title: Phase- and density-dependent population dynamics in Norwegian lemmings: interaction between deterministic and stochastic processes.
abstract: We analysed two 26-year long (1970-1995) time-series on annual population growth rates of Norwegian lemmings (Lemmus lemmus) from Finse, south Norway, using a threshold autoregressive (TAR) approach. We demonstrate that the population dynamics is both phase- and density-dependent. The phase-dependence accounts for the observed nonlinearity. We used the deduced stochastic model structure as a basis for evaluating the dynamic properties of this system. The dynamics is characterized either by limit cycles or chaos (the latter with a strong semi-periodic component). Stochasticity is seen to play an important role in the determination of the periodicity. The ecological implications of these statistical and mathematical results are discussed.
authors.affiliation: Centre for Advanced Study, Norwegian Academy of Science and Letters, Oslo, Norway. n.c.stenseth@bio.uio.no
authors.forename: N C
authors.initials: NC
authors.lastname: Stenseth
authors.forename: K S
authors.initials: KS
authors.lastname: Chan
authors.forename: E
authors.initials: E
authors.lastname: Framstad
authors.forename: H
authors.initials: H
authors.lastname: Tong
mesh_terms: D000818:Animals; D003411:Arvicolinae; D017753:Ecosystem; D008954:Models, Biological; D017711:Nonlinear Dynamics; D009664:Norway; D011156:Population Density; D011157:Population Dynamics; D013269:Stochastic Processes