1,721,066 research outputs found
Do the predators of Yamal have a learning effect of artificial nests?
Full text linkMany artificial nest studies that goes over several years place the nests in the same location each placement. Over the years there is a chance that the predators learn where the nests are placed and that can give skewed results. The goal of my study is to see if the predators learn where the nests are located. This was done over three study sites on the Yamal peninsula. In two of the study sites the nests were placed over 4 years with an early and late incubation timing. The last study site had 2 years and only one placement each year. Each time the nests were placed half of the nests where covered nests while the rest was uncovered. The results were tested using glmer in R. The results show an increase in predation over the years. The results also show a difference between the early and late incubation timing, but this difference decreased over the years. The increase over the years suggests that the predators do learn where the nests are placed each year since more nests are predated each year. The difference between the early and late predation of nests might be caused by the shift in search image for the predators, but the decrease in this difference suggests that the learning effect over the years negate this shift. Overall there is an indication that there is a learning effect for the predators and should be taken into consideration when using multiannual artificial nests
The effect of trapping on Arctic Foxes in Svalbard : demography and genetics
No full textFor hundreds of years arctic foxes on the Svalbard archipelago have been hunted and trapped for their warm and attractive fur. However, little is known about the effect that trapping has on this species population structure. Here I assess the effect of trapping on arctic foxes by comparing the demographic and genetic structure of foxes from the Austfjordnes area in Svalbard over three consecutive hunting seasons. The investigation focusses on changes to the demographic makeup of age structure, sex ratio, female reproduction and body weight from a population that had been low to moderately harvested (2008 – 2009) to those which had been intensively harvested (2009 – 2010 and 2010 – 2011). I also address whether there is a significant change in genetic diversity between the 2008 – 2009 and 2009 – 2010 trapping seasons and test for genetic subdivision within the population. Analyses of age structure revealed a breakdown in the usual population structure by a significant decrease of reproductive adults (especially females) and higher numbers of juveniles in the trapping area. Trapping did not seem to significantly alter the sex ratio or the proportion of females reproducing. However, the lack of reproductive females over three years old would influence future population numbers. Changes to body weight were thought to be related to reproduction and the effects of weather. Genetic analyses showed an increase in allelic richness and significant genetic differentiation between trapping seasons suggesting high immigration rates into the area.
Keywords: Hunting; Demography; Age structure; Sex Ratio; Reproduction; Body Weight; Genetics; Genetic diversity; Genetic subdivision
Microbial eukaryotes and their functional importance in the Arctic. A Svalbardian perspective
Full text linkMicrobial eukaryotes, including protists and fungi, play diverse functions in virtually all ecosystems. In the High Arctic, their high biomass and diversity reflects crucial ecological importance and the performance of key ecological processes. Protists are the main primary producers in arctic seas, whereas fungi are an important group of decomposers and symbiotic partners of plants in terrestrial habitats. During the last decade, along with the development of new high-throughput sequencing methods, our knowledge regarding arctic microbial eukaryotes has expanded. Previous studies have identified the major groups of microbial eukaryotes present in Svalbard and how their richness and abundance may vary along various temporal and spatial scales. Those studies used high-throughput sequencing to reveal the dynamics, biodiversity patterns and community composition of diverse microbial eukaryotes such as marine protists, soil and root-associated fungi. However, altogether these studies have just scratched the surface of disentangling the biodiversity and its drivers. Basic questions regarding taxonomic diversity, community composition and their drivers are addressed in a limited manner, often leaving most of the observed variation unexplained. Regarding functionality of these organisms, even less is known. At the same time, these findings have also increased the amount of questions about microbial eukaryotes, their life histories, strategies, seasonality, sensitivity to changes in environmental conditions, as well as functional importance of these organisms at different scales.
Previously unexplained variation and other emerging knowledge gaps regarding microbial eukaryotes formed a backstage for this thesis. The main focus was to look at these organisms from a functional angle regarding variation related to methodology, seasonality and biotic factors through case studies addressing the following knowledge gaps. Firstly, to understand the functionality of biodiversity in a temporal and spatial context of cold soils, we need to determine if our methods estimate biodiversity of the active community of microbial eukaryotes. In other words, does DNA-based detection of species provide good enough approximation to continue or is a different methodology needed? We found that the choice of marker gene template influenced diversity measures and read numbers in abundant fungal groups such as Helotiales and Agaricales. However, it did not impact the community structure. Secondly, the aim was to understand the role of biodiversity and functionality of plant root-associated fungi in relation to host plant performance. We explored putative effects of fungal diversity on plant morphology and the interplay between functional diversity and abiotic factors in a spatial context. Our results revealed the importance of fungal richness and functional diversity, but no impact of community structure on plant morphometrics. Moreover, we showed that temperature affects fungal richness, below- and aboveground parts of the plant in different ways, making it difficult to predict its impact on the biological outcomes in natural systems. The third aim was to address the lack of polar night investigations of microbial eukaryotes in general, especially with a strong focus on their functions. Here, we investigated the impact of strong seasonality on functions of microbial eukaryotes in the marine environment. Community-level gene expression was driven primarily by seasonal patterns of light availability. Among the most expressed transcripts, nearly ⅔ transcripts were not functionally annotated, providing further evidence for distinct genetic makeup of the Arctic Ocean.
Through these three case studies, this thesis contributed some building blocks to close important knowledge gaps, but also revealed that there are more unknowns to be addressed. This thesis aimed to increase awareness of the importance of functional understanding of the roles of microbial eukaryotes in the High Arctic ecosystems. Finally, it highlights further possibilities and developments that could improve the understanding of possible future responses of these organisms and processes that they control
Arctic fox diet in Yamal peninsula
Full text linkArctic fox in inland areas has been typically described as a species dependent on rodent populations, but being able to use alternative prey, therefore named an opportunistic specialist. Rodent populations in the low shrub tundra of southern Yamal peninsula exhibit at present low amplitude cycles. The hypothesis for this thesis is that the low abundance of small rodents is not enough to sustain arctic fox population numbers, and there is a need for alternative prey resources. This study uses four methods to assess the diet of the arctic fox in the low shrub tundra of southern Yamal peninsula: picture identification, identification of prey remains, scat analysis and stable isotope analysis. Results of the scat analysis showed that there was no differences between the presence of rodents in the diet in 2013 and 2014, a year with relatively higher and lower small rodent abundance respectively. The presence of birds was higher in the diet during 2013 than 2014. PCA showed a more varied diet in 2014 than in 2013, likely due to the presence of reindeer carcasses in the tundra. Stable isotope analysis supported the importance of Microtus species, previously found in the scat analysis. Correlation between numerical responses of the arctic foxes, quantified as the number of active dens, and the rodent abundance was not found. It seems that arctic foxes in the low shrub tundra of southern Yamal peninsula are following a generalist strategy
Changes in environment cause dietary shifts in the Svalbard Arctic fox: A stable isotope study
Full text linkIn this thesis, shift in diet of Arctic foxes on Svalbard over a long time frame was analyzed. The Svalbard Arctic fox is a generalist who links the terrestrial and marine ecosystems. The objectives were 1) investigate whether there are spatial and temporal trends in Arctic fox diet on Svalbard, 2) determine how important the changes in the environmental variables are for dietary shifts of the Arctic fox in different seasons and 3) determine whether other parameters like the distance to the coast and age class have any impact on the diet as inferred from stable isotopes. Stable isotope values of carbon and nitrogen from Arctic fox muscle (representing winter diet) and fur (representing autumn diet) samples over the winter seasons 1997/1998 to 2019/2020 were used to assess dietary shifts. Arctic fox isotope values fitted mainly linearly between marine and resident terrestrial prey (reindeer and ptarmigan). Both negative temporal trends and differences between regions were found, signifying a shift towards more use of terrestrial resources in both winter and autumn. This was also found when analyzing environmental effects, where the number of geese and year to year fluctuations in reindeer carcass number were significant in shifting diet towards more use of terrestrial resources in winter. The distance to the coast also showed significant difference in the diet between coastal and inland Arctic foxes. The value of long time data series was shown in this thesis as these gave significant results, while short time data series usually did not. Continued monitoring and sampling, as well as including other parameters like seabird population estimates and the fox’s preference of marine invertebrates are of interest to improve models and give more accurate estimates
Long-term fluctuations in an arctic fox (Vulpes lagopus) population: a matter of diet?
Full text linkThe long-term dynamics of predator populations may be driven by fluctuations in resource availability and reflect ecosystem changes in response to climate change. The Icelandic arctic fox population has known major fluctuations in size since the 1950s, starting with a decreasing period until late 1970s, followed by a six-fold increase until 2008 when the population dropped to half its size within five years until it recently bounced back again.
Using stable isotope analysis of bone collagen over a long-time series (1979-2018), I aimed at identifying the main resources used by Icelandic arctic foxes during periods of growth and decline to assess if the recent variations in their population size are linked to fluctuations in the availability of resources. Building on the results of Carbonell Ellgutter & al. (2020), I hypothesized that the decline in seabirds abundance was responsible for the decrease in the fox population. Additionally, I expected that the preceding growth period led to increased competition among foxes, causing a rise in inter-individual variations in their diet, ultimately leading to variations in their isotopic niches at the population scale. The isotopic signatures of arctic foxes differed drastically between their habitats, as well as trends in δ13C and δ15N ratios over time. Inland foxes showed an overall shift towards more terrestrial preys, whereas coastal foxes displayed a relatively stable use of marine resources over the years. Stable isotopes mixing models suggested that marine resources and rock ptarmigans were the most important food sources, and highlighted a rather stable diet in coastal habitats compared to inland habitats where more fluctuations in dietary composition were observed. Isotopic niche breadths showed broader niches for coastal foxes than inland foxes, and also highlighted more variations in inland habitats where foxes seemed to diversify their diet during periods of growth, when their preferred prey became scarce and when the number of conspecifics increased. On the other hand, coastal foxes had a constant niche breadth throughout the study period and seemed to adopt a more generalist behavior.
Fluctuations in the Icelandic arctic foxes population occurred without major changes in their dietary composition despite the variations in the abundance of their main resources
Corvids response to fluctuating abundance of resources in tundra ecosystems
Full text linkAim Despite the numerous studies on corvids’ behaviour, their dynamics in different ecosystems is unknown. Ravens and hooded crows are opportunistic generalists acting as both predators and scavengers. Ravens are probably the most specialized scavengers on ungulate carcasses and both species are known as efficient hunters of small rodents. Small rodents are a key species in the tundra as they represent the main prey for many terrestrial predators. A study about nest predation using artificial nests, suggested that corvids may respond numerically to the Norwegian lemming in tundra ecosystems. Here I used a 13 year time series to investigate whether two potentially important food resources, small rodents and reindeer carcasses, drive the corvids fluctuations in the ecosystems of Northern Fennoscandia.
Methods To investigate the corvid population dynamics, I used data from camera traps baited with reindeer meat collected in eastern Finnmark during winter between 2005 and 2017, in addition to time series data from small rodent trapping.
Main conclusions This is the first study to assess temporal and spatial variation in corvids dynamics in the tundra of Northern Fennoscandia. The results showed a great deal of temporal and spatial variation in the presence of each species between the time series of three regions. The assumption that the corvids’ populations fluctuate with the lemming cycles appears not to be supported here. However, the presence of the ravens was positively correlated with the fluctuations of voles that were in higher density compare to lemming during the study period. The statistical models did not reveal any impact of the relative amount of carcasses in eastern Finnmark on the dynamics of the corvid data. Based on the results, I discuss the different responses of these generalist predators in the arctic tundra
An assessment of three survey methods on common bird species in low Arctic tundra.Comparing line transect distance sampling, repeated point counts and double observer point counts
Full text linkLong-term studies of bird communities in Arctic regions are rare in comparison to studies performed in temperate regions, particularly studies that takes detectability into consideration. Finding a suitable and robust method for long-term monitoring of bird populations in the low Arctic which includes a correction of imperfect detection, can contribute to increased ecological understanding and easier identification of changes over time. During two field seasons (June-July) in 2015 and 2016, the bird population on Erkuta tundra monitoring site, Yamal, Russia, was surveyed using the three different methods: distance sampling on line transects, repeated point counts and double observer point counts. The comparison between the methods was done by estimating abundances and densities of the three most common species in the area, i.e. Lapland bunting (Calcarius lapponicus), Red-throated pipit (Anthus cervinus) and Wood sandpiper (Tringa glareola). I found that the most plausible density estimates of the common target species were provided by the line transect distance sampling. Although all assumptions were difficult to completely fulfil in the field, the method could be improved by more exact distance measurements in the field, since the degree of overestimation is limited to the extent of which the assumptions are violated. In addition, the line transect distance sampling method have the least impact of “floaters” (non-breeders), which also makes this method more robust. Repeated point counts heavily overestimated the densities, and the models fitted poorly for Red-throated pipit. The overestimation was likely due to violation of the assumption of closed population, and could be reduced by using a model allowing for temporary emigration. Also, too short distance between points, and thus a risk of double counting, could have contributed to the overestimation. However, the double observer point counts offer an alternative approach for long-term monitoring, where the slight overestimation also can be decreased with increased distance between points. In addition, the double observer method requires less effort than the other two methods
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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