The standard adaptive dynamics framework assumes two timescales, i.e. fast population dynamics and slow evolutionary dynamics. We further assume a third timescale, which is even slower than the evolutionary timescale. We call this the geological timescale and we assume that slow climatic change occurs within this timescale. We study the evolution of our model population over this very slow geological timescale with bifurcation plots of the standard adaptive dynamics framework. The bifurcation parameter being varied describes the abiotic environment that changes over geological timescales. We find that branching and extinctions are very pronounced for phenotypes in the middle of the phenotype space. We also concur with the established notion that branching of a monomorphic population in a spatially variable environment only happens when the gradient of the environment is not too shallow or too steep. However, we show that steep gradients can be populated by polymorphic populations, if the gradient at some point in the past has been shallow enough for the monomorphic population to branch.

adaptive dynamics; environmental gradient; geological time-scale; patterns of evolution