Using isolation-by-distance to jointly estimate effective population density and dispersal distance: a practical...

Area of Science:

• Population Biology
• Ecology
• Conservation Genetics

Background:

• Estimating effective population density and dispersal is crucial for understanding population dynamics.
• Empirical estimation of these parameters is particularly challenging for small, mobile organisms like wild bees.

Purpose of the Study:

• To apply and evaluate an underutilized method for estimating effective density and dispersal distance in bumble bees (Bombus, Apidae).
• To investigate the impact of spatial sampling extent on effective density estimates.

Main Methods:

• Utilized 10 North American bumble bee datasets.
• Applied the relationship between genetic isolation-by-distance and Wright's neighborhood size to define a density-dispersal isocline.
• Used external estimates of dispersal distances to refine effective colony density.
• Subsampled datasets to simulate varying study extents and re-analyzed data.

Main Results:

• Estimated effective colony densities were significantly lower (1-41 colonies/km²) compared to prior census density estimates.
• Effective densities tended to decrease when measured across larger spatial extents, indicating scale-dependent patterns.
• Demonstrated an inverse relationship between effective density and dispersal distance.

Conclusions:

• The study highlights a valuable, under-appreciated method for estimating population parameters in small, mobile species.
• Researchers must carefully consider the spatial extent of sampling when interpreting effective density estimates for bumble bees.
• Findings underscore the importance of scale in ecological and genetic studies.