Limited by the roof of the world: mountain radiations of Apollo swallowtails controlled by diversity-dependence processes
Résumé
Mountainous areas contain a substantial part of the world species richness,
but the evolutionary origins and diversification of this biodiversity remain
elusive. Diversification may result from differences in clade age (longer time
to diversify), net diversification rates (faster speciation rate) or carrying
capacities (number of niches). The likelihood of these macroevolutionary scenarios
was assessed for six clades of Apollo swallowtails (Parnassius) that
diversified mainly in the Himalayan–Tibetan region. The analyses suggest
that neither the clade age nor the speciation rate could explain the mountain
butterfly diversification. Instead diversity-dependence models were strongly
supported for each group. Models further estimated clades’ carrying
capacities, which approximate to the current number of species, indicating
that diversity equilibrium has been reached (or close to being reached).
The results suggest that diversification of mountain butterflies was controlled
by ecological limits, which governed the number of niches, and provide
macroevolutionary justification for regarding mountains as islands.