Eco-evolutionary partitioning metrics: assessing the importance of ecological and evolutionary contributions to population and community change

Interest in eco-evolutionary dynamics is rapidly increasing thanks to ground-breaking research indicating that evolution can occur rapidly and can alter the outcome of ecological processes. A key challenge in this sub-discipline is establishing how important the contribution of evolutionary and ecological processes and their interactions are to observed shifts in population and community characteristics. Although a variety of metrics to separate and quantify the effects of evolutionary and ecological contributions to observed trait changes have been used, they often allocate fractions of observed changes to ecology and evolution in different ways. We used a mathematical and numerical comparison of two commonly used frameworks - the Price equation and reaction norms - to reveal that the Price equation cannot partition genetic from non-genetic trait change within lineages, whereas the reaction norm approach cannot partition among- from within-lineage trait change. We developed a new metric that combines the strengths of both Price-based and reaction norm metrics, extended all metrics to analyse community change and also incorporated extinction and colonisation of species in these metrics. Depending on whether our new metric is applied to populations or communities, it can correctly separate intraspecific, interspecific, evolutionary, non-evolutionary and interacting eco-evolutionary contributions to trait change.