Spatial ecology of wolves in Scandinavia : From spatio-temporal dynamics of wolf pairs to wolf population dynamics

PHD in applied ecology, 2016Understanding how spatial and temporal variations shape populations is necessary to develop trustworthy conservation and management planning. In this thesis, I used individual-based long-term monitoring data of the grey wolf (Canis lupus) collected in Scandinavia during its recolonization phase since the early 1990’s. My main goal was to identify how habitat could affect the demography of this social carnivore species living in packs. Packs are generally composed of a territorial breeding pair and their offspring. Because the pair plays an important role in the pack, they are generally considered as the functional unit of wolf populations. I therefore focused my analyses on the territorial pair. My results suggest that wolf pairs generally avoided habitat characterized by humans when establishing a territory. Wolf pair bond duration was short (on average 3 consecutive winters), and dissolutions were mostly caused by humans. Furthermore, I showed that the effect of wolf culling (i.e. legal harvest) on population growth was complex. Culling interacted with the intrinsic characteristics of the species and other causes of mortality making any predictions of the effect of culling rather challenging. However, I found that temporal pair bond stability was a better predictor of growth rate than individual culling mortality. Additionally, I found that interspecific competition with brown bears (Ursus arctos) could have contributed to shape spatial patterns of wolf recolonization. The spatio-temporal avoidance of bears by wolves could occur at several scales, from decisions on territory establishment to the habitat selected by wolves within their home ranges. My results showed how data from long-term monitoring programs can be used to provide key information linking demography with habitat in a social large carnivore. In this thesis, I also highlighted the importance of a functional unit (i.e. the wolf pair for wolves) for the population dynamics of a socially-living species. I therefore recommend monitoring, management and conservation programs to further focus their actions at the level of the wolf pair.For å kunne utvikle gode planer for bevaring og forvaltning av en art, er det nødvendig å forstå hvordan variasjoner i tid og rom kan forme populasjoner. I denne doktorgraden har jeg benyttet data fra langtidsstudier av ulv (Canis lupus), som er samlet inn i Skandinavia etter dens rekolonisering på begynnelsen av 1990-tallet. Mine hovedmål var å finne ut hvordan habitat kunne påvirke demografien til denne sosiale flokk-levende rovdyrarten. Flokkene er stort sett sammensatt av et revirhevdende ynglende par og deres avkom. Siden det revirhevdende paret spiller en viktig rolle i flokken, er de ofte sett på som den funksjonelle enheten av ulvebestanden. Jeg har derfor valgt å fokusere analysene mine på de revirhevdende parene. Ulveparene unngikk i hovedsak habitater som var påvirket av mennesker når de etablerte et revir. Tiden ei tispe og en hann klarte å holde sammen som et revirhevdende par viste seg å være kort (gjennomsnittlig 3 påfølgende vintre), og oppløsningen av paret var som oftest forårsaket av mennesker. Videre fant jeg ut at effekten av uttak (lisensjakt, skadefelling eller ekstraordinært uttak) på populasjonsveksten var sammensatt, da det også er andre årsaker (f.eks. innavl, illegal jakt, sykdom) som påvirker populasjonsvekst, noe som gjorde det vanskelig å finne effekten av selve uttaket. Jeg fant derimot ut at evnen parene hadde til å holde sammen over tid var en bedre faktor for å forutse populasjonsveksten enn dødelighet forårsaket av uttak. I tillegg fant jeg ut at konkurranse med brunbjørn (Ursus arctos) kan ha påvirket det romlige mønsteret for rekoloniseringen av ulv. At ulven unngår bjørn i både tid og rom kan forekomme på flere skalaer, helt fra avgjørelsen om hvor de skal etablere et revir, til habitatvalg innenfor det etablerte reviret. Mine resultater viser hvordan data fra langtidsstudier av ulv kan bli brukt for å gi viktig informasjon som setter demografi i sammenheng med habitat hos et sosialt rovdyr. I denne syntesen får jeg også frem viktigheten av en funksjonell enhet (det revirhevende paret hos ulver) for populasjonsdynamikken til en sosial art. Jeg anbefaler derfor overvåknings- og forvaltningsprogram til i fremtiden å ha fokus på par-nivå

Wolverine density distribution reflects past persecution and current management in Scandinavia

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A flexible and efficient Bayesian implementation of point process models for spatial capture‐recapture data

Spatial capture–recapture (SCR) is now routinely used for estimating abundance and density of wildlife populations. A standard SCR model includes sub-models for the distribution of individual activity centers (ACs) and for individual detections conditional on the locations of these ACs. Both sub-models can be expressed as point processes taking place in continuous space, but there is a lack of accessible and efficient tools to fit such models in a Bayesian paradigm. Here, we describe a set of custom functions and distributions to achieve this. Our work allows for more efficient model fitting with spatial covariates on population density, offers the option to fit SCR models using the semi-complete data likelihood (SCDL) approach instead of data augmentation, and better reflects the spatially continuous detection process in SCR studies that use area searches. In addition, the SCDL approach is more efficient than data augmentation for simple SCR models while losing its advantages for more complicated models that account for spatial variation in either population density or detection. We present the model formulation, test it with simulations, quantify computational efficiency gains, and conclude with a real-life example using non-invasive genetic sampling data for an elusive large carnivore, the wolverine (Gulo gulo) in Norway. area search, binomial point process, continuous sampling, NIMBLE, non-invasive genetic sampling, Poisson point process, spatial capture–recapture, wolverinepublishedVersio

Small rodent monitoring at Birkebeiner road, Norway

Background. Northern small mammal populations are renowned for their multi-annual population cycles. Population cycles are multi-faceted and have extensive impacts on the rest of the ecosystem. In 2011, we started a student-based research activity to monitor the variation of small rodent density along an elevation gradient following the Birkebeiner Road, in southeast Norway. Fieldwork was conducted by staff and students at the University campus Evenstad, Inland Norway University of Applied Sciences, which has a long history of researching cyclic population dynamics. The faculty has a strong focus on engaging students in all parts of the research activities, including data collection. Small rodents were monitored using a set of snap trap stations. Trapped animals were measured (e.g. body mass, body length, sex) and dissected to assess their reproductive status. We also characterised the vegetation at trapping sites. New information. We provide a dataset of small rodent observations that show fluctuating population dynamics across an elevation gradient (300 m to 1,100 m a.s.l) and in contrasting habitats. This dataset encompasses three peaks of the typical 3-4-year vole population cycles; the number of small rodents and shrews captured show synchrony and peaked in years 2014, 2017 and 2021. The bank vole Myodes glareolus was by far (87%) the most common species trapped, but also other species were observed (including shrews). We provide digital data collection forms and highlight the importance of long-term data collection.publishedVersio

Let’s stay together? Intrinsic and extrinsic factors involved in pair bond dissolution in a recolonizing wolf population

For socially monogamous species, breeder bond dissolution has important consequences for population dynamics, but the extent to which extrinsic or intrinsic population factors causes pair dissolution remain poorly understood, especially among carnivores. Using an extensive life-history data set, a survival analysis and competing risks framework, we examined the fate of 153 different wolf (Canis lupus) pairs in the recolonizing Scandinavian wolf population, during 14 winters of snow tracking and DNA monitoring. Wolf pair dissolution was generally linked to a mortality event and was strongly affected by extrinsic (i.e. anthropogenic) causes. No divorce was observed, and among the pair dissolution where causes have been identified, death of one or both wolves was always involved. Median time from pair formation to pair dissolution was three consecutive winters (i.e. approximately 2 years). Pair dissolution was mostly human-related, primarily caused by legal control actions (36·7%), verified poaching (9·2%) and traffic-related causes (2·1%). Intrinsic factors, such as disease and age, accounted for only 7·7% of pair dissolutions. The remaining 44·3% of dissolution events were from unknown causes, but we argue that a large portion could be explained by an additional source of human-caused mortality, cryptic poaching. Extrinsic population factors, such as variables describing the geographical location of the pair, had a stronger effect on risk of pair dissolution compared to anthropogenic landscape characteristics. Population intrinsic factors, such as the inbreeding coefficient of the male pair member, had a negative effect on pair bond duration. The mechanism behind this result remains unknown, but might be explained by lower survival of inbred males or more complex inbreeding effects mediated by behaviour. Our study provides quantitative estimates of breeder bond duration in a social carnivore and highlights the effect of extrinsic (i.e. anthropogenic) and intrinsic factors (i.e. inbreeding) involved in wolf pair bond duration. Unlike the effects of intrinsic and extrinsic factors that are commonly reported on individual survival or population growth, here we provide quantitative estimates of their potential effect on the social unit of the population, the wolf pair

Wolves, people, and brown bears influence the expansion of the recolonizing wolf population in Scandinavia

Interspecific competition can influence the distribution and abundance of species and the structure of ecological communities and entire ecosystems. Interactions between apex predators can have cascading effects through the entire natural community, which supports broadening the scope of conservation from single species to a much wider ecosystem perspective. However, competition between wild large carnivores can hardly be measured experimentally. In this study, we analyzed the expansion of the Scandinavian wolf ( Canis lupus ) population during its recovery from the early 1990s. We took into account wolf-, habitat-, human- and brown bear ( Ursus arctos )-related factors, because wolf expansion occurred within an area partially sympatric with bears. Wolf pair establishment was positively related to previous wolf presence and was negatively related to road density, distance to other wolf territories, and bear density. These findings suggest that both human-related habitat modification and interspecific competition have been influential factors modulating the expansion of the wolf population. Interactions between large carnivores have the potential to affect overall biodiversity. Therefore, conservation-oriented management of such species should consider interspecific interactions, rather than focusing only on target populations of single species. Long-term monitoring data across large areas should also help quantify and predict the influence of biotic interactions on species assemblages and distributions elsewhere. This is important because interactive processes can be essential in the regulation, stability, and resilience of ecological communitie

Individual variation in predatory behavior, scavenging and seasonal prey availability as potential drivers of coexistence between wolves and bears

Several large carnivore populations are recovering former ranges, and it is important to understand interspecific interactions between overlapping species. In Scandinavia, recent research has reported that brown bear presence influences gray wolf habitat selection and kill rates. Here, we characterized the temporal use of a common prey resource by sympatric wolves and bears and described individual and seasonal variation in their direct and/or indirect interactions. Most bear–wolf interactions were indirect, via bear scavenging of wolf kills. Bears used >50% of wolf kills, whereas we did not record any wolf visit at bear kills. Adult and subadult bears visited wolf kills, but female bears with cubs of the year, the most vulnerable age class to conspecifics and other predators, did not. Wolf and bear kill rates peaked in early summer, when both targeted neonate moose calves, which coincided with a reduction in bear scavenging rate. Some bears were highly predatory and some did not kill any calf. Individual and age-class variation (in bear predation and scavenging patterns) and seasonality (in bear scavenging patterns and main prey availability of both wolves and bears) could mediate coexistence of these apex predators. Similar processes likely occur in other ecosystems with varying carnivore assemblages

Spatial variation in red deer density in a transboundary forest ecosystem

Forests in Europe are exposed to increasingly frequent and severe disturbances. The resulting changes in the structure and composition of forests can have profound consequences for the wildlife inhabiting them. Moreover, wildlife populations in Europe are often subjected to differential management regimes as they regularly extend across multiple national and administrative borders. The red deer Cervus elaphus population in the Bohemian Forest Ecosystem, straddling the Czech-German border, has experienced forest disturbances, primarily caused by windfalls and bark beetle Ips typographus outbreaks during the past decades. To adapt local management strategies to the changing environmental conditions and to coordinate them across the international border, reliable estimates of red deer density and abundance are highly sought-after by policymakers, wildlife managers, and stakeholders. Covering a 1081-km2 study area, we conducted a transnational non-invasive DNA sampling study in 2018 that yielded 1578 genotyped DNA samples from 1120 individual red deer. Using spatial capture-recapture models, we estimated total and jurisdiction-specific abundance of red deer throughout the ecosystem and quantified the role of forest disturbance and differential management strategies in shaping spatial heterogeneity in red deer density. We hypothesised that (a) forest disturbances provide favourable habitat conditions (e.g., forage and cover), and (b) contrasting red deer management regimes in different jurisdictions create a differential risk landscape, ultimately shaping density distributions. Overall, we estimated that 2851 red deer (95% Credible Interval = 2609–3119) resided in the study area during the sampling period, with a relatively even overall sex ratio (1406 females, 95% CI = 1229–1612 and 1445 males, 95% CI = 1288–1626). The average red deer density was higher in Czechia (3.5 km−2, 95% CI = 1.2–12.3) compared to Germany (2 km−2, 95% CI = 0.2–11). The effect of forest disturbances on red deer density was context-dependent. Forest disturbances had a positive effect on red deer density at higher elevations and a negative effect at lower elevations, which could be explained by partial migration and its drivers in this population. Density of red deer was generally higher in management units where hunting is prohibited. In addition, we found that sex ratios differed between administrative units and were more balanced in the non-intervention zones. Our results show that the effect of forest disturbances on wild ungulates is modulated by additional factors, such as elevation and ungulate management practices. Overall density patterns and sex ratios suggested strong gradients in density between administrative units. With climate change increasing the severity and frequency of forest disturbances, population-level monitoring and management are becoming increasingly important, especially for wide-ranging species as both wildlife and global change transcend administrative boundaries.publishedVersio

Oppvekstrevirets effekt på habitatvalg hos voksne ulver

Vi undersøkte hvorvidt graden av menneskelig påvirkning i skandinaviske ulvers oppvekstrevir kunne forklare noe av variasjonen i deres habitatvalg og områdebruk i forhold til menneskelig aktivitet og infrastruktur. Først testet vi hypotesen om oppvekstpåvirket habitatpreferanse (OPHP) ved etablering av eget revir, det vil si hvorvidt ulver under spredning var påvirket av egenskaper ved oppvekstreviret, deriblant faktorer relatert til menneskelig aktivitet, når de valgte å etablere seg i eget revir. Siden spredningsavstand kan ha en betydning for likhetsgraden mellom oppvekstrevir og etablert revir, og hanner ofte sprer seg lenger enn hunner, testet vi om spredningsavstand og kjønn kan være av betydning, og vi testet ulike metoder for å definere tilgjengelig habitat. Deretter testet vi hypotesen om OPHP ved ulvers habitatvalg innenfor det etablerte reviret, med to konkurrerende hypoteser: A) Ulver som er eksponert for høy grad av menneskelig aktivitet i oppvekstreviret vil senere unngå menneskelig aktivitet og infrastruktur innenfor sitt etablerte revir. B) Ulver som er eksponert for høy grad av menneskelig aktivitet i oppvekstreviret vil senere selektere for menneskelige strukturer i det etablerte reviret på grunn av en tilpasning eller habituering til menneskelig aktivitet. Vi fant at ulvetisper, og til en viss grad hanner, med kort spredningsavstand fra oppvekstreviret fortrinnsvis valgte å etablere revir i områder som lignet oppveksthabitatet, uavhengig av definisjonene på tilgjengelig habitat og habitatlikhet. Dette var ikke tilfellet for ulver som vandret over lengre avstander. Vi fant også svak men konsistent støtte for at ulvepar der tispa var oppvokst et område med stor grad av menneskelig aktivitet unngikk menneskelig påvirkning innenfor sitt etablerte revir. For hanner var dette mønsteret mindre tydelig. Noe av bakgrunnen for denne utredningen var en bekymring blant folk bosatt i ulveområder for om ulver som vokser opp i områder med stor grad av menneskelig aktivitet vil vise oppsøkende atferd overfor mennesker. Våre funn antyder derimot at ulver som er blitt eksponert for større grad av menneskelig påvirkning i oppvekstreviret muligens unngår nærhet til menneskelig bosetting og infrastruktur innenfor sine revir senere i livet. Metodene brukt i denne studien kan være nyttige for videre forskning på og forvaltningen av ulv i Skandinavia og andre steder, både for å vurdere om ulvenes respons på erfaring med menneskelig aktivitet endrer seg med eventuelle endringer i ulvebestanden eller menneskenes bosettingsmønstre, men også for å sammenligne ulvers respons i Skandinavia med andre deler av Europa der ulven er i ferd med å reetablere seg i områder med langt høyere befolkningstetthet