DOI: 10.5061/dryad.6t1g1jx7x
title: Seasonal role of a specialist predator in rodent cycles: Ermine-lemming interactions in the High Arctic

description: The exact mechanisms behind population cycles remain elusive. An ongoing
 debate centers on whether predation by small mustelids is necessary and
 sufficient to generate rodent cycles, as stipulated by the specialist
 predator hypothesis (SPH). Specifically, the SPH predicts that the
 predator should respond numerically to the abundance of its prey with a
 delay of approximately one year, leading to delayed density-dependence in
 the dynamics of the prey population. Here, we analyze the numerical
 response of a small mustelid, the seasonality of its interaction with
 rodents and its impact on population cycles using long-term seasonal data
 on ermines and cyclic lemmings in the High Arctic. Our results show that
 the numerical response of ermines to lemming fluctuations was delayed by
 one year and could mediate delayed density-dependence in lemming growth
 rate. The impact of ermines on the growth rate of lemmings was small but
 mostly circumscribed to winter, a critical period when shifts in cycle
 phases occur and direct density-dependence seems relaxed. Our simulations
 of lemming population with and without ermines suggest that these small
 mustelids are neither necessary, nor sufficient to generate cycles per se.
 However, presence of small mustelids may be necessary to prolong the low
 abundance phase and delay the recovery of lemming populations, promoting
 the presence of a multiannual low phase typical of lemming cycles. Our
 study corroborates the idea that population declines of cyclic populations
 are best explained by direct density-dependence but that the delayed
 response of specialized predators induces the multiannual low phase and
 leads to longer periodicities, which are typically of 3 to 5-yrs in
 rodents.
description: # Seasonal role of a specialist predator in rodent cycles: Ermine-lemming
 interactions in the High Arctic
 [https://doi.org/10.5061/dryad.6t1g1jx7x](https://doi.org/10.5061/dryad.6t1g1jx7x) ## Description of the data and file structure The data here provided covers different wildlife censuses conducted on Bylot Island, NU, Canada, between 1993 and 2022. These census are snap- or live-trapping of two species of lemmings (*Lemmus trimucronatus* &* Dicrostonyx groenlandicus*), transects to estimate winter nest densities and surveys of opportunistic observations to get an idea of ermine (*Mustela richardsonii*) abundance. Methods are well described in Fauteux et al., (2018) regarding lemming live trapping and winter nest and in Bolduc et al., (2023) for ermine abundance.      ### Files and variables #### File: Densites\_BrunsVariables\_2004-2022.csv **Description:** Densities of lemmings estimates from live-trapping on Bylot Island, NU, Canada. ##### Variables * site: Site where live-trapping is conducted * species: Specie of lemmings, either brown (*Lemmus trimucronatus)* or collared (*Dicrostonyx groenlandicus*) * grid: ID of live-trapping grid. * habitat: Habitat were live-trapping is conducted * year: Year when live-trapping is conducted * period: Trapping period, between P1 and P4. P1 usually occurs mid-June, followed by P2 in mid-July and P3 in mid-August. Exact dates can be found in NordicanaD_lemming_live_trapping_data_2004-2019_GAUTHIER.csv * density: Estimated density of lemmings in number of individuals per hectare (ind/ha).  * se: Standard error on density estimation. #### File: Part\_per\_Year\_2022.csv **Description:** Describes the number of participants to ermine abundance survey each year.  ##### Variables * Year: Year of survey * Nb.Part: Number of participants #### File: Lemming\_prop\_growth\_data\_2022.csv **Description:** Calculations of lemmings growth rate when considering habitat cover of the study area. Both specie are combined.  ##### Variables * Year: Year * SR: Summer growth rate, between mid-June and mid-August.  * SR_se: Standard error of SR. * SRc: Daily summer growth rate, between mid-June and mid-August, corrected for the exact number of days between trapping sessions.  * SRc_se: Standard error of SRc. * WR: Winter growth rate, between mid-August of year t and mid-June of year t+1. * WR_se: Standard error of WR.  * WRc: Daily winter growth rate corrected for the exact number of days between trapping sessions.  * WRc_se: Standard error of WRc. * P1_dens: Density of lemming during the first trapping session in mid-June.  * P1_d_se:  Standard error of P1_dens * P3_dens: Density of lemming during the last trapping session in mid-August.  * P3_d_se: Standard error of P3_dens * NY_P1_dens: Density of lemming during the first trapping session in mid-Juneof year t+1.  * NY_P1_d_se: Standard error of NY_P1_dens. * DurW: Duration of winter in days as the time between trapping sessions P3 and NY_P1. * DurS: Duration of summer in days as the time between P1 and P3. * Nest_dens: Density of winter nests as estimated from distance sampling in different habitat and corrected for habitat cover. Density is in number of nest per hectare.  * lemm_se: Standard error of Nest_Dens * Herm_dens: Density of lemming winter nests depredated by ermines as estimated from distance sampling in different habitat and corrected for habitat cover. Density is in number of nest per hectare.  * se_herm: Standard error of Herm_Dens * Herm_index: Ermine abundance index derived from surveys of opportunistic observations. The index is bounded between 0 and 3. See Bolduc, D., Fauteux, D., Gagnon, C. A., Gauthier, G., Bêty, J., & Legagneux, P. (2023). Testimonials to reconstruct past abundances of wildlife populations. *Basic and Applied Ecology*, *68*, 23-34 for details. * Pred.ratio: Predation ratio as the ratio between the number of depredated winter nests and total lemming winter nest density. * Nest.ratio: Proxy of growth rate as the ratio between NY_P1 and Nest_Dens * Fall_NR: Proxy of growth rate as the ratio between Nest_Dens and P3_Dens. * YF: Year as factor. * LPR: Log of Pred.ratio * N_trans: Number of transects walked to estimate nest density.  #### File: Winter\_dens\_proportional\_Lemming.csv **Description:** Density of lemming and ermine-depredated winter nests as estimated from distance-sampling and corrected for habitat cover. ##### Variables * Sp: Specie (Lemming or Ermine) * Year: Year of survey. * Density: Estimated density of winter nests. Density is in number of nests per hectare.  * Up95: Upper bound of the 95% confidence interval of Density. * Bot95: Lower bound of the 95% confidence interval of Density. * area: Sampled area, as estimated from distance sampling. Area is in hectare.  #### File: Herm\_index\_IC95.csv **Description:** Ermine index and it's 95% confidence interval. ##### Variables * Year: Year of survey. * Upper: Upper bound of 95% CI. * Lower: Lower bound of 95% CI. * Mean: Ermine index. The index is bounded between 0 and 3. See Bolduc, D., Fauteux, D., Gagnon, C. A., Gauthier, G., Bêty, J., & Legagneux, P. (2023). Testimonials to reconstruct past abundances of wildlife populations. *Basic and Applied Ecology*, *68*, 23-34 for details. #### File: Annual\_data\_2022.csv **Description:** Main dataset describing annual changes in abundance of lemmings and ermines.  ##### Variables * LemmD: Lemming density in mid-July. Density is in individual per hectare.  * Herm_index: Ermine abundance index over the summer. The index is bounded between 0 and 3. See Bolduc, D., Fauteux, D., Gagnon, C. A., Gauthier, G., Bêty, J., & Legagneux, P. (2023). Testimonials to reconstruct past abundances of wildlife populations. *Basic and Applied Ecology*, *68*, 23-34 for details. * Year: Year of survey. * LY_Dens: Last-year lemming density. * LogLYD: Log of LY_Dens * HermBin: Ermine index divided by 3 to give an number between 0 and 1. * LogDens: Log of LemmD * R: Lemming interannual growth rate.  * Nb.Part: Number of participants in ermine abundance surveys.  #### File: Transect\_per\_year.csv **Description:** Describes the number of transects walked every year to survey lemming winter nests. ##### Variables * Year: Year of survey. * N_trans: Number of walked transects.  #### File: NordicanaD\_lemming\_live\_trapping\_data\_2004-2019\_GAUTHIER.csv **Description:** Detailled data on lemming live trapping ##### Variables * Year: Year of survey. * Day: Day of trapping. * Time: Time of trapping.  * Trapping_Period: Trapping period (P1-P4) * Site_Name: Name of the site where trapping is conducted. * Trap_ID: ID of the trap. * Tag_Number: Ear- or pit-tag ID given to the animal. * Species: Specie of lemming. * Sex: Sex of lemming. * Age: Approximate lemming age.  * Mass: Mass of the individual in grams.  * Zygomatic_Width: Zygomathic width of the individual in milimetre.  * Reproductive_Condition: Reproductive condition of the individual. * Released: Was the individual released after capture? * Notes: Any comments ## Code/software We used R v.4.4.1 to run this script. Main packages are lme4, WaveletComp and ggplot2.