Consumer‐mediated indirect interaction with a native plant lowers the fitness of an invasive competitor

Abstract

Seed dispersal is a primary driver, via propagule pressure, of biological invasions. In animal‐dispersed plants, theory predicts that indirect ecological interactions at the neighbourhood scale may determine landscape‐scale patterns of seed dispersal and predation, and thus invasion. Indirect interactions in seed dispersal may arise between two plant species if shared seed dispersal agents adjust their foraging decisions to the relative frequencies of co‐occurring seeds. We used seed‐tracking experiments and empirically parameterized simulations to test the hypothesis that an indirect interaction between two plant species, mediated by scatterhoarding rodents that both consume and disperse seeds, affects recruitment of an invasive tree. We predicted that acorns of Quercus rubra (invasive in Central Europe) would experience higher caching (and therefore survival) rates when they co‐occurred with native Quercus petraea than when they occurred in isolation, that Q. petraea acorns would survive at lower rates with Q. rubra relative to isolation, and that this interaction would facilitate Q. rubra seedling recruitment in Q. petraea forests. Contrary to expectations, the presence of Q. petraea reduced caching of Q. rubra acorns, and co‐occurrence with Q. rubra increased caching of Q. petraea. Thus, a rodent‐mediated indirect interaction may be slowing rather than facilitating the Q. rubra invasion. However, our simulations indicate that the magnitude of this indirect interaction will change nonlinearly as Q. rubra becomes more dominant on the landscape, and that the pace of invasion will accelerate as the alien species is released from the rodent‐mediated effect of Q. petraea. Synthesis. The presence of native Quercus petraea decreases recruitment rates of Quercus rubra, and consequently, slows down the invasion process. The strong dependence of pairwise interactions on the presence of a third‐party species emphasizes the role of indirect interactions in the invasion processes.

Interspecific synchrony of seed rain shapes rodent‐mediated indirect seed–seed interactions of sympatric tree species in a subtropical forest

“…Veech ; Dangremond et al ; Norghauer & Newbery ). A few studies revealed that apparent mutualism (Kitzberger et al ; Xiao & Zhang ) and apparent predation (Lichti et al ; Pesendorfer & Koenig ; Bogdziewicz et al ) occur among tree species through seeds by rodents and birds. Moreover, recent studies showed that seed predation and dispersal of a given tree species can be indirectly affected by other sympatric tree species at the neighbourhood scale (Yi et al ; Garzon‐Lopez et al ; Yi & Wang ).…”

“…Moreover, recent studies showed that seed predation and dispersal of a given tree species can be indirectly affected by other sympatric tree species at the neighbourhood scale (Yi et al ; Garzon‐Lopez et al ; Yi & Wang ). However, strict assessments of the seed–seed interactions under animal predation and dispersal for a given tree species within or without a neighbourhood have been largely ignored (but see: Albrecht et al ; Xiao & Zhang ; Bogdziewicz et al ).…”

“…In seed communities, indirect interactions may arise because seeds vary in size and palatability to animals (Emerson et al ; Ostoja et al ) or due to differences in the perishability of sympatric seed species (Lichti et al ; Xiao & Zhang ). Although the identification of certain seed traits by seed predators has been shown to cause indirect seed–seed interactions among sympatric tree species (Lichti et al ; Yi & Wang ; Xiao & Zhang ), most of these studies used only a few paired seed species in evaluating the indirect interactions (Garzon‐Lopez et al ; Xiao & Zhang ; Bogdziewicz et al ; Yang et al ).…”

Differential impacts of soil microbes on native and co‐occurring invasive tree species

“…, Bogdziewicz et al. , c). We should also note that seedlings and saplings of both oaks were rather rare on our transects, limiting our power to detect patterns in their distribution.…”

“…petraea and with conspecifics in the native range (Bogdziewicz et al. , c). Furthermore, it is less often consumed by rodents than the native oak, but also less readily dispersed by mice ( Apodemus flavicollis ) and jays ( Garrulus glandarius ; Wróbel unpublished manuscript , Myczko et al.…”