High Frequency of Apodemus Mice Boosts Inverse Activity Pattern of Bank Voles, Clethrionomys glareolus, through Non-Aggressive Intraguild Competition

Animals : an Open Access Journal from MDPI · 2 authors, 1 centre

AI SUMMARY

FIDELITY 100%

POPULATIONBank voles (Clethrionomys glareolus) and Apodemus mice (Apodemus flavicollis and/or A. sylvaticus) in an inner-Alpine mixed forest in Carinthia, southern Austria

INTERVENTIONHigh frequency of Apodemus mice (natural variation driven by a seed mast year vs. non-mast year)

COMPARISONMast year (high Apodemus density) vs. non-mast year (low Apodemus density)

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TL;DR

This 2-year camera-trap study in an inner-Alpine mixed forest found that bank voles (Clethrionomys glareolus) shifted to more diurnal activity when populations of the larger, nocturnal Apodemus mice were high during a seed mast year. The temporal partitioning occurred without frequent aggressive encounters, suggesting an active avoidance strategy shaped by long co-evolution. The findings indicate that intraguild competition, rather than abiotic factors or predation risk, drives the inverse activity pattern in bank voles.

Full summary

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**Background:** Ecologically similar species can coexist only if they differ in at least one niche dimension—habitat, food, or time. Bank voles (Clethrionomys glareolus) and Apodemus mice (primarily A. flavicollis and A. sylvaticus) are small forest rodents that overlap extensively in resource use. Apodemus mice are larger, stronger, and considered the superior competitor. Previous studies on whether bank voles shift their activity to avoid competition with Apodemus have yielded conflicting results, often due to small sample sizes, incomplete control of confounding variables, or short study durations. The authors conducted a 2-year camera-trapping study in an inner-Alpine mixed forest in Carinthia, southern Austria, to test whether bank voles increase diurnal activity when Apodemus mice are abundant, while controlling for abiotic factors (temperature, precipitation, lunar illumination), predation risk, and habitat cover.

**Methods:** Camera traps (Wild-Vision Full HD 5.0 with Black-LED flash) were deployed at 83 randomly allocated sites over a 4.8 ha study area from September 2020 to September 2022. The first year was a mast year (extreme pollen production in Norway spruce, European beech, and hazelnut), and the second was a non-mast year. Bait (0.5 kg unpeeled sunflower seeds per deployment) was used to attract rodents. A total of 19,138 analyzable 1-minute videos (319.0 h) were recorded over 215 camera trap-nights (102 in the mast year, 113 in the non-mast year). To ensure independence, only the single recording with the highest number of each species per 30-minute period was retained. Activity patterns were analyzed using Hermans–Rasson tests, overlap coefficients (Δ4) with 95% bootstrapped confidence intervals, and multivariate logistic regression to test the dichotomous day–night activity of bank voles against seven predictors: mast year/non-mast year, lunar illumination (%), minimum temperature (°C), nocturnal precipitation (mm), predator presence (number of 30-min periods with predators), cover (% deadwood, snags, rocks within 10 m), and Apodemus frequency.

**Key Results:** Bank vole frequency did not differ between the mast year and non-mast year (U = 5965, p = 0.63). In contrast, Apodemus mice were significantly more frequent in the mast year (U = 9297, p < 0.001, rg = 0.612). Bank voles showed significantly more diurnal activity in the mast year (56.5%) than in the non-mast year (37.4%; χ²(1) = 47.029, p < 0.001, Cramér's V = 0.188). Apodemus mice were predominantly nocturnal in both years (mast year: 6.3% diurnal; non-mast year: 2.7% diurnal), though diurnal activity was significantly higher in the mast year (χ²(1) = 13.14, p < 0.001, Cramér's V = 0.072). The overlap in activity rhythms between the two taxa was lower in the mast year (Δ4 = 0.501, 95% CI: 0.463–0.538) than in the non-mast year (Δ4 = 0.647, 95% CI: 0.609–0.684), with an overall overlap of 59% (Δ4 = 0.591, 95% CI: 0.564–0.619). Multivariate logistic regression showed that the probability of nocturnal activity in bank voles was significantly higher in the non-mast year (p < 0.001, OR = 2.329). Nocturnal precipitation significantly reduced bank vole nocturnal activity (p < 0.001, OR = 0.932). Lunar illumination (p = 0.051, OR = 0.997) and Apodemus activity (p = 0.060, OR = 0.992) showed marginal trends toward increased diurnal activity. In the mast year, univariate analysis confirmed that bank voles were significantly more diurnal when Apodemus mice were more numerous (U = 41,794, p = 0.01, rg = 0.125). Only 350 out of 15,931 videos (2.20%) captured both taxa together. Encounters were equally frequent in both years, but Apodemus mice were less aggressive in the mast year, while in the non-mast year bank voles more often avoided or were chased by Apodemus (χ²(2) = 7.240, p = 0.027, Cramér's V = 0.144).

**Clinical Implications:** This study provides strong observational evidence that intraguild competition, rather than abiotic factors or predation risk, drives temporal niche partitioning in small forest rodents. The finding that bank voles shift to diurnal activity without frequent aggressive encounters suggests that the mere presence and 'omnipresence' of a dominant competitor can reshape activity patterns through avoidance. This has implications for understanding how species coexist under varying population densities, particularly in the context of resource pulses like masting events. The results also highlight the importance of controlling for multiple confounding variables when studying behavioral plasticity in wild populations. From a broader ecological perspective, changes in activity patterns can affect seed dispersal, predation dynamics, and disease transmission, given that both taxa are keystone species and disease vectors.

PICO

PPOPULATION

Bank voles (Clethrionomys glareolus) and Apodemus mice (Apodemus flavicollis and/or A. sylvaticus) in an inner-Alpine mixed forest in Carinthia, southern Austria

IINTERVENTION

High frequency of Apodemus mice (natural variation driven by a seed mast year vs. non-mast year)

OOUTCOME

Diurnal vs. nocturnal activity pattern of bank voles; overlap coefficient of activity rhythms; frequency of interspecific encounters and aggression

STUDY TYPE

cohort

SPECIALTY

ecology

SUMMARISED BY

AI pipeline

FIDELITY CHECK

100% · A

ORIGINAL PAPER

PMC10044290

High Frequency of Apodemus Mice Boosts Inverse Activity Pattern of Bank Voles, Clethrionomys glareolus, through Non-Aggressive Intraguild Competition

Animals : an Open Access Journal from MDPI

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ABSTRACT

Simple Summary Ecologically similar animals can only co-occur if resources are used in a sufficiently diverse manner. The necessary separation can be made according to habitat, food choice and activity pattern. We investigated this question in an inner-alpine mixed forest for bank voles, Clethrionomys glareolus , and mice of the genus Apodemus , the latter being larger and stronger. In the presence of many Apodemus mice, bank voles were indeed more diurnal. We found no alternative explanation for this temporal partitioning, despite considering possible other influencing factors, such as exposure to lunar illumination, temperature, precipitation, the presence of predators or the availability of cover. Our video footage showed that this temporal separation hardly requires any physical interaction between the small forest rodents. We attribute this to the long common evolution of these animals. Abstract Sympatric animals with similar requirements can separate their ecological niches along the microhabitat, food and time axes. There may be alternative reasons for an interspecific different activity pattern, such as intraspecific social constraints, predator avoidance or physical conditions such as temperature, precipitation and illumination. We investigated the importance of intraguild competition in a 2-year study in an inner-alpine mixed forest, using small forest rodents as our model species. Apodemus mice were the physically superior, and bank voles, Clethrionomys glareolus , the inferior competitor. We predicted that bank voles would exhibit increased diurnal activity when frequencies of the almost exclusively nocturnal Apodemus mice were high during a seed mast year. To investigate this, we recorded 19,138 1 min videos. Controlling for confounding variables, bank vole diurnal activity was significantly related to the frequency of Apodemus mice. We assume that at high densities of Apodemus mice, a purely nocturnal separation in the niche dimensions of time, habitat and microhabitat is no longer sufficient, and therefore an inverse activity pattern by the bank voles is reinforced. Our videos showed, however, that this does not require persistent aggressive meetings and we explain this by the long co-evolution of the taxa under study.

CITATION EXPORT

Remo Probst, Renate Probst. High Frequency of Apodemus Mice Boosts Inverse Activity Pattern of Bank Voles, Clethrionomys glareolus, through Non-Aggressive Intraguild Competition. Animals : an Open Access Journal from MDPI. (2023). https://doi.org/10.3390/ani13060981

AUTHORS

2 · 1 CENTRES

Remo Probst, Renate Probst

Ornis—Biology Engineering Office and Research Institute, Dr. G. H. Neckheimstr. 18/3, A-9560 Feldkirchen, Austria