A recurring question in ecology is whether herbivore populations are regulated by their predators (top-down) or their food supply (bottom-up). In lemmings you will find evidence for both. Parametrised differential equation models to explain lemming cycles have been developed for the interaction between collared lemmings and their predators in Greenland (Gilg et al. 2003), as well as between brown lemmings and their plant foods in Alaska (Turchin and Batzli 2001). There is a large variation in the maximum densities attained and the cycle amplitude, which means a single, universal explanation for lemming dynamics is unlikely. We are interested in finding out if one can tease apart the factors (predators or food) that are most important in the various places where lemmings are studied. [joint work with J.A. Henden, R. Ims, N.G. Yoccoz, O Gilg].
To find out the interaction behind the cycle, the shape of cycles is thought to be indicative (Turchin 2003). Actually, I've been even more interested in the shape of the underlying density-dependence, notably in common voles (joint work with A. Pinot).
Publications:
Barraquand F.∗ , Pinot A.∗ , Yoccoz N.G. & Bretagnolle V. Overcompensation and phase effects in a cyclic common vole population: between first and second order cycles. Journal of Animal Ecology, in press. Data and computer files stored in Dryad.