Mediation of plant-herbivore interactions by resource sharing in clonal plants

Clonal plants can maximize their performance by selectively placing ramets in the environment and exchanging resources between ramets that remain physiologically connected. This ability allows clonal plants to rapidly colonize space, to maximize the number of ramets in high resource areas, and to exchange complementary resources between ramets in heterogeneous environments. Here, I test whether this ability may also allow clones of Fragaria virginiana [Rosaceae] to ameliorate the negative effects of herbivory. I used computer simulations, field observations of the effects of herbivory, and a series of field and greenhouse experiments in which I varied the number of intact stolons and defoliated different ramets. I measured the costs and benefits of clonality for the total clone as well as individual ramets.; The computer simulation predicted that more highly integrated clones always outperform less integrated clones, regardless of the intensity of herbivory. Field observations showed that the intensity of herbivory varies in intensity over the season but has few effects on clonal performance or expansion. In one greenhouse experiment the number of unrooted ramets supported by an older ramet had no effect on either the older ramet's ability to recover from herbivory or total clone performance. In a second greenhouse experiment, connected clones were able to recover from defoliation faster and better than clones that had connections between ramets severed. In contrast, in the field there was no difference in regrowth after defoliation or clonal expansion between connected and severed clones. I hypothesize that active connections between ramets did not benefit plants in the field because the environment was too uniformly harsh (due to drought conditions), negating any advantage of resource sharing. Studies show that clonal resource sharing is advantageous in heterogeneous environments. Overall, my results show that clonality can ameliorate the negative effects of herbivory, but the costs and benefits are conditional upon the environment.