A beacon of dung: using lemming (Lemmus lemmus) winter nests and DNA analysis of faeces to further understand predator–prey dynamics in Northern Sweden

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.

Abundance, predation, and habitat associations of lemming winter nests in northern Sweden

“…Hence, a lack of a relationship between nest abundance and probability of nest predation is in agreement with a strong type II functional response (sensu Holling, 1959a, 1959b), if the abundances are above where the predators maintain a high preference for its main prey. A strong type II functional response would also agree with recent suggestions that most winter predation on lemming nests in the study area is carried out by the least weasel, which seems to be more dependent on rodents than the stoat (Elmeros, 2006; Korpimäki et al, 1991), during all phases of the lemming cycle (Vigués et al, 2021). We suggest that specialized mustelid predation on lemmings during the decrease phase may have accelerated lemming population decline, and hence contributed to lemming population fluctuations in this region (Ekerholm et al, 2004).…”

“…Two species of small mustelid are sympatric in northern Scandinavia: the stoat ( Mustela erminea ) and the least weasel ( Mustela nivalis ) (Stoessel et al, 2019). However, a recent study suggests that over 80% of the winter predation on lemmings is carried out by the least weasel (Vigués et al, 2021). Although resource constraints may impact lemming distribution and abundance during the winter months (Korslund & Steen, 2006; Le Vaillant et al, 2018), small mustelids are prone to cause disruptions to lemming winter demographics because they prey on lemmings throughout the winter (Sittler, 1995; Stoessel et al, 2019).…”

“…Furthermore, lemmings are often predated on by small mustelids in the nests (Maclean et al, 1974). This leaves conspicuous traces within the nest allowing quantification of mustelid predation on lemmings during winter through nest surveys (Sittler, 1995; Vigués et al, 2021). We will hereafter refer to nests where predation events have occurred as “predated” nests, although we acknowledge that it is not the nests themselves that have suffered the predation events.…”

Predation patterns on the tundra—genetic barcoding of scats from two sympatric fox species

“…Fresh scats are important to ensure for a higher amount of prey DNA within the samples (De Barba et al 2014). In our study, late snow melt, allowed for preservation of scats until late June and early July when the samples were collected, minimising the risk of degraded DNA (Vigués et al 2021). Additionally, only soft fresh scats were collected on or close to known active dens, dried with silica pellets and frozen as soon as possible to ensure quality of sampling (e.g.…”