| 1. |
- 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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| 2. |
- Bezemer, TM, et al.
(författare)
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Plant species and functional group effects on abiotic and microbial soil properties and plant-soil feedback responses in two grasslands
- 2006
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 94:5, s. 893-904
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 1 Plant species differ in their capacity to influence soil organic matter, soil nutrient availability and the composition of soil microbial communities. Their influences on soil properties result in net positive or negative feedback effects, which influence plant performance and plant community composition. 2 For two grassland systems, one on a sandy soil in the Netherlands and one on a chalk soil in the United Kingdom, we investigated how individual plant species grown in monocultures changed abiotic and biotic soil conditions. Then, we determined feedback effects of these soils to plants of the same or different species. Feedback effects were analysed at the level of plant species and plant taxonomic groups (grasses vs. forbs). 3 In the sandy soils, plant species differed in their effects on soil chemical properties, in particular potassium levels, but PLFA (phospholipid fatty acid) signatures of the soil microbial community did not differ between plant species. The effects of soil chemical properties were even greater when grasses and forbs were compared, especially because potassium levels were lower in grass monocultures. 4 In the chalk soil, there were no effects of plant species on soil chemical properties, but PLFA profiles differed significantly between soils from different monocultures. PLFA profiles differed between species, rather than between grasses and forbs. 5 In the feedback experiment, all plant species in sandy soils grew less vigorously in soils conditioned by grasses than in soils conditioned by forbs. These effects correlated significantly with soil chemical properties. None of the seven plant species showed significant differences between performance in soil conditioned by the same vs. other plant species. 6 In the chalk soil, Sanguisorba minor and in particular Briza media performed best in soil collected from conspecifics, while Bromus erectus performed best in soil from heterospecifics. There was no distinctive pattern between soils collected from forb and grass monocultures, and plant performance could not be related to soil chemical properties or PLFA signatures. 7 Our study shows that mechanisms of plant-soil feedback can depend on plant species, plant taxonomic (or functional) groups and site-specific differences in abiotic and biotic soil properties. Understanding how plant species can influence their rhizosphere, and how other plant species respond to these changes, will greatly enhance our understanding of the functioning and stability of ecosystems.
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| 3. |
- Lankinen, Åsa
(författare)
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Root competition influences pollen competitive ability in Viola tricolor: effects of presence of a competitor beyond resource availability?
- 2008
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 96:4, s. 756-765
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Tidskriftsartikel (refereegranskat)abstract
- 1. It has recently been suggested that not only nutrients but also presence of a competitor can influence competitive ability in plants, for example, by strategic changes in allocation to roots (a 'tragedy of the commons' effect). Such strategic changes might occur also in pollen, because this has potential to increase siring success during pollen competition in the pistil. 2. I tested the new hypothesis that pollen competitive ability - a trait often strongly affected by resources of the pollen parent - was influenced by presence of a root competitor using glasshouse-grown Viola tricolor in 2 years. Plants of two maternal families were combined in pairs with their roots either separated or intermingled in the same amount of resources. 3. Maternal families varied in response to root competition, with pollen performance increasing in some families, decreasing in others and unchanged in others. An increase did not mirror a decrease in the competing family, suggesting an explanation beyond differential ability to gain resources. The responses to competitive environment were often consistent across three independent competitors. 4. There was a positive correlation between family responses in pollen performance and family responses in plant size to root competitors. Larger plants did not produce better pollen per se, indicating that the change in pollen performance was not a pure side effect of altered plant size. There was no support for a 'tragedy of the commons' effect on root production. With the experimental design used, an effect of rooting volume could not be completely ruled out. 5. The currently unknown mechanism of the below-ground interactions between plants of V. tricolor was strong enough to change relative pollen competitive ability. These interactions might thus promote variation in the outcome of pollen competition. 6. Synthesis. The results of this study indicate the presence of a competitor on pollen competitive ability beyond the effect of nutrients. Even though the underlying mechanism needs to be explored further, the detected link between pollen competition and soil competition suggests a phenomenon well worth investigating. Further studies may lead to increased understanding of the evolutionary consequences of selection operating in response to interactions with neighbours.
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| 4. |
- Miller, Paul, et al.
(författare)
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Exploring climatic and biotic controls on Holocene vegetation change in Fennoscandia
- 2008
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 96:2, s. 247-259
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Tidskriftsartikel (refereegranskat)abstract
- # 1. We investigated the potential drivers of Holocene vegetation changes recorded at four Scandinavian pollen sites, two in Sweden and two in Finland, at a time when they were largely free of anthropogenic influence. # 2. We used the generalized dynamic vegetation model LPJ-GUESS forced with climate anomaly output from an atmospheric general circulation model to simulate tree species dynamics from 10 000 years ago to the present. The model results were compared to high-resolution pollen accumulation rates gathered at the sites. # 3. Our results indicate that both the observed northern distributional limits of temperate trees, and the limits of Pinus sylvestris and Alnus incana at the tree line, are a result of millennial variations in summer and winter temperatures. The simulation of several distinct trends in species occurrence observed in the pollen record indicates that a time lag due to the slow spreading of species need not be invoked for most species. # 4. Sensitivity studies indicate that competition, natural disturbance and the magnitude of interannual variability play key roles in determining the biomass, establishment and even the presence of species near their bioclimatic limits. However, neither disturbance due to fire nor limits on establishment due to drought were likely to have been major determinants of the observed trends on the timescales considered. # 5. We were unable to limit the modelled occurrence of Picea abies at the study sites to the periods at which it was observed in the pollen records, indicating that we have still not completely understood the driving or limiting factors for Holocene changes in Picea abies abundance. # 6. Synthesis. This study shows that by combining quantitative vegetation reconstructions with a modern, process-based dynamic vegetation model, we may gain new insights into the potential biotic and abiotic drivers of Holocene vegetation dynamics, and their relative importance. This knowledge will be crucial in enabling us to assess more confidently the response of northern European vegetation to future climate change.
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| 5. |
- Partel, M, et al.
(författare)
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Grassland diversity related to the Late Iron Age human population density
- 2007
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 95:3, s. 574-582
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Tidskriftsartikel (refereegranskat)abstract
- 1 Species-rich semi-natural grasslands in Europe developed during prehistoric times and have endured due to human activity. At the same time, intensive grassland management or changes in land use may result in species extinction. As a consequence, plant diversity in semi-natural calcareous grasslands may be related to both historical and current human population density. 2 We hypothesize that current vascular plant diversity in semi-natural calcareous grasslands is positively correlated with the Late Iron Age (c. 800-1000 years ago) density of human settlements (indicated by Late Iron Age fortresses and villages) due to enhancement of grassland extent and species dispersal, and negatively correlated with current human population density due to habitat loss and deterioration. 3 We described the size of the community vascular plant species pool, species richness per 1 m(2) and the relative richness (richness divided by the size of the species pool) in 45 thin soil, calcareous (alvar) grasslands in Estonia. In addition to historical and current human population density we considered simultaneously the effects of grassland area, connectivity to other alvar grasslands, elevation above sea level (indicating grassland age), soil pH, soil N, soil P, soil depth, soil depth heterogeneity, geographical east-west gradient, precipitation and spatial autocorrelation. 4 Both the size of the community species pool and the species richness are significantly correlated with the Late Iron Age human population density. In addition, species richness was unimodally related to the current human population density. The relative richness (species 'packing density') was highest in the intermediate current human population densities, indicative of moderate land-use intensity. 5 Community species pool size decreased non-linearly with increasing soil N, and was highest at intermediate elevation. Small-scale richness was greater when sites were well connected and when the elevation was intermediate. Spatial autocorrelation was also significant for both species pool size and small-scale richness. 6 In summary, human land-use legacy from prehistoric times is an important aspect in plant ecology, which could be an important contributor to the current variation in biodiversity.
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| 6. |
- Prentice, Honor C., et al.
(författare)
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Gene diversity in a fragmented population of Briza media: grassland continuity in a landscape context
- 2006
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 94:1, s. 87-97
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Tidskriftsartikel (refereegranskat)abstract
- 1. We investigated patterns of allozyme variation in demes of the grass Briza media in semi-natural grassland fragments within a mosaic agricultural landscape on the Baltic island of Öland. In the study area, Briza is both a characteristic species of old pastures and an early colonizer of young grasslands developing on previously forested or arable sites. 2 Generalized linear models revealed that descriptors of both present landscape structure and past grassland history are significant determinants of genetic variation in the Briza demes. Genetic structure and levels of within-deme diversity are influenced by the size of grassland fragments, the type of habitat surrounding the grasslands, the size/spatial extent of the demes, the geographic position of the demes and the historical continuity of the grassland fragments. 3 Gene diversity (H) was higher in demes from grassland polygons with a high proportion of adjacent grassland, higher in the more extensive demes, and decreased northwards within the study area. 4 The negative association between the inbreeding coefficient (FIS) and grassland continuity is interpreted in terms of a two-stage colonization process: recruitment into young grasslands leads initially to spatial patchiness, but subsequent selection in maturing pastures occurs within an increasingly uniform and dense sward. 5 Despite a weak overall genetic structure (as indicated by Bayesian cluster analysis) the between-deme FST was significant. Linear discriminant analysis of within-deme allele frequencies grouped the demes according to the age and previous land-use history of their grassland polygons. The convergence of the allele frequency profiles in the younger grasslands towards those of the old grasslands is consistent with convergence of selective regimes as pastures mature towards an increasingly uniform, dense sward and characteristic species assemblage. 6 The genetic composition of demes of a grassland species appears to be influenced by the process of plant community convergence during grassland development – complementing the recent finding that convergence of species composition in experimental assemblages of grassland plants is dependent on the genotypic composition of the component species
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| 7. |
- Bengtson, Per, et al.
(författare)
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Spatial distributions of plants and gross N transformation rates in a forest soil
- 2006
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 94:4, s. 754-764
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 1 This work demonstrates that spatial distribution of understorey vegetation and gross N transformation rates in a mixed beach-oak forest is closely correlated within a distance of a few metres. The findings imply that plant diversity and productivity have a major influence on gross rates of N transformation and vice versa. 2 A geostatistical analysis was used to evaluate the spatial relationships between abundance and species composition of the understorey vegetation and in situ gross N mineralization, NH4+ immobolization and nitrification rates. 3 The gross N transformation rates and the plants spatial variation were correlated within the forest, but plant distribution was more dependent on the fraction of mineralized N that was nitrified than on individual N transformation rates. 4 The total cover of the understorey vegetation varied more in space than the species composition, and was higher in areas with high N transformation rates. 5 Plant species benefiting from high net nitrification rates were more common in areas with a low activity of mineralizing and nitrifying microorganisms, possibly because the net and gross rates were independent of each other. In fact, those species occurred most often in areas in which a large fraction of mineralized N was nitrified. 6 Beech and oak trees also had an effect on the spatial variation of the understorey vegetation. Beech trees provided conditions more suitable for plants benefiting from NO3-, whereas the vascular plant cover was greater under oak trees, probably in response to a higher light interception than under beech trees. 7 Oak generally had a positive impact on gross N transformation rates compared with beech, perhaps reflecting differences in litter quality and climate caused by the two species. 8 The influence of trees alone could not explain the full magnitude of the variation of N transformation rates or the presence of overlapping areas with high mineralization and immobilization rates. These were probably caused by other factors, such as soil moisture content. 9 This work sheds new light on the small-scale spatial links between above-ground plant diversity and abundance, and below-ground microbial N transformations.
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| 8. |
- Bruun, Hans Henrik
(författare)
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Rosa rugosa Thunb. ex Murray
- 2005
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 93:2, s. 441-470
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Forskningsöversikt (refereegranskat)
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| 9. |
- Dorrepaal, E, et al.
(författare)
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Are growth forms consistent predictors of leaf litter quality and decomposability across peatlands along a latitudinal gradient?
- 2005
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 93:4, s. 817-828
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Tidskriftsartikel (refereegranskat)abstract
- Plant growth forms are widely used to predict the effects of environmental changes, such as climate warming and increased nitrogen deposition, on plant communities, and the consequences of species shifts for carbon and nutrient cycling. We investigated whether the relationship between growth forms and patterns in litter quality and decomposition are independent of environmental conditions and whether growth forms are as good as litter chemistry at predicting decomposability. We used a natural, latitudinal gradient in NW Europe as a spatial analogue for future increases in temperature and nitrogen availability. Our screening of 70 species typical of Sphagnum-dominated peatlands showed that leaf litters of Sphagnum mosses, evergreen and deciduous shrubs, graminoids and forbs differed significantly in litter chemistry and that the ranking of the growth forms was independent of the region for all litter chemistry variables. Differences among growth forms were usually larger than differences related to the environmental gradient. After 8 and 20 months incubation in outdoor, Sphagnum-based decomposition beds, growth forms generally differed in decomposability, but these patterns varied with latitude. Sphagnum litters decomposed slower than other litters in all regions, again explaining its high representation in organic deposits of peatlands. Forb litters generally decomposed fastest, while the differences among the other growth forms were small, particularly at higher latitudes. Multiple regression analyses showed that growth forms were better at predicting leaf litter decomposition than chemical variables in warm-temperate peatlands with a high N-load, but less so in the subarctic, low-N region. Our results indicate that environmental changes may be less important in determining ecosystem leaf litter chemistry directly than are their indirect effects through changes in the relative abundance of growth forms. However, climatic and nutritional constraints in high-latitude peatlands promote convergence towards nutrient-efficient plant traits, resulting in similar decomposition rates of vascular growth forms despite differences in litter chemistry. The usefulness of the growth-form concept in predicting plant community controls on ecosystem functioning is therefore somewhat limited.
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| 10. |
- Rinnan, Riikka, et al.
(författare)
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Responses of vegetation and soil microbial communities to warming and simulated herbivory in a subarctic heath
- 2009
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 97:4, s. 788-800
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Tidskriftsartikel (refereegranskat)abstract
- 1. Climate warming increases the cover of deciduous shrubs in arctic ecosystems and herbivory is also known to have a strong influence on the biomass and composition of vegetation. However, research combining herbivory with warming is largely lacking. Our study describes how warming and simulated herbivory affect vegetation, soil nutrient concentrations and soil microbial communities after 10-13 years of exposure. 2. We established a factorial warming and herbivory-simulation experiment at a subarctic tundra heath in Kilpisjarvi, Finland, in 1994. Warming was carried out using the open-top chamber setup of the International Tundra Experiment (ITEX). Wounding of the dominant deciduous dwarf shrub Vaccinium myrtillus L. to simulate herbivory was carried out annually. We measured vegetation cover in 2003 and 2007, soil nutrient concentrations in 2003 and 2006, soil microbial respiration in 2003, and composition and function of soil microbial communities in 2006. 3. Warming increased the cover of V. myrtillus, whereas other plant groups did not show any response. Simulated herbivory of V. myrtillus cancelled out the impact of warming on the species cover, and increased the cover of other dwarf shrubs. 4. The concentrations of NH4+-N, and microbial biomass C and N in the soil were significantly reduced by warming after 10 treatment years but not after 13 treatment years. The reduction in NH4+-N by warming was significant only without simultaneous herbivory treatment, which indicates that simulated herbivory reduced N uptake by vegetation. 5. Soil microbial community composition, based on phospholipid fatty acid (PLFA) analysis, was slightly altered by warming. The activity of cultivable bacterial and fungal communities was significantly increased by warming and the substrate utilization patterns were influenced by warming and herbivory. 6. Synthesis. Our results show that warming increases the cover of V. myrtillus, which seems to enhance the nutrient sink strength of vegetation in the studied ecosystem. However, herbivory partially negates the effect of warming on plant N uptake and interacts with the effect of warming on microbial N immobilization. Our study demonstrates that effects of warming on soil microorganisms are likely to differ in the presence and absence of herbivores.
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