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Snorre Hagen

Norwegian Institute of Bioeconomy Research (NIBIO), Biology and Environment, Faculty Member

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Papers by Snorre Hagen

Hair trapping versus field sampling of feces and hair – a comparison of two strategies to collect brown bear samples in 2007 and 2011 at the Pasvik Valley, Norway

Noninvasive genetic sampling became an important part in brown bear monitoring in many countries.... more Noninvasive genetic sampling became an important part in brown bear monitoring in many countries. Mainly feces and hairs collected in the field as well as systematical hair trapping are the two major sampling strategies to acquire bear samples for DNA analysis. In Pasvik, northern Norway, both sampling methods are applied and we looked at the results and effort of applying these two strategies in a part of the Pasvik Valley. Field sampling was conducted throughout the year from April to November, whereas hair trapping was conducted only between mid-June and mid-August. Field sampling and hair trapping were applied simultaneously in the Norwegian territory of the tri-lateral hair trapping project between Norway, Finland and Russia in 2007 and 2011. We focused on the Norwegian part with a size of about 500 km2 and compared the results of hair trapping and of samples collected in the field. Based on the results, we can conclude that none of the two methods is preferable and therefore a...

Populasjonsovervåking av brunbjørn DNA-analyse av prøver innsamlet i Norge i 2014

I 2014 ble det for sjette år på rad samlet inn prøver med antatt opphav fra brunbjørn (Ursus arct... more I 2014 ble det for sjette år på rad samlet inn prøver med antatt opphav fra brunbjørn (Ursus arctos) gjennom det nasjonale overvåkingsprogrammet for rovvilt i Norge. Det ble samlet inn 962 prøver i 2014 (703 ekskrementprøver, 247 hårprøver, 11 vevsprøver og 1 blodprøve), noe som er betydelig lavere antall prøver enn forrige år (1246 prøver i 2013). Av disse prøvene var 60 % positive for brunbjørn, og det ble påvist 136 ulike bjørner, hvorav 54 hunnbjørner og 82 hannbjørner. Dette er en reduksjon sammenlignet med forrige år da det ble påvist 55 hunnbjørner og 93 hannbjørner. I løpet av de siste seks årene har andelen hunnbjørner økt, og i 2014 var andelen økt til 40 %. Beregninger av antall ynglinger i samme periode ligger relativt stabilt på ca. 6 ynglinger. Som tidligere år er forekomsten av brunbjørn i hovedsak konsentrert i fylkene Hedmark (43), Finnmark (34) og Nord-Trøndelag (29). Av de 136 individbestemte bjørnene i Norge i 2014 var 93 individer (68 %) tidligere påvist i Norge...

DNA-based monitoring of bear recolonization and numbers in Norway using hais and scats during 2006-2012

Cover image Proceedings B

About the cover image: Male brown bear (Ursus arctos) photographed during a summer night in Finla... more About the cover image: Male brown bear (Ursus arctos) photographed during a summer night in Finland, close to the Russian border. See the paper by Snorre B. Hagen et al. “Evidence of rapid change in genetic structure and diversity during range expansion in a recovering large terrestrial carnivore” published in Proceedings B (http://dx.doi.org/10.1098/rspb.2015.0092). Photo credit: Alexander Kopatz.

Evidence of rapid change in genetic structure and diversity during range expansion in a recovering large terrestrial carnivore

by Alexander Kopatz, Jouni Aspi, and Snorre Hagen

Proceedings. Biological sciences / The Royal Society, Jan 22, 2015

Recovery of natural populations occurs often with simultaneous or subsequent range expansions. Ac... more Recovery of natural populations occurs often with simultaneous or subsequent range expansions. According to population genetic theory, genetic structuring emerges at the expansion front together with decreasing genetic diversity, owing to multiple founder events. Thereupon, as the expansion proceeds and connectivity among populations is established, homogenization and a resurgence of genetic diversity are to be expected. Few studies have used a fine temporal scale combined with genetic sampling to track range expansions as they proceed in wild animal populations. As a natural experiment, the historical eradication of large terrestrial carnivores followed by their recovery and recolonization may facilitate empirical tests of these ideas. Here, using brown bear (Ursus arctos) as model species, we tested predictions from genetic theory of range expansion. Individuals from all over Finland were genotyped for every year between 1996 and 2010 using 12 validated autosomal microsatellite ma...

Monitoring the spatio-temporal dynamics of geometrid moth outbreaks in birch forest using MODIS-NDVI data

Remote Sensing of Environment, 2009

Defoliation caused by repeated outbreaks of cyclic geometrid moths is the most prominent natural ... more Defoliation caused by repeated outbreaks of cyclic geometrid moths is the most prominent natural disturbance factor in the northern-boreal birch forest. Evidence suggests that recent changes in outbreak distribution and duration can be attributed to climate warming. There is hence an immediate need for methods that can be applied to characterize the geographical distribution of outbreaks. Here we assess the reliability of MODIS (Moderate Resolution Imaging Spectroradiometer) 16-day NDVI data for generating time series of the distribution of defoliation caused by moths attacking birch forest in Fennoscandia. We do so by first establishing the relationship between ground measures of moth larval density and a defoliation score based on MODIS-NDVI. We then calibrate and validate a model with the MODIS-NDVI defoliation score as a classifier to discriminate between areas with and without visible defoliation as identified from orthophotos and provide two examples of application of the model. We found the MODIS defoliation score to be a valid proxy for larval density (R 2 = 0.88-0.93) above a certain, low threshold (a defoliation score of~5%). Areas with and without visible defoliation could be discriminated based on defoliation score with a substantial strength of agreement (max kappa = 0.736), and the resulting model was able to predict the proportion of area with visible defoliation in independent test areas with good reliability across the range of proportions. We conclude that satellite-derived defoliation patterns can be an invaluable tool for generating indirect population dynamical data that permits the development of targeted monitoring on relevant regional scales.

Autumn coloration as a signal of tree condition

Proceedings of the Royal Society B: Biological Sciences, 2004

Hamilton and Brown suggested that bright autumn coloration in trees is an energetically expensive... more Hamilton and Brown suggested that bright autumn coloration in trees is an energetically expensive and therefore honest (handicap) signal of defensive commitment against insects. If this is so, one should expect that the intensity of the proposed signal should depend strongly on tree health. However, to the best of our knowledge, the link between vigour and autumn colour has never been tested. We explored the relationship between autumn coloration and tree condition (i.e. leaf fluctuating asymmetry) in mountain birch (Betula pubescens).

Benzo(a)pyrene shows low toxicity to three species of terrestrial plants, two soil invertebrates, and soil-nitrifying bacteria

Ecotoxicology and Environmental Safety, 2007

We examined the toxicity of benzo(a)pyrene (BaP) to several standard test organisms including the... more We examined the toxicity of benzo(a)pyrene (BaP) to several standard test organisms including the seed emergence and early lifestage growth of three terrestrial plants (Trifolium pratense, Lolium perenne, and Brassica alba), the survival and reproduction of enchytraeids (Enchytraeus crypticus), and the nitrifying ability of soil bacteria. To also have a look at possible food-chain effects, we included a two-species reproduction test with predatory mites (Hypoaspis aculeifer) and collembolan (Folsomia fimetaria) prey. No effect or only weak effects even at very high BaP concentrations were observed for all tests. None of the soil invertebrates were affected within the concentration range tested (up to 947 mg kg À1 ). For soil-nitrifying bacteria, significant effects were recorded at 977 mg kg À1 , leaving a no observable effect concentration (NOEC) of 293 mg kg À1 . BaP did not affect seed emergence for any of the plants, but the growth of B. alba was significantly reduced at the highest concentration tested (375 mg kg À1 ), leaving a NOEC of 69 mg kg À1 . Compared to a number of other polycyclic aromatic compounds previously tested in the same soil type, BaP is generally less toxic. r

Autumn colouration and herbivore resistance in mountain birch (Betula pubescens)

Ecology Letters, 2003

We explored Hamilton and Brown's autumn signalling hypothesis in mountain birch (Betula pubescens... more We explored Hamilton and Brown's autumn signalling hypothesis in mountain birch (Betula pubescens). As predicted by the hypothesis, early autumn colour change (i.e. high degree of autumn colouration in September) was negatively correlated with insect damage the following season. Furthermore, as expected, indices of physiological stress (i.e. leaf fluctuating asymmetry) and reproductive investment (i.e. catkin production) were positively correlated with insect damage the following season. Indirectly, we also found support for the idea that the proposed handicap signal (i.e. early autumn senescence) might be associated with an honesty ensuring cost in terms of lost primary production. Further work is, however, required to determine whether the link between autumn colours and insect damage observed in this study is causal.

Responses of great tits Parus major to small tortoiseshells Aglais urticae in feeding trials; evidence of aposematism

Ecological Entomology, 2003

1. The small tortoiseshell Aglais urticae (Lepidoptera, Nymphalidae) is one of several red-colour... more 1. The small tortoiseshell Aglais urticae (Lepidoptera, Nymphalidae) is one of several red-coloured butterflies and moths that are active in early spring in Norway. It has been suggested that tortoiseshells may be warningly coloured and unpalatable to birds, however no experiments have been carried out to test this hypothesis.

Sources of variation in larval parasitism of two sympatrically outbreaking birch forest defoliators

Ecological Entomology, 2012

1. Studies of insect communities rarely support the parasitoid-host regulation hypothesis. Spatio... more

Comparative toxicity of acrylic acid to marine and freshwater microalgae and the significance for environmental effects assessments

Chemosphere, 2001

In this study, we compared the sensitivity of freshwater and marine organisms to two structurally... more In this study, we compared the sensitivity of freshwater and marine organisms to two structurally similar substances, acrylic acid and methacrylic acid. Reported acute toxicity data (LEC 50 -values) for freshwater organisms range from 0.1 to 222 mg/l and 85 to >130 mg/l for acrylic acid and methacrylic acid, respectively. The large variation in toxicity data for acrylic acid is due to a speci®c toxicity to certain species of freshwater microalgae, with algae EC 50 -values being two to three orders of magnitude lower than LEC 50 -values reported for ®sh and invertebrates. To evaluate the sensitivity of marine organisms, ecotoxicity data was generated for ten species of microalgae, one invertebrate species and one ®sh species. For methacrylic acid, we found a marine acute toxicity that ranged from 110 to >1260 mg/l, which is comparable to reported data on freshwater organisms. In strong contrast, the resulting LEC 50 -values for acrylic acid ranged from 50 to >1000 mg/l, and there was no speci®c sensitivity of marine algae when compared to marine invertebrates and ®sh. For acrylic acid, therefore, use of the available freshwater toxicity data for an eects assessment for the marine environment is likely to overestimate the hazard and risk from this substance. Overall, the results of the study suggest that ecotoxicity data generated on freshwater species may not always be appropriate for the eects assessments of organic chemicals in the marine environment, thus emphasising the importance of using ecologically relevant data to assess environmental risk. Ó

Phenological diversity in the interactions between winter moth (Operophtera brumata) larvae and parasitoid wasps in sub-arctic mountain birch forest

Bulletin of Entomological Research, 2011

Population cycles of the winter moth (Operophtera brumata) in sub-arctic coastal birch forests sh... more Population cycles of the winter moth (Operophtera brumata) in sub-arctic coastal birch forests show high spatiotemporal variation in amplitude. Peak larval densities range from levels causing little foliage damage to outbreaks causing spatially extensive defoliation. Moreover, outbreaks typically occur at or near the altitudinal treeline. It has been hypothesized that spatiotemporal variation in O. brumata cycle amplitude results from climate-induced variation in the degree of phenological matching between trophic levels, possibly between moth larvae and parasitoids. The likelihood of mismatching phenologies between larvae and parasitoids is expected to depend on how specialized parasitoids are, both as individual species and as a guild, to attacking specific larval developmental stages (i.e. instars). To investigate the larval instar-specificity of parasitoids, we studied the timing of parasitoid attacks relative to larval phenology. We employed an observational study design, with sequential sampling over the larval period, along an altitudinal gradient harbouring a pronounced treeline outbreak of O. brumata. Within the larval parasitoid guild, containing seven species groups, the timing of attack by different groups followed a successional sequence throughout the moth's larval period and each group attacked 1-2 instars. Such phenological diversity within parasitoid guilds may lower the likelihood of climate-induced trophic mismatches between victim populations and many/all of their enemies. Parasitism rates declined with increasing altitude for most parasitoid groups and for the parasitoid guild as a whole. However, the observed spatiotemporal parasitism patterns provided no clear evidence for or against altitudinal mismatch between larval and parasitoid phenology.

How rapidly do invasive birch forest geometrids recruit larval parasitoids? Insights from comparison with a sympatric native geometrid

Biological Invasions, 2013

Two related issues in studies of biological invasions are how quickly the enemy complexes of inva... more Two related issues in studies of biological invasions are how quickly the enemy complexes of invasive species become as species-rich and efficient as those of native species and how important enemy release is for the establishment and spread of invaders. We addressed these issues for the geometrid moths Operophtera brumata and Agriopis aurantiaria, who invaded the coastal mountain birch forest of northern Norway by range expansion approximately a century and 15 years ago, respectively. This was done by comparing larval parasitoid species richness and prevalence among the invaders and the native geometrid Epirrita autumnata. We found that E. autumnata and O. brumata both hosted seven parasitoid species groups, whereas A. aurantiaria hosted only one.

Populasjonsovervåkning av brunbjørn 2009-2012: DNA analyse av prøver samlet i Norge i 2009

by Snorre Hagen and Hans Eiken

bioforsk.no

Responses of domestic chicks (Gallus gallus domesticus) to multimodal aposematic signals

Behavioral Ecology, 2006

Many aposematic prey combine their visual warning signals with additional signals. Together, thes... more Many aposematic prey combine their visual warning signals with additional signals. Together, these signals constitute a multimodal or multicomponent warning display. The additional signals are thought to increase the effects of the visual signals on predators. Olfactory signals are much emphasized, but later studies have shown that also auditory signals like the buzzing of certain insects might have multimodal effects. The wasp displays typical visual aposematic signals, black and yellow stripes, but does also emit a characteristic buzzing. We wanted to test if, and in what way, the visual and acoustic display of the wasp has an aversive function on the predators. We therefore conducted a 12-trial discrimination-learning task on inexperienced chicks to study whether there are innate biases toward these signals and how they affect the speed of avoidance learning. We also performed three extinction-learning trials to study how memorable the signals were to the chicks. We show that the visual signals in the display of the wasp contribute to the protection from predators but in different ways; the yellow color had an aversive effect on inexperienced predators, while the striped pattern improved the aversion learning. The sound did not enhance the innate aversions but increased the aversion learning of stripes in green prey.

A Modification of the Hair-Trapping Method for Surveillance of Problematic Bear Activity Close to a Farm — a Case Study from the Pasvik Valley in Norway

by Alexander Kopatz and Snorre Hagen

Annales Zoologici Fennici, 2013

A forensic DNA profiling system for Northern European brown bears (Ursus arctos)

by Julia Schregel, Snorre Hagen, and Jouni Aspi

Forensic Science International: Genetics, 2012

Limited gene flow among brown bear populations in far Northern Europe? Genetic analysis of the east-west border population in the Pasvik Valley

by Julia Schregel, Snorre Hagen, Ilpo Kojola, Jouni Aspi, and Steinar Wikan

Molecular Ecology, 2012

Noninvasively collected genetic data can be used to analyse large-scale connectivity patterns amo... more Noninvasively collected genetic data can be used to analyse large-scale connectivity patterns among populations of large predators without disturbing them, which may contribute to unravel the species' roles in natural ecosystems and their requirements for long-term survival. The demographic history of brown bears (Ursus arctos) in Northern Europe indicates several extinction and recolonization events, but little is known about present gene flow between populations of the east and west. We used 12 validated microsatellite markers to analyse 1580 hair and faecal samples collected during six consecutive years (2005)(2006)(2007)(2008)(2009)(2010) in the Pasvik Valley at 70°N on the border of Norway, Finland and Russia. Our results showed an overall high correlation between the annual estimates of population size (N c ), density (D), effective size (N e ) and N e ⁄ N c ratio. Furthermore, we observed a genetic heterogeneity of 0.8 and high N e ⁄ N c ratios of 0.6, which suggests gene flow from the east. Thus, we expanded the population genetic study to include Karelia (Russia, Finland), Västerbotten (Sweden) and Troms (Norway) (477 individuals in total) and detected four distinct genetic clusters with low migration rates among the regions. More specifically, we found that differentiation was relatively low from the Pasvik Valley towards the south and east, whereas, in contrast, moderately high pairwise F ST values (0.91-0.12) were detected between the east and the west. Our results indicate ongoing limits to gene flow towards the west, and the existence of barriers to migration between eastern and western brown bear populations in Northern Europe.

Connectivity and population subdivision at the fringe of a large brown bear (Ursus arctos) population in North Western Europe

by Julia Schregel, Snorre Hagen, Jouni Aspi, and Rodrigo Esparza-salas

Conservation Genetics, 2012