Abstract
The hypothesis that predation is the cause of the regular small rodent population oscillations observed in boreal and Arctic regions has long been debated. Within this hypothesis, it is proposed that the most likely predators to cause these destabilizing effects are sedentary specialists, with small mustelids being possible candidates. One such case would be the highly specialized least weasel (Mustela nivalis) driving the Norwegian lemming (Lemmus lemmus) cycle in Fennoscandia. These predators are often elusive and therefore distribution data can only be based on field signs, which is problematic when various mustelid species are sympatric, such as weasels and stoats (Mustela erminea). Here we present the results of using mustelid faeces in predated winter lemming nests to correctly identify the predator and thus discern which species exerts the strongest predation pressure on lemming winter populations. Samples were obtained during different phases in the lemming cycle, spanning 6 years, to account for different prey densities. Faecal mitochondrial DNA extraction and amplification of a 400-bp fragment was successful in 92/114 samples (81%); the sequencing of these samples proved that most predation occurrences (83%) could be attributed to the least weasel. These findings support the hypothesis that weasels in particular show high specificity in predation and could therefore be candidates to driving the lemming cycle in this area. We conclude that DNA analysis of faecal remains around predated nests can be a useful tool for further investigations concerning predator–prey interactions in the tundra.
Highlights
The concept of predation as the causal factor in the observed regular oscillations of small mammal populations, especially in Arctic regions, has long been proposed in the research of the so-called “rodent cycle” (Elton 1924; Hanski et al 1991, 2001; Andersson and Erlinge 1977; Sittler 1995; Legagneux et al 2012; Krebs 2013; Hoset et al 2014)
1 Department of Zoology, Stockholm University, 106 91 Stockholm, Sweden caused by sedentary specialist predators on rodent populations (Andersson and Erlinge 1977; Hanski et al 1991; Reid et al 1997). This hypothesis has been highly controversial in the study of the rodent cycle (Graham and Lambin 2002), with many other authors proposing food availability (Krebs 2011), parasites (Forbes et al 2014), stress (Boonstra and Boag 1992) or a combination of factors (Turchin et al 2000; Fauteux et al 2016) as being the causes of cyclicity (Andreassen et al 2021). Due to their specialist and sedentary nature, small mustelids have been suggested as possible drivers of the rodent cycle (Hanski et al 2001; Gilg et al 2003; Ekerholm et al 2004)
This study focuses on the direct predator–prey interaction, using lemming winter nests predated by mustelids (MacLean et al 1974; Duchesne et al 2011) as a beacon to facilitate mustelid faecal sample collection (Feige et al 2012)
Summary
The concept of predation as the causal factor in the observed regular oscillations of small mammal populations, especially in Arctic regions, has long been proposed in the research of the so-called “rodent cycle” (Elton 1924; Hanski et al 1991, 2001; Andersson and Erlinge 1977; Sittler 1995; Legagneux et al 2012; Krebs 2013; Hoset et al 2014). The separation of predators into three different types: resident specialists, nomadic specialists and generalists (Andersson and Erlinge 1977) and their subsequent implications, have been established within the predator hypothesis (Hanski et al 2001) One such implication is the destabilizing effect. In the case of the Fennoscandian tundra, two species of mustelid are sympatric; the stoat (Mustela erminea) and the least weasel (Mustela nivalis) (Elmeros 2006) Both species are known to prey on the Norwegian lemming (Lemmus lemmus) all year round (Ims and Fuglei 2005; King and Powell 2007) and have shown the time-lagging population growth necessary to cause regular. Lemmings are key-stone species in the tundra ecosystem showing cyclic population patterns of 3–5 years (Hanski et al 2001; Le Vaillant et al 2018) and the correct identification of mustelids, potentially able to destabilize rodent populations, is essential in understanding these dynamics
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