Evol Ecol Res 10: 415-434 (2008) Full PDF with comments if your library subscribes.
Arctic lemmings, Lemmus spp. and Dicrostonyx spp.: integrating ecological and evolutionary perspectives
Tarja Oksanen,1* Lauri Oksanen,2 Jonas Dahlgren1 and Johan Olofsson1
1Department of Ecology and Environmental Sciences, Umeå University, SE-901 87 Umeå, Sweden and 2Department of Biology, Section of Ecology, University of Turku, FI-200 14 Turku, Finland
Author to whom all correspondence should be addressed.
Question: What do the evolution and the fluctuation patterns of arctic lemmings – Lemmus spp. and Dicrostonyx spp. – tell us about their population dynamics and the influence of lemmings on the ecology and evolution of arctic plants?
Methods: We reviewed the literature concerning the evolution of arctic lemmings and analysed their current fluctuation patterns with a focus on the following aspects: (1) changes in morphology related to feeding ecology; (2) per capita rate of population growth during the year preceding the peak (rp), predicted to be high for arvicoline rodents interacting with the winter forage plants and low for arvicoline rodents interacting with specialized predators; (3) the skew of logarithmically transformed density data (skd), predicted to be zero for arvicolines interacting with their winter forage plants, negative for arvicolines interacting with specialized predators, and positive for arvicolines interacting with both seasonally renewed and depletable winter forage plants (the ‘Barrow model’ of Turchin and Batzli, 2001). Moreover, we conducted spectral analysis of those density records, which were at least 15 years long. Here predator–arvicoline models predict that similar spectral density profiles, with statistically significant peaks, are obtained with untransformed and logarithmically transformed data, whereas arvicoline–plant models predict that such profiles are only obtained using logarithmically transformed data.
Key insights: Arctic lemmings differ from other microtine rodents by having several features which increase their foraging efficiency under harsh conditions at the cost of reduced agility. These features were acquired rapidly at the dawn of the Pleistocene. Density fluctuations of all arctic lemming populations, for which sufficient data are available, correspond to the predictions of the ‘Barrow model’ and differ from the predictions of predator–arvicoline models. Our interpretation is as follows. When the Polar Sea froze, the primary productivity of northernmost Eurasia and North America was reduced, causing a shift from predation-controlled to food-limited dynamics in microtine rodents. This change in population dynamics triggered an extraordinarily rapid change in the characteristics of lemmings and precipitated an intense, sustained lemming–vegetation interaction, as old as the tundra itself, which has probably played a major role in the evolution of arctic plants.
Predictions: Increasing primary productivity along the southern (lower) boundary of the ranges of arctic lemmings should lead to their elimination by voles via apparent competition. Exclusion of lemmings should initiate dramatic changes in the vegetation of those tundra habitats, which have at least moderate snow cover and do not freeze in solid ice in winter. Exclusion of predators should have no impact on dynamics of inland populations of arctic lemmings.
Keywords: Arctic, Dicrostonyx, herbivory, Lemmus, outbreaks, population cycles, time trajectories, vegetation.
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