COS 7-1 - Historical dispersal and the maintenance of biodiversity in a fluctuating climate

Monday, August 15, 2022

1:30 PM – 1:45 PM EDT

Location: 513F

Presenting Author(s)

JK

Jessica Kowalski

University of British Columbia, British Columbia, Canada

Coauthor(s)

BG

Benjamin Gilbert

University of Toronto, Department of Ecology & Evolutionary Biology
Toronto, Ontario, Canada
RG

Rachel Germain

University of British Columbia
Vancouver, British Columbia, Canada

Background/Question/Methods

In variable environments, community structure depends on interactions between climate, local site conditions, and the structure of the local species pool, where local pools are shaped by dispersal. Dispersal can maintain diversity via population rescue or by allowing species to track favourable conditions over space or through time (e.g., through dormancy or population-level storage). However, species losses may also occur if site conditions do not match a species’ niche or if competition intensifies under extreme conditions. Despite a growing recognition that temporal and spatial dimensions of dispersal interactively determine diversity and species persistence, most empirical research focuses on only one dimension at a time. To determine how both dimensions of dispersal contribute to community assembly in a spatially and temporally variable environment, we simulated varying scales of dispersal for 240 serpentine annual plant communities by collecting, aggregating, and redistributing the seed bank from 30 sites across five nested spatial scales (~1 m, 5 m, 100 m, 5 km, and 10 km). Communities were then annually censused over a three-year period (2014-2016) to assess how community diversity varied among and within dispersal scales over time.

Results/Conclusions

We found a positive relationship between the spatial scale of dispersal and species richness that persisted for three years following the initial dispersal event (X2 = 382.7; p < 0.001), but the slope of the relationship varied over time (X2 = 40.1; p < 0.001). This relationship was weakest in 2014 and 2016 and strongest in 2015, with 2015 representing a transition year between historic drought (2014) and average-to-wet climate conditions (2015-2016). Our results suggest that species gained in 2015 were balanced by the loss of species in 2016 (i.e., species turnover among plots subject to the same scale of dispersal remained constant across years (X2 = 0.6; p = 0.44)). Initial gains were likely driven by germination of dormant seeds in the seed bank in 2015 once climate conditions improved, followed by the loss of less competitive species once densities increased in 2016. These preliminary results suggest that environmental fluctuations can introduce lag effects, where transition years between environmental extremes can either delay or prevent local extinctions in subsequent years. As such, it is important to consider both spatial and temporal dimensions of ecological processes to understand and predict the impacts of process interactions on community assembly.