Trond Reitan

• Tjessem, Ingrid Vesterdal; Brysting, Anne Krag; Reitan, Trond; Hjelle, Simen Salomonsen & Eidesen, Pernille Bronken (2026). A shift in species niche through autopolyploidy: From sexual to vegetative reproduction in Saxifraga oppositifolia. Annals of Botany. ISSN 0305-7364. doi: 10.1093/aob/mcag116. Full text in Research Archive Show summary

  Background and Aims Polyploidy has been essential in the evolution of angiosperms, facilitating novel adaptations, enhancing speciation and contributing to the establishment of larger evolutionary lineages. However, newly formed polyploids require sufficient niche differentiation to survive and coexist with the diploid ancestor. Polyploids are commonly reproductively challenged, which may lead to rapid development of asexual reproduction, which may, in turn, lead to reproductive barriers or ecological niche divergence. Through this study, we investigate whether autopolyploidization has induced a shift from sexual reproduction to vegetative propagation in the arctic–alpine Saxifraga oppositifolia (Saxifragaceae) and thus facilitated the establishment of polyploids in mixed-cytotype populations. Methods We sampled data on capsule and seed production, seed germination, rooting ability, and leaf production among cytotypes through a combination of growth chamber experiments and in situ observations in a field set-up across different habitats (ridges, slopes, riverbeds) in Svalbard including >700 georeferenced S. oppositifolia plants with known cytotype (diploid, triploid or tetraploid). Through hypothesis testing and an explorative model search for relevant covariates (e.g. growth form, habitat, soil type), we tested the effect of cytotype on sexual and vegetative reproductive outcomes. Key Results Polyploids had lower sexual reproductive investment (i.e. capsule production and seed production) and higher vegetative investment (i.e. leaf production and rooting ability), showing that polyploidy has significantly affected both sexual reproduction and vegetative propagation. Conclusions Our findings confirm a shift in reproductive strategy towards less sexual investment and enhanced vegetative investment in triploid and tetraploid individuals. This shift may enhance polyploid survival in habitats with shorter growing season and limited pollinator availability, and thus explains their higher frequency in such habitats. These results support autopolyploidy as an evolutionary mechanism that may allow Arctic species to adapt to ongoing, rapid changes.

• Wilson, Connor J.; Reitan, Trond & Liow, Lee Hsiang (2024). Unveiling the underlying drivers of Phanerozoic marine diversification. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 291. doi: 10.1098/rspb.2024.0165. Full text in Research Archive Show summary

  In investigating global patterns of biodiversity through deep time, many large-scale drivers of diversification have been proposed, both biotic and abiotic. However, few robust conclusions about these hypothesized effectors or their roles have been drawn. Here, we use a linear stochastic differential equation (SDE) framework to test for the presence of underlying drivers of diversification patterns before examining specific hypothesized drivers. Using a global dataset of observations of skeletonized marine fossils, we infer origination, extinction and sampling rates (collectively called fossil time series) throughout the Phanerozoic using a capture–mark–recapture approach. Using linear SDEs, we then compare models including and excluding hidden (i.e. unmeasured) drivers of these fossil time series. We find evidence of large-scale underlying drivers of marine Phanerozoic diversification rates and present quantitative characterizations of these. We then test whether changing global temperature, sea-level, marine sediment area or continental fragmentation could act as drivers of the fossil time series. We show that it is unlikely any of these four abiotic factors are the hidden drivers we identified, though there is evidence for correlative links between sediment area and origination/extinction rates. Our characterization of the hidden drivers of Phanerozoic diversification and sampling will aid in the search for their ultimate identities.

• Sydenham, Markus A. K.; Dupont, Yoko L.; Nielsen, Anders; Olesen, Jens M.; Madsen, Henning Bang & Skrindo, Astrid Brekke [Show all 19 contributors for this article] (2024). Climatic conditions and landscape diversity predict plant–bee interactions and pollen deposition in bee-pollinated plants. Ecography. ISSN 0906-7590. 2024(9), p. 1–14. doi: 10.1111/ecog.07138. Full text in Research Archive Show summary

  Climate change, landscape homogenization, and the decline of beneficial insects threaten pollination services to wild plants and crops. Understanding how pollination potential (i.e. the capacity of ecosystems to support pollination of plants) is affected by climate change and landscape homogenization is fundamental for our ability to predict how such anthropogenic stressors affect plant biodiversity. Models of pollinator potential are improved when based on pairwise plant–pollinator interactions and pollinator's plant preferences. However, whether the sum of predicted pairwise interactions with a plant within a habitat (a proxy for pollination potential) relates to pollen deposition on flowering plants has not yet been investigated. We sampled plant–bee interactions in 68 Scandinavian plant communities in landscapes of varying land-cover heterogeneity along a latitudinal temperature gradient of 4–8°C, and estimated pollen deposition as the number of pollen grains on flowers of the bee-pollinated plants Lotus corniculatus and Vicia cracca. We show that plant–bee interactions, and the pollination potential for these bee-pollinated plants increase with landscape diversity, annual mean temperature, and plant abundance, and decrease with distances to sand-dominated soils. Furthermore, the pollen deposition in flowers increased with the predicted pollination potential, which was driven by landscape diversity and plant abundance. Our study illustrates that the pollination potential, and thus pollen deposition, for wild plants can be mapped based on spatial models of plant–bee interactions that incorporate pollinator-specific plant preferences. Maps of pollination potential can be used to guide conservation and restoration planning.

• Reitan, Trond; Martino, Emanuela Di & Liow, Lee Hsiang (2023). Estimating relative species abundance using fossil data identified to different taxonomic levels. Ecography. ISSN 0906-7590. 2024(1). doi: 10.1111/ecog.06866. Full text in Research Archive Show summary

  Site‐occupancy modelling is widely used in ecology for understanding species distribution, habitat‐use and community changes but its application is still limited in paleoecology, where incomplete detection is also routine. Here, we make extensive expansions to an earlier multispecies occupancy model used to estimate the dynamics of relative species abundance in fossil communities. These expansions include incorporating counts of individuals at sites, explicitly allowing for the inclusion of specimens assignable to genus – but not species‐level, a situation common in paleontology, and modelling regional presence/absence. We provide simulations to check the performance of this new model, as well as simulations to quantify the benefits of using individual count data versus subsample occupancy data, and model estimates versus face‐value (raw) estimates, respectively. We also provide an empirical case study using occupancy data from a community of marine benthic colonial animals preserved in the Pleistocene of New Zealand. We find that the new model performs well, especially when it comes to recovering relative abundance dynamics and that it is well worth the effort to both collect individual count data and to include individuals unidentified to species‐level in the site‐occupancy modelling framework. This extended model can be widely applied in paleoecological settings and is necessary when both the average and uncertainty values of relative abundance dynamics need to be robustly estimated.

• Kibaja, Mohamed Julius; Mekonnen, Addisu; Reitan, Trond; Nahonyo, Cuthbert L.; Levi, Matana & Stenseth, Nils Christian [Show all 7 contributors for this article] (2023). On the move: Activity budget and ranging ecology of endangered Ashy red colobus monkeys (Piliocolobus tephrosceles) in a savanna woodland habitat. Global Ecology and Conservation. 43, p. 1–15. doi: 10.1016/j.gecco.2023.e02440. Full text in Research Archive Show summary

  The majority of primate species are under the threat of extinction and their numbers are decreasing worldwide mainly due to human activities. Most primates outside protected areas survive in habitats with different degrees of anthropogenic alterations. Thus, the persistence of a primate species across its geographic range partly depends on the ability of its populations to adapt to diverse habitats with different spatiotemporal patterns of food availability. Understanding the ecological and behavioral adaptations of a particular species to the different habitats it occupies is crucial for designing a comprehensive conservation approach that can also benefit sympatric wildlife species. Ashy red colobus (Piliocolobus tephrosceles) are arboreal, folivorous and endangered monkeys that occur in Uganda and Tanzania. They have been studied in forest habitats, but very little is known about their behavior and ecology in savanna woodland and how these arboreal and folivorous monkeys can survive in such dry habitats. To better understand this species’ range of adaptations, from July 2016 to June 2018 we conducted a comparative study of habitat quality, activity budget and ranging ecology of two groups of Ashy red colobus monkeys living in distinct habitats in western Tanzania: savanna woodland and forest mosaic. We found that the savanna woodland group spent significantly more time moving and less time feeding than the forest mosaic group. We also found that the savanna woodland group had a larger home range, core areas and mean daily travel distance than the forest mosaic group. The savanna woodland group had the largest home range size ever reported for Ashy red colobus monkeys or other red colobus species. Seasonal differences in home range and core area size were found for the forest mosaic group (both were larger in the dry than in the wet season) but not for the savanna woodland group. The patchy spatial distribution and lower density of most of the preferred food tree species of Ashy red colobus monkeys in the savanna woodland seemed to influence their ranging behavior in this habitat. These results expand our understanding of colobine behavioral and ecological flexibility and provide critical data to formulate workable conservation strategies that encompass the whole range of habitats occupied by Ashy red colobus monkeys. Our study also helps to better understand the ecological constraints that savanna woodland habitats pose on primates.

• Saulsbury, James; Parins-Fukuchi, C. Tomomi; Wilson, Connor J.; Reitan, Trond & Liow, Lee Hsiang (2023). Age-dependent extinction and the neutral theory of biodiversity. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 121(1). doi: 10.1073/pnas.2307629121. Full text in Research Archive Show summary

  Red Queen (RQ) theory states that adaptation does not protect species from extinction because their competitors are continually adapting alongside them. RQ was founded on the apparent independence of extinction risk and fossil taxon age, but analytical developments have since demonstrated that age-dependent extinction is widespread, usually most intense among young species. Here, we develop ecological neutral theory as a general framework for modeling fossil species survivorship under incomplete sampling. We show that it provides an excellent fit to a high-resolution dataset of species durations for Paleozoic zooplankton and more broadly can account for age-dependent extinction seen throughout the fossil record. Unlike widely used alternative models, the neutral model has parameters with biological meaning, thereby generating testable hypotheses on changes in ancient ecosystems. The success of this approach suggests reinterpretations of mass extinctions and of scaling in eco-evolutionary systems. Intense extinction among young species does not necessarily refute RQ or require a special explanation but can instead be parsimoniously explained by neutral dynamics operating across species regardless of age.

• Reinar, William Brynildsen; Greulich, Anne; Stø, Ida Myhrer; Knutsen, Jonfinn Mordekai Blix; Reitan, Trond & Tørresen, Ole K. [Show all 9 contributors for this article] (2023). Adaptive protein evolution through length variation of short tandem repeats in Arabidopsis. Science Advances. 9(12), p. 1–10. doi: 10.1126/sciadv.add6960. Full text in Research Archive Show summary

  Intrinsically disordered protein regions are of high importance for biotic and abiotic stress responses in plants. Tracts of identical amino acids accumulate in these regions and can vary in length over generations because of expansions and retractions of short tandem repeats at the genomic level. However, little attention has been paid to what extent length variation is shaped by natural selection. By environmental association analysis on 2514 length variable tracts in 770 whole-genome sequenced Arabidopsis thaliana, we show that length variation in glutamine and asparagine amino acid homopolymers, as well as in interaction hotspots, correlate with local bioclimatic habitat. We determined experimentally that the promoter activity of a light-stress gene depended on polyglutamine length variants in a disordered transcription factor. Our results show that length variations affect protein function and are likely adaptive. Length variants modulating protein function at a global genomic scale has implications for understanding protein evolution and eco-evolutionary biology.

• Reitan, Trond; Ergon, Torbjørn & Liow, Lee Hsiang (2022). Relative species abundance and population densities of the past: Developing multispecies occupancy models for fossil data. Paleobiology. ISSN 0094-8373. 49(1), p. 23–38. doi: 10.1017/pab.2022.17. Full text in Research Archive Show summary

  Abstract The number of individuals of species varies, but estimating abundance, given incomplete and biased sampling in both contemporary and fossilized communities, is challenging. Here, we describe a new occupancy model in a hierarchical Bayesian framework with random effects, in which multispecies occupancy and detection are modeled as a means to estimate relative species abundance and relative population densities. The modeling framework is suited for temporal samples of fossil communities with repeated sampling including multiple species with similar preservation potential. We demonstrate our modeling framework using a fossil community of benthic organisms to estimate relative species abundance dynamics and changing relative population densities of focal species in nine (geological) time intervals over 2.3 Myr. We also explore potential explanatory factors (paleoenvironmental proxies) and temporal autocorrelation that could provide extra information on unsampled time intervals. The modeling framework is applicable across a wide range of questions on species-level dynamics in paleoecological community settings.

• Sydenham, Markus A. K.; Venter, Zander; Moe, Stein Ragnar; Eldegard, Katrine; Kuhlmann, M. & Reitan, Trond [Show all 15 contributors for this article] (2022). Neutral processes related to regional bee commonness and dispersal distances are important predictors of plant–pollinator networks along gradients of climate and landscape conditions. Ecography. ISSN 0906-7590. 2022(12). doi: 10.1111/ecog.06379. Full text in Research Archive Show summary

  Understanding how niche-based and neutral processes contribute to the spatial varia-tion in plant–pollinator interactions is central to designing effective pollination con-servation schemes. Such schemes are needed to reverse declines of wild bees and other pollinating insects, and to promote pollination services to wild and cultivated plants. We used data on wild bee interactions with plants belonging to the four tribes Loteae, Trifolieae, Anthemideae and either spring- or summer-flowering Cichorieae, sampled systematically along a 682 km latitudinal gradient to build models that allowed us to 1) predict occurrences of pairwise bee–flower interactions across 115 sampling locations, and 2) estimate the contribution of variables hypothesized to be related to niche-based assembly structuring processes (viz. annual mean temperature, landscape diversity, bee sociality, bee phenology and flower preferences of bees) and neutral processes (viz. regional commonness and dispersal distance to conspecifics). While neutral processes were important predictors of plant–pollinator distributions, niche-based processes were reflected in the contrasting distributions of solitary bee and bumble bees along the temperature gradient, and in the influence of bee flower preferences on the distri-bution of bee species across plant types. In particular, bee flower preferences separated bees into three main groups, albeit with some overlap: visitors to spring-flowering Cichorieae; visitors to Anthemideae and summer-flowering Cichorieae; and visitors to Trifolieae and Loteae. Our findings suggest that both neutral and niche-based pro-cesses are significant contributors to the spatial distribution of plant–pollinator inter-actions so that conservation actions in our region should be directed towards areas: Page 2 of 11near high concentrations of known occurrences of regionally rare bees; in mild climatic conditions; and that are surrounded by heterogenous landscapes. Given the observed niche-based differences, the proportion of functionally distinct plants in flower-mixes could be chosen to target bee species, or guilds, of conservation concern. Keywords: ecological networks, machine learning, plant–pollinator interactions, spatial, wild bees

• Sydenham, Markus A. K.; Venter, Zander; Reitan, Trond; Rasmussen, Claus; Skrindo, Astrid Brekke & Skoog, Daniel Ingvar Jeuderan [Show all 12 contributors for this article] (2021). MetaComNet: A random forest-based framework for making spatial predictions of plant–pollinator interactions. Methods in Ecology and Evolution. 13(2), p. 500–513. doi: 10.1111/2041-210X.13762. Full text in Research Archive Show summary

  1. Predicting plant–pollinator interaction networks over space and time will improve our understanding of how environmental change is likely to impact the functioning of ecosystems. Here we propose a framework for producing spatially explicit predictions of the occurrence and number of pairwise plant–pollinator interactions and of the species richness, diversity and abundance of pollinators visiting flowers. We call the framework ‘MetaComNet’ because it aims to link metacommunity dynamics to the assembly of ecological networks. 2. To illustrate the MetaComNet functionality, we used a dataset on bee–flower networks sampled at 16 sites in southeast Norway along with random forest models to predict bee–flower interactions. We included variables associated with climatic conditions (elevation) and habitat availability within a 250 m radius of each site. Regional commonness, site-specific distance to conspecifics, social guild and floral preference were included as bee traits. Each plant species was assigned a score reflecting its site-specific abundance, and four scores reflecting the bee species that the plant family is known to attract. We used leave-one-out cross-validations to assess the models' ability to predict pairwise plant–bee interactions across the landscape. 3. The relationship between observed occurrence or absence of interactions and the predicted probability of interactions was nearly proportional (GLMlogistic regression slope = 1.09), matching the data well (AUC = 0.88), and explained 30% of the variation. Predicted probability of interactions was also correlated with the number of observed pairwise interactions (r = 0.32). The sum of predicted probabilities of bee–flower interactions were positively correlated with observed species richness (r = 0.50), diversity (r = 0.48) and abundance (r = 0.42) of wild bees interacting with plant species within sites. 4. Our findings show that the MetaComNet framework can be a useful approach for making spatially explicit predictions and mapping plant–pollinator interactions. Such predictions have the potential to identify areas where the pollination potential for wild plants is particularly high, and where conservation action should be directed to preserve this ecosystem function. interactions, network, plants, pollinators, predict, random forest

• Reinar, William Brynildsen; Olsson, Vilde; Reitan, Trond; Jakobsen, Kjetill Sigurd & Butenko, Melinka Alonso (2021). Length variation in short tandem repeats affects gene expression in natural populations of Arabidopsis thaliana. The Plant Cell. ISSN 1040-4651. 33(7), p. 2221–2234. doi: 10.1093/plcell/koab107. Full text in Research Archive Show summary

  Abstract The genetic basis for the fine-tuned regulation of gene expression is complex and ultimately influences the phenotype and thus the local adaptation of natural populations. Short tandem repeats (STRs) consisting of repetitive DNA motifs have been shown to regulate gene expression. STRs are variable in length within a population and serve as a heritable, but semi-reversible, reservoir of standing genetic variation. For sessile organisms, such as plants, STRs could be of major importance in fine-tuning gene expression as a response to a shifting local environment. Here, we used a transcriptome dataset from natural accessions of Arabidopsis thaliana to investigate population-wide gene expression patterns in light of genome-wide STR variation. We empirically modeled gene expression as a response to the STR length within and around the gene and demonstrated that an association between gene expression and STR length variation is unequivocally present in the sampled population. To support our model, we explored the promoter activity in a transcriptional regulator involved in root hair formation and provided experimentally determined causality between coding sequence length variation and promoter activity. Our results support a general link between gene expression variation and STR length variation in A. thaliana.

• Luo, Tian-Tong; Zhu, Jian-Long; Reitan, Trond & Yedid, Gabriel (2020). Alteration of (FrequencyDependent) Fitness in Time-Shift Experiments Reveals Cryptic Coevolution and Uncoordinated Stasis in a Virtual Jurassic Park. Artificial Life. ISSN 1064-5462. 26(2), p. 196–216. doi: 10.1162/artl_a_00305. Full text in Research Archive Show summary

  Among the major unresolved questions in ecosystem evolution are whether coevolving multispecies communities are dominated more by biotic or by abiotic factors, and whether evolutionary stasis affects performance as well as ecological profile; these issues remain difficult to address experimentally. Digital evolution, a computer-based instantiation of Darwinian evolution in which short self-replicating computer programs compete, mutate, and evolve, is an excellent platform for investigating such topics in a rigorous experimental manner. We evolved model communities with ecological interdependence among community members, which were subjected to two principal types of mass extinction: a pulse extinction that killed randomly, and a selective press extinction involving an alteration of the abiotic environment to which the communities had to adapt. These treatments were applied at two different strengths (Strong and Weak), along with unperturbed Control experiments. We performed several kinds of competition experiments using simplified versions of these communities to see whether long-term stability that was implied previously by ecological and phylogenetic metrics was also reflected in performance, namely, whether fitness was static over long periods of time. Results from Control and Weak treatment communities revealed almost completely transitive evolution, while Strong treatment communities showed higher incidences of temporal intransitivity, with pre-treatment ecotypes often able to displace some of their post-recovery successors. However, pre-treatment carryovers more often had lower fitness in mixed communities than in their own fully native conditions. Replacement and invasion experiments pitting single ecotypes against pre-treatment reference communities showed that many of the invading ecotypes could measurably alter the fitnesses of one or more residents, usually with depressive effects, and that the strength of these effects increased over time even in the most stable communities. However, invaders taken from Strong treatment communities often had little or no effect on resident performance. While we detected periods of time when the fitness of a particular evolving ecotype remained static, this stasis was not permanent and never affected an entire community at once. Our results lend support to the fitness-deterioration interpretation of the Red Queen hypothesis, and highlight community context dependence in determining fitness, the shaping of communities by both biotic factors and abiotic forcing, and the illusory nature of evolutionary stasis. Our results also demonstrate the potential of digital evolution studies to illuminate many aspects of evolution in interacting multispecies communities.

• Hernandez-Aguilar, Raquel Adriana & Reitan, Trond (2020). Deciding Where to Sleep: Spatial Levels of Nesting Selection in Chimpanzees (Pan troglodytes) Living in Savanna at Issa, Tanzania. International Journal of Primatology. ISSN 0164-0291. 41, p. 870–900. doi: 10.1007/s10764-020-00186-z. Full text in Research Archive Show summary

  Abstract To understand how animals select resources we need to analyze selection at different spatial levels or scales in the habitat. We investigated which physical characteristics of trees (dimensions and structure, e.g., height, trunk diameter, number of branches) determined nesting selection by chimpanzees ( Pan troglodytes ) on two different spatial scales: individual nesting trees and nesting sites. We also examined whether individual tree selection explained the landscape pattern of nesting site selection. We compared the physical characteristics of actual ( N = 132) and potential ( N = 242) nesting trees in nesting sites (in 15 plots of 25 m × 25 m) and of all trees in actual and potential nesting sites ( N = 763 in 30 plots of 25 m × 25 m). We collected data in May and June 2003 in Issa, a dry and open savanna habitat in Tanzania. Chimpanzees selected both the site they used for nesting in the landscape and the trees they used to build nests within a nesting site, demonstrating two levels of spatial selection in nesting. Site selection was stronger than individual tree selection. Tree height was the most important variable for both nesting site and tree selection in our study, suggesting that chimpanzees selected both safe sites and secure trees for sleeping.

• Nilsson, Anna L. K.; Skaugen, Thomas; Reitan, Trond; L'Abee-Lund, Jan Henning; Gamelon, Marlène & Jerstad, Kurt [Show all 11 contributors for this article] (2020). Hydrology influences breeding time in the white-throated dipper. BMC Ecology. 20(1). doi: 10.1186/s12898-020-00338-y. Full text in Research Archive Show summary

  Abstract Background Earlier breeding is one of the strongest responses to global change in birds and is a key factor determining reproductive success. In most studies of climate effects, the focus has been on large-scale environmental indices or temperature averaged over large geographical areas, neglecting that animals are affected by the local conditions in their home ranges. In riverine ecosystems, climate change is altering the flow regime, in addition to changes resulting from the increasing demand for renewable and clean hydropower. Together with increasing temperatures, this can lead to shifts in the time window available for successful breeding of birds associated with the riverine habitat. Here, we investigated specifically how the environmental conditions at the territory level influence timing of breeding in a passerine bird with an aquatic lifestyle, the white-throated dipper Cinclus cinclus . We relate daily river discharge and other important hydrological parameters, to a long-term dataset of breeding phenology (1978–2015) in a natural river system. Results Dippers bred earlier when winter river discharge and groundwater levels in the weeks prior to breeding were high, and when there was little snow in the catchment area. Breeding was also earlier at lower altitudes, although the effect dramatically declined over the period. This suggests that territories at higher altitudes had more open water in winter later in the study period, which permitted early breeding also here. Unexpectedly, the largest effect inducing earlier breeding time was territory river discharge during the winter months and not immediately prior to breeding. The territory river discharge also increased during the study period. Conclusions The observed earlier breeding can thus be interpreted as a response to climate change. Measuring environmental variation at the scale of the territory thus provides detailed information about the interactions between organisms and the abiotic environment.

• Luo, Tian-Tong; Heier, Lise; Khan, Zaki Ahmad; Hasan, Faraz; Reitan, Trond & III, Abdool S. Yasseen [Show all 9 contributors for this article] (2019). Examining Community Stability in the Face of Mass Extinction in Communities of Digital Organisms. Artificial Life. ISSN 1064-5462. 24(4), p. 250–276. doi: 10.1162/artl_a_00272. Full text in Research Archive Show summary

  Digital evolution is a computer-based instantiation of Darwinian evolution in which short self-replicating computer programs compete, mutate, and evolve. It is an excellent platform for addressing topics in long-term evolution and paleobiology, such as mass extinction and recovery, with experimental evolutionary approaches. We evolved model communities with ecological interdependence among community members, which were subjected to two principal types of mass extinction: a pulse extinction that killed randomly, and a selective press extinction involving an alteration of the abiotic environment to which the communities had to adapt. These treatments were applied at two different strengths, along with unperturbed control experiments. We examined how stability in the digital communities was affected from the perspectives of division of labor, relative shift in rank abundance, and genealogical connectedness of the community's component ecotypes. Mass extinction that was due to a Strong Press treatment was most effective in producing reshaped communities that differed from the pre-treatment ones in all of the measured perspectives; weaker versions of the treatments did not generally produce significant departures from a Control treatment; and results for the Strong Pulse treatment generally fell between those extremes. The Strong Pulse treatment differed from others in that it produced a slight but detectable shift towards more generalized communities. Compared to Press treatments, Pulse treatments also showed a greater contribution from re-evolved ecological doppelgangers rather than new ecotypes. However, relatively few Control communities showed stability in any of these metrics over the whole course of the experiment, and most did not represent stable states (by some measure of stability) that were disrupted by the extinction treatments. Our results have interesting, broad qualitative parallels with findings from the paleontological record, and show the potential of digital evolution studies to illuminate many aspects of mass extinction and recovery by addressing them in a truly experimental manner.

• Solbakken, Monica Hongrø; Jentoft, Sissel; Reitan, Trond; Mikkelsen, Helene; Jakobsen, Kjetill Sigurd & Seppola, Marit (2019). Whole transcriptome analysis of the Atlantic cod vaccine response reveals subtle changes in adaptive immunity. Comparative Biochemistry and Physiology - Part D:Genomics and Proteomics. ISSN 1744-117X. 31:100597, p. 1–12. doi: 10.1016/j.cbd.2019.100597. Full text in Research Archive Show summary

  Atlantic cod has lost the Major Histocompatibility complex class II pathway – central to pathogen presentation, humoral response and immunity. Here, we investigate the immunological response of Atlantic cod subsequent to dip vaccination with <i>Vibrio anguillarum</i> bacterin using transcriptome sequencing. The experiment was conducted on siblings from an Atlantic cod family found to be highly susceptible towards vibriosis where vaccination has demonstrated improved pathogen resistance. Gene expression analyses at 2, 4, 21 and 42 days post vaccination revealed GO-term enrichment for muscle, neuron and metabolism-related pathways. In-depth characterization of immune-related GO terms demonstrated down-regulation of MHCI antigen presentation, C-type lectin receptor signaling and granulocyte activation over time. Phagocytosis, interferon-gamma signaling and negative regulation of innate immunity were increasingly up-regulated over time. Individual differentially expressed immune genes implies weak initiation of acute phase proteins with little or no inflammation. Furthermore, gene expression indicates presence of T-cells, NK-like cells, B-cells and monocytes/macrophages. Three <i>MHCI</i> transcripts were up-regulated with <i>B2M</i> and <i>SEC61</i>. Overall, we find no clear immune-related transcriptomic response which could be attributed to Atlantic cod's alternative immune system. However, we cannot rule out that this response is related to vaccination protocol/sampling strategy. Earlier functional studies demonstrate significant memory in Atlantic cod post dip vaccination and combined with our results indicate the presence of other adaptive immunity mechanisms. In particular, we suggest that further investigations should look into CD8+ memory T-cells, γδ T-cells, T-cell independent memory or memory induced through NK-like/other lymphoid cells locally in the mucosal lining for this particular vaccination strategy.

• Nilsson, Anna; Slagsvold, Tore; Røstad, Ole Wiggo; Knudsen, Endre; Jerstad, Kurt & Cadahia, Luis [Show all 10 contributors for this article] (2019). Territory location and quality, together with climate, affect the timing of breeding in the white-throated dipper. Scientific Reports. 9, p. 1–11. doi: 10.1038/s41598-019-43792-5. Full text in Research Archive Show summary

  Recent climate change has led to advanced spring phenology in many temperate regions. The phenological response to variation in the local environment, such as the habitat characteristics of the territories birds occupy, is less clear. The aim of this study is to understand how ecological conditions affect breeding time, and its consequences for reproduction, in a white-throated dipper Cinclus cinclus population in a river system in Norway during 34 years (1978–2011). Hatching date advanced almost nine days, indicating a response to higher temperatures and the advanced phenology in the area. Earlier breeding was found in warm springs and at lower altitudes. High population density facilitated earlier breeding close to the coast. Furthermore, when population density was low, breeding was early at territories that were rarely occupied, while in years with high density, breeding was early at territories that were frequently occupied. Also, when population density was low, earlier breeding occurred at territories that on average produced more offspring than other territories, while there was no difference in breeding time in high population years. Selection for early breeding was dependent on spring temperatures and high spring temperatures contributed to higher breeding success during the study period. We found that breeding phenology may have strong effects on fitness in the white-throated dipper, and thus that breeding time is an important ecological factor in a species that feeds mainly on aquatic rather than terrestrial prey.

• Solbakken, Monica Hongrø; Jentoft, Sissel; Reitan, Trond; Mikkelsen, Helene; Gregers, Tone Fredsvik & Bakke, Oddmund [Show all 8 contributors for this article] (2019). Disentangling the immune response and host-pathogen interactions in Francisella noatunensis infected Atlantic cod. Comparative Biochemistry and Physiology - Part D:Genomics and Proteomics. ISSN 1744-117X. 30, p. 333–346. doi: 10.1016/j.cbd.2019.04.004. Full text in Research Archive Show summary

  The genetic repertoire underlying teleost immunity has been shown to be highly variable. A rare example is Atlantic cod and its relatives Gadiformes that lacks a hallmark of vertebrate immunity: Major Histocompatibility Complex class II. No immunological studies so far have fully unraveled the functionality of this particular immune system. Through global transcriptomic profiling, we investigate the immune response and host-pathogen interaction of Atlantic cod infected with the facultative intracellular bacterium <i>Francisella noatunensis</i>. We find that Atlantic cod displays an overall classic innate immune response with inflammation, acute-phase proteins and cell recruitment through up-regulation of e.g. <i>IL1B</i>, fibrinogen, cathelicidin, hepcidin and several chemotactic cytokines such as the neutrophil attractants <i>CXCL1</i> and <i>CXCL8</i>. In terms of adaptive immunity, we observe up-regulation of interferon gamma followed by up-regulation of several <i>MHCI</i> transcripts and genes related to antigen transport and loading. Finally, we find up-regulation of immunoglobulins and down-regulation of T-cell and NK-like cell markers. Our analyses also uncover some contradictory transcriptional findings such as up-regulation of anti-inflammatory <i>IL10</i> as well as down-regulation of the NADPH oxidase complex and myeloperoxidase. This we interpret as the result of host-pathogen interactions where <i>F. noatunensis</i> modulates the immune response. In summary, our results suggest that Atlantic cod mounts a classic innate immune response as well as a neutrophil-driven response. In terms of adaptive immunity, both endogenous and exogenous antigens are being presented on MHCI and antibody production is likely enabled through direct B-cell stimulation with possible neutrophil help. Collectively, we have obtained novel insight in the orchestration of the Atlantic cod immune system and determined likely targets of <i>F. noatunensis</i> host-pathogen interactions.

• Liow, Lee Hsiang; Reitan, Trond; Voje, Kjetil L.; Taylor, Paul D. & Martino, Emanuela Di (2019). Size, weapons, and armor as predictors of competitive outcomes in fossil and contemporary marine communities. Ecological Monographs. ISSN 0012-9615. p. 1–15. doi: 10.1002/ecm.1354. Full text in Research Archive
• Reitan, Trond & Liow, Lee Hsiang (2019). layeranalyzer: inferring correlative and causal connections from time series data in R. Methods in Ecology and Evolution. 10(12), p. 2183–2188. doi: 10.1111/2041-210X.13299. Full text in Research Archive Show summary

  1. Distinguishing correlative and causal connections among time series is an important challenge in evolutionary biology, ecology, macroevolution and palaeobiology. 2. Here, we present layeranalyzer, an r package that uses linear stochastic differential equations as a tool for parametrically describing evolutionary and ecological processes and for modelling temporal correlation and Granger causality between two or more time series. 3. We describe the basic functions in layeranalyzer and briefly discuss modelling strategies by demonstrating our tool with three disparate case studies. First, we model a single time series of phenotypic evolution in a bird species; second, we extract cyclical connections in the well‐known hare‐lynx dataset; third, we infer the correlative and causal connections among the genus origination and extinction rates of brachiopods and bivalves. 4. We summarize the advantages and limitations of using linear stochastic differential equations and layeranalyzer for studying correlative and causal connections.

• Ragulina, Galina & Reitan, Trond (2017). Generalized extreme value shape parameter and its nature for extreme precipitation using long time series and the Bayesian approach. Hydrological Sciences Journal. ISSN 0262-6667. 62(6), p. 863–879. doi: 10.1080/02626667.2016.1260134. Full text in Research Archive Show summary

  Assessing the probability of extreme precipitation events is consequential in civil planning. This requires an understanding of how return values change with return periods, which is essentially described by the generalized extreme value (GEV) shape parameter. Some works in the field suggest a constant shape parameter, while our analysis indicates a non-universal value. We re-analysed an older precipitation dataset (169 stations) extended by Norwegian data (71 stations). We showed that while each set seems to have a constant shape parameter, it differs between the two datasets, indicating regional differences. For a more comprehensive analysis of spatial effects, we examined a global dataset (1495 stations). We provided shape parameter maps for two models and found clear evidence that the shape parameter depends on elevation, while the effect of latitude remains uncertain. Our results confirm an explanation in terms of dominating precipitation systems based on a proxy derived from the Köppen-Geiger climate classification.

• Nielsen, Anders; Reitan, Trond; Rinvoll, Andreas & Brysting, Anne Krag (2017). Effects of competition and climate on a crop pollinator community. Agriculture, Ecosystems & Environment. ISSN 0167-8809. 246, p. 253–260. doi: 10.1016/j.agee.2017.06.006. Full text in Research Archive Show summary

  Plant-pollinator interactions are ubiquitous in nature where both wild and domesticated pollinators interact with wild plant communities and entomophilous crops. Honeybees are important pollinators in many crop systems, but recent declines in honeybee stocks in Europe and the US have caused concern about the sustainability of crop systems solely depending on honeybees. In addition, several studies have shown that honeybees might negatively affect native pollinator populations, bumblebees in particular. Here we have studied flower visitation to two raspberry farms and surrounding wildflower communities in SE Norway. Bumblebees were excluded from the raspberry field by means of exploitative competition from honeybees ( > 97% of flower visits in the raspberry fields were conducted by honeybees). More than 55% of the visits recorded in wild plant communities surrounding the farms were conducted by bumblebees, showing that bumblebees were present in the system. Pollinator taxa were affected differently by temperature; honeybee visits showed a unimodal relationship with maximum flower visitation activity at a temperature of 24.1 °C, while flower visits by bumblebees showed a positive, linear relationship with temperature. The effect of temperature was much weaker for bumblebees than for honeybees (∼2.2% of the variation was explained by temperature, compared to ∼46% for honeybees). Farming practice affected flower visitation, as flowers within growing tunnels received fewer visits. However, the number of flower visits, also within the growing tunnels, was far above what other studies have shown to be sufficient for optimal pollination in raspberry. We conclude that the raspberry fields were sufficiently pollinated by honeybees but that the system should be considered vulnerable as it is solely dependent on this particular pollinator species. The honeybees were sensitive to ambient temperature suggesting that they might suffer more from future climate change than bumblebees.

• Hannisdal, Bjarte; Haaga, Kristian Agasøster; Reitan, Trond; Castro, David Diego & Liow, Lee Hsiang (2017). Common species link global ecosystems to climate change: Dynamical evidence in the planktonic fossil record. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 284(1858), p. 1–9. doi: 10.1098/rspb.2017.0722. Full text in Research Archive Show summary

  Common species shape the world around us, and changes in their commonness signify large-scale shifts in ecosystem structure and function. However, our understanding of long-term ecosystem response to environmental forcing in the deep past is centred on species richness, neglecting the disproportional impact of common species. Here, we use common and widespread species of planktonic foraminifera in deep-sea sediments to track changes in observed global occupancy (proportion of sampled sites at which a species is present and observed) through the turbulent climatic history of the last 65 Myr. Our approach is sensitive to relative changes in global abundance of the species set and robust to factors that bias richness estimators. Using three independent methods for detecting causality, we show that the observed global occupancy of planktonic foraminifera has been dynamically coupled to past oceanographic changes captured in deep-ocean temperature reconstructions. The causal inference does not imply a direct mechanism, but is consistent with an indirect, time-delayed causal linkage. Given the strong quantitative evidence that a dynamical coupling exists, we hypothesize that mixotrophy (symbiont hosting) may be an ecological factor linking the global abundance of planktonic foraminifera to long-term climate changes via the relative extent of oligotrophic oceans.

• Reitan, Trond & Liow, Lee Hsiang (2017). An unknown Phanerozoic driver of brachiopod extinction rates unveiled by multivariate linear stochastic differential equations. Paleobiology. ISSN 0094-8373. 43(4), p. 537–549. doi: 10.1017/pab.2017.11. Full text in Research Archive
• Reitan, Trond & Nielsen, Anders (2016). Do not divide count data with count data; a story from pollination ecology with implications beyond. PLOS ONE. 11(2). doi: 10.1371/journal.pone.0149129. Full text in Research Archive Show summary

  Studies in ecology are often describing observed variations in a certain ecological phenomenon by use of environmental explanatory variables. A common problem is that the numerical nature of the ecological phenomenon does not always fit the assumptions underlying traditional statistical tests. A text book example comes from pollination ecology where flower visits are normally reported as frequencies; number of visits per flower per unit time. Using visitation frequencies in statistical analyses comes with two major caveats: the lack of knowledge on its error distribution and that it does not include all information found in the data; 10 flower visits in 20 flowers is treated the same as recording 100 visits in 200 flowers. We simulated datasets with various “flower visitation distributions” over various numbers of flowers observed (exposure) and with different types of effects inducing variation in the data. The different datasets were then analyzed first with the traditional approach using number of visits per flower and then by using count data models. The analysis of count data gave a much better chance of detecting effects than the traditionally used frequency approach. We conclude that if the data structure, statistical analyses and interpretations of results are mixed up, valuable information can be lost.

• Steinbakk, Gunnhildur Högnadóttir; Thorarinsdottir, Thordis Linda; Reitan, Trond; Schlichting, Lena; Hølleland, Sondre & Engeland, Kolbjørn (2016). Propagation of rating curve uncertainty in design flood estimation. Water Resources Research. ISSN 0043-1397. 52(9), p. 6897–6915. doi: 10.1002/2015WR018516. Full text in Research Archive Show summary

  Statistical flood frequency analysis is commonly performed based on a set of annual maximumdischarge values which are derived from stage measurements via a stage-discharge rating curve model.Such design flood estimation techniques often ignore the uncertainty in the underlying rating curve model.Using data from eight gauging stations in Norway, we investigate the effect of curve and sample uncertain-ty on design flood estimation by combining results from a Bayesian multisegment rating curve model and aBayesian flood frequency analysis. We find that sample uncertainty is the main contributor to the designflood estimation uncertainty. However, under extrapolation of the rating curve, the uncertainty bounds forboth the rating curve model and the flood frequency analysis are highly skewed and ignoring these featuresmay underestimate the potential risk of flooding. We expect this effect to be even more pronounced in aridand semiarid climates with a higher variability in floods.

• Wolff, Mareile Astrid; Isaksen, Ketil; Petersen-Øverleir, Asgeir; Ødemark, Karianne; Reitan, Trond & Brækkan, Ragnar (2015). Derivation of a new continuous adjustment function for correcting wind-induced loss of solid precipitation: results of a Norwegian field study. Hydrology and Earth System Sciences (HESS). ISSN 1027-5606. 19(2), p. 951–967. doi: 10.5194/hess-19-951-2015. Full text in Research Archive
• Liow, Lee Hsiang; Reitan, Trond & Harnik, Paul G. (2015). Ecological interactions on macroevolutionary time scales: clams and brachiopods are more than ships that pass in the night. Ecology Letters. ISSN 1461-023X. 18(10), p. 1030–1039. doi: 10.1111/ele.12485. Full text in Research Archive
• Nygård, Ståle; Reitan, Trond; Clancy, Trevor; Nygaard, Vegard; BJØRNSTAD, JOHANNES & Skrbic, Biljana [Show all 9 contributors for this article] (2014). Identifying pathogenic processes by integrating microarray data with prior knowledge. BMC Bioinformatics. 15(1). doi: 10.1186/1471-2105-15-115. Full text in Research Archive Show summary

  Background It is of great importance to identify molecular processes and pathways that are involved in disease etiology. Although there has been an extensive use of various high-throughput methods for this task, pathogenic pathways are still not completely understood. Often the set of genes or proteins identified as altered in genome-wide screens show a poor overlap with canonical disease pathways. These findings are difficult to interpret, yet crucial in order to improve the understanding of the molecular processes underlying the disease progression. We present a novel method for identifying groups of connected molecules from a set of differentially expressed genes. These groups represent functional modules sharing common cellular function and involve signaling and regulatory events. Specifically, our method makes use of Bayesian statistics to identify groups of co-regulated genes based on the microarray data, where external information about molecular interactions and connections are used as priors in the group assignments. Markov chain Monte Carlo sampling is used to search for the most reliable grouping. Results Simulation results showed that the method improved the ability of identifying correct groups compared to traditional clustering, especially for small sample sizes. Applied to a microarray heart failure dataset the method found one large cluster with several genes important for the structure of the extracellular matrix and a smaller group with many genes involved in carbohydrate metabolism. The method was also applied to a microarray dataset on melanoma cancer patients with or without metastasis, where the main cluster was dominated by genes related to keratinocyte differentiation. Conclusion Our method found clusters overlapping with known pathogenic processes, but also pointed to new connections extending beyond the classical pathways.

• Nielsen, Anders; Dauber, Jens; Kunin, William E.; Lamborn, Ellen; Jauker, Birgit & Moora, Mari [Show all 18 contributors for this article] (2012). Pollinator community responses to the spatial population structure of wild plants: A pan-European approach. Basic and Applied Ecology. ISSN 1439-1791. 13(6), p. 489–499. doi: 10.1016/j.baae.2012.08.008. Full text in Research Archive
• Natvig, Bent; Gåsemyr, Jørund Inge & Reitan, Trond (2012). Bayesian Assessment of Availabilities and Unavailabilities of Multistate Monotone Systems. Methodology and Computing in Applied Probability. ISSN 1387-5841. 14(4), p. 1075–1095. doi: 10.1007/s11009-011-9221-3. Full text in Research Archive
• Reitan, Trond; Schweder, Tore & Henderiks, Jorijntje (2012). Phenotypic evolution studied by layered stochastic differential equations. Annals of Applied Statistics. ISSN 1932-6157. 6, p. 1531–1551. doi: 10.1214/12-AOAS559. Full text in Research Archive Show summary

  Time series of cell size evolution in unicellular marine algae (division Haptophyta; Coccolithus lineage), covering 57 million years, are studied by a system of linear stochastic differential equations of hierarchical structure. The data consists of size measurements of fossilized calcite platelets (coccoliths) that cover the living cell, found in deep-sea sediment cores from six sites in the world oceans and dated to irregular points in time. To accommodate biological theory of populations tracking their fitness optima, and to allow potentially interpretable correlations in time and space, the model framework allows for an upper layer of partially observed site-specific population means, a layer of site-specific theoretical fitness optima and a bottom layer representing environmental and ecological processes. While the modeled process has many components, it is Gaussian and analytically tractable. A total of 710 model specifications within this framework are compared and inference is drawn with respect to model structure, evolutionary speed and the effect of global temperature.

• Price, Katie; Jackson, C. R.; Parker, A. J.; Reitan, Trond; Dowd, J. & Cyterski, Mike (2011). Effects of watershed land use and geomorphology on stream low flows during severe drought conditions in the southern Blue Ridge Mountains, Georgia and North Carolina, United States. Water Resources Research. ISSN 0043-1397. 47. doi: 10.1029/2010WR009340. Full text in Research Archive
• Reitan, Trond & Petersen-Øverleir, Asgeir (2011). Dynamic rating curve assessment in unstable rivers using Ornstein-Uhlenbeck processes. Water Resources Research. ISSN 0043-1397. 47. doi: 10.1029/2010WR009504. Full text in Research Archive Show summary

  We use a simple stochastic differential equation model known as the Ornstein-Uhlenbeck model to deal if unstable stage-discharge relationships in hydraulics. Rating curves parameters used for relating stage and discharge are now allowed to change as stochastic processes in time.

• Reitan, Trond & Aas, Kjersti (2011). A new robust importance-sampling method for measuring value-at-risk and expected shortfall allocations for credit portfolios. The Journal of Credit Risk. ISSN 1744-6619. 6(4). Full text in Research Archive
• Reitan, Trond & Aas, Kjersti (2010). A new robust importance-sampling method for measuring value-at-risk and expected shortfall allocations for credit portfolios. The Journal of Credit Risk. ISSN 1744-6619. 6(4), p. 113–149. Full text in Research Archive
• Reitan, Trond & Aas, Kjersti (2010). A New Robust Importance Sampling Method for Measuring VaR and ES Allocations for Credit Portfolios. The Journal of Credit Risk. ISSN 1744-6619. 6(4). Full text in Research Archive Show summary

  The paper explores different ways to estimate Value-at-Risk and similar financial measures using normal copula assumptions. We made a new method based on Markov chain Monte Carlo (MCMC), which we compared to the existing estimation methods and which turned out to work well. We also tried our method on t distribution copulas, and it still seemed to work well.

• Petersen-Øverleir, Asgeir; Soot, André & Reitan, Trond (2009). Bayesian Rating Curve Inference as a Streamflow Data Quality Assessment Tool. Water resources management. ISSN 0920-4741. 23(9), p. 1835–1842. doi: 10.1007/s11269-008-9354-5. Full text in Research Archive
• Petersen-Øverleir, Asgeir & Reitan, Trond (2009). Bayesian analysis of stage-fall-discharge models for gauging stations affected by variable backwater. Hydrological Processes. ISSN 0885-6087. 23(21), p. 3057–3074. doi: 10.1002/hyp.7417. Full text in Research Archive
• Reitan, Trond & Petersen-Øverleir, Asgeir (2009). Bayesian methods for estimating multi-segment discharge rating curves. Stochastic environmental research and risk assessment (Print). ISSN 1436-3240. 23(5), p. 627–642. doi: 10.1007/s00477-008-0248-0. Full text in Research Archive
• Petersen-Overleir, A & Reitan, Trond (2009). Accounting for rating curve imprecision in flood frequency analysis using likelihood-based methods. Journal of Hydrology. ISSN 0022-1694. 366(1-4), p. 89–100. doi: 10.1016/j.jhydrol.2008.12.014. Full text in Research Archive
• Reitan, Trond & Petersen-Øverleir, Asgeir (2008). Bayesian power-law regression with a location parameter, with applications for construction of discharge rating curves. Stochastic environmental research and risk assessment (Print). ISSN 1436-3240. 22. doi: 10.1007/s00477-007-0119-0. Full text in Research Archive
• Burgess, Mark & Reitan, Trond (2007). A risk analysis of disk backup or repository maintenance. Science of Computer Programming. ISSN 0167-6423. 64, p. 312–331. doi: 10.1016/j.scico.2006.06.003. Full text in Research Archive
• Reitan, Trond & Petersen-Overleir, A (2006). Existence of the frequentistic estimate for power-law regression with a location parameter, with applications for making discharge rating curves. Stochastic environmental research and risk assessment (Print). ISSN 1436-3240. 20, p. 445–453. Full text in Research Archive
• Petersen-Overleir, A & Reitan, Trond (2005). Uncertainty in flood discharges from urban and small rural catchments due to inaccurate head measurement. Nordic Hydrology. ISSN 0029-1277. 36. Full text in Research Archive
• Petersen-Øverleir, Asgeir & Reitan, Trond (2005). Objective Segmentation in Compound Rating Curves. Journal of Hydrology. ISSN 0022-1694. 311(1-4), p. 188–201. Full text in Research Archive
• Burgess, Mark; Reitan, Trond; Haugerud, Hårek & Straumsnes, Sigmund (2002). Measuring system normality. ACM Transactions on Computer Systems. ISSN 0734-2071. 20(2), p. 125–160. Full text in Research Archive

View all works in NVA

• Saulsbury, James; Parins-Fukuchi, C. Tomomi; Wilson, Connor J.; Reitan, Trond & Liow, Lee Hsiang (2025). Reply to Johnson: Holistic evaluation of ecological models in paleobiology. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 122(10). doi: 10.1073/pnas.2415303122. Full text in Research Archive
• Wilson, Connor J.; Reitan, Trond & Liow, Lee Hsiang (2023). Using linear stochastic differential equations to guide the search for the drivers of marine origination and extinction. Full text in Research Archive
• Liow, Lee Hsiang; Reitan, Trond & Martino, Emanuela Di (2023). ESTIMATING COMPETITION AND ITS EFFECTS OVER MACROEVOLUTIONARY TIME SCALES. Full text in Research Archive
• Reitan, Trond & Liow, Lee Hsiang (2022). ESTIMATING CHANGING RELATIVE ABUNDANCE IN FOSSIL COMMUNITIES. Full text in Research Archive
• Saulsbury, James Gabriel; Parins-Fukuchi, Caroline; Reitan, Trond; Wilson, Connor J. & Liow, Lee Hsiang (2022). AGE-DEPENDENT EXTINCTION AND THE NEUTRAL THEORY OF BIODIVERSITY. Full text in Research Archive
• Sydenham, Markus A. K.; Chipperfield, Joseph; Dupont, Yoko L.; Eldegard, Katrine; Hegland, Stein Joar & Madsen, Henning Bang [Show all 13 contributors for this article] (2022). Spatial predictions of pairwise plant-pollinator interactions. Full text in Research Archive
• Nilsson, Anna L.K.; Reitan, Trond; Skaugen, Thomas; L'Abee-Lund, Jan Henning; Gamelon, Marlène & Jerstad, Kurt [Show all 11 contributors for this article] (2020). Location Is Everything, but Climate Gets a Share: Analyzing Small-Scale Environmental Influences on Breeding Success in the White-Throated Dipper. Frontiers in Ecology and Evolution. doi: 10.3389/fevo.2020.542846. Full text in Research Archive Show summary

  Ecological and evolutionary effects of environmental variation on wild populations are of particular interest in a changing world. Large-scale environmental indices are classically used as environmental explanatory variables to study climate change effects on wild populations. However, these measures neglect the fact that individuals are affected by the local conditions in their home ranges. Freshwater ecosystems are particularly sensitive to climate change induced alterations in precipitation and discharge affecting lower trophic level prey and cascading up the food chain to impact keystone species. Here, we study how small-scale environmental variation at the level of each territory affects fitness-related traits and in particular reproductive success in the white-throated dipper Cinclus cinclus, a bird dependent on aquatic prey. We take advantage of a long-term study of breeding dippers in a natural river system in Norway (1978–2015). We relate daily river discharge and other important hydrological and territory location variables to clutch and brood size simultaneously, while accounting for male and female age, polygyny, and population density. We also address uncertainty in estimates of both clutch and brood size when modeling reproductive success. The most influential variable overall was the altitudinal gradient, where birds breeding at higher altitudes laid fewer eggs and fledged fewer young. Clutch size decreased with increased population density and high temperatures, while it was positively affected by female age. Brood size varied greatly among territories, where some territories had consistently larger broods than others. Increased minimum and maximum temperatures, river discharge above 10 l/s and increased variability in snow depth had a positive effect on brood size, whereas polygyny had a negative effect. In conclusion, territory-specific variables explained a large amount of the variation in the reproductive output in the dipper, emphasizing the importance of the local habitat, and not only climatic variation, in a keystone species in freshwater ecosystems.

• Tscheulin, Thomas; Tatas, Ch; Reitan, Trond & Nielsen, Anders (2018). Spatiotemporal variation in the visitation of melon flowers by bees. Full text in Research Archive
• Nielsen, Anders; Reitan, Trond & Heiberg, Nina (2018). Optimal temperatur for honningbier i tunnel. Gartner Tidende. ISSN 0106-8393. 2018(4), p. 48–49. Full text in Research Archive
• Nielsen, Anders; Reitan, Trond & Heiberg, Nina (2017). Optimal temperatur for honningbier i tunnel. Norsk frukt og bær. ISSN 1501-4584. 20(2), p. 20–21. Full text in Research Archive
• Nielsen, Anders; Reitan, Trond & Tscheulin, Thomas (2017). Understanding the Unexplainable Nature of an Ecosystem Service. Full text in Research Archive
• Steinbakk, Gunnhildur Högnadóttir; Thorarinsdottir, Thordis Linda; Reitan, Trond; Schlichting, Lena; Hølleland, Sondre & Engeland, Kolbjørn (2016). Propagation of rating curve uncertainty in design flood estimation. Full text in Research Archive
• Nielsen, Anders; Reitan, Trond & Garratt, Michael (2016). The nature of unexplained variation in flower visitation data. If it wasn't complicated enough. Full text in Research Archive
• Nielsen, Anders & Reitan, Trond (2016). The nature of unexplained variation in flower visitation data. If it wasn't complicated enough! Full text in Research Archive
• Nielsen, Anders & Reitan, Trond (2016). Proper use of flower visitation data. Full text in Research Archive
• Reitan, Trond (2015). Further revisiting the bivalve and brachiopod saga; beyond pairwise analysis. Full text in Research Archive
• Reitan, Trond (2015). The nature of unexplained variation in flower visitation data. Full text in Research Archive
• Reitan, Trond & Nielsen, Anders (2015). Do not divide count data with count data; a story from pollination ecology. Full text in Research Archive
• Reitan, Trond & Nielsen, Anders (2015). The nature of unexplained variation in flower visitation data. Full text in Research Archive
• Reitan, Trond & Nielsen, Anders (2015). The nature of unexplained variation in flower visitation data. Full text in Research Archive
• Glad, Per Alve; Stenius, Seija & Reitan, Trond (2015). Nasjonalt formelverk for flomberegning i små nedbørfelt. Full text in Research Archive Show summary

  Rapporten presenterer 165 målestasjoner med små nedbørfelt og data med både døgnoppløsning og oppløsning som er finere enn døgn. For alle stasjonene er den største årlige flommen tatt ut. Det er utført flomfrekvensanalyser for alle målestasjonene. Det er også sett på hvor vidt det er rimelig å anta en fordelingsfamilie for hele landet fremfor å bestemme dette basert på lokal analyse som er vanlig i dag

• Glad, Per Alve; Stenius, Seija & Reitan, Trond (2014). Regionalt formelverk for flomberegning i små nedbørfelt. Full text in Research Archive Show summary

  Rapporten presenterer 165 målestasjoner med små nedbørfelt og data med både døgnoppløsning og oppløsning som er finere enn døgn. For alle stasjonene er den største årlige flommen tatt ut. Det er utført flomfrekvensanalyser for alle målestasjonene. Det er også sett på hvor vidt det er rimelig å anta en fordelingsfamilie for hele landet fremfor å bestemme delte basert på lokal analyse som er vanlig i dag. Del er utført regresjonsanalyser og etablert et formelverk for beregning av middelflom og vekstkurver for å estimere flommer med høyere returperioder. Resultatet er et nasjonalt formelverk for nedbørfelt under 50 km2. Formelverket er testet på over 4000 nedbørfelt for å undersøke utfallsrommet.

• Nygård, Ståle; Reitan, Trond; Clancy, Trevor; Nygaard, Vegard; BJØRNSTAD, JOHANNES & Tønnessen, Theis [Show all 8 contributors for this article] (2011). Identifying pathogenic signaling and regulatory networks by integrating microarray data with prior knowledge. Full text in Research Archive
• Nygård, Ståle; Reitan, Trond; Clancy, Trevor; Nygaard, Vegard; BJØRNSTAD, JOHANNES & Tønnessen, Theis [Show all 8 contributors for this article] (2011). Identifying pathogenic signaling and regulatory networks by integrating microarray data with prior knowledge. Full text in Research Archive
• Reitan, Trond; Schweder, Tore & Henderiks, Jorijntje (2010). Modelling Phenotypic Evolution by Stochastic Differential Equations. Full text in Research Archive Show summary

  In this presentation, we described how to use layered linear stochastic differential equations to model evolutionary processes. This model family was used in order to analyse microfossil data spanning several tens of millions of years.

• Aas, Kjersti & Reitan, Trond (2009). A new robust importance sampling method for measuring VaR and ES allocations for credit portfolios. Full text in Research Archive
• Reitan, Trond (2008). Reasoning Under Uncertainty. Full text in Research Archive Show summary

  In this video series I describe probabilistic reasoning, or as I call it, reasoning under uncertainty. Several basic principles are described as well as the mathematical foundation and a few mathematical as well as categorical results are shown.

• Thorarinsdottir, Thordis Linda; Engeland, Kolbjørn; Lawrence, Deborah; Pedersen, Øyvind; Tveito, Ole Einar & Hellton, Kristoffer Herland [Show all 27 contributors for this article] (2018). Nytt rammeverk for flomestimering i Norge: Sluttrapport fra forskningsprosjektet FlomQ. Energi Norge. ISSN 9788243610484. Full text in Research Archive
• Steinbakk, Gunnhildur Högnadóttir; Thorarinsdottir, Thordis Linda; Reitan, Trond; Schlichting, Lena; Hølleland, Sondre & Engeland, Kolbjørn (2016). Progagation of rating curve uncertainty in design flood estimation. Norsk Regnesentral. Full text in Research Archive Show summary

  Statistical flood frequency analysis is commonly performed based on a set of annual maximum discharge values which are derived from stage measurements via a stagedischarge rating curve model. However, design flood estimation techniques often ignore the uncertainty in the underlying rating curve model. Using data from seven gauging stations in Norway, we investigate the effect of curve and sample uncertainty on design flood estimation. Accounting for curve uncertainty may strongly influence the results if an extrapolation of the rating curve is necessary.

• Natvig, Bent; Gåsemyr, Jørund Inge & Reitan, Trond (2010). Bayesian assessment of availabilities and unavailabilities of multistate monotone systems. Universitetet i Oslo. Full text in Research Archive Show summary

  In the present paper we consider a multistate monotone system of multistate components. Following a Bayesian approach, the ambition is to arrive at the posterior distributions of the system availabilities and unavailabilities to the various levels in a fixed time interval based on both prior information and data on both the components and the system. We argue that a realistic approach is to start out by describing our uncertainty on the component availabilities and unavailabilities to the various levels in a fixed time interval, based on both prior information and data on the components, by the moments up till order m of their marginal distributions. From these moments analytic bounds on the corresponding moments of the system availabilities and unavailabilities to the various levels in a fixed time interval are arrived at. Applying these bounds and prior system information we may then fit prior distributions of the system availabilities and unavailabilities to the various levels in a fixed time interval. These can in turn be updated by relevant data on the system. This generalizes results given in (Natvig and Eide 1987) considering a binary monotone system of binary components at a fixed point of time. Furthermore, considering a simple network system, we show that the analytic bounds can be slightly improved by straightforward simulation techniques.

• Reitan, Trond & Aas, Kjersti (2008). A new robust IS method for measuring VaR and ES allocations for credit portfolios. Norsk Regnesentral. Full text in Research Archive
• Reitan, Trond & Petersen-Øverleir, Asgeir (2005). Estimating the discharge rating curve by nonlinear regression - The frequentist approach. Universitetet i Oslo. Full text in Research Archive Show summary

  This report provides a discussion about the fundamentals of the frequentist approach to the classical nonlinear least squares head - discharge power-law rating curve model, which is a vital procedure in practical hydrology. It is shown that the multivariate minimization problem of the classical nonlinear least squares rating curve model is equivalent to the maximization of a single argument function. We propose four general criteria which the discharge measurements should meet if a trustable frequentist least squares rating curve estimate should exist. The proposed criteria are applied to a large number of real-life discharge measurements, which suggest that the criteria are particularly useful in practice. We also show that the breakdown of one of the criteria implies an exponential law relationship between the head and the discharge. Numerical maximization of the single argument function and inference are discussed.

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