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

Aim: 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: (a) equilibrium dynamics, where diversity is always positively related to energy availability in both time and space; (b) 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 relationships; and (c) disequilibrium dynamics where the equilibrium does not exist or is irrelevant. We attempt to distinguish these scenarios using spatio-temporal palaeoecological data.Location: USA and Canada.Time period: 21,000- 1,000 years before present.Major taxa studied: Woody plants.Methods: 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 1,000- year time steps.Results: 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.Main conclusions: 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 relationships. To understand diversity dynamics, it is crucial to simultaneously consider both the spatial and temporal dimensions of diversity variation.