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Kristjansson B.K.,Holar University College | Malmquist H.J.,Natural History Museum of Kopavogur | Ingimarsson F.,Natural History Museum of Kopavogur | Antonsson T.,Institute of Freshwater Fisheries | And 2 more authors.
Biological Journal of the Linnean Society | Year: 2011

The common occurrence of parallel phenotypic patterns suggests that a strong relationship exists between ecological dynamics and micro-evolution. Comparative studies from a large number of populations under varying sets of ecological drivers could contribute to a better understanding of this relationship. We used data on morphology of arctic charr (Salvelinus alpinus) and ecological factors from 35 Icelandic lakes to test the hypothesis that morphological patterns among monomorphic charr populations from different lakes are related to interlake variation in ecological characteristics. There is extensive phenotypic diversity among populations of Icelandic charr, and populations are easily distinguished based on overall body morphology. The results obtained in the present study showed that the morphological diversity of charr was related to large-scale diversity in lake ecology. Variation in charr morphology was related to water origin (e.g. spring fed versus run-off), bedrock age, and fish community structure. The present study shows how various ecological factors can shape the biological diversity that we observe. © 2011 The Linnean Society of London.

Jeppesen E.,University of Aarhus | Jeppesen E.,Greenland Institute of Natural Resources | Jeppesen E.,Sino Danish Center for Education and Research | Mehner T.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | And 21 more authors.
Hydrobiologia | Year: 2012

Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10-100 years) fish data series from 24 European lakes (area: 0. 04-5,648 km 2; mean depth: 1-177 m; a north-south gradient from Sweden to Spain). Along with an annual temperature increase of about 0. 15-0. 3°C per decade profound changes have occurred in either fish assemblage composition, body size and/or age structure during recent decades and a shift towards higher dominance of eurythermal species. These shifts have occurred despite a reduction in nutrient loading in many of the lakes that should have benefited the larger-sized individuals and the fish species typically inhabiting cold-water, low-nutrient lakes. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal brown trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch has apparently been stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore, Italy. Where introduced, roach seems to take advantage of the higher temperature after years of low population densities. Eurythermal species such as common bream, pike-perch and/or shad are apparently on the increase in several of the lakes. The response of fish to the warming has been surprisingly strong and fast in recent decades, making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems. © 2012 Springer Science+Business Media B.V.

Brodersen J.,University of Aarhus | Brodersen J.,Lund University | Brodersen J.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Malmquist H.J.,Natural History Museum of Kopavogur | And 10 more authors.
Environmental Biology of Fishes | Year: 2012

Trophic niche divergence is considered to be a major process by which species coexistence is facilitated. When studying niche segregation in lake ecosystems, we tend to view the niche on a one-dimensional pelagic-littoral axis. In reality, however, the niche use may be more complex and individual fidelity to a niche may be variable both between and within populations. In order to study this complexity, relative simple systems with few species are needed. In this paper, we study how competitor presence affects the resource use of brown trout (Salmo trutta) in 11 species-poor Faroese lakes by comparing relative abundance, stable isotope ratios and diet in multiple habitats. In the presence of three-spined sticklebacks (Gasterosteus aculeatus), a higher proportion of the trout population was found in the pelagic habitat, and trout in general relied on a more pelagic diet base as compared to trout living in allopatry or in sympatry with Arctic charr (Salvelinus alpinus). Diet analyses revealed, however, that niche-segregation may be more complex than described on a one-dimensional pelagic-littoral axis. Trout from both littoral and offshore benthic habitats had in the presence of sticklebacks a less benthic diet as compared to trout living in allopatry or in sympatry with charr. Furthermore, we found individual habitat specialization between littoral/benthic and pelagic trout in deep lakes. Hence, our findings indicate that for trout populations interspecific competition can drive shifts in both habitat and niche use, but at the same time they illustrate the complexity of the ecological niche in freshwater ecosystems. © 2011 Springer Science+Business Media B.V.

Jeppesen E.,University of Aarhus | Meerhoff M.,University of Aarhus | Meerhoff M.,University of the Republic of Uruguay | Holmgren K.,Institute of Freshwater Research | And 17 more authors.
Hydrobiologia | Year: 2010

Fish play a key role in the trophic dynamics of lakes, not least in shallow systems. With climate warming, complex changes in fish community structure may be expected owing to the direct and indirect effects of temperature, and indirect effects of eutrophication, water-level changes and salinisation on fish metabolism, biotic interactions and geographical distribution. We review published and new data supporting the hypotheses that, with a warming climate, there will be changes in: fish community structure (e. g. higher or lower richness depending on local conditions); life history traits (e. g. smaller body size, shorter life span, earlier and less synchronised reproduction); feeding mode (i. e. increased omnivory and herbivory); behaviour (i. e. stronger association with littoral areas and a greater proportion of benthivores); and winter survival. All these changes imply higher predation on zooplankton and macroinvertebrates with increasing temperatures, suggesting that the changes in the fish communities partly resemble, and may intensify, the effects triggered by eutrophication. Modulating factors identified in cold and temperate systems, such as the presence of submerged plants and winter ice cover, seem to be weaker or non-existent in warm(ing) lakes. Consequently, in the future lower nutrient thresholds may be needed to obtain clear-water conditions and good ecological status in the future in currently cold or temperate lakes. Although examples are still scarce and more research is needed, we foresee biomanipulation to be a less successful restoration tool in warm(ing) lakes without a strong reduction of the nutrient load. © Springer Science+Business Media B.V. 2010.

Petersen A.,Brautarland 2 | Jensen J.-K.,I Geilini 37 | Jenkins P.,Natural History Museum in London | Bloch D.,Foroya Natturugripasavn | Ingimarsson F.,Natural History Museum of Kopavogur
Acta Chiropterologica | Year: 2014

The bats recorded from Iceland, the Faroe Islands, the Shetland Islands, the Orkney Islands, and North Sea installations are reviewed to the end of 2012. In total 12 species have been positively identified, while a considerable proportion of all records are sightings of unidentified bats. Eight of the species are European in origin and four originate from the New World. The largest number of species (8) has been recorded in Iceland, but the greatest number of individuals (180) has been found in Orkney. The bat invasion on the Faroe Islands in 2010 is without precedence, when 70 observations of a minimum of 45 individuals were noted. Most bat observations in the study area occurred in the autumn, with fewer in the spring. Most observations were of single animals, but there were also sightings of up to 12 individuals. There has been a marked increase in bat records in the past three decades. We discuss whether this is a real increase, or due to improved communications, increased public awareness, increased shipping, changes in weather patterns and/or the effects of climate change. All factors appear to be involved. © Museum and Institute of Zoology PAS.

Woods P.J.,Holar University College | Woods P.J.,University of Iceland | Woods P.J.,University of Washington | Skulason S.,Holar University College | And 4 more authors.
Evolutionary Ecology Research | Year: 2012

Background: Finite-mixture models allow sub-populations to be described by separate parameter sets, but do not require the members of sub-populations to be identified. Although the accessibility of these methods has greatly increased in recent years, they are rarely used in studies of ecology and evolution, despite their ability to address basic and common questions regarding the detection of biological diversity. Questions: Do mixture models uncover previously unknown polymorphism of Arctic charr (Salvelinus alpinus) within populations across Iceland? How many groups can be defined based on morphology and growth curves? How differentiated are these groups, and do these groups correspond with other differences, e.g. in life history and habitat use? Data incorporated: Length-at-age, maturity, diet, and morphology data on Arctic charr from 50 lakes sampled in the Ecological Survey of Icelandic Lakes. Analysis methods: We used mixture models to detect polymorphism as the presence of (1) multiple von Bertalanffy growth curves and (2) multimodality in multivariate morphology. We also analysed whether timing of maturity was related to growth and whether sexual dimorphism confounded the results. Dietary patterns were used to confirm a relationship between polymorphism and resource use. Metrics were defined to indicate the relative degree of differentiation. Conclusions: Polymorphism occurs in more lakes than previously documented. In many cases, polymorphism in growth curves or morphology was mirrored by differences in diet. Mixture models are useful tools for identifying multimodal diversity below the species level (e.g. resource polymorphism). These results yield an important first step in understanding how the functional role of a species can vary within and among localities and how this may relate to processes of divergence. © 2012 Pamela J. Woods.

Woods P.J.,Holar University College | Woods P.J.,University of Iceland | Woods P.J.,University of Washington | Skulason S.,Holar University College | And 4 more authors.
Environmental Biology of Fishes | Year: 2013

This study investigated how dietary habits vary with lake characteristics in a fish species that exhibits extensive morphological and ecological variability, the Arctic charr Salvelinus alpinus. Iceland is a hotspot of geological activity, so its freshwater ecosystems vary greatly in physical and chemical attributes. Associations of dietary items within guts of charr were used to form prey categories that reflect habitat-specific feeding behavior. Six prey categories were defined and dominated by snails (Radix peregra), fish (Gasterosteus aculeatus), tadpole shrimp (Lepidurus arcticus), chironomid pupae, pea clam (Pisidium spp.), and the cladoceran Bosmina sp. These reflected different combinations of feeding in littoral stone, offshore benthic, and limnetic habitats. Certain habitat-specific feeding strategies consistently occurred alongside each other within lakes. For example, zooplanktivory occurred in the same lakes as consumption from offshore habitats; piscivory occurred in the same lakes as consumption from littoral benthic habitats. Redundancy analyses (RDA) were used to investigate how lake environment was related to consumption of different prey categories. The RDA indicated that piscivory exhibited by Arctic charr was reduced where brown trout were abundant and lakes were shallow, greater zooplanktivory occurred at lower latitudes and under decreased nutrient but higher silicon dioxide concentrations, and benthic resource consumption was associated with shallower lakes and higher altitudes. This study showed that trends previously observed across fish species were supported at the intraspecific level, indicating that a single species with flexible dietary habits can fill functional roles expected of multiple species in more diverse food webs. © 2013 Springer Science+Business Media Dordrecht.

Woods P.J.,Holar University College | Woods P.J.,University of Iceland | Woods P.J.,University of Washington | Skulason S.,Holar University College | And 4 more authors.
Evolutionary Ecology Research | Year: 2012

Background: The mechanisms causing resource polymorphism are not well understood, but likely include frequency-dependent selection. However, other selection mechanisms could also explain the development of resource polymorphism. Comparative analyses of polymorphic and monomorphic systems are uncommon, making it difficult to distinguish the effects of geography, frequency-dependent selection, niche expansion, and species interactions. Detailing ecological conditions associated with the development of resource polymorphism is necessary to discern demographic and environmental processes that may cause it. Goal: Test for environmental correlations with (a) the presence of resource polymorphism and (b) the degree of differentiation in polymorphic systems, to evaluate the hypotheses that the development of resource polymorphism results from (1) frequency dependence, (2) expansion to include a zooplanktivorous niche, or (3) lower survivorship due to predation on intermediate trait values. Trends in prey consumption, as they related to the presence of polymorphism and limnetic lake characteristics, were also analysed. Organism: Arctic charr (Salvelinus alpinus) populations from lakes sampled in 1994-2004 across Iceland. Methods: Random forest and multiple regression models assessing the presence and degree of resource polymorphism using environmental variables reflecting physical, chemical, and biological conditions. Prey consumption was fitted to the presence of polymorphism and brown trout abundance in negative binomial generalized linear models. The proportion of individuals consuming zooplankton within monomorphic versus polymorphic populations was also measured to test the idea that more widespread zooplankton consumption reflects niche expansion. Results: In Iceland, polymorphic populations tended to occur in cooler lakes with few brown trout (Salmo trutta), a trophic competitor, and in lakes where Arctic charr consumed more zooplankton. Lakes with greater limnetic habitat, fewer nutrients, and greater potential to consume zooplankton appeared to promote resource polymorphism, thereby supporting the presence of niche expansion. The overall results supported the frequency dependence hypothesis, as well as the niche expansion hypothesis in most cases. However, morphs thatdiffered in consumption of fish or chironomid pupae rather than zooplankton were also evident, indicating that mechanisms other than niche expansion may also be important. Relative resource availability and its link with the environment need to be accounted for when trying to predict the occurrence of polymorphism. © 2012 Pamela J. Woods.

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