COS 9-8
A shift in competition through time for invasive Microstegium vimineum
Invasive plants often become the dominant species in the community and can be capable of out competing native species. This competitive advantage could be due to a lack of coevolution with the community in the invaded range; specifically an escape from specialized enemies. However, it is unclear how long this escape from enemies actually lasts since specialized pests and pathogens could accumulate through time in the invaded range. If accumulation occurs then the invader’s competitive advantage could decrease through invasion time, potentially allowing invasive and native plants to coexist. The objective of this experiment was to test whether intra- and interspecific competition has changed for invasive Microstegium vimineum and the native plant, Pilea pumila, through invasion time. We planted monoculture and polyculture microcosms of M. vimineum and P. pilea in the field at 7 sites that vary in invasion age. We hypothesized that M. vimineum’s competitive advantage would decrease through time causing for its percent of total biomass in polyculture plots to decline. We also hypothesized that M. vimineum would have decreasing biomass in monoculture relative to polyculture through invasion time if pathogen accumulation is affecting high frequency plots (monoculture) more than low frequency plots (polyculture).
Results/Conclusions
We observed declining fitness of M. vimineum in monoculture relative to polyculture across the invasion age gradient. We also found a shift in the dominant species in the polyculture through invasion time. M. vimineum started as the dominant species in the polyculture and then it shifted through the invasion age gradient to P. pilea being the dominant species. These shifts could be caused by a loss of M. vimineum’s competitive advantage due to an accumulation of pathogens decreasing its fitness, although the mechanism is not clear from this study. The increase in intraspecific competition, coupled with a decrease in interspecific competitive effect on P. pumila, suggests that M. vimineum may become less invasive through invasion time, allowing for its integration into the native community and the promotion of coexistence. Future work will focus on understanding the possible mechanisms behind the competition and coexistence patterns observed. This experiment will also be repeated to observe any temporal variation.