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Sökning: WFRF:(Ehrlén Johan) > (2015-2019)

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  • Föregående 123[4]
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  • Thomann, Michel, et al. (författare)
  • Grazers affect selection on inflorescence height both directly and indirectly and effects change over time
  • 2018
  • Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 99:10, s. 2167-2175
  • Tidskriftsartikel (refereegranskat)abstract
    • Selection mediated by one biotic agent will often be modified by the presence of other biotic interactions, and the importance of such indirect effects might change over time. We conducted an 11-yr field experiment to test the prediction that large grazers affect selection on floral display of the dimorphic herb Primula farinosa not only directly through differential grazing damage, but also indirectly by affecting vegetation height and thereby selection mediated by pollinators and seed predators. Exclusion of large grazers increased vegetation height and the strength of pollinator-mediated selection for tall inflorescences and seed-predator-mediated selection for short inflorescences. The direct effect of grazers on selection resulting from differential grazing damage to the two scape morphs showed no temporal trend. By contrast, the increase in vegetation height in exclosures over time was associated with an increase in selection mediated by pollinators and seed predators. In the early years of the experiment, the indirect effects of grazers on selection mediated by pollinators and seed predators were weak, whereas at the end of the experiment, the indirect effects were of similar magnitude as the direct effect due to differential grazing damage. The results demonstrate that the indirect effects of a selective agent can be as strong as its direct effects, and that the relative importance of direct vs. indirect effects on selection can change over time. A full understanding of the ecological processes governing variation in selection thus requires that both direct and indirect effects of biotic interactions are assessed.
  • Toftegaard, Tenna, et al. (författare)
  • Butterfly-host plant synchrony determines patterns of host use across years and regions
  • 2019
  • Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 128:4, s. 493-502
  • Tidskriftsartikel (refereegranskat)abstract
    • Variation in the degree of synchrony among host plants and herbivores can disrupt or intensify species interactions, alter the strength of natural selection on traits associated with phenological timing, and drive novel host plant associations. We used field observations from three regions during four seasons to examine how timing of the butterfly herbivore Anthocharis cardamines relative to six host plant species (Arabis hirsuta, Cardamine pratensis, Arabis glabra, Arabidopsis thaliana, Thlaspi caerulescens and Capsella bursa-pastoris) influenced host species use and the choice of host plant individuals within populations. Butterflies laid a larger fraction of their eggs on species that were closer to the butterfly's preferred stage of development than on other host species. Within host plant populations, butterflies showed a stronger preference for individuals with a late phenology when plants within the population were on average more developed at the time of butterfly flight. Our results suggest that changes in synchrony between herbivores and their host plants are associated with changes in both host species use and the choice of host plant individuals differing in phenology within populations. This is likely to be an important mechanism generating variation in interaction intensities and trait selection in the wild, and therefore also relevant for understanding how anthropogenic induced changes, such as global warming, will influence natural communities.
  • Toftegaard, Tenna, 1982- (författare)
  • Temperature and the synchrony of plant-insect interactions
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Increasing temperatures resulting from climate change have within recent years been shown to advance phenological events in a large number of species worldwide. Species can differ in their response to increasing temperatures, and understanding the mechanisms that determine the response is therefore of great importance in order to understand and predict how a warming climate can influence both individual species, but also their interactions with each other and the environment. Understanding the mechanisms behind responses to increasing temperatures are however largely unexplored.The selected study system consisting of host plant species of the Brassicaceae family and their herbivore Anthocharis cardamines, is assumed to be especially vulnerable to climatic variations. Through the use of this study system, the aim of this thesis is to study differences in the effect of temperature on development to start of flowering within host plant species from different latitudinal regions (study I), and among host plant species (study II). We also investigate whether different developmental phases leading up to flowering differ in sensitivity to temperature (study II), and if small-scale climatic variation in spring temperature influence flowering phenology and interactions with A. cardamines (study III). Finally, we investigate if differences in the timing of A. cardamines relative to its host plants influence host species use and the selection of host individuals differing in phenology within populations (study IV).Our results showed that thermal reaction norms differ among regions along a latitudinal gradient, with the host plant species showing a mixture of co-, counter- and mixed gradient patterns (study I). We also showed that observed differences in the host plant species order of flowering among regions and years might be caused by both differences in the distribution of warm days during development and differences in the sensitivity to temperature in different phases of development (study II). In addition, we showed that small-scale variations in temperature led to variation in flowering phenology among and within populations of C. pratensis, impacting the interactions with the butterfly herbivore A. cardamines. Another result was that the less the mean plant development stage of a given plant species in the field deviated from the stage preferred by the butterfly for oviposition, the more used was the species as a host by the butterfly (study IV). Finally, we showed that the later seasonal appearance of the butterflies relative to their host plants, the higher butterfly preference for host plant individuals with a later phenology, corresponding to a preference for host plants in earlier development stages (study IV).For our study system, this thesis suggest that climate change will lead to changes in the interactions between host plants and herbivore, but that differences in phenology among host plants combined with changes in host species use of the herbivore might buffer the herbivore against negative effects of climate change. Our work highlights the need to understand the mechanisms behind differences in the responses of developmental rates to temperature between interacting species, as well as the need to account for differences in temperature response for interacting organisms from different latitudinal origins and during different developmental phases in order to understand and predict the consequences of climate change. 
  • Toftegaard, Tenna, et al. (författare)
  • Variation in plant thermal reaction norms along a latitudinal gradient - more than adaptation to season length
  • 2016
  • Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 125:5, s. 622-628
  • Tidskriftsartikel (refereegranskat)abstract
    • Little is known about the extent to which observed phenological responses to changes in climate are the result of phenotypic plasticity or genetic changes. We also know little about how plasticity, in terms of thermal reaction norms, vary spatially. We investigated if the thermal reaction norms for flower development of five crucifer species (Brassicaceae) differed among three regions along a south-north latitudinal gradient in replicated experiments. The mean response (elevation) of thermal reaction norms of flowering differed among regions in all study species, while sensitivity of flower development to temperature (slope) differed in only one of the species. Differences in mean responses corresponded to cogradient patterns in some species, but countergradient patterns in other. This suggests that differences among regions were not solely the result of adaptation to differences in the length of the growing season, but that other factors, such as herbivory, play an important role. Differences in development rate within species were mainly explained by variation in early phases of bud formation in some species but by variation in later phases of bud formation in other species. The differences in latitudinal patterns of thermal reaction norms among species observed in this study are important, both to identify agents of selection and to predict short- and long-term responses to a warming climate.
  • Valdés, Alicia, et al. (författare)
  • A natural heating experiment : Phenotypic and genotypic responses of plant phenology to geothermal soil warming
  • 2019
  • Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 25:3, s. 954-962
  • Tidskriftsartikel (refereegranskat)abstract
    • Under global warming, the survival of many populations of sedentary organisms in seasonal environments will largely depend on their ability to cope with warming in situ by means of phenotypic plasticity or adaptive evolution. This is particularly true in high‐latitude environments, where current growing seasons are short, and expected temperature increases large. In such short‐growing season environments, the timing of growth and reproduction is critical to survival. Here, we use the unique setting provided by a natural geothermal soil warming gradient (Hengill geothermal area, Iceland) to study the response of Cerastium fontanum flowering phenology to temperature. We hypothesized that trait expression and phenotypic selection on flowering phenology are related to soil temperature, and tested the hypothesis that temperature‐driven differences in selection on phenology have resulted in genetic differentiation using a common garden experiment. In the field, phenology was related to soil temperature, with plants in warmer microsites flowering earlier than plants at colder microsites. In the common garden, plants responded to spring warming in a counter‐gradient fashion; plants originating from warmer microsites flowered relatively later than those originating from colder microsites. A likely explanation for this pattern is that plants from colder microsites have been selected to compensate for the shorter growing season by starting development at lower temperatures. However, in our study we did not find evidence of variation in phenotypic selection on phenology in relation to temperature, but selection consistently favoured early flowering. Our results show that soil temperature influences trait expression and suggest the existence of genetically based variation in flowering phenology leading to counter‐gradient local adaptation along a gradient of soil temperatures. An important implication of our results is that observed phenotypic responses of phenology to global warming might often be a combination of short‐term plastic responses and long‐term evolutionary responses, acting in different directions.
  • Valdés, Alicia, et al. (författare)
  • Caterpillar seed predators mediate shifts in selection on flowering phenology in their host plant
  • 2017
  • Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 98:1, s. 228-238
  • Tidskriftsartikel (refereegranskat)abstract
    • Variation in selection among populations and years has important implications for evolutionary trajectories of populations. Yet, the agents of selection causing this variation have rarely been identified. Selection on the time of reproduction within a season in plants might differ both among populations and among years, and selection can be mediated by both mutualists and antagonists. We investigated if differences in the direction of phenotypic selection on flowering phenology among 20 populations of Gentiana pneumonanthe during 2 yr were related to the presence of the butterfly seed predator Phengaris alcon, and if butterfly incidence was associated with the abundance of the butterfly's second host, Myrmica ants. In plant populations without the butterfly, phenotypic selection favored earlier flowering. In populations where the butterfly was present, caterpillars preferentially attacked early-flowering individuals, shifting the direction of selection to favoring later flowering. Butterfly incidence in plant populations increased with ant abundance. Our results demonstrate that antagonistic interactions can shift the direction of selection on flowering phenology, and suggest that such shifts might be associated with differences in the community context.
  • Valdés, Alicia, et al. (författare)
  • Direct and plant trait-mediated effects of the local environmental context on butterfly oviposition patterns
  • 2018
  • Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 127:6, s. 825-833
  • Tidskriftsartikel (refereegranskat)abstract
    • Variation in the intensity of plant-animal interactions over different spatial scales is widespread and might strongly influence fitness and trait selection in plants. Differences in traits among plant individuals have been shown to influence variation in interaction intensities within populations, while differences in environmental factors and community composition are shown to be important for variation over larger scales. However, little is still known about the relative importance of the local environmental context vs. plant traits for the outcome of interactions within plant populations. We investigated how oviposition by the seed-predator butterfly Phengaris alcon on its host plant Gentiana pneumonanthe was related to host plant traits and to local environmental variation, as well as how oviposition patterns translated into effects on host plant fruit set. We considered the local environmental context in terms of height of the surrounding vegetation and abundance of the butterfly's second host, Myrmica ants. The probability of oviposition was higher in plants that were surrounded by lower vegetation, and both the probability of oviposition and the number of eggs increased in early-flowering and tall plants with many flowers in the three study populations. Flowering phenology, shoot height and flower production were, in turn, related to higher surrounding vegetation. Myrmica abundance was correlated with vegetation height, but had no effect on oviposition patterns. Oviposition and subsequent seed predation by the caterpillars strongly reduced host plant fruit set. Our results show that plant-animal interactions are context-dependent not only because the context influences the abundance or the behavior of the animal interactor, but also because it influences the expression of plant traits that affect the outcome of the interaction. The results also demonstrate that heterogeneity in environmental conditions at a very local scale can be important for the outcomes of interactions.
  • Valdés, Alicia, et al. (författare)
  • Resource overlap and dilution effects shape host plant use in a myrmecophilous butterfly
  • 2019
  • Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 88:4, s. 649-658
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of consumers on fitness of resource organisms are a complex function of the spatio-temporal distribution of the resources, consumer functional responses and trait preferences, and availability of other resources. The ubiquitous variation in the intensity of species interactions has important consequences for the ecological and evolutionary dynamics of natural populations. Nevertheless, little is known about the processes causing this variation and their operational scales. Here, we examine how variation in the intensity of a consumer-resource interaction is related to resource timing, resource density and abundance of other resources. Using the butterfly consumer Phengaris alcon and its two sequential resources, the host plant Gentiana pneumonanthe and the host ants Myrmica spp., we investigated how butterfly egg-laying depended on focal host plant phenology, density and phenology of neighbouring host plants and host ant abundance. Butterflies preferred plants that simultaneously maximized the availability of both larval resources in time and space, that is, they chose early-flowering plants that were of higher nutritional quality for larvae where host ants were abundant. Both the probability of oviposition and the number of eggs were lower in plant individuals with a high neighbour density than in more isolated plants, and this dilution effect was stronger when neighbours flowered early. Our results show that plant-herbivore interactions simultaneously depend on the spatio-temporal distribution of a focal resource and on the small-scale spatial variation in the abundance of other herbivore resources. Given that consumers have negative effects on fitness and prefer certain timing of the resource organisms, this implies that processes acting at the levels of individuals, populations and communities simultaneously contribute to variation in consumer-mediated natural selection.
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  • Föregående 123[4]
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