Swedish Polar Research Secretariat
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Using mathematical modelling to investigate the adaptive divergence of whitefish in Fennoscandia
No full textModern speciation theory has greatly benefited from a variety of simple mathematical models focusing on the conditions and patterns of speciation and diversification in the presence of gene flow. Unfortunately the application of general theoretical concepts and tools to specific ecological systems remains a challenge. Here we apply modeling tools to better understand adaptive divergence of whitefish during the postglacial period in lakes of northern Fennoscandia. These lakes harbor up to three different morphs associated with the three major lake habitats: littoral, pelagic, and profundal. Using large-scale individual-based simulations, we aim to identify factors required for in situ emergence of the pelagic and profundal morphs in lakes initially colonized by the littoral morph. The importance of some of the factors we identify and study - sufficiently large levels of initial genetic variation, size- and habitat-specific mating, sufficiently large carrying capacity of the new niche - is already well recognized. In addition, our model also points to two other factors that have been largely disregarded in theoretical studies: fitness-dependent dispersal and strong predation in the ancestral niche coupled with the lack of it in the new niche(s). We use our theoretical results to speculate about the process of diversification of whitefish in Fennoscandia and to identify potentially profitable directions for future empirical research
Responses to declining zoobenthos abundance : Changes over time in diet and growth of Arctic charr (Salvelinus alpinus)
No full textA decline in the density of zoobenthos has taken place in Lake Abiskojaure in the northern Swedish mountains between 1988 and 2019 but no response can be seen in the abundance (CPUE) of Arctic charr (Salvelinus alpinus) that feed mainly on benthic invertebrates. To evaluate if possible shifts in resource use of charr explain this lack of change in population abundance, stomach contents (i.e. diet) of charr between 1985 and 2020 were analyzed. Charr diets changed during the study period, with decreasing contributions to the diet of larger sized prey and increasing contribution of smaller sized prey and zooplankton. A corresponding recent decline in charr growth, size, and condition factor was observed. The proportion of large prey in diets and charr growth both show a hump-shaped relationship with time before the recent decline, indicating consumption of large prey had a positive effect on charr growth. Densities of zooplankton in the lake did not change with time, meaning increases in diet proportions are driven by something else. Declines in nitrogen and phosphorous over time may have contributed to the decline in zoobenthos densities through nutrient limitation of primary production. The results from this study suggest charr has changed diet towards smaller, less energetically efficient prey as a response to declining zoobenthos levels, and that this has had a negative effect on charr growth, size, and condition factor. Additional declines in nutrients and zoobenthos abundance may further worsen charr performance and eventually be manifested as declining charr abundance.
Rhizosphere allocation by canopy-forming species dominates soil CO2 efflux in a subarctic landscape
No full textIn arctic ecosystems, climate change has increased plant productivity. As arctic carbon (C) stocks predominantly are located belowground, the effects of greater plant productivity on soil C storage will significantly determine the net sink/source potential of these ecosystems, but vegetation controls on soil CO2 efflux remain poorly resolved. In order to identify the role of canopy‐forming species in belowground C dynamics, we conducted a girdling experiment with plots distributed across 1 km2 of treeline birch (Betula pubescens ) forest and willow (Salix lapponum ) patches in northern Sweden and quantified the contribution of canopy vegetation to soil CO2 fluxes and belowground productivity. Girdling birches reduced total soil CO2 efflux in the peak growing season by 53%, which is double the expected amount, given that trees contribute only half of the total leaf area in the forest. Root and mycorrhizal mycelial production also decreased substantially. At peak season, willow shrubs contributed 38% to soil CO2 efflux in their patches. Our findings indicate that C, recently fixed by trees and tall shrubs, makes a substantial contribution to soil respiration. It is critically important that these processes are taken into consideration in the context of a greening arctic because productivity and ecosystem C sequestration are not synonymous
Changes in alpine plant population sizes in response to climate change
No full textAlpine plants are assumed to be in particular danger as the climate changes rapidly worldwide. Specialist alpine species in Norrbotten County, northern Sweden have been surveyed over the last 20 years, providing insight to population dynamics and how the plants might respond to the changing climate. The main current threat to the species is habitat destruction as the climate changes. Variation in the number of plants among populations and years, and correlations with environmental variables were examined. Some species had increased while others had decreased over the years. No uniform relationship for all species and populations were discovered, but some of the species exhibited relationships between population size changes and temperature and precipitation. However, if the future climate in Norrbotten County changes according to the predictions, the habitats of the specialist alpine plants may be severely altered, leaving the species with no alternative places to establish and grow
Säsongsbunden samhällsstruktur hos makroevertebrater i ett vattendrag i Arktis
No full textArctic ecosystems are amongst the most vulnerable on Earth to ongoing climate change. While the responses to these changes are well studied on land, less is known about how aquatic communities may respond to a warmer arctic. For stream invertebrate communities, predicting such responses requires basic understanding of how and why different taxonomic groups fluctuate throughout the year. However, few studies have assessed the community dynamics of stream macroinvertebrates across seasons in the Arctic. In this project, I asked how macroinvertebrate community structure changes between months and across seasons in a small Arctic stream in northern Sweden. I expected that community change over time would reflect changes in the supply of organic matter (e.g., leaf litter and algae) to dominant consumers. A total of five transects were sampled for macroinvertebrates each month from July to April using Surber sampling. I used descriptive and multivariate analyses to evaluate changes in community structure between months and seasons. Marked differences in community composition were found between the seasons with detritivores (shredders) dominating the autumn months possibly reflecting input of birch litter and high abundances of grazers during and post winter, possibly reflecting primary production early in spring. Expected climate change effects in the Arctic include warmer temperatures and increases in the terrestrial plant productivity. My results suggest that these shifts could cause changes in stream community composition, driven by increases in deciduous litter inputs that promote shredders and/or by increases in primary production during spring that favour grazers and collector-gatherers, which feed on algae
Expedition report: SWEDARTIC Arctic Ocean 2018
No full textThe expedition Arctic Ocean 2018 with the icebreaker I/B Oden was conducted by the Swedish Polar Research Secretariat in collaboration with National Science Foundation. The main theme for the research was the “Life cycle of clouds in the high Arctic summer with linkages to the microbial life in ocean and ice”.To obtain the best circumstances, I/BO den sailed into the High Arctic where the ship, logistics and scientific staff scouted for asuitable ice floe to sample from. I/B Oden was moored to this floe for approx. 5 weeks in mid-August 2018 such that the scientific work could cover the minimum ice extent period and, most importantly, the refreezing processes. Arctic Ocean 2018 used 5 work packages (WP) to achieve the stated aims of understanding the controlling factors of the proposed negative feedback involving micro-organism and clouds over the Arctic pack ice area. This 5 WP grouping reflects the outcome of the 2 science workshops held prior to the expedition and agreed upon by the participating scientists at the time. WP1: Meteorology and vertical profiling WP2: In-situ characterization of ambient gases, aerosols and clouds WP3: Air-sea interaction WP4: Sea surface microlayer composition WP5: Physics, microbiology and biogeochemistry of ocean water and ice
A study of factors controlling pH in Arctic tundra soils
No full textIn Arctic tundra soils pH serves as an important parameter related to several biotic parameters such as, plant and microbial community composition, biodiversity, nutrient dynamics and productivity. Both abiotic and biotic factors, for instance, base saturation (BS) and plant nutrient uptake may exert a control on soil pH, while it is still unclear to what extent different factors can explain soil pH across different tundra vegetation types. The aim of this study was to investigate to what extent different abiotic and biotic factors influence soil pH in the humus layer across different tundra vegetation types. To do so, eight different tundra vegetation types of which four were underlaid by permafrost (Arctic Alaska) and four with no permafrost (Arctic Sweden) were studied in detail with regard to different properties affecting soil pH. I found that BS was the main factor controlling soil pH across the different vegetation types regardless if the soil was underlain by permafrost or not. Factors, such as, ionic strength or soil water content could not explain any overall pH variation and did only significantly affect the heath soils. Further, the uptake of the most abundant base cations (Ca2+, Mg2+ and K+) from meadow and heath vegetation revealed a high difference between plant functional groups within the same vegetation types. The higher dominance of slow growing woody species in heath vegetation which had a lower uptake corresponded with a lower BC content (especially (Ca2+), pH and BS in the humus soil relative the meadow meanwhile the content of K+ was more than three times higher in heath. Overall, this study suggests that the degree of neutralization (base saturation) regulates pH either via the influence of bedrock and hydrogeochemistry and/or via plant traits that affects the uptake and turnover of base cations.
Autumn phenology of plant communities in the Swedish mountains.
No full textAlthough the autumn phenology of plants is important for a wide range of processes including primary production, carbon sequestration and food availability for herbivores, few studies have addressed spatial variation of autumn phenology and how it changes with climate change. The greatest increase of temperature is predicted near the pole and therefor it is important to estimate how this change will affect Arctic ecosystems. The phenology of vegetation is a valuable indicator of climate change and knowledge about phenology will give indications how the Arctic terrestrial ecosystems will react on climate changes. So far, the spring phenology is well-known compared to the autumn phenology. The aim of this study was to examine how autumn phenology varies among and within locations in forest-tundra ecotone in Northwestern Sweden. The phenology of the plant communities was measured spectrally with the Normalized Difference Vegetation Index [NDVI]. This allow me to directly compare the results of this study with the results from large scale studies using satellite-derived indices. I found that the timing of the autumn senescence varies among locations, topographic positions and vegetation types. These results are important because they contribute to a more nuanced understanding of the processes regulating primary production and food availability for herbivores in the Scandinavian mountains, and provide important information for forecasting the responses of these ecosystems to future climate changes.
The West Palaearctic Pseudodineura and Endophytus species (Hymenoptera, Tenthredinidae)
No full textSix valid species of Pseudodineura are now recognised as occurring in the West Palaearctic, and the only described species of the related genus Endophytus. Larvae of all species are leaf-miners in Ranunculaceae. An identification key to adults is provided, followed by species commentaries which include summarised data on taxonomy, larval host plants, and distribution, with particular reference to Sweden. Whereas identification of some specimens using morphological characters may not be possible, each species apparently has a distinct COI barcode sequence. Pseudodineura heringi(Enslin, 1921) is a new junior synonym of P. parvula (Klug, 1816). Pseudodineura mocsaryi Zombori, 1976 and P. scaligera Zombori, 1979 are new junior synonyms of P. clematidisrectae Hering, 1935. Lectotypes are designated for: Dolerus minutus Hartig, 1837, Pelmatopus clematidis Hering, 1932, P. enslini Hering, 1923, P. heringi Enslin, 1921, and P. mentiens var. konowi Enslin, 1921.The Swedish Nematinae Projec
Seasonality of resource limitation of stream biofilm : Nutrient limitation of an arctic stream in northern Sweden
No full textArctic ecosystems are sensitive to climate change and this biome is experiencing accelerated warming. Climate change in the arctic is projected to further alter precipitation and temperature patterns, which may influence land-water interactions in the future. Such changes have the potential to affect aquatic biofilm communities (i.e., algae, bacteria, and fungi) that form the base of riverine food webs, yet are sensitive to changes in thermal and light regimes, and are potentially limited by macronutrients like carbon (C), nitrogen (N) and phosphorus (P). This study investigated the patterns of resource limitation for autotrophic and heterotrophic biofilms in the Arctic using nutrient diffusing substrata (NDS) in a river network in northern Sweden (Miellajokka). Continuous NDS deployments (March until September) in a birch forest stream were combined with a spatial survey of nutrient limitation in late summer across 20 sites that encompassed a variety of nutrient, light, and temperature combinations. Results show that nutrient limitation of autotrophic processes was common during summer, but also that light inhibited algal growth in early season, and that temperature accelerated rates of activity throughout the growing season. By comparison, heterotrophic processes were less influenced by temperature, unless experimentally supplied with N and P. Alongside persistent N limitation, co-limitation by macronutrients (NP: autotrophic and heterotrophic biofilm, or CNP: heterotrophic biofilm) dominated the overall pattern of limitation over time and space. However, results from the spatial survey suggested that the identity of the primary limiting nutrient can change from N to P, based on differences in chemistry that arise from varying catchment features. As arctic studies are often conducted at individual sites during summer, they may miss shifts in the drivers of stream productivity that arise from variable nutrient, temperature, and light regimes. This study attempted to capture those changes and identify conditions where one might expect to see transitions in the relative importance of physical and chemical factors that limit biofilm development. These results also highlight the challenge of identifying the single most important limiting nutrient (e.g., N versus P) in streams and rivers across the Arctic, as I found that both nutrients could play this role within a single, relatively small drainage system