strength of this interaction is predicted to gradually vanish as native plants are displaced from communities.

The full text is available at the journal website:

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