A residence-time framework for biodiversity

Residence time (τ) is the average amount of time that particles spend in an ecosystem. Often estimated from the ratio of volume to flow rate, τ equates the physical environment with dynamics of growth. Here, we propose that τ is key to understanding relationships between biodiversity and the physical ecosystem. We hypothesize that τ acts as a force of selection on traits related to growth and persistence by coupling dispersal and resource supply. We test a suite of predictions using >10,000 stochastic individual-based models that simulate resource-limited life history among ecologically distinct species within complex environments. Predicted relationships between τ and abundance, productivity, and diversity emerged alongside realistic macroecological patterns. Abundance and productivity were greatest when τ equaled an emergent property ϕ, which captures energy-based trade-offs between growth and persistence. From individual metabolism to the dynamics of bioreactors, soils, lakes, and oceans, ecological systems should inherently be governed by τ.