Mast seeding and population dynamics of rodents: one factor is not enough

The new 'mast depression hypothesis' by Selas to explain population cycles more generally is scrutinized with particular attention to rodent dynamics. It is found not to explain, e.g., synchrony between species with different trophic adaptations, or differences between continents in cycle length for the same or similar species. It relies on changes in plant defences that either are not well supported or are unnecessary for explaining particular fluctuations. It cannot explain the very low densities occurring after population crashes. This hypothesis is one idea in a large series of recent putative one-factor explanations of rodent population cycles. I suggest that, instead, we have to look for several factors to explain different population phases, to explain regional and temporal differences in cycle magnitudes and intervals, or to explain any specific cycle anatomy, Still, certain factors may emerge to he more important than others.