Pale terricolous lichens are a vital component of Arctic ecosystems, significantly contributing to carbon balance, energy regulation, and serving as a primary food source for reindeer. Their characteristically high albedo also impacts land surface temperature (LST) dynamics across various spatial scales. However, remote sensing of lichens is challenging due to their complex spectral signatures and large spatial variations in coverage and biomass even within local landscape scales. This study evaluates the influence of pale lichens on LST at local and landscape scales by integrating RGB, multispectral, and thermal infrared imagery from an Unmanned Aerial Vehicle (UAV) with multi-temporal Landsat 8 thermal data. An Extreme Gradient Boosting algorithm was employed to map pale lichen biomass, areal extent, and the occurrence of major plant functional types in the sub-arctic heath tundra landscape in the Jávrrešduottar and Sieiddečearru areas on the Finland-Norway border. Generalized Additive Models (GAMs) were used to elucidate the factors affecting LST. The UAV model accurately predicted pale lichen biomass (R2 0.63) and vascular vegetation cover (R2 0.70). GAMs revealed that pale lichens significantly influence thermal regimes, with increased biomass leading to decreased LST, an effect more pronounced at the landscape scale (deviance explained 47.26 % and 65.8 % for local and landscape models, respectively). Pale lichen biomass was identified as the second most important variable affecting LST at both scales, with elevation being the most important variable. This research demonstrates the capability of UAV-derived models to capture the heterogeneous and fine-scale structure of tundra ecosystems. Furthermore, it underscores the effectiveness of combining high spatial resolution UAV and high temporal resolution satellite platforms. Finally, this study highlights the pivotal role of pale lichens in Arctic thermal dynamics and showcases how advanced remote sensing techniques can be used for ecological monitoring and management.

We analysed the history behind the current contrasting lichen covers of two adjacent reindeer herding districts at the Finnish–Norwegian border. We conducted vegetation field inventories across the border fence and reconstructed a lichen cover history from 1959 to 2020 using aerial and satellite images. The oldest images showed only a slight difference in lichen cover between the different sides of the border fence. Since the late 1950s, lichen cover has decreased in both districts. At present, lichen biomass is approximately three times greater in in the Norwegian winter pasture than in the Finnish herding district, which has less strictly defined seasonal pastures. A lichen biomass model indicated that lichen intake by reindeer cannot explain the decline in lichen biomass in either of the districts. We suggest that the lichen decline is mainly due to trampling and foraging-induced loss, while other unknown ecological and climatological factors may also be involved.

Diseases and parasites are important drivers of population dynamics in wild mammal populations. Small and endangered populations that overlap with larger, reservoir populations are particularly vulnerable to diseases and parasites, especially in ecosystems highly influenced by climate change. Sarcoptic mange, caused by a parasitic mite Sarcoptes scabiei, constitutes a severe threat to many wildlife populations and is today considered a panzootic. The Scandinavian arctic fox Vulpes lagopus is endangered with a fragmented distribution and is threatened by e.g. red fox Vulpes vulpes expansion, prey scarcity and inbreeding depression. Moreover, one of the subpopulations in Scandinavia has suffered from repeated outbreaks of sarcoptic mange during the past decade, most likely spread by red foxes. This was first documented in 2013 and then again 2014, 2017, 2019, 2020 and 2021. We used field inventories and wildlife cameras to follow the development of sarcoptic mange outbreaks in this arctic fox subpopulation with specific focus on disease transmission and consequences for reproductive output. In 2013–2014, we documented visual symptoms of sarcoptic mange in about 30% of the total population. Despite medical treatment, we demonstrate demographic consequences where the number of arctic fox litters plateaued and litter size was reduced after the introduction of S. scabiei. Furthermore, we found indications that mange likely was transmitted by a few arctic foxes travelling between several dens, i.e. ‘super-spreaders'. This study highlights sarcoptic mange as a severe threat to small populations and can put the persistence of the entire Scandinavian arctic fox population at risk.

The fine-scale spatial heterogeneity of low-growth Arctic tundra landscapes necessitates the use of high-spatial-resolution remote sensing data for accurate detection of vegetation patterns. While multispectral satellite and aerial imaging, including the use of uncrewed aerial vehicles (UAVs), are common approaches, hyperspectral UAV imaging has not been thoroughly explored in these ecosystems. Here, we assess the added value of hyperspectral UAV imaging relative to multispectral UAV imaging in modelling plant communities in low-growth oroarctic tundra heaths in Saariselkä, northern Finland. We compare three different spectral compositions: 4-channel broadband aerial images, 5-channel broadband UAV images and 112-channel narrowband UAV images. Based on field vegetation plot data, we estimate vascular plant aboveground biomass, leaf area index, species richness, Shannon's diversity index, and community composition. We use spectral and topographic information to compile 12 explanatory datasets for random forest regression and classification.

For aboveground biomass and leaf area index, the highest R² values were 0.60 and 0.65, respectively, and broadband variables were most important. In the best models for biodiversity metrics species richness and Shannon's index R² values were 0.53 and 0.46, respectively, with hyperspectral, topographic, and multispectral variables having high importance. For 4 floristically determined community clusters, both random forest classifications and fuzzy cluster membership regressions were conducted. Overall accuracy (OA) for classification was 0.67 at best, while cluster membership was estimated with an R² of 0.29–0.53. Variable importance was heavily dependent on community composition, but topographic, multispectral, and hyperspectral data were all selected for these community composition models. Hyperspectral models generally outperformed multispectral ones when topographic data were excluded. With topographic data, this difference was diminished, and performance improvements from added hyperspectral data were limited to 0–10 percentage point increases in R², the largest occurring in the metrics with lowest R². These results suggest that while hyperspectral can outperform multispectral imaging, multispectral and topographic data are mostly sufficient in practical applications in tundra heaths.

In socially flexible species, the tendency to live in groups is expected to vary through a trade-off between costs and benefits, determined by ecological conditions. The Resource Dispersion Hypothesis predicts that group size changes in response to patterns in resource availability. An additional dimension is described in Hersteinsson's model positing that sociality is further affected by a cost-benefit trade-off related to predation pressure. In the arctic fox (Vulpes lagopus), group-living follows a regional trade-off in resources' availability and intra-guild predation pressure. However, the effect of local fluctuations is poorly known, but offers an unusual opportunity to test predictions that differ between the two hypotheses in systems where prey availability is linked to intra-guild predation. Based on 17-year monitoring of arctic fox and cyclic rodent prey populations, we addressed the Resource Dispersion Hypothesis and discuss the results in relation to the impact of predation in Hersteinsson's model. Group-living increased with prey density, from 7.7% (low density) to 28% (high density). However, it remained high (44%) despite a rodent crash and this could be explained by increased benefits from cooperative defence against prey switching by top predators. We conclude that both resource abundance and predation pressure are factors underpinning the formation of social groups in fluctuating ecosystems.

Nature-based recreational and tourism activities can exert significant direct and indirect impacts on wildlife, through behavioral, physiological and distributional changes. Despite many studies demonstrating such changes, few attempts have been made to quantify the fitness consequences and evaluate their biological significance. Helagsfjallen in Sweden is a core area of the endangered Fennoscandian arctic foxVulpes lagopus, and a popular area for recreational tourism. Some dens in the area experience daily disturbance from tourism during the summer season, while others are virtually undisturbed. We used a long-term dataset (2008-2017) of 553 juveniles in 74 litters to investigate summer juvenile survival, which is an important fitness component for the arctic fox. We found that the mean juvenile survival rate increased from 0.56 at undisturbed dens to 0.83 at disturbed den during years of decreasing small-rodent abundance, where predation on the arctic fox is presumed to be highest. We suggest that the increased survival could be mediated by a human activity-induced predator refuge for the arctic foxes in close proximity of trails and mountain huts. Our study demonstrates a possible positive indirect effect of nature-based tourism on wildlife and is one of a few studies attempting to quantify this impact. It highlights the importance of context for how animals are affected by disturbance. We also demonstrate that studying how the effects of tourism activity vary depending on the context could provide opportunities for identifying the mechanisms behind these effects, which can be an important link between scientific research and the management of wildlife and tourism activities.

Studies of ecological processes should focus on a relevant spatial scale, as crude spatial resolution will fail to detect small scale variation which is of potentially critical importance. Remote sensing methods based on multispectral satellite images are used to assess primary productivity and aerial photos to map vegetation structure. Both methods are based on the principle that photosynthetically active vegetation has a characteristic spectral signature. Yet they are applied differently due to technical differences. Satellite images are suitable for calculations of vegetation indices, for example Normalized Difference Vegetation Index (NDVI). Colour infrared aerial photography was developed for visual interpretation and never regarded for calculation of indices since the spectrum recorded and post processing differ from satellite images. With digital cameras and improved techniques for generating colour infrared orthophotos, the implications of these differences are uncertain and should be explored. We tested if plant productivity can be assessed using colour infrared aerial orthophotos (0.5 m resolution) by applying the standard NDVI equation. With 112 vegetation samples as ground truth, we evaluated an index that we denote rel‐NDVI_ortho in two areas of the Fennoscandian mountain tundra. We compared the results with conventional SPOT5 satellite‐based NDVI (10 m resolution). rel‐NDVI_ortho was related to plant productivity (Northern area: P = <0.001, R² = 0.73; Southern area: P = <0.001, R² = 0.39), performed similar to SPOT5 satellite NDVI (Northern area: P = <0.001, R² = 0.76; Southern area: P = <0.001, R² = 0.40) and the two methods were highly correlated (cor = 0.95 and cor = 0.84). Despite different plant composition, the results were consistent between areas. Our results suggest that vegetation indices based on colour infrared aerial orthophotos can be a valuable tool in the remote sensing toolbox, offering a high‐spatial resolution proxy for plant productivity with less signal degradation due to atmospheric interference and clouds, compared to satellite images. Further research should aim to investigate if the method is applicable to other ecosystems.

Life history theory predicts that individuals will differ in their risk-taking behavior according to their expected future fitness. Understanding consequences of such individual variation within a behavioral trait is crucial in explaining potential trade-offs between different traits and in predicting future dynamics in changing environments. Here, we studied individuals in a wild arctic fox population to explore if (1) individual variation in risk-taking behaviors of adult arctic foxes and in stress-dealing behaviors of their juveniles exist and are consistent over time to verify the existence of personality traits; (2) those behavioral traits in adults and juveniles are correlated; (3) they can explain fitness-related components (i.e., juvenile physical condition, mortality rate). We presented simple field experiments assessing behavioral traits by observing adult reactions toward approaching observers, and juvenile behaviors while trapping. Through the experiments, we found highly consistent individual variation of adults in vigilance and boldness levels, and more flexible juvenile behavioral traits categorized as investigating, passive, and escaping. The offspring of bolder adults exhibited more investigating behaviors and were less passive than the offspring of shy adults. Juvenile physical condition was not related to their mortality nor any behavioral traits of either parents or themselves. Lastly, highly investigating and active juveniles with bold parents had significantly lower mortality rates. This shows that interactions between parent personality and juvenile behavioral traits affect a fitness-related component in the life history of individuals. Significance statement The recent surge of interest in consistent individual difference in behavior, also called as animal personality, has already focused on its fitness consequences, but few studies have investigated the interactions between parent and offspring personality, and their ecological consequences. Moreover, this has rarely been studied in wild canids. The arctic fox is a charismatic species showing wide individual variation in behaviors. They live in highly fluctuating tundra ecosystems providing different selection regimes, making it even more eco-evolutionarily intriguing. Yet, few studies looked into behavioral traits and their importance in this system. While introducing simple methods to improve personality research in the wild, we provide a unique example of how variation in both parents and their juveniles collectively works for group dynamics in a cyclic population. This provides a firm basic for understanding behavior-mediated dynamics and opens up broader questions on how fluctuating environments exert varying pressures on individual differences.

It is well known that competition, predation and fluctuating food resources can have strong effect on individual fitness and population dynamics. The complexity of natural systems can make it complicate to disentangle those processes, but environments with relatively simple food webs, and strong cyclic population dynamics offer contrasting conditions resembling experimental treatments. This thesis concerns the spatial and temporal implications of fluctuations in small rodent abundance on two trophic levels in a highly cyclic ecosystem, the Scandinavian mountain tundra. The first two chapters focus on plant biomass and spatiotemporal distribution in the Norwegian lemming (Lemmus lemmus), while the three last papers focus on the direct and indirect effects of small rodent fluctuations and territory quality on reproductive success, juvenile survival and group living in a lemming specialist mesopredator, the arctic fox (Vulpes lagopus). By developing, validating and applying a novel application of aerial photos for remote sensing of plant biomass (Chapter I), we found that food availability predicted lemming distribution during population peaks, but that they were more habitat specific during increase years when intraspecific competition was lower (Chapter II). Arctic fox reproduction is tightly connected to small rodent abundance but the effects of geographical variation in food availability is less well known. We used 17 years of population surveys of an arctic fox subpopulation in mid Sweden (Helagsfjällen) to investigate potential effects. During small rodent increase years, we found that arctic fox litter sizes were smaller in territories of intermediate plant productivity, compared to both more and less productive territories (Chapter III). This could be an effect of limited food availability together with increased presence of red foxes (Vulpes vulpes), a stronger and potentially lethal competitor. However, when small rodents peaked, and competition would be expected to decrease, we saw no effect of territory productivity. Based on a smaller data set concerning juvenile summer survival, we found that the mortality rate among juveniles born by first time breeding arctic fox females were more sensitive to low small rodent prey abundance (Chapter IV). We explain it with an increased predation pressure from top-predators that switch from small rodents to alternative prey when small rodents decline, as suggested by an observed positive effect on juvenile survival by adult presence on den sites. Arctic foxes are socially flexible, and several adults can share a den with the resident pair, potentially increasing juvenile survival and help in territorial defence. Returning to the 17-year data set, we tested the Resource Dispersion Hypothesis predicting that increased resource availability should increase group size (Chapter V). We found support for this prediction as group living increased during the small rodent peak phase. However, it remained unexpectedly high during the decrease phase, when resources are scarce. This could however be related to increased predation pressure, and an increasing benefit of group living.

Isolation of small populations can reduce fitness through inbreeding depression and impede population growth. Outcrossing with only a few unrelated individuals can increase demographic and genetic viability substantially, but few studies have documented such genetic rescue in natural mammal populations. We investigate the effects of immigration in a subpopulation of the endangered Scandinavian arctic fox (Vulpes lagopus), founded by six individuals and isolated for 9 years at an extremely small population size. Based on a long-term pedigree (105 litters, 543 individuals) combined with individual fitness traits, we found evidence for genetic rescue. Natural immigration and gene flow of three outbred males in 2010 resulted in a reduction in population average inbreeding coefficient (f), from 0.14 to 0.08 within 5 years. Genetic rescue was further supported by 1.9 times higher juvenile survival and 1.3 times higher breeding success in immigrant first-generation offspring compared with inbred offspring. Five years after immigration, the population had more than doubled in size and allelic richness increased by 41%. This is one of few studies that has documented genetic rescue in a natural mammal population suffering from inbreeding depression and contributes to a growing body of data demonstrating the vital connection between genetics and individual fitness.