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  • 1. Franzen, Markus
    et al.
    Nilsson, Sven G.
    Johansson, Victor
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences.
    Ranius, Thomas
    Population Fluctuations and Synchrony of Grassland Butterflies in Relation to Species Traits2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 10, p. e78233-Article in journal (Refereed)
    Abstract [en]

    Population fluctuations and synchrony influence population persistence; species with larger fluctuations and more synchronised population fluctuations face higher extinction risks. Here, we analyse the effect of diet specialisation, mobility, length of the flight period, and distance to the northern edge of the species' distribution in relation to between-year population fluctuations and synchrony of butterfly species. All butterfly species associated with grasslands were surveyed over five successive years at 19 grassland sites in a forest-dominated landscape (50 km(2)) in southern Sweden. At both the local and regional level, we found larger population fluctuations in species with longer flight periods. Population fluctuations were more synchronous among localities in diet specialists. Species with a long flight period might move more to track nectar resources compared to species with shorter flight period, and if nectar sources vary widely between years and localities it may explain that population fluctuations increase with increasing flight length. Diet generalists can use different resources (in this case host plants) at different localities and this can explain the lower synchrony in population fluctuations among generalist species. Higher degree of synchrony is one possible explanation for the higher extinction risks that have been observed for more specialised species. Therefore, diet specialists are more often threatened and require more conservation efforts than generalists.

  • 2.
    Johansson, Victor
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lönnell, Niklas
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Sundberg, Sebastian
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Release thresholds for moss spores: the importance of turbulence and sporophyte length2014In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 102, no 3, p. 721-729Article in journal (Refereed)
    Abstract [en]

    Adequately describing the dispersal mechanisms of a species is important for understanding and predicting its distribution dynamics in space and time. For wind-dispersed species, the transportation of airborne propagules is comparatively well studied, while the mechanisms triggering propagule release are poorly understood, especially for cryptogams. We investigated the effect of wind speed and turbulence on spore release in the moss Atrichum undulatum in a wind tunnel. Specifically, we measured the amount of spores released from sporophytes when exposed to different wind speeds, in high and low turbulence, using a particle counter. We also related spore release to variation in vibrations of the sporophyte and investigated how the vibrations were affected by wind speed, turbulence and sporophyte length (here including capsule, seta and the top part of the shoot). We show that in high turbulence, the amount of spores released increased with increasing wind speed, while in low turbulence, it did not, within the wind speed range 0.8-4.3ms(-1). However, there was a threshold in wind speed (similar to 2.5-3ms(-1)) before large amounts of spores started to be released in turbulent flow, which coincided with incipient vibrations of the sporophyte. Thresholds in wind variation, rather than average wind speed, seemed to initiate sporophyte vibrations. The vibration threshold increased with decreasing sporophyte length. The deposition of spores near the source decreased with increasing wind variation during the time of their release, based on simulated spore deposition from another study of moss dispersal. Synthesis. We suggest that vibration of moss sporophytes is an important mechanism to regulate spore release and that turbulence and sporophyte length regulate the onset of sporophyte vibration. Spore release thresholds affect dispersal distances and have implications for our understanding and predictions of species distribution patterns, population dynamics and persistence. The mechanisms of this phase of the dispersal process are also important to explore for other species, as there may be a substantial variation depending on the species' different traits.

  • 3.
    Johansson, Victor
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences, Sweden.
    Wikström, Carl-Johan
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Time-lagged lichen extinction in retained buffer strips 16.5 years after clear-cutting2018In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 225, p. 53-65Article in journal (Refereed)
    Abstract [en]

    Tree retention on clear-cuts is a relatively new measure in forestry aimed at lifeboating' forest species during young seral periods. However, the effectiveness of tree retention for maintaining biodiversity for more than a few years is still poorly known. We investigated lichen persistence in retained buffer strips along small streams after clear-cutting of the surrounding forest, and compared with clear-cuts and un-cut references. Specifically, we compared richness and frequency of red-listed/signal species, calicioids and pendulous species before clear cutting with 2.5 years and 16.5 years after clear-cutting, and also analysed their colonization-extinction dynamics over time. The results show that the richness of red-listed/signal species and calicioids in buffer strips had declined significantly after 16.5 years, but not after 2.5 years, while frequency displayed a significant difference already after 2.5 years. The richness of pendulous lichens remained relatively stable over time, but the frequency had declined significantly after 16.5 years. In clear-cuts all groups declined more than in buffer-strips (-2-3.5 times more) and the main decline had occurred already after 2.5 years. References remained stable over time. The colonization-extinctions dynamics reflected the richness declines, with high early extinction in clear cuts and lower but late extinction in buffer-strips, and low (re)colonization. We conclude that retained buffer strips cannot maintain lichen richness over time due to time-lagged extinction, but they are clearly more effective than clear-cuts. Wider buffer strips could potentially reduce tree mortality and decrease lichen extinction. The large amounts of standing dead wood makes buffer strips potential future colonization targets.

  • 4. Ranlund, Åsa
    et al.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Johansson, Victor
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences, Sweden.
    Jonsson, Fredrik
    Nordin, Ulrika
    Gustafsson, Lena
    Epiphytic lichen responses to environmental change due to clear-cutting differ among tree taxa2018In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 29, no 6, p. 1065-1074Article in journal (Refereed)
    Abstract [en]

    Question Many species-rich communities are associated with a foundation species. While we often have detailed information about the foundation species, we know less about its associated species. We explore such a situation, comparing the responses of lichen species associated with different tree taxa, which differ in successional strategy, to the environmental change that takes place when the surrounding trees are clear-cut. Location Boreal forests in Sweden. Methods We illustrated general differences in lichen species composition among four tree taxa and three stand categories using ordination of species occurrences. To analyse responses to clear-cutting we modelled the occurrence probability individually for 144 epiphytic lichen species from the lower 2 m of 2,400 tree trunks of four tree taxa in 130 stands, and compared trees in closed-canopy forests with those retained in logged stands, using Bayesian hierarchical models. Results The composition of lichens on aspen trees deviated clearly from that on the other tree species. Also lichen responses to logging differed among main host tree taxa, where lichen species associated with birches, European aspen, and Scots pine increased in probability of occurrence on trees in logged areas compared to intact forest, while lichen species associated with Norway spruce decreased. We found that time lags for changes in occupancy existed primarily in the increase, but not in the decline, of the groups of lichens associated with different tree taxa. Conclusions Lichens associated with different tree taxa vary in their response to the environmental change brought about by logging, but in a way that differs from the differences in species composition among host trees. Our results highlight the importance of considering the taxa of trees in forest management for the conservation of their associated lichen species. The extent to which the ecology of foundation species influences their associated species merits further inquiry, since such knowledge may facilitate predictions of responses of associated species also in other species-rich communities.

  • 5. Zanatta, Florian
    et al.
    Vanderpoorten, Alain
    Hedenäs, Lars
    Johansson, Victor
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences, Sweden.
    Patiño, Jairo
    Lönnell, Niklas
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Under which humidity conditions are moss spores released? A comparison between species with perfect and specialized peristomes2018In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 8, no 23, p. 11484-11491Article in journal (Refereed)
    Abstract [en]

    Dispersal is a fundamental biological process that can be divided into three phases: release, transportation, and deposition. Determining the mechanisms of diaspore release is of prime importance to understand under which climatic conditions and at which frequency diaspores are released and transported. In mosses, wherein spore dispersal takes place through the hygroscopic movements of the peristome, the factors enhancing spore release has received little attention. Here, we determine the levels of relative humidity (RH) at which peristome movements are induced, contrasting the response of species with perfect (fully developed) and specialized (reduced) peristomes. All nine investigated species with perfect peristomes displayed a xerochastic behavior, initiating a closing movement from around 50%–65% RH upon increasing humidity and an opening movement from around 90% RH upon drying. Five of the seven species with specialized peristomes exhibited a hygrochastic behavior, initiating an opening movement under increasing RH (from about 80%) and a closing movement upon drying (from about 90%). These differences between species with hygrochastic and xerochastic peristomes suggest that spore dispersal does not randomly occur regardless of the prevailing climate conditions, which can impact their dispersal distances. In species with xerochastic peristomes, the release of spores under decreasing RH can be interpreted as an adaptive mechanism to disperse spores under optimal conditions for long‐distance wind dispersal. In species with hygrochastic peristomes, conversely, the release of spores under wet conditions, which decreases their wind long‐distance dispersal capacities, might be seen as a safe‐site strategy, forcing spores to land in appropriate (micro‐) habitats where their survival is favored. Significant variations were observed in the RH thresholds triggering peristome movements among species, especially in those with hygrochastic peristomes, raising the question of what mechanisms are responsible for such differences.

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