Ecology and macroevolution - evolutionary niche monopolisation as a mechanisms of niche conservatism

Explaining macroevolution from microevolution is a key issue in contemporary evolutionary theory. A recurrent macroevolutionary pattern is that some niche-related traits consistently evolve slower than others, so called niche conservatism. Despite a growing amount of data, the underlying evolutionary processes are not fully understood. I here analyse adaptive radiations in an individual-based eco-evolutionary model. I find a coevolutionary mechanism - evolutionary niche monopolisation - as a possibly important generator of niche conservatism. A single lineage of a radiating clade can monopolise, and later diversify within, a substantial part of the available niche space - much larger than what can be explained by limiting similarity. This leads to niche conservatism, since no species evolves into or out of the monopolised region. The region can in this sense also be described as an adaptive zone. The model indicates that evolutionary niche monopolisation is operative in a large part of parameter space, underlining its possible importance. The mechanism is driven by competitive interactions and differences in niche widths in alternative niche dimensions. I discuss plausible examples of evolutionary niche monopolisation in well-studied natural systems.