| 1. |
- Lönnell, Niklas, et al.
(författare)
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Testing a mechanistic dispersal model against a dispersal experiment with a wind-dispersed moss
- 2015
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 124:9, s. 1232-1240
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Tidskriftsartikel (refereegranskat)abstract
- Wind is the main dispersal agent for a wide array of species and for these species the environmental conditions under which diaspores are released can potentially modify the dispersal kernel substantially. Little is known about how bryophytes regulate spore release, but conditions affecting peristome movements and vibration of the seta may be important. We modelled airborne spore dispersal of the bryophyte species Discelium nudum (spore diameter 25 m), in four different release scenarios, using a Lagrangian stochastic dispersion model and meteorological data. We tested the model predictions against experimental data on colonization success at five distances (5, 10, 30, 50 and 100 m) and eight directions from a translocated point source during seven two-day periods. The model predictions were generally successful in describing the observed colonization patterns, especially beyond 10 m. In the laboratory we established spore release thresholds; horizontal wind speed sd > 0.25 m s(-1) induced the seta to vibrate and in relative humidity < 75% the peristome was open. Our dispersal model predicts that the proportion of spores dispersing beyond 100 m is almost twice as large if the spores are released under turbulent conditions than under more stable conditions. However, including release thresholds improved the fit of the model to the colonization data only minimally, with roughly the same amount of variation explained by the most constrained scenario (assuming both vibration of the seta and an open peristome) and the scenario assuming random release. Model predictions under realised experimental conditions suggest that we had a low statistical power to rank the release scenarios due to the lack of measurements of the absolute rate of spore release. Our results hint at the importance of release conditions, but also highlight the challenges in dispersal experiments intended for validating mechanistic dispersal models.
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| 2. |
- Vrede, Tobias, et al.
(författare)
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Ecological stoichiometry of Eurasian perch : intraspecific variation due to size, habitat and diet
- 2011
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 120:6, s. 886-896
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Tidskriftsartikel (refereegranskat)abstract
- The turnover and distribution of energy and nutrients in food webs is influenced by consumer stoichiometry. Although the stoichiometry of heterotrophs is generally considered to vary only little, there may be intraspecific variation due to factors such as habitat, resources, ontogeny and size. We examined intraspecific variation in Eurasian perch Perca fluviatilis stoichiometry, a common species that exhibits habitat and resource specialization, ontogenetic niche shifts and a large size range. This study investigated the elemental stoichiometry of a wide size range of perch from littoral and pelagic habitats. The mean C:N:P stoichiometry of whole perch was 37:9:1 (molar ratios). However, %C, %P, C:N, C:P and N:P varied with size, morphology, habitat and diet category. These factors together explained 24–40% of the variation in C:N:P stoichiometry. In contrast, perch stoichiometry was not related to diet stoichiometry, suggesting that the former is homeostatically regulated. The results suggest that the high P content of perch may result in stoichiometric constraints on the growth of non-piscivorous perch, and that piscivory is an efficient strategy for acquiring P. Resource polymorphism, individual diet specialization and intraspecific size variation are widespread among animals. Thus changes in stoichiometry with size, habitat, morphology and resource use, and therefore also stoichiometric demands, are probably common.
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| 3. |
- Lankinen, Åsa, et al.
(författare)
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Allocation to pollen competitive ability versus seed production in Viola tricoloras an effect of plant size, soil nutrients and presence of a root competitor
- 2012
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Ingår i: Oikos. - : John Wiley & Sons. - 0030-1299 .- 1600-0706. ; 122:5, s. 779-789
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Tidskriftsartikel (refereegranskat)abstract
- In hermaphroditic plants, the effect of a social environment on sex allocation has not been studied to our knowledge, while in hermaphroditic animals such effects are known to be common. In recent years, studies on root competition beyond the effects of nutrients have shown that plants can respond to their conspecific root competitors (social environment), making it interesting to ask if these effects could also influence sex allocation in addition to more commonly studied factors, such as plant size or resources. In this study on hermaphroditic Viola tricolor, we investigated how plant size, soil nutrients and presence of a root competitor influenced allocation to pollen competitive ability versus seed production, i.e. male and female reproductive functions. We allowed plants to grow in pairs with partly intermingled or separate roots in the same amount of soil. In additional treatments with intermingled roots (as part of the same experiment) one of the two competitors was given combinations of nitrogen (N), phosphorous (P) and micro nutrients. We found that pollen performance but not seed production increased when plants were in contact in the soil. Additionally, pollen performance was negatively correlated to plant size across fertilisation treatments. For seed production, the opposite relation to plant size was seen, indicating that large, fertilized plants invest relatively more in the female function. In conclusion, in violets, sex allocation appears to be size-dependent and influenced by both the presence of a root competitor and by nutrients. These results suggest that social environment can influence sex allocation in plants as well as in animals, indicating that such effects are important to consider in sex allocation studies across taxa.
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| 4. |
- Sundqvist, Maja K., et al.
(författare)
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Interactive effects of vegetation type and elevation on aboveground and belowground properties in a subarctic tundra
- 2011
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Ingår i: Oikos. - Copenhagen : Munksgaard. - 0030-1299 .- 1600-0706. ; 120:1, s. 128-142
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Tidskriftsartikel (refereegranskat)abstract
- An improved knowledge of how contrasting types of plant communities and their associated soil biota differ in their responses to climatic variables is important for better understanding the future impacts of climate change on terrestrial ecosystems. Elevational gradients serve as powerful study systems for answering questions on how ecological processes can be affected by changes in temperature and associated climatic variables. In this study, we evaluated how plant and soil microbial communities, and abiotic soil properties, change with increasing elevation in subarctic tundra in northern Sweden, for each of two dominant but highly contrasting vegetation types, namely heath (dominated by woody dwarf shrubs) and meadow (dominated by herbaceous species). To achieve this, we measured plant community characteristics, microbial community properties and several soil abiotic properties for both vegetation types across an elevation gradient of 500 to 1000 m. We found that the two vegetation types differed not only in several above- and belowground properties, but also in how these properties responded to elevation, pointing to important interactive effects between vegetation type and elevation. Specifically, for the heath, available soil nitrogen and phosphorus decreased with elevation whereas fungal dominance increased, while for the meadow, idiosyncratic responses to elevation for these variables were found. These differences in belowground responses to elevation among vegetation types were linked to shifts in the species and functional group composition of the vegetation. Our results highlight that these two dominant vegetation types in subarctic tundra differ greatly not only in fundamental aboveground and belowground properties, but also in how these properties respond to elevation and are therefore likely to be influenced by temperature. As such they highlight that vegetation type, and the soil abiotic properties that determine this, may serve as powerful determinants of how both aboveground and belowground properties respond to strong environmental gradients.
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| 5. |
- Hambäck, Peter, et al.
(författare)
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Mating affects resource selection and modulates associational effects between neighbouring resources
- 2017
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 126, s. 1708-1716
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Tidskriftsartikel (refereegranskat)abstract
- Associational effects occur when the attack rate on a resource depends on neighbouring resources in the environment. These effects are predicted to result from mismatches experienced by the consumer organism in resource selection along hierarchical search levels. As resource selection depends on sensory information used during search behaviour, we expected that different physiological states of an insect might modulate the outcome of associational effects due to differences in resource selection. We used Drosophila melanogaster, as a model organism for olfactory-guided behaviour in insects, to study the effects of mating induced behavioural changes on associational effects between two alternative resources. We found that mating has no effect on the ability of D. melanogaster to locate resource patches, but rather affects the perception of the resources within the patch. Consequently, we only found associational effects in the experiments with unmated females and not in the experiments with mated females. Our results suggest that the lack of associational effects for mated females resulted from changes in the use of short-range olfactory cues, leading to random selection among the resources. In conclusion, our results suggest that the physiological state of an insect modulates associational effects by affecting resource selection rates within the patch.
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| 6. |
- von Euler, Tove, 1976-, et al.
(författare)
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Floral display and habitat quality affect cost of reproduction in Primula farinosa
- 2012
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 121:9, s. 1400-1407
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Tidskriftsartikel (refereegranskat)abstract
- Costs of reproduction should depend on resource availability and on reproductive effort, which in turn may depend on traits influencing reproductive success. Therefore, variation in both habitat quality and reproductive traits should be considered when assessing reproductive costs. We investigated the effect of habitat quality and floral display on the costs of reproduction in the perennial herb Primula farinosa. In the study area, P. farinosa occurs in habitats that differ in water availability, which strongly influences plant performance. Furthermore, it displays a scape length dimorphism, with two distinct scape morphs differing in attractiveness to pollinators and reproductive success. To test the hypothesis that the cost of fruit production is higher in the long-scaped than in the short-scaped morph, and depends on water availability, we manipulated reproductive investment in eight P. farinosa populations along a gradient of soil moisture. Fruit set was higher in long-scaped individuals, and prevention of fruit set increased flower production in the following year among long-scaped, but not among short-scaped plants. Furthermore, costs of fruit production were evident at low and high moisture levels but not at intermediate levels. The results demonstrate an association between a genetically determined difference in floral display and cost of reproduction, and suggest that costs of reproduction are non-linearly related to water availability. They thus indicate links between the evolution of plant reproductive traits and plant life histories, and between habitat quality and optimal life history.
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| 7. |
- Andersson, Petter, et al.
(författare)
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How insects sense olfactory patches : the spatial scaling of olfactory information
- 2013
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 122:7, s. 1009-1016
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Tidskriftsartikel (refereegranskat)abstract
- When searching for resources in heterogeneous environments, animals must rely on their abilities to detect the resources via their sensory systems. However, variation in the strength of the sensory cue may be mediated by the physical size of the resource patch. Patch detection of insects are often predicted by the scaling of sensory cues to patch size, where visual cues has been proposed to scale proportional to the diameter of the patch. The scaling properties of olfactory cues are, however, virtually unknown. Here, we investigated scaling rules for olfactory information in a gradient of numbers of odour sources, relevant to odour-mediated attraction under field conditions. We recorded moth antennal responses to sex pheromones downwind from pheromone patches and estimated the slope in the scaling relationship between the effective length of the odour plumes and the number of odour sources. These measurements showed that the effective plume length increased proportional to the square root of the number of odour sources. The scaling relationship, as estimated in the field experiment, was then evaluated against field data of the slope in the relationship between trap catch and release rate of chemical attractants for a wide range of insects. This meta-analysis revealed an average slope largely consistent with the estimated scaling relationship between the effective plume length and the number of odour sources. This study is the first to estimate the scaling properties of olfactory cues empirically and has implications for understanding and predicting the spatial distributions of insects searching by means of olfactory cues in heterogeneous environments.
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| 8. |
- Albrectsen, Benedicte R., 1960-, et al.
(författare)
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Nutrient addition extends flowering display, which gets tracked by seed predators, but not by their parasitoids
- 2008
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Ingår i: Oikos. - : Wiley-Blackwell. - 0030-1299 .- 1600-0706. ; 117, s. 473-480
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Tidskriftsartikel (refereegranskat)abstract
- Although phenological matching between two and three trophic interactions has received some attention, it has largely been disregarded in explaining the lack of strong cascade dynamics in terrestrial systems. We studied the response of the specialist seed predator, Paroxyna plantaginis (Tephritidae) and associated generalist parasitoids (Chalcidoidea) to controlled fertilisation of individuals of naturally growing Tripolium vulgare (Asteraceae) on four island populations (Skeppsvik Archipelago, Sweden). We consistently found evidence of nutrient limitation: fertilised plants increased their biomass, produced more capitula (the oviposition units for tephritid flies), were more at risk of attack by the tephritids, and puparia were heavier in fertilised plants. During some parts of the season tephritids became more heavily parasitized, supporting the presence of cascade dynamics, however net parasitism over season decreased in response to nutrient addition. We found no evidence that capitulum size complicated parasitoid access to the tephritids, however the extended bud production prolonged the flowering season. Thus, tephritids utilized the surplus production of capitula throughout the entire season, while parasitoids did not expand their oviposition time window accordingly. Implications for top down regulation and cascade dynamics in the system are discussed.
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| 9. |
- Bengtson, Per, et al.
(författare)
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Relieving substrate limitation-soil moisture and temperature determine gross N transformation rates
- 2005
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 111:1, s. 81-90
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Tidskriftsartikel (refereegranskat)abstract
- A field experiment was designed with the objective to reveal the interactions between soil moisture, temperature, total, dissolved, and phosphate buffer extractable C and N, and microbial activity in the control of in situ gross N mineralization and immobilization rates in a deciduous forest. We had three alternative hypotheses to explain variations of the gross N transformations: 1) microorganisms are C limited, 2) microorganisms are N limited, or 3) neither C nor N limit the microorganisms but moisture and temperature conditions. Each hypothesis had specific criteria to be fulfilled for its acceptance. The results demonstrated that gross N transformation rates were more dependent on and variable with soil moisture and temperature than the size of the different C and N pools. The immobilization of N was dependent on the gross mineralization rate, suggesting that the production of enzymes for mineralization of organic N and the immobilization of N from the surrounding soil is disconfirmed when the intracellular N content of the microorganisms is sufficiently high. If the microorganisms are starved for N, enzyme systems involved in both the assimilation and mineralization of N are activated. The mean in situ gross N mineralization rate was two orders of magnitude higher than the natural N deposition in the area and the N addition in the NITREX experiments, meaning that a reduction in the gross N mineralization rate of about 1% would be enough to compensate for the addition of inorganic N. This decrease would hardly be detectable given the great spatial and temporal variability of N transformation rates.
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| 10. |
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