Henrik Andrén

Ecosystem dynamics are shaped by interacting top‐down and bottom‐up processes, yet their relative importance may vary through time following disturbances such as disease outbreaks and changes in apex predator communities. Using a 52‐year time series in south‐central Sweden, we examined how disease, apex predators, and prey availability jointly impact a mesopredator, the red fox Vulpes vulpes , and how these dynamics propagate to secondary prey. Potential drivers of fox dynamics (number of litters) were vole Clethrionomys glareolus and Microtus agrestis abundance, sarcoptic mange outbreaks, and the re‐establishment of Eurasian lynx Lynx lynx and wolves Canis lupus , and we assessed potential subsequent effects on hare Lepus europaeus and L. timidus and woodland grouse Lyrurus tetrix and Tetrao urogallus densities. Fox litter numbers were positively associated with vole abundance throughout the study period, indicating persistent bottom‐up regulation. In contrast, top‐down effects were evident through reductions in the number of fox litters during sarcoptic mange outbreaks and following the simultaneous presence of lynx and wolves. Support for the mesopredator release hypothesis was context‐dependent: densities of secondary prey increased during the mange outbreak but declined after apex predator re‐establishment, despite reduced number of fox litters. Moreover, the characteristic synchrony between voles and secondary prey weakened following the return of apex predators, suggesting direct and indirect effects beyond mesopredator suppression. Our results demonstrate that fox reproduction is regulated by concurrent top‐down and bottom‐up processes and that apex predator recovery can alter trophic relationships and not only reverse mesopredator release.

Reproductive lifespan and age-specific reproductive performance are key life-history traits, shaping individual fitness and population dynamics. Here, we examine age-specific variation in reproductive success in a wild large carnivore, the Eurasian lynx (Lynx lynx), using 38 years of longitudinal data from 173 known-age females across Europe and western Asia. Female lynx exhibited age-related reproductive patterns: (i) breeding probability increased with age before declining at older ages, (ii) litter size remained generally stable at two kittens, although it declined to one kitten in older mothers at northern latitudes, and (iii) offspring survival peaked at intermediate female ages, with variation across individuals, years and latitudes. These patterns likely reflect physiological maturation and increased experience (ages 2 to 8), followed by declines due to reproductive and maternal effect senescence in older females. Temporal and latitudinal variations suggest that environmental conditions shape reproductive patterns in Eurasian lynx, with senescence particularly pronounced in resource-scarce environments. Our findings enhance the understanding of age-related reproductive patterns in carnivores across environmental contexts, contributing to life-history theory and improving evidence-based management by accounting for age structure in population forecasting.

Extra-territorial mating excursions (i.e. short-term movements beyond established home ranges to seek mating opportunities) represent an underexplored reproductive strategy in felids. Using telemetry data from 125 Eurasian lynx (172 lynx-years, 1995–2023) across Europe, we investigated sex-specific spatio-temporal patterns and drivers of these excursions during the mating season. Overall, 33% of males and 11% of females undertook excursions, with males having higher rates than females. Male excursions mostly occurred in March, coinciding with the peak of the conception period, while females tended to undertake excursions either before or after this peak. The median Euclidean distance travelled beyond the home range was 6.8 km for males and 2.6 km for females, with corresponding median durations of 119 h and 85 h, respectively. Translocated individuals exhibited higher excursion rates than those in established populations, suggesting mate-searching in novel environments. We found no evidence that human influences affected excursion rates or distances. Our findings highlight a mating tactic that is often overlooked and provide new insight into sex-specific and context-dependent movement strategies in Eurasian lynx. By linking extra-territorial excursions to reproduction patterns, our study informs future research on mate-searching behaviour in felids and offers implications for conservation planning, particularly in isolated or reintroduced populations.

Naturvårdsverket uppdrog (Ärende NV-01405-24, Kontrakt 365-24-002) åt Henrik Andrén, Malin Aronsson och Jens Persson vid SLU, Institutionen för ekologi, Grimsö Forskningsstation att prognostisera järvpopulationen 2027 vid olika beskattningsnivåer under 2026 för Sverige, för norra och mellersta rovdjursförvaltningsområdena och dessutom för Norrbottens, Västerbottens, Jämtlands län separat, samt sammantaget för övriga län med järvförekomst (Västernorrlands, Dalarnas, Gävleborgs och Värmlands län).

Animal movement and reproductive behaviour are crucial components of ecological and evolutionary processes. After parturition, the behaviour of reproducing females adapts to the needs of their offspring, including thermoregulation, protection and food provisioning. However, little is known about how these adaptations vary across environmental conditions at larger scales in species with large distribution ranges. Here, we explored how female Eurasian lynx Lynx lynx movement and predation patterns change during the denning season. We analysed GPS telemetry data from two different climatic regions in Europe, cold and temperate, and evaluated the effect of explanatory variables on movement metrics and kill‐to‐den distances using generalized additive mixed models. Female lynx moved significantly longer daily distances in the cold region (central and northern Scandinavia) compared to the temperate region (southern Scandinavia and continental Europe) both before and after parturition. Reproducing females in both regions considerably reduced their movement after the start of the denning season. The typical pattern of increasing daily movements and decreasing time spent at the den with time persisted across regions, and the presence of females at the den followed a similar circadian rhythm, regardless of the markedly different daylight period. Only in the cold region females increased the distances of their excursions from the den as time passed. The distances between den and kill sites spanned from 1 to 3 km over the latitudinal range. The kill‐to‐den distances did not increase with time, but in the cold region the larger prey killsites were farther from the den than in the temperate region. Overall, our results show how some behaviours of female lynx during the denning season remain constant over a large latitudinal range, while others vary. This suggests local adaptations to particular environments, and possible increased energetic demands of reproducing females in more extreme environmental conditions.

In the face of ongoing habitat loss and fragmentation, examining the genetic effects of range expansion can provide insight into the resilience and adaptability of large carnivore populations returning to parts of their former range. This study investigates the genetic structure of the Eurasian lynx (Lynx lynx) population during its natural range expansion into southern Sweden, an area from which it had been extirpated for over a century. We utilized genomic data from 600 individual lynx collected throughout the recolonization period to assess heterozygosity, inbreeding, and genetic differentiation. Our results indicate no significant genetic structure or barriers to gene flow during this recolonization event, despite potential physical barriers such as lakes, farmland, and human infrastructure. Observed and expected heterozygosity, as well as the inbreeding coefficient did not show significant variation over time or across latitude, suggesting that connectivity with the source population was maintained. Spatial principal component analysis, cluster analysis, and discriminant analysis of principal components further supported these findings, showing little spatial or temporal structure. This lack of genetic structure contrasts with the experience of smaller and more isolated lynx populations, which have become inbred. Our study, thus, provides valuable insights into the natural range expansion of a large carnivore in human-dominated landscapes and underscores the importance of ensuring genetic connectivity for successful recolonization and conservation efforts.

Survival and cause‐specific mortality rates are vital for evidence‐based population forecasting and conservation, particularly for large carnivores, whose populations are often vulnerable to human‐caused mortalities. It is therefore important to know the relationship between anthropogenic and natural mortality causes to evaluate whether they are additive or compensatory. Further, the relation between survival and environmental covariates could reveal whether specific landscape characteristics influence demographic performance. We used telemetry data on 681 Eurasian lynx ( Lynx lynx ), a model apex predator with large spatial requirements, that were tracked across their European distribution. Through time‐to‐event analyses, we sought to determine the variables associated with differences in their survival. Illegal killing was the main cause of mortality (33.8%), and mortality rates were similar in protected and hunted populations (8.6% and 7.0% per year, respectively). Survival varied greatly across populations (70–95% per year). Across all study sites, higher hunting and anthropogenic mortality rates were partially compensated by lower rates of other mortality causes but not by natural mortality alone. Variation in survival depended on sex (female survival was 1.5 times greater than male survival) and seasonality (highest risk during hunting season and winter), and lower survival rates were correlated with higher human modification of landscapes at both coarse (home range composition) and fine (habitat use within home range) scales. Some variation in survival was driven by unobserved factors, which, given the high rates of human‐caused mortalities, including illegal killing, are of foremost concern. Due to the low natural mortality rates in protected and hunted populations, we conclude that anthropogenic causes of mortality are likely close to additive, such that maintaining or increasing refuge habitat with little human disturbance is critical to lynx conservation.