| 31. |
- Hu, Nan
(författare)
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Climate change effects on marine species across trophic levels
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate change and anthropogenic activities are producing a range of new selection pressures, both abiotic and biotic, on marine organisms. While there are numerous studies that have investigated the response of individual marine organisms to climate change, few studies have focused on differences in organismal responses across trophic levels. Such trophic differences in response to climate change may disrupt ecological interactions and thereby threaten marine ecosystem function. In addition, predation is known as a strong driver that impacts individuals and populations. Despite this, we still do not have a comprehensive understanding of how different trophic levels respond to climate change stressors, predation and their combined effects in marine ecosystems.The main focus of this thesis is to identify whether marine trophic levels respond differently to climatic stressors and predation. To explore these questions, I have used a combination of traditional mesocosm experiments, together with a statistical method called meta-analysis. I initiated the research by study the responses of marine gastropods at two trophic levels to ocean acidification and predation using long-term mesocosm experiments together with a gastropod-specific meta-analyses. I focused on the amount of phenotypic plasticity in morphological traits of snails when exposed to the two stressors. In order to generalise and test these assumptions among a greater number of marine taxa, I used the meta-analysis approach to investigate the effects of ocean acidification and warming, as well as their combined effects on four marine trophic levels. Finally, to study the individual and combined effects of ocean acidification and predation with respect to inducible defences, I again applied a mesocosm experiment and used blue mussels as a model species. By using long-term mesocosm experiments and the gastropod-specific meta-analysis on marine gastropods from two trophic levels, I showed that these trophic levels varied in their responses to both ocean acidification and predation. Gastropods at lower trophic levels exhibited greater phenotypic plasticity against predation, while those from higher trophic levels showed stronger tolerance to ocean acidification. Next, by using a meta-analysis, including a large number of species and taxa, examining the effects of ocean acidification and warming, I revealed that top-predators and primary producers were most tolerant to ocean acidification compared to other trophic levels. Herbivores on the other hand, were the most vulnerable trophic level against abiotic stress. Again, using the meta-analysis approach, but this time incorporating only factorial experimental data that included the interactive effects of ocean acidification and ocean warming, I showed that higher trophic levels again were the most tolerant trophic level, and herbivores being most sensitive, with respect to the combined effect of the two stressors. Contrary to previous discussions in the literature concerning multiple climate-related stressors, antagonistic and additive effects occurred most frequently, while synergistic effects were less common and which decreased with increasing trophic rank. Finally, by conducting a fully-factorial experiment using blue mussels, I found that mussels with previous experience contact with predator has developed greater inducible defences than ones without previous experience. However, levels of ocean acidification may mask predator cues, or obstruct shell material, and consequently disrupt blue mussels inducible defence from crab predation. In summary, marine trophic levels respond differently to both biotic and climatic stressors. Higher trophic levels, together with primary producers, were often more robust against abiotic stress and may therefore be better prepared for future oceans compare species from lower trophic levels. These results may provide vital information for: implementing effective climate change mitigation, to understand which stressors to act on, and when and where to intervene for prioritizing conservation actions.
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| 32. |
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| 33. |
- Hu, Nan, et al.
(författare)
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Elevated temperatures increase growth and enhance foraging performances of a marine gastropod
- 2021
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Ingår i: Aquaculture Environment Interactions. - 1869-215X. ; 13, s. 177-188
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Tidskriftsartikel (refereegranskat)abstract
- The oceans continue to warm due to rising atmospheric greenhouse gas concentrations. Most climate-change studies of aquaculture species use temperature changes based on coarse-resolution climate models and without considering thermal ranges of an animal. Coarse-resolution climate models are generated by global-scale data, which is insufficient to capture the conditions of coastal areas where most aquaculture activity occurs. Therefore, ocean warming research on coastal organisms requires a more comprehensive design to include broad temperature gradients. By using the ecologically and commercially important coastal whelk Rapana venosa, we combined long-term and short-term experiments and selected 4 temperature treatments (19, 23, 27, and 30°C) to simulate different scenarios to test ocean warming effects on growth rates and foraging performances of whelks. We found that elevated temperature within the whelk’s thermal range (23 and 27°C) significantly increased growth rates and enhanced foraging performances of marine whelks when compared to the current temperature (19°C). Conversely, the whelk’s performance collapsed at 30°C in terms of both growth and foraging behavior. Our research clearly shows that local conditions and the tolerance range of a species must be considered to develop meaningful information for testing the effects of a changing climate. Our study suggests that rapa whelks may increase their feeding and reach larger sizes during warmer periods. Moreover, our study may provide a foundation for future climate research on aquaculture species.
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| 34. |
- Hu, Nan, et al.
(författare)
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Handling- or digestion-limited predators : the role of body mass and habitat complexity in predator functional response
- 2023
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Ingår i: Marine Ecology Progress Series. - 0171-8630. ; 725, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- The predator functional response quantifies the per capita feeding rate of predators as a function of prey density and is a key element of feeding interactions. Variations in its parameters are strongly associated with interaction strength and population dynamics. We examined 18 functional responses within marine whelk−bivalve systems, varying predator body size, prey species, and habitat structure. Our findings suggest that the marine whelk Rapana venosa is handling-limited, a predator type that has received less attention in previous research. We propose further categorizing handling-limited predators into 2 types: pursuit-limited (where maximum feeding rate could be influenced by habitat complexity) and ingestion-limited (where maximum feeding rate is impacted not by habitat complexity, but by predator−prey body mass ratios and prey defense strategy). We found that handling time scales negatively with predator−prey body mass ratios, but this trend exhibits layers of complexity. We propose that the transition from handling to digestion limitation with increasing predator−prey body mass ratios underlies this trend. Our study also confirms the importance of prey types, in addition to known effects of body mass ratios and habitat structure. In summary, our study reveals that simple assumptions about body masses and prey defense strategy may usefully refine estimates of feeding interactions in complex food webs.
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| 35. |
- Hu, Nan, et al.
(författare)
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Marine gastropods at higher trophic level show stronger tolerance to ocean acidification
- 2022
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706.
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Tidskriftsartikel (refereegranskat)abstract
- Climate change and anthropogenic activities are producing a range of new selection pressures, both abiotic and biotic, on marine organisms. Although it is known that climate change can differentially affect fitness-related traits at different trophic levels of the food web, it is not clear if different trophic levels will respond via phenotypic plasticity in the form of maintenance of phenotypes in the face of abiotic and biotic environmental stress similarly. To answer this question, we combined a mesocosm experiment (120 days) using a food web comprising three gastropod species from two trophic levels (grazers and meso-predators) and a meta-analysis including 38 studies to address whether different trophic levels exhibit similar phenotypic responses to abiotic and biotic variables. Abiotic (ocean acidification) and biotic (predation) stress significantly influenced body mass, shell mass, shell thickness and shell strength in both grazers and meso-predators in the mesocosm experiment, with the magnitude of OA effects greater on the meso-predator than the grazers; a result supported by the meta-analysis. In contrast, both mesocosm experiment and meta-analysis found that predation risk induced stronger responses in shell morphology for grazers compared to meso-predators. Together, our findings indicate that higher trophic level species are better able to maintain aspects of their phenotype under OA, suggesting that they may show greater tolerance to climate change effects in general, while lower trophic levels express higher levels of plastic inducible defences to maintain function when under threat of predation. By using marine snails as a model, our study provides new knowledge for understanding how changing environmental conditions may alter biological interactions, and increases our understanding of how climate change may affect ecological communities in which gastropods play a key role.
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| 36. |
- Hu, Nan, et al.
(författare)
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Meta-analysis reveals variance in tolerance to climate change across marine trophic levels
- 2022
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 827
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Forskningsöversikt (refereegranskat)abstract
- Marine ecosystems are currently facing a variety of anthropogenic perturbations, including climate change. Trophic differences in response to climate change may disrupt ecological interactions and thereby threaten marine ecosystem function. Yet, we still do not have a comprehensive understanding of how different trophic levels respond to climate change stressors in marine ecosystems. By including 1278 experiments, comprising 236 different marine species from 18 different phyla in a meta-analysis of studies measuring the direct effect of ocean acidification and ocean warming on marine organisms, we found that higher trophic level species display greater tolerance to ocean acidification but greater sensitivity to warming. In contrast, marine herbivores were the most vulnerable trophic level to both acidification and warming. Such imbalances in the community and a general reduction of biodiversity and biomass in lower trophic levels can significantly disrupt the system and could drive negative bottom-up effects. In conclusion, with ocean acidification and elevated temperatures, there is an alarming risk that trophic disparity may disrupt species interactions, and thereby drive community destabilization under ocean climate change.
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| 37. |
- Hu, Nan, et al.
(författare)
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Responses of marine trophic levels to the combined effects of ocean acidification and warming
- 2024
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Ingår i: Nature Communications. - 2041-1723. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Marine organisms are simultaneously exposed to anthropogenic stressors associated with ocean acidification and ocean warming, with expected interactive effects. Species from different trophic levels with dissimilar characteristics and evolutionary histories are likely to respond differently. Here, we perform a meta-analysis of controlled experiments including both ocean acidification and ocean warming factors to investigate single and interactive effects of these stressors on marine species. Contrary to expectations, we find that synergistic interactions are less common (16%) than additive (40%) and antagonistic (44%) interactions overall and their proportion decreases with increasing trophic level. Predators are the most tolerant trophic level to both individual and combined effects. For interactive effects, calcifying and non-calcifying species show similar patterns. We also identify climate region-specific patterns, with interactive effects ranging from synergistic in temperate regions to compensatory in subtropical regions, to positive in tropical regions. Our findings improve understanding of how ocean warming, and acidification affect marine trophic levels and highlight the need for deeper consideration of multiple stressors in conservation efforts.
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| 38. |
- Hu, Nan, et al.
(författare)
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Review of experimental measurements on particle size distribution and airflow behaviors during human respiration
- 2024
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Ingår i: Building and Environment. - : Elsevier. - 0360-1323 .- 1873-684X. ; 247
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, pandemic outbreaks have raised concerns about the spread of respiratory infections and their impact on public health. Since the pathogen emission during human respiration is recognized as the primary source, characterizing the physical properties of exhaled particles and airflow has become a crucial focus of attention. This article critically reviews experimental studies in exhaled particles and airflow, examines the uncertainty introduced by different measurement methods, analyzes how it is reflected in measurement outcomes, and provides an in-depth understanding of particle size distribution and airflow behaviors of human respiration. The measurement techniques assessment highlights the variability among particle sizing techniques in detection size range, collection efficiency, hydration status of captured particles, and experimental protocols. A combination of sampling-based instruments and laser imaging systems is recommended for particle sizing to cover a wider detection range, with refined setups in thermal conditions, sampling distance, volume, and duration. Meanwhile, it identifies the complementary nature of qualitative and quantitative measurements of airflow characterization techniques. Image recording systems plus data reconstruction programs are suggested to capture dynamic airflow features while accuracy validation by other techniques is required at the same time. Subsequent analysis of the measurement data showed that the various experimental measurements provided substantial information, but they also revealed disagreements and challenges in quantification. The dominance of submicron aerosols in exhaled particles and jet-like transport in exhaled airflow is obvious. More efforts should be made to measure particles larger than 20 μm, capture airflow dynamics in a high temporal and spatial resolution, and quantify the impact of face coverings to improve the understanding of human respiratory emissions.
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| 39. |
- Hu, Nan, et al.
(författare)
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Ventilation performance evaluation of an operating room with temperature-controlled airflow system in contaminant control : A numerical study
- 2024
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Ingår i: Building and Environment. - : Elsevier Ltd. - 0360-1323 .- 1873-684X. ; 259
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates the efficacy of temperature-controlled airflow systems in modern operating rooms for contaminant control, a critical factor in preventing surgical site infections. We have conducted experimental measurements in an operating room equipped with temperature-controlled ventilation to map the airflow field and contaminant dispersion (airborne particles with diameters ranging from 0.5 to 1 μm). The results were used to validate the computational fluid dynamics code, which was then employed to simulate and examine different conditions, including contaminant release locations and air supply rates. Realizable k-epsilon and passive scalar models were utilized to simulate airflow and airborne particle phases. We assessed the airflow distribution and contaminant dispersion, utilizing indices such as ventilation and air change efficiency scales. The analysis provided quantitative insights into the distribution and removal of contaminants, as well as the speed at which the room air was replaced. Contamination was found to be effectively reduced when contaminants were released near exhaust outlets or under central unidirectional inlets. The presence of the operating table caused a big distortion of the central downward airflow, forming a horizontal air barrier at the periphery. Under this unique interior configuration, an appropriate air supply ratio between central and periphery zones was required to achieve optimal overall ventilation performance.
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| 40. |
- Hu, Zhang Nan, et al.
(författare)
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Hausdorff dimension of recurrence sets
- 2024
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Ingår i: Nonlinearity. - 0951-7715. ; 37:5
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Tidskriftsartikel (refereegranskat)abstract
- We consider linear mappings on the 2-dimensional torus, defined by T ( x ) = A x ( mod 1 ) , where A is an invertible 2 × 2 integer matrix, with no eigenvalues on the unit circle. In the case det A = ± 1 , we give a formula for the Hausdorff dimension of the set { x ∈ T 2 : d ( T n ( x ) , x ) < e − α n for infinitely many n } .
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