Seasonality, density dependence, and population cycles in Hokkaido voles

doi:10.1073/pnas.1935306100

Seasonality, density dependence, and population cycles in Hokkaido voles

^†Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, P.O. Box 1031 Blindern, N-0316 Oslo, Norway; ^§Field Science Center, Hokkaido University, North 11, West 10, Sapporo 060-0811, Japan; ^¶Department of Biological Science, Florida State University, Conradi Building, Tallahassee, FL 32306; and ^∥Department of Mathematics, University of Oslo, P.O. Box 1053 Blindern, N-0316 Oslo, Norway

Edited by Thomas W. Schoener, University of California, Davis, CA, and approved July 11, 2003 (received for review September 2, 2002)

Abstract

Voles and lemmings show extensive variation in population dynamics regulated across and within species. In an attempt to develop and test generic hypotheses explaining these differences, we studied 84 populations of the gray-sided vole (Clethrionomys rufocanus) in Hokkaido, Japan. We show that these populations are limited by a combination of density-independent factors (such as climate) and density-dependent processes (such as specialist predators). We show that density-dependent regulation primarily occurs in winter months, so that populations experiencing longer winters tend to have a stronger delayed density-dependence and, as a result, exhibit regular density cycles. Altogether, we demonstrate that seasonality plays a key role in determining whether a vole population is cyclic or not.

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: n.c.stenseth{at}bio.uio.no.
This paper was submitted directly (Track II) to the PNAS office.
↵ †† Our estimates for the relative length of the winter (τ_w) provide the best prediction [(WI – ŴI)²] for Groups 1 and 2. To observe that Group 5 (the more mountainous group) is more difficult to estimate seems reasonable because topographic effects in mountainous regions (north/south sloping) are likely to be more pronounced.