Using graph theory to quantify dynamic connectivity of temporary wetlands in the southern Great Plains

Background/Question/Methods

We examined temporal fluctuations in the status of habitat patches as stepping-stones, cutpoints, or hubs within a network of temporary wetlands of the southern Great Plains of North America (called playas) that are regional foci for biodiversity.  Charged by precipitation runoff, these closed-basin wetlands are subject to land conversion and climate change, which may disrupt the connectivity of the naturally dynamic playa network for wildlife such as migratory waterfowl.  We used remote sensing imagery to delineate the location of surface waters in >8000 playas in a ~34,225 km²portion of Texas and quantified connectivity in this area from 2007-2011, ranking stepping-stones, cutpoints, and hubs of the playa network during differing times of habitat availability (regionally wet, dry, and average periods of precipitation) and for different dispersal distances ranging from 0.5-20 km (representing a range of vagility for wetland-dependent wildlife), to provide a baseline of connectivity dynamics within an area likely to experience disrupted connectivity due to anthropogenic activities.

Results/Conclusions

Whereas an individual playa’s status as a stepping-stone, cutpoint, or hub was dynamic over time, there was some consistency in regions of the network where these important wetlands tended to occur.  Hubs were located in areas of high playa density, cutpoints were primarily situated around the focal area’s edges (likely as artifacts of focusing on only a portion of a larger network), and stepping-stones were typically in topographically constricted portions of the focal area.  Coalescence of the network was usually at >10 km dispersal distance and dependent on wetland density, indicating a synergistic effect of dispersal ability (spatial scale) and habitat availability (wet vs. dry periods) on critical thresholds in connectivity.  Moreover, our results indicate that playa-associated organisms with more restricted movement capabilities (<10 km) routinely experienced effective isolation during our four-year focal span.  Connectivity is thus a dynamic trait within a landscape that is likely to be affected by climate and land-use changes in the foreseeable future, and management for maintaining connectivity for wildlife within the playa network will likely need to focus on larger regions within the network rather than current efforts at the scale of individual wetlands.