The dynamics of the diversity-energy relationship during the last 21,000 years

Spatial diversity patterns are linked to energy availability, but how the diversity-energy relationship changes in space and time is unclear. There are three possible scenarios: (1) equilibrium dynamics, where diversity is always positively related to energy availability in both time and space, (2) out-of-equilibrium dynamics, where diversity is determined by energy availability in equilibrium, but diversity variation lags behind changes in energy availability, leading to a mismatch between temporal and spatial diversity-energy relationship, and (3) disequilibrium dynamics where the equilibrium does not exist or is irrelevant. We attempt to distinguish these scenarios using spatiotemporal paleoecological data. We tested for the strength and direction of temporal and spatial relationships between pollen type diversity of woody species and energy availability (estimated from temperature and precipitation) in the USA and Canada in 1000-year time steps.

Whereas the temporal diversity-energy relationship appears only when energy levels rapidly change, the spatial diversity-energy relationship is pronounced only when these levels stabilize. Our findings are consistent with the out-of-equilibrium scenario – diversity equilibria do exist and act as attractors of diversity dynamics, but diversity is often out of equilibrium. Consequently, current rapid climate changes can disrupt spatially consistent diversity-energy relationship. To understand diversity dynamics, it is crucial to simultaneously consider both the spatial and temporal dimensions of diversity variation.