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  • Warner, Emily, et al. (författare)
  • Impacts of soil temperature, phenology and plant community composition on invertebrate herbivory in a natural warming experiment
  • 2021
  • Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 130:9, s. 1572-1582
  • Tidskriftsartikel (refereegranskat)abstract
    • Species and community-level responses to warming are well documented, with plants and invertebrates known to alter their range, phenology or composition as temperature increases. The effects of warming on biotic interactions are less clearly understood, but can have consequences that cascade through ecological networks. Here, we used a natural soil temperature gradient of 5–35°C in the Hengill geothermal valley, Iceland, to investigate the effects of temperature on plant community composition and plant–invertebrate interactions. We quantified the level of invertebrate herbivory on the plant community across the temperature gradient and the interactive effects of temperature, plant phenology (i.e. development stage) and vegetation community composition on the probability of herbivory for three ubiquitous plant species, Cardamine pratensis, Cerastium fontanum and Viola palustris. We found that the percentage cover of graminoids and forbs increased, while the amount of litter decreased, with increasing soil temperature. Invertebrate herbivory also increased with soil temperature at the plant community level, but this was underpinned by different effects of temperature on herbivory for individual plant species, mediated by the seasonal development of plants and the composition of the surrounding vegetation. This illustrates the importance of considering the development stage of organisms in climate change research given the variable effects of temperature on susceptibility to herbivory at different ontogenetic stages.
  • Wickander, Niklas J., et al. (författare)
  • Ecological and evolutionary responses of an arctic plant to variation in microclimate and soil
  • 2021
  • Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 130:2, s. 211-218
  • Tidskriftsartikel (refereegranskat)abstract
    • The arctic and alpine regions are predicted to experience some of the highest rates of climate change, and the arctic vegetation is expected to be especially sensitive to such changes. Understanding the ecological and evolutionary responses of arctic plant species to changes in climate is therefore a key objective. Geothermal areas, where natural temperature gradients occur over small spatial scales, and without many of the confounding environmental factors present in latitudinal and other gradient studies, provide a natural experimental setting in which to examine the response of arctic-alpine plants to increasing temperatures. To test the ecological and evolutionary response of the circumpolar alpine bistort Persicaria vivipara to temperature, we collected plant material and soil from areas with low, intermediate and high soil temperatures and grew them at three different temperatures in a three-factorial growth chamber experiment. At higher experimental soil temperatures, sprouting was earlier and plants had more leaves. Sprouting was earlier in soil originating from intermediate temperature and plants had more leaves when grown in soil originating from low temperatures. We did not find evidence of local adaptation or genetic variation in reaction norms among plants originating from areas with low, intermediate and high soil temperature. Our findings suggest that the alpine bistort has a strong plastic response to warming, but that differences in soil temperature have not resulted in genetic differentiation. The lack of an observed evolutionary response may, for example, be due to the absence of temperature-mediated selection on P. vivipara, the low rate of sexual recombination, or high levels of gene flow balancing differences in selection. When placed within the context of other studies, we conclude that arctic-alpine plant species often show strong plastic responses to spring warming, while evidence of evolutionary responses varies among species.
  • Ågren, Jon, et al. (författare)
  • Mutualists and antagonists drive among-population variation in selection and evolution of floral display in a perennial herb
  • 2013
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 110:45, s. 18202-18207
  • Tidskriftsartikel (refereegranskat)abstract
    • Spatial variation in the direction of selection drives the evolution of adaptive differentiation. However, few experimental studies have examined the relative importance of different environmental factors for variation in selection and evolutionary trajectories in natural populations. Here, we combine 8 y of observational data and field experiments to assess the relative importance of mutualistic and antagonistic interactions for spatial variation in selection and short-term evolution of a genetically based floral display dimorphism in the short-lived perennial herb Primula farinosa. Natural populations of this species include two floral morphs: long-scaped plants that present their flowers well above the ground and short-scaped plants with flowers positioned close to the ground. The direction and magnitude of selection on scape morph varied among populations, and so did the frequency of the short morph (median 19%, range 0-100%; n = 69 populations). A field experiment replicated at four sites demonstrated that variation in the strength of interactions with grazers and pollinators were responsible for among-population differences in relative fitness of the two morphs. Selection exerted by grazers favored the short-scaped morph, whereas pollinator-mediated selection favored the long-scaped morph. Moreover, variation in selection among natural populations was associated with differences in morph frequency change, and the experimental removal of grazers at nine sites significantly reduced the frequency of the short-scaped morph over 8 y. The results demonstrate that spatial variation in intensity of grazing and pollination produces a selection mosaic, and that changes in biotic interactions can trigger rapid genetic changes in natural plant populations.
  • Ågren, Jon, et al. (författare)
  • Selection on floral display in insect-pollinated Primula farinosa : Effects of vegetation height and litter accumulation
  • 2006
  • Ingår i: Oecologia. - 0029-8549 .- 1432-1939. ; 150:2, s. 225-232
  • Tidskriftsartikel (refereegranskat)abstract
    • Grazing reduces litter thickness and vegetation height and may thereby indirectly affect reproductive success and selection on floral characters in plants with prostrate growth. Reductions in litter thickness and vegetation height should influence both the resource status of plants with leaves positioned close to the ground and the significance of inflorescence height for interactions with pollinators and seed predators. We experimentally examined how simulated grazing of surrounding vegetation affected pollen limitation, fruit predation and fecundity of short-scaped and long-scaped Primula farinosa, which differ markedly in floral display and therefore in expected attractiveness to pollinators. Litter removal and pruning of surrounding vegetation increased fruit and seed production per plant in the year of the treatment and the probability of flowering in the following year. Pollen limitation of fruit and seed production was stronger in the short-scaped morph than in the long-scaped morph, but was not significantly affected by litter removal and simulated grazing of surrounding vegetation. Supplemental hand-pollination reduced seed size in the year of the treatment and flowering probability in the second year, and these effects did not differ among scape morphs or grazing treatments. The results suggest that grazing indirectly favours seed production in P. farinosa, mainly because it increases the resource status of plants that escape damage. Contrary to expectation, there was no strong evidence that litter accumulation and tall vegetation increase the severity of pollen limitation or reduce the relative performance of the short-scaped morph.
  • Ågren, Jon, et al. (författare)
  • Spatio-temporal variation in fruit production and seed predation in a perennial herb influenced by habitat quality and population size
  • 2008
  • Ingår i: Journal of Ecology. - 0022-0477 .- 1365-2745. ; 96:2, s. 334-345
  • Tidskriftsartikel (refereegranskat)abstract
    • 1.  In patchily distributed plant species, seed production is likely to be influenced both by local abiotic factors affecting plant size and conditions for fruit maturation, and by population characteristics affecting the intensity of interactions with mutualists and antagonists. However, the relative importance of these effects is poorly known. 2. We used multiple regression and path models to examine the importance of abiotic factors (sun exposure, soil depth) and population characteristics (size, density and connectivity) for variation in flower and fruit production and intensity of seed predation among 39 populations of the long-lived herb Vincetoxicum hirundinaria in three consecutive years. In addition, we manipulated water availability in a field experiment and recorded short-term and long-term effects on fruit output, and conducted a supplemental hand-pollination experiment. 3.  Flower production varied little, while fruit initiation, fruit abortion and fruit predation varied considerably among years. Sun exposure and soil depth affected fruit production per plant indirectly and positively through their effects on flower number. Population density affected fruit production negatively through its effect on flower number. Both fruit initiation and the proportion of fruits attacked by the tephritid fly Euphranta connexa were related positively to population size. 4.  The number of full-size fruits per plant was related positively to sun exposure and population size in two years each, and related negatively to population density in one year. However, because of seed predation, the number of intact mature fruits was related significantly to population characteristics in only one of three years. 5.  The field experiments showed that both shortage of water and insufficient pollination may limit fruit set in V. hirundinaria. 6.  Synthesis. These results demonstrate that the relative importance of local abiotic conditions and population characteristics may vary considerably along the chain of events from flower formation to intact fruit, and also among years. They further show that, at least in species with a naturally patchy distribution, connectivity may be relatively unimportant for variation in reproductive output compared to effects of habitat quality, population size and density.  
  • Östergård, Hannah, 1969- (författare)
  • Plant-seed predator interactions – ecological and evolutionary aspects
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Plant-animal interactions are affected by both abundance and distribution of interacting species and the community context in which they occur. However, the relative importance of these factors is poorly known. I examined the effects of predator host range, environmental factors, host plant populations, plant traits and fruit abortion on the intensity of pre-dispersal seed predation in 46 host populations of the perennial herb Lathyrus vernus. I recorded damage by beetle pre-dispersal seed predators, mainly Apion opeticum and Bruchus atomarius with different host ranges on L. vernus as well as on two additional host plants. Local seed predator population size was mainly influenced by plant population size, current seed production and beetle population size in the previous year, but was not strongly affected by connectivity. The monophagous seed predator was less abundant and had lower densities than the oligophagous. Both predator species had a strong ability to track fluctuations in seed production; intensity of predation increased with relative increases in seed production. Oligophagous predation on L. vernus increased with the abundance of alternative hosts, but presence of L. vernus did not affect predation on alternative hosts. Abundances and trait preferences differed among three co-occurring seed predators, but were also associated with the abundance of the other species. Overall, seed predation influenced selection on flower number. I found clear indications of seed predator offence but no obvious plant defence. The pattern of fruit abortion was associated with reduced plant fitness since the seed predator had an advanced ability to locate fruits with high probability of retention. Taken together, different factors influencing abundance of the seed predator species, different preferences, and context dependent trait selection are likely to result in complex spatio-temporal variation in overall seed losses and trait selection in the common host plant.
  • Östergård, Hannah, et al. (författare)
  • Responses of a specialist and a generalist seed predator to variation in their common resource
  • 2009
  • Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 118:10, s. 1471-1476
  • Tidskriftsartikel (refereegranskat)abstract
    • Fluctuations of resources in time and space will influence not only species abundance but also interactions among species. For plant–consumer interactions, the effects of resource variation have mostly been studied in systems with high resource variability. Systems with moderate variations are less studied, although ecological and evolutionary dynamics of plants and consumers are likely to be affected also by less extreme variability. The effects of variation in a particular resource should depend on consumer diet width.We examined how spatial and temporal variation in seed production in the perennial herb Lathyrus vernus influenced population dynamics and resource utilization in two beetle pre-dispersal seed predators with different host ranges over six years. The monophagous Apion opeticum occupied fewer patches and had lower densities than the oligophagous Bruchus atomarius. The proportion of seeds attacked increased with increases in seed production between years for both seed predators. A possible explanation for these patterns is that population dynamics of beetles are driven largely by local factors and that the same factors influence both beetle performance and seed production. In B. atomarius, patterns may also be influenced by a more pronounced preference for L. vernus in years with a high seed production in L. vernus. We conclude that relatively modest variation in seed production may result in responses that differ in both direction and extent from those usually observed in systems with high variation in seed production.
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