A Cautionary Note Regarding the Consequences of Balancing for Fair Comparisons in Population Ecology

Population ecology has amassed a significant volume of demographic data across the Tree of Life. Together, these data enable comparative analyses at unprecedented taxonomic and biogeographic scales to examine patterns of demographic performance and their mechanisms. However, macroecological analysis of heterogeneous data and models from diverse study systems comes with risks, and care must be taken to ensure that the patterns from comparative approaches are biologically meaningful, rather than driven by model-specific artifacts. Recently, a balancing approach has been proposed as a solution to “distorted” population structure, particularly for evaluating transient (short-term) population dynamics. We argue that some distortion is the result of true biological processes, and that balancing over-corrects for distortion due to census timing (pre- vs. post-breeding). We lay out the relationship between demographic census design and the issues purported to be solved by balancing. Using a large dataset of carefully-selected matrix population models from plants and animals, we demonstrate that balancing changes biological interpretation of the relationship between reproductive traits and demographic resilience. We also highlight how application of balancing outside of its narrow original application to transient metrics can be problematic. We argue that meaningful comparisons require tailored approaches that respect the structure and context of demographic data. A more nuanced strategy–based on the biological realities of life cycles, census design, and reproductive strategies–will improve the robustness and interpretation of comparative demographic analyses.