| 1. |
- Jonsson, Micael, et al.
(författare)
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Divergent responses of beta-diversity among organism groups to a strong environmental gradient
- 2016
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Ingår i: Ecosphere. - : Wiley. - 2150-8925 .- 2150-8925. ; 7:10
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Tidskriftsartikel (refereegranskat)abstract
- A limited understanding of how variation in the species composition among communities (i.e., beta-diversity) changes along natural environmental gradients, and the mechanisms responsible, inhibits our ability to understand large-scale biodiversity change resulting from either natural or anthropogenic drivers. Therefore, our aim was to test key drivers of beta-diversity patterns along a strong, natural environmental gradient for seven widely different organisms groups, that is, root-associated fungi, litter fungi, soil nematodes, vascular plants, epiphytic lichens, beetles, and spiders. Using previously published community-level data from boreal-forested islands, we calculated alpha-diversity and beta-diversity for each of the seven organism groups. Out of several available environmental variables, we identified four variables, that is, ecosystem age, total C storage, net primary productivity (NPP), and N-to-P ratio, as potential predictors of variation in beta-diversity. We found that ecosystem age was the variable with the highest overall importance. We then used two different methods to quantify the relative importance of stochastic and deterministic processes underlying patterns in beta-diversity along the ecosystem age gradient, and our detailed knowledge based on prior data collection in the study system to mechanistically explain among-group differences in these patterns. We found divergent responses in beta-diversity along the age gradient for the seven different organism groups, due to among-group differences in the relative importance of deterministic vs. stochastic community assembly, and attributed these results to reliance on resources from different energy channels that are not always related to NPP. Our results highlight the necessity to consider the importance of taxon-specific resources, and not only NPP, to obtain an understanding of beta-diversity patterns among organism groups and ecosystems, as well as large-scale patterns in biodiversity. They therefore also suggest that management and protection of beta-biodiversity in the landscape requires explicit consideration of a wide range of habitats.
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| 2. |
- Kumordzi, Bright Boye, et al.
(författare)
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Changes in local-scale intraspecific trait variability of dominant species across contrasting island ecosystems
- 2014
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Ingår i: Ecosphere. - 2150-8925. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- There is growing recognition of the need to incorporate intraspecific trait variability (ITV) into trait-based studies to improve understanding of community assembly and how plant communities drive ecosystem processes. However, most studies have focused on ITV across plant communities, with few quantifying it at local scales. Further, little is known about how ITV at local scales differs among communities or across environmental gradients. Here, we studied a well characterized 5000-year-old chronosequence involving 30 islands that differed greatly in size, soil fertility, spatial heterogeneity, and species diversity. On each island we measured foliar and litter (including nutrient resorption) traits for ten individuals for each of three species that occur on all islands, i.e., Betula pubescens, Vaccinum myrtillus and Vaccinium vitis-idaea. For each trait for each species we estimated its within- island mean, and coefficient of variation as a measure of local scale ITV. We predicted within- island ITV should be highest for larger islands that have the greatest spatial heterogeneity of soil resources but lowest species diversity. Further, we predicted that the species most dominant in the most resource heterogeneous environment (V. myrtillus) should have the greatest within- island ITV. First, we found that within- island ITV of foliar traits was generally unresponsive to island size, while for litter traits it was responsive to island size only for V. myrtillus in a direction consistent with our prediction. The within- island ITV of resorption efficiency of C,N and P for the three species was often responsive to island size, but not in a consistent direction. Second, against our prediction, V. myrtillus had the lowest within- island ITV for most traits, but its within- island ITV was generally more responsive than that of the other species to island size. While plant traits are well known to vary among and within species at broad spatial scales across environmental gradients, our results show that at local scales, ITV can also be highly responsive to fine scale environmental gradients, particularly for litter and nutrient resorptive traits. Understanding how local scale ITV varies across communities offers opportunities for improving our understanding of what drives community assembly, functional diversity and ecosystem processes.
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| 3. |
- Kumordzi, Bright Boye
(författare)
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Distinct physiological responses underlie defoliation tolerance in African lawn and bunch grasses
- 2013
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Ingår i: International journal of plant sciences. - : University of Chicago Press. - 1058-5893 .- 1537-5315. ; 174, s. 769-778
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Tidskriftsartikel (refereegranskat)abstract
- Conclusions. The varied responses of lawn and bunch grasses to defoliation appear to arise from their different investments in defense and carbon assimilation subsequent to defoliation. Bunch grasses invest relatively more in carotenoid production, likely as a mechanism to enhance regrowth and protect costly leaves from photodamage. Moreover, bunch grasses maintain efficient carbon assimilation by structural adjustments in leaves (decreasing LDMC subsequent to defoliation), while lawn grasses maintain efficient water use by increasing leaf [N] subsequent to defoliation. Thus, we conclude that a key difference between lawn and bunch grasses is not defoliation tolerance per se but physiological adaptations that constrain them to environments with different moisture availability subsequent to defoliation.
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| 4. |
- Kumordzi, Bright Boye
(författare)
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Ecological significance of within-species leaf trait variability : a test using an island area gradient
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is growing recognition of the need to incorporate within-species trait variability into trait-based studies to improve understanding of community assembly and how plant communities drive ecosystem processes. Given that many plant species can occupy a wide range of environmental conditions, studies that have traditionally focused solely on between-species trait variability and neglected within-species trait variability could lead to an incomplete picture of how plant traits influence community- and ecosystem-level properties. In this thesis, within-species trait variability of all component species across a well-studied system of 30 forested lake islands in the boreal zone of northern Sweden were characterized to understand how differences among individual species traits contribute to community level properties and community assembly. Collectively, the islands represent a long-term chronosequence across which there are large changes in plant community composition, diversity and above- and belowground resource availability and heterogeneity. Significant within-species trait variability was found among all dominant species that were widespread across the chronosequence. In addition, within-species trait variability was highly responsive to differences in environmental conditions among ecosystems, in a manner mostly consistent with patterns observed at the across- species level. Across contrasting environments, trait variability within species sometimes explained a greater amount of variation in overall community-level responses than did among-species variation. There was also significant within-species variation in biomass allocation patterns of co-occurring dominant dwarf shrub species across the chronosequence. This, together with directional shifts in within- and between-species functional trait diversity of both dominant and subordinate species across the gradient, provides insights on how changes in resource availability drive community trait composition, species coexistence and consequently community responses. These findings overall highlight the importance of within-species variability for understanding the responses of whole plant communities to environmental changes, and potentially to ongoing global changes. Further, given the importance of plant traits in governing ecosystem processes such as net primary productivity, carbon sequestration, biogeochemical cycling and decomposition, knowledge of the extent and magnitude of within-species trait variability is imperative for better understanding these processes and their drivers, especially in ecosystems with low species diversity and turnover such as boreal forests.
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| 5. |
- Kumordzi, Bright Boye, et al.
(författare)
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Linkage of plant trait space to successional age and species richness in boreal forest understorey vegetation
- 2015
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 103, s. 1610-1620
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Tidskriftsartikel (refereegranskat)abstract
- Determining the changes in within- and between-species functional diversity in plant communities, and their contribution to overall species trait overlap, can enhance efforts at understanding mechanisms of species coexistence. However, little is known about how variation in species functional diversity influences variation in species trait overlap among contrasting environments. Here, we studied the understorey vegetation in a well-characterized 5000-year-old chronosequence involving 30 forested islands that differ greatly in size, soil fertility and species diversity. Across this chronosequence, we expected consistent changes in both within- and between-species functional diversity that would lead to decreasing overall species trait overlap with increasing successional age, species richness, understorey vegetation density and spatial heterogeneity of soil resources. For each island, we measured specific leaf area (SLA) of each of ten individuals of each plant species present. Using a variance decomposition method, we partitioned the total community functional diversity of SLA on each island into within- and between-species functional diversity. Further, we estimated overall species trait overlap as the ratio of within-species functional diversity to total functional diversity. Using regression analyses, we then explored relationships of within- and between-species functional diversity, and of overall species trait overlap, with several environmental variables across the 30 islands. Consistent with our hypotheses, overall species trait overlap decreased with successional age due to a statistically significant decrease in within-species functional diversity, and decreased with species richness due to a simultaneous decrease in within-species functional diversity and increase in between-species functional diversity. Against our predictions, overall species trait overlap increased in more competitive environments and did not change with increasing spatial heterogeneity of soil N or P.Synthesis. Our study suggests niche packing as a key mechanism for species coexistence in plant communities. Using SLA as an integrator of plant ecological strategy, we show that community successional age and species richness are significantly linked to trait space distribution of plant individuals of boreal forest understorey vegetation and therefore to local species coexistence. Our results also suggest that the trait space of dominant and subordinate species may respond differently to local environmental variables.
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| 6. |
- Kumordzi, Bright Boye, et al.
(författare)
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Plant assemblages do not respond homogenously to local variation in environmental conditions: functional responses differ with species identity and abundance
- 2015
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 26, s. 32-45
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Tidskriftsartikel (refereegranskat)abstract
- QuestionsWe investigated some commonly held assumptions of community assembly theory needed to provide accurate predictions of changes in plant species assemblages across environmental gradients or following environmental change. Do (1) dominant and subordinate species respond in the same way to changes in environmental variables; (2) plant species assemblages show higher interspecific than intraspecific trait responses; and (3) co-existing dominant species differ in their responses to the same environmental variables?LocationIslands in Lakes Uddjaure and Hornavan, northern Sweden.MethodsWe explored the responses of forest understorey vegetation assemblages to variation in environmental resources across a chronosequence of 30 lake islands that differ in fire history, above-ground and below-ground resource availability and species diversity. For one plot on each island, we measured specific leaf area, leaf dry matter content and foliar N and P of all dominant and subordinate understorey plant species to assess species-specific and weighted and non-weighted community-level trait responses to variation across islands in all major local environmental drivers.ResultsConsistent with our expectations, we found that species responses to environmental conditions were not homogenous within assemblages, and that responses of dominant and subordinate species differed. Further, intraspecific variation was often an important component of local-scale plant community-level responses. Responses were often relatively consistent across species, but dominant species sometimes showed contrasting responses of the same trait to the same environmental factor. Finally, environmental factors that influenced community average trait values also affected functional diversity.ConclusionsThis study has shown that several common assumptions that underpin community assembly theory do not necessarily hold, and this can cause inaccuracies in predicting plant functional composition responses to changes in environmental variables. Because these assumptions are central to current models that predict vegetation responses to environmental change, it is crucial to further test in which particular environmental context and to what extent these assumptions are critical for model accuracy.
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| 7. |
- Kumordzi, Bright Boye, et al.
(författare)
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Shifts in Aboveground Biomass Allocation Patterns of Dominant Shrub Species across a Strong Environmental Gradient
- 2016
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Most plant biomass allocation studies have focused on allocation to shoots versus roots, and little is known about drivers of allocation for aboveground plant organs. We explored the drivers of within-and between-species variation of aboveground biomass allocation across a strong environmental resource gradient, i.e., a long-term chronosequence of 30 forested islands in northern Sweden across which soil fertility and plant productivity declines while light availability increases. For each of the three coexisting dominant understory dwarf shrub species on each island, we estimated the fraction of the total aboveground biomass produced year of sampling that was allocated to sexual reproduction (i.e., fruits), leaves and stems for each of two growing seasons, to determine how biomass allocation responded to the chronosequence at both the within-species and whole community levels. Against expectations, within-species allocation to fruits was least on less fertile islands, and allocation to leaves at the whole community level was greatest on intermediate islands. Consistent with expectations, different coexisting species showed contrasting allocation patterns, with the species that was best adapted for more fertile conditions allocating the most to vegetative organs, and with its allocation pattern showing the strongest response to the gradient. Our study suggests that co-existing dominant plant species can display highly contrasting biomass allocations to different aboveground organs within and across species in response to limiting environmental resources within the same plant community. Such knowledge is important for understanding how community assembly, trait spectra, and ecological processes driven by the plant community vary across environmental gradients and among contrasting ecosystems.
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| 8. |
- Metcalfe, Daniel, et al.
(författare)
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Nutrient fluxes from insect herbivory increase during ecosystem retrogression in boreal forest
- 2016
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 97, s. 124-132
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Tidskriftsartikel (refereegranskat)abstract
- Ecological theory, developed largely from ungulates and grassland systems, predicts that herbivory accelerates nutrient cycling more in productive than unproductive systems. This prediction may be important for understanding patterns of ecosystem change over time and space, but its applicability to other ecosystems and types of herbivore remain uncertain. We estimated fluxes of nitrogen (N) and phosphorus (P) from herbivory of a common tree species (Betula pubescens) by a common species of herbivorous insect along a similar to 5000-yr boreal chronosequence. Contrary to established theory, fluxes of N and P via herbivory increased along the chronosequence despite a decline in plant productivity. The herbivore-mediated N and P fluxes to the soil are comparable to the main alternative pathway for these nutrients via tree leaf litterfall. We conclude that insect herbivores can make large contributions to nutrient cycling even in unproductive systems, and influence the rate and pattern of ecosystem development, particularly in systems with low external nutrient inputs.
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