| 1. |
- Diekmann, M, et al.
(författare)
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Prediction of species response to atmospheric nitrogen deposition by means of ecological measures and life history traits
- 2002
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 90:1, s. 108-120
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Tidskriftsartikel (refereegranskat)abstract
- 1 The main objective of this study was to predict the responses of vascular plant species to atmospheric nitrogen deposition and enhanced soil nitrogen levels. The study was carried out in deciduous forests located in three regions of southern Sweden. The abundance of vascular plants, as well as soil pH and nitrogen mineralization rates, were studied in a total of 661 sample plots. 2 We calculated an ecological measure (N-dev value) for all species based on their observed vs. expected nitrification ratios at a given soil pH, and compared its accuracy in predicting abundance changes with results using life history traits. Data from long-term field studies and fertilization experiments were used for validation. 3 N-dev values were positively correlated between neighbouring regions. Values for the southernmost region (Skane) were also positively related to the changes in species frequency observed in large-scale flora surveys and permanent plot studies in that area and with species changes reported from Central Europe. Values from one of two other regions were also consistent. N-dev values from Skane (but no other region) predicted species responses in short-term fertilization experiments. 4 No life history trait was as good a predictor as N-dev, although plant height, leaf anatomy, leaf nitrogen concentration and phenology showed significant correlations. Attributes related to taxonomy, life form, relative growth rate and habitat type showed no agreement with the changes in species abundance. 5 We predict that species with the following attribute syndrome will increase in abundance in response to enhanced nitrogen levels: those favoured by a high soil nitrification ratio relative to other species at a given soil pH, tall stature, hydro- to helomorph anatomy, high leaf nitrogen concentration and a late phenological development.
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| 2. |
- Olsson, Pål Axel, et al.
(författare)
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Occurrence of non-mycorrhizal plant species in south Swedish rocky habitats is related to exchangeable soil phosphate
- 2004
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 92:5, s. 808-815
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Tidskriftsartikel (refereegranskat)abstract
- 1 Plant species that do not typically form mycorrhiza are most likely to be successful under conditions where mycorrhizal fungi are not important for plant coexistence or where the costs of symbiosis outweigh the benefits. The relative occurrence of non-mycorrhizal species was investigated in relationship to exchangeable soil P in herbaceous vegetation, where arbuscular mycorrhizal (AM) associations are generally common. We investigated a total of 439 sites in rocky habitats with sparse vegetation and 110 meadows with dense vegetation. 2 In both rocky habitats and meadows, soil pH was inversely related to exchangeable P. In rocky habitats plant species richness increased greatly between pH 3 and 5 and was also inversely related to P. 3 Plant communities in rocky habitats contained a relatively larger proportion of non-mycorrhizal species than those in meadows. More non-mycorrhizal species occurred at high soil P in the rocky habitats, but no such relation was found in meadows. 4 Non-mycorrhizal species in rocky habitats were most common at low soil pH (high P availability). Plant species that thrived at extreme soil pH were often non-mycorrhizal. 5 The occurrence of fewer non-mycorrhizal plants in meadows than in rocky habitats supports the hypothesis that AM associations are more important in ecosystems with intense competition among plants. In rocky habitats, where abiotic stress may restrict photosynthesis more than nutrient limitation does, it is adaptive for plant species to utilize strategies other than mycorrhiza, particularly at low pH sites where P availability is likely to be adequate.
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| 3. |
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| 4. |
- Waites, Anna R., et al.
(författare)
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Pollinator visitation, stigmatic pollen loads, and among-population variation in seed set in Lythrum salicaria
- 2004
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Ingår i: Journal of Ecology. - Oxford : Blackwell. - 0022-0477 .- 1365-2745. ; 92:3, s. 512-526
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Tidskriftsartikel (refereegranskat)abstract
- Small populations of reward-producing plants are likely to be less attractive to animal pollinators than large populations. As a result, both the quantity and the proportion of compatible pollen deposited on receptive stigmas, and seed output per plant, may be lower in small than in large populations. We examined whether pollinator visitation, pollen deposition and seed set varied with population size in the self-incompatible, tristylous herb Lythrum salicaria, in the Skeppsvik archipelago, northern Sweden. We documented both the number of compatible and incompatible conspecific and heterospecific pollen grains received per flower, seed set and degree of pollen limitation of long-styled plants in 14 populations of different size in two consecutive years, and recorded the visitation rate to individual plants and the number of flowers visited per plant in eight of the populations. As predicted, the visitation rate tended to increase, while the number of flowers visited per plant tended to decrease with increasing population size. However, visitation rates were low overall and temporally highly variable, and these relationships only approached statistical significance. The proportion and absolute number of compatible pollen grains received increased with population size, while the total amounts of conspecific and heterospecific pollen grains received did not vary significantly with population size. The results of supplemental hand-pollinations indicated that the among-population variation in seed set was due to insufficient transfer of compatible pollen in small populations. Seed output increased with the receipt of compatible pollen grains up to about 200 compatible pollen grains received per flower. Between 73% and 98% of the L. salicaria pollen grains received were incompatible, and between 9% and 81% of the pollen grains deposited were heterospecific (population means). However, there was no evidence that the deposition of high numbers of incompatible conspecific and heterospecific pollen grains reduced seed set. In the study populations of L. salicaria, variation in seed output and pollen limitation are apparently governed primarily by factors influencing the transfer of compatible pollen. The results are consistent with the hypothesis that a reduction in the efficiency of pollen transfer among compatible mating types may markedly reduce the reproductive output in small populations of self-incompatible plants. In light of the current rapid transformation and fragmentation of habitats, there is a pressing need both to clarify how the pollination success of plants with different pollination systems is affected by large-scale changes in population size, density and isolation, and to determine the demographic consequences of differences in pollination intensity.
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| 5. |
- Eckstein, Rolf Lutz, et al.
(författare)
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The effect of reproduction on nitrogen use-efficiency of three species of the carnivorous genus Pinguicula
- 2001
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 89:5, s. 798-806
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Tidskriftsartikel (refereegranskat)abstract
- Life history theory predicts that reproduction incurs costs in terms of future growth and survival. In infertile environments reproductive events may accelerate nutrient turnover such that losses of limiting nutrients cannot be replenished by uptake from the soil. We compared the effect of reproduction on nitrogen (N) turnover and N use-efficiency, i.e. the annual dry matter produced per unit N lost, of three carnivorous species of the genus Pinguicula on an infertile subarctic heath. We hypothesized that reproduction should increase N turnover, unless a larger N pool or improved N resorption can compensate for the losses associated with reproduction.These carnivorous herbs showed a nitrogen use strategy similar to that of non-carnivorous plants (herbs and grasses) with a relatively low mean residence time (MRT) of N and a large dry matter productivity per unit N in the plant (annual N productivity). N pool size and the efficiency of N resorption from senescent leaves were similar in reproductive and non-reproductive individuals. Reproductive individuals had significantly larger annual N losses and thus a lower average MRT (0.8 vs. 1.8 years), with values < 1 indicating that the annual N losses are greater than the annual average N pool. Unless plants can enhance their nutrient acquisition, flowering may therefore impact on future growth and survival.This study presents evidence for a direct link between reproduction, reflected in a higher relative allocation to inflorescences, turnover and N use-efficiency; the latter being reduced because of increased N turnover. The ranking of species in terms of reproductive allocation was the reverse of their ranking in terms of their N use-efficiency.
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| 6. |
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| 7. |
- Aerts, R, et al.
(författare)
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Nutritional constraints on Sphagnum-growth and potential decay in northern peatlands
- 2001
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 89:2, s. 292-299
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Tidskriftsartikel (refereegranskat)abstract
- 1 In a 4-year fertilization experiment we studied the effects of increased nitrogen (N) or phosphorus (P) supply on productivity and potential decay in the acrotelm of Sphagnum-dominated Swedish peatlands at northern (low atmospheric N input: low-N site) and southern (high atmospheric N input: high-N site) sites. 2 During the experimental period, there was a severe summer drought at the high-N site which led to strong limitations on Sphagnum growth, especially in the fertilized treatments. There were no significant effects of the nutrient treatments on cumulative length growth and productivity at either site. There were, however, significant effects of site and nutrient treatment on nutritional variables of the Sphagnum species. 3 Nitrogen concentration in living capitula was lower, but P concentration was higher at the low-N site than at the high-N site. However, at both sites N and P concentration in the living capitula showed only minor responses to the nutrient additions. 4 Litter chemistry variables differed significantly among sites and treatments. Sphagnum litter had lower N concentration, higher P concentration, a higher C : N ratio, a lower C : P ratio and a lower N : P ratio at the low-N site. Litter chemistry was significantly affected by the nutrient treatments only at the high-N site, where litter P concentrations increased significantly in the P-fertilized treatment, whereas C : P and N : P ratios showed a significant reduction. 5 Although potential rates of decay of Sphagnum litter were higher at the high-N site than at the low-N site, they were not significantly affected by nutrient additions. Potential decay rates did, however, show significant relations with all the litter chemistry variables we had determined. 6 An increase in nitrogen input to Sphagnum-dominated bogs appears to lead to higher N concentrations in litter and, as a result of dilution, to lower P concentrations. This change in litter chemistry leads to a higher potential decay rate of the litter and this may seriously affect the carbon balance in the acrotelm of these systems. 7 Our results also show that carbon balance characteristics of Sphagnum bogs can be strongly affected by unpredictable extreme climatic conditions. This suggests that the occurrence and consequences of these events need more attention when long-term responses of ecosystems to global change are studied.
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| 8. |
- Aldea, Jorge, et al.
(författare)
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Timing and duration of drought modulate tree growth response in pure and mixed stands of Scots pine and Norway spruce
- 2022
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Ingår i: Journal of Ecology. - : John Wiley & Sons. - 0022-0477 .- 1365-2745. ; 110:11, s. 2673-2683
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is increasing the severity and frequency of droughts around the globe, leading to tree mortality that reduces production and provision of other ecosystem services. Recent studies show that growth of mixed stands may be more resilient to drought than pure stands. The two most economically important and widely distributed tree species in Europe are Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.), but little is known about their susceptibility to drought when coexist.This paper analyses the resilience (resistance, recovery rate and recovery time) at individual-tree level using a network of tree-ring collections from 22 sites along a climatic gradient from central Europe to Scandinavia. We aimed to identify differences in growth following drought between the two species and between mixed and pure stands, and how environmental variables (climate, topography and site location) and tree characteristics influence them.We found that both the timing and duration of drought drive the different responses between species and compositions. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time than Scots pine. Mixtures provided higher drought resistance for both species compared to pure stands, but the benefit decreases with the duration of the drought. Especially climate sensitive and old trees in climatically marginal sites were more affected by drought stress.Synthesis. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change. However, if future droughts become longer, the advantage of mixed stands could disappear which would be especially negative for Norway spruce.
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| 9. |
- Altizer, Sonia, et al.
(författare)
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Do threatened hosts have fewer parasites? : A comparative study in primates
- 2007
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745 .- 0021-8790 .- 1365-2656. ; 76, s. 304-314
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Tidskriftsartikel (refereegranskat)abstract
- 1. Parasites and infectious diseases have become a major concern in conservation biology, in part because they can trigger or accelerate species or population declines. Focusing on primates as a well-studied host clade, we tested whether the species richness and prevalence of parasites differed between threatened and non-threatened host species. 2. We collated data on 386 species of parasites (including viruses, bacteria, protozoa, helminths and arthropods) reported to infect wild populations of 36 threatened and 81 non-threatened primate species. Analyses controlled for uneven sampling effort and host phylogeny. 3. Results showed that total parasite species richness was lower among threatened primates, supporting the prediction that small, isolated host populations harbour fewer parasite species. This trend was consistent across three major parasite groups found in primates (helminths, protozoa and viruses). Counter to our predictions, patterns of parasite species richness were independent of parasite transmission mode and the degree of host specificity. 4. We also examined the prevalence of selected parasite genera among primate sister-taxa that differed in their ranked threat categories, but found no significant differences in prevalence between threatened and non-threatened hosts. 5. This study is the first to demonstrate differences in parasite richness relative to host threat status. Results indicate that human activities and host characteristics that increase the extinction risk of wild animal species may lead simultaneously to the loss of parasites. Lower average parasite richness in threatened host taxa also points to the need for a better understanding of the cascading effects of host biodiversity loss for affiliated parasite species.
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| 10. |
- Amsten, Karin, et al.
(författare)
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Fire- and herbivory-driven consumer control in a savanna-like temperate wood-pasture: An experimental approach
- 2021
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 109, s. 4103-4114
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Tidskriftsartikel (refereegranskat)abstract
- 1. Fire and herbivory are fundamental top-down processes, structuring grass-tree ratios in ecosystems across a diversity of climates. Both are plant consumers that can strongly control the recruitment of woody seedlings and saplings to taller height classes. Without consumer control, many grass-dominated ecosystems would convert into woodlands or forests. While extensively studied in savannas, few have explored the effects of these disturbance regimes on woody recruitment under temperate conditions.2. We exposed saplings of five common European tree species to fire and herbivory in a full factorial experiment in a savanna-like wood-pasture. After 3 years, we evaluated the effects of fire and herbivory on tree sapling survival and height increment. The tree species used, varying in traits and in expected response to fire and herbivory, were Scots pine Pinus sylvestris, Norway spruce Picea abies, European oak Quercus robur, Silver birch Betula pendula and Small-leaved lime Tilia cordata.3. Fire and herbivory had a negative effect on sapling survival for all species except for Q. robur, which was not affected by fire. Both processes reduced height increment of B. pendula, while only herbivory reduced the height increment of P. sylvestris and Q. robur. At the same time, B. pendula and P. sylvestris had some of the highest increments, together with P. abies, which had unaffected height increment in all treatments. T. cordata, on the other hand, had a negative height increment across all treatments. Overall, the combined effect of fire and herbivory was similar to the effect of herbivory alone on both survival and height increment, indicating no additional effect of fire when herbivores were present.4. Synthesis. Our experiment showed how fire and herbivory can strongly affect the recruitment of European temperate tree saplings on a wood-pasture, potentially leading to comparable consumer control described for ecosystems elsewhere (e.g. savannas). Two strategies to deal with fire and herbivory were identified: tolerance (Q. robur) and avoidance (P. sylvestris and B. pendula). We conclude that both fire and herbivory may have been important drivers of structure and species composition in open ecosystems in temperate Europe in the past.
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