Open Collections

Description

Abstract

While investigating how historical contingencies manifest in ecological communities is common, research has yet to uncover how species distributions and abundances may be impacted by ecological processes interacting across spatial and temporal scales. We assessed the influence of a historical dispersal event on community assembly by simulating five scales of dispersal for 240 serpentine annual plant communities that experienced a large shift from drought to high rainfall conditions over three years. We collected, aggregated, and redistributed the aboveground seed bank from 30 sites across five nested spatial scales (~1 m, 5 m, 100 m, 5 km, and 10 km), and annually censused communities over a three-year period to identify change in community structure among dispersal scales and over time. We assessed the change in community composition and diversity that occurred over the study period by comparing contrasts of Bray-Curtis disimilarity and net changes in species richness between a baseline control plot and each experimental dispersal treatment plot. We also determined how species turnover through time was affected by dispersal scale, including how the number of established, sink, and intermittent species found in experimental plots were impacted by our past dispersal manipuation. Finally, we examined species’ differences in response to environmental fluctuations (i.e. stress-tolerant vs. stress-intolerant) and whether dispersal enhances these differences to increase turnover in dominant species groups. Our one-time dispersal manipulation diversified local seed banks, thereby providing insurance against temporal variability and supporting community re-assembly toward a new compositional state when drought was lifted. We also found evidence that various forms of temporal lags directed community responses to environmental fluctuations, preventing rare species extirpations and providing subordinate species discrete windows of time to supplement their seed banks. This experiment underscores the importance of dispersal and dormancy for diversity maintenance in the face of future climate where the degree and magnitude of fluctuations are uncertain.