OOS 57-5 - Evolution following invasions drives differences in community states and trajectories

Following biological invasions, evolution of both invading and resident species has the potential to cause widespread changes to ecological communities. It remains unknown the extent to which post-invasion evolution may result in alternative community states that can persist over multiple generations. We used a community-level study of experimental evolution in two compositionally different assemblages of protists and rotifers to explore whether initial differences in species abundances among communities resulting from their evolutionary history with invasion persisted over multiple generations. In each assemblage, trajectory analysis revealed significant convergence among two of the treatments differing in evolutionary history over a period of approximately 40-80 generations (first assemblage: tau = -0.72, p = 0.009; second assemblage: tau = -0.61, p = 0.03). In the first assemblage, the observed convergence across the two evolutionary history treatments appeared to be driven by similar declines in the abundance of the invader and one resident species. In contrast, convergence among select treatments in the second assemblage was driven by the decline of one resident, but an increase in the invader. Nonetheless, community structure failed to converge completely across all invaded treatments to a single structure (p > 0.05 for all other comparisons of community convergence across treatments). In the first assemblage, we also observed a concurrent increase in variability among replicate communities over time, suggesting that ecological drift may be another factor contributing to community change. Our results demonstrate that while the species present in a community assemblage represent a common selective regime, differences in populations reflecting their evolutionary history can produce long-lasting transient alternative community states. While subtle, these transient alternative states, in which communities differed in the abundance of interacting species, could nonetheless have important functional consequences for the impact of biological invasions.