Environmental Variables Temperature Research Articles

The relationship between thermal spatial variability and mean temperature alters movement and population dynamics

AbstractThe importance of spatial and temporal environmental variation in shaping ecosystem dynamics is well appreciated, yet the ecological consequences of dynamic spatial variability, that is, the temporal patterning of spatial variation, remain unresolved. Here, we experimentally generate temporally fluctuating thermal environments that have either a negative, positive, or neutral relationship between the mean spatial environmental temperature and the degree of thermal spatial heterogeneity. We test the hypothesis that the timing of spatial variation relative to diel temperature cycles can meaningfully alter movement patterns and population dynamics, using the motile green algae Chlamydomonas reinhardtii. Our results indicate that C. reinhardtii individuals growing in environments with positive relationships between spatial variability and mean temperature show reduced population growth rates, more directed movement as indicated by a reduced turning angle, and decreased negative thermotaxis over time, relative to those growing in environments with a negative relationship between spatial variability and mean temperature. We additionally document substantial regional variation in the dynamics of natural spatial variability by collecting summer water temperature measurements from five ponds in the Mount Saint Helens watershed, WA, USA. Our results collectively suggest that the dynamics of spatial variation are an underappreciated but salient feature within the broader interwoven fabric of spatiotemporal variation.

Long-term in-situ monitoring on foundation settlement and service performance of a novel pile-plank-supported ballastless tram track in soft soil regions

An innovative pile-plank structure for differential settlement control in soft soil area is employed in Shanghai Tram projects. In this specially designed infrastructure, the rails are directly combined with the foundation treatment structure by fasteners and pads. The soil pressure beneath the plank, foundation layered settlement, track settlement, temperature field and internal forces of the structure are investigated based on a series of in-situ tests. Measurement data revealed that the soil pressure decreased from 10.1 kPa to 5.3 kPa during the first 12 months of the operation. The layered foundation settlement increased most rapidly in the initial stage of the operation. The track settlement was basically in accordance with the foundation settlement. The internal forces of the plank were mainly influenced by environmental temperature variation in this stage. The measurement data provide a strong base for the development of the design theory of the buried pile-plank structure for ballastless tracks.

When the Eel Meets Dams: Larger Dams’ Long-Term Impacts on Anguilla anguilla (L., 1758)

Diadromous fish, like the European eel Anguilla anguilla (L., 1758), are highly threatened by dams that disrupt river connectivity, consequently impeding fish movements to reach feeding and spawning habitats. In this study, variation in eel occurrence between a historical period (1940–1970) and recent data (2016–2020) was assessed throughout the Sardinian rivers’ network (more than 450 sites). Using Boosted Regression Trees (BRT) we investigated relationships between eel’s occurrence and a set of spatial and temporal environmental variables including a set of dams’ construction features for each period. An overall decrease by 65% of eel’s occurrence was noticed during the ca. 80-years period under scrutiny. Considering a subset (105 and 88 sites for the historical and the recent period, respectively) characterized by the presence of larger dams (height >15 m), eel’s occurrence dropped by 85%. Conversely, eel’s occurrence dropped only by ca. 44% in dam-free sites. During the historical period, eel’s occurrence was mostly affected by time since the initial habitat fragmentation, flow, distance to dams, connectivity, and dams’ height. In the most recent period, eel’s occurrence is mostly affected by dams’ building year, dam-to-sea distance, and, again, dams’ height. Results pinpoint that dams’ construction features and the time from their construction have significant negative effects on eel’s occurrence. Addition of future effective eel restoration practices, apart any other adverse environmental stressor, must consider dams’ removal, wherever socially sustainable or alternatively, the modification of construction features of dams (like excessive height) and the addition of fish ladders.

Natural selection favours drought escape and an acquisitive resource‐use strategy in semi‐arid Mediterranean shrubs

AbstractNatural selection is the major force driving adaptive evolution in natural populations, varying in strength, direction, and form through space and time, especially in highly variable environments such as Mediterranean ecosystems. Although a conservative resource‐use strategy has been hypothesized to be adaptive in Mediterranean taxa, patterns of selection at the intraspecific level, that is, the suite of traits determining individual fitness, are largely unknown.Using a phenotypic selection experiment in natural semi‐arid conditions, we measured direct and indirect selection acting through two different fitness components (survival and reproduction), to assess the adaptive value of 20 ecophysiological traits on individuals of two gypsum endemic species,Centaurea hyssopifoliaandHelianthemum squamatum, dwelling in environments with contrasting abiotic conditions (south‐ and north‐facing slopes) during two climatically contrasting years (dry and mesic). This allowed quantifying the magnitude and direction of natural selection at different spatiotemporal scales.Our results revealed that different abiotic conditions did not alter selection patterns, being the magnitude of selection more strongly affected by temporal environmental variation. Selection through reproduction indicated consistent selection for early phenology, low water use efficiency, high specific leaf area, low leaf dry matter content, and high leaf N across slopes and years in both species. In contrast, phenotypic trait variation was not linked to survival in either species. Furthermore, while individual reproductive output was higher or similar in environments with higher abiotic stress in both species and years, survival was similar across environmental conditions, and it was neither affected by plant size nor reproductive output.Contrary to our expectations, natural selection via reproductive fitness consistently favoured a drought‐escape, acquisitive resource‐use strategy in Mediterranean semi‐arid plants, rather than a conservative resource‐use strategy, even under conditions of higher abiotic stress (i.e. south slopes and dry year). Such acquisitive strategy could allow rapid development by maximizing resource assimilation and reproduction before the most limiting climatic conditions of mid‐late summer. Our results shed light on adaptive functional strategies of Mediterranean taxa at the intraspecific level, providing insight on future responses to environmental change, and highlight remarkable differences in selection acting through different fitness components.Read the freePlain Language Summaryfor this article on the Journal blog.

Effect Of Climatic Conditions On Performance Of ORC Using Environment-Friendly Working Fluids – Special Reference To India

<p>Efficient heat recovery from low-grade heat sources is an achievable scientific frontier in the coming decade. One of the promising technologies in waste heat recovery is the organic Rankine cycle (ORC) system. Major obstacles to low-grade heat recovery include economic viability, scale, system efficiency, and exergy efficiency. In low temperature ORC systems, the cost of condenser becomes significant and hence air-cooled condenser is a feasible option. However, the performance of the air-cooled condenser is sensitive to the variation in ambient air conditions. India, being a tropical country, have villages and cities whose average temperature varies from -2oC in winter to 50oC in summer. The present work involves the study of heat transfer effects on the condenser using common organic working fluids and quantifying the consequences of environmental temperature variations. The constant thermal evaporator load is supplied with a medium-enthalpy heat source at 100 and 150oC. The atmospheric temperature associated with heat rejection from the condenser is varied from 273K to 313K for 5 working fluids. A MATLAB model of the ORC system is developed to study the effect of condenser performance on the first and second law efficiency of the ORC system. The MATLAB model is used to investigate the effect of varying inlet temperatures of the working fluid on the performance of ORC system to choose an organic working fluid suitable for Indian climatic conditions. R365 mfc, and R1233zd exhibit higher expander work and show higher heat rejection. At higher heat source temperatures of 150oC, the simulation shows a higher second law efficiency for the working fluid R1224yd(Z), which has critical temperature closed to the heat source temperature.</p>

Signal Pick-Up Technique for Sapphire Fiber External Fabry-Perot Interferometer Using Tapered Multimode Fibers

A tapered multimode fiber (MMF) to sufficiently and stably pick up the interference signal of a sapphire fiber external Fabry-Perot interferometer (EFPI) is proposed and investigated. The tapered MMF was fabricated following the adiabaticity criteria for the local tapering angle such that the excited fundamental mode in MMF barely couples to the higher-order modes, ensuring a high-visibility interference output from the sapphire fiber EFPI. Tapered MMF also guarantees a robust fusion splice between the leading single-mode fiber and the sapphire fiber. Experimental results show that using tapered MMF the excitation coefficient of fundamental mode can be improved by more than 3.5 times comparing with conventional technique using non-tapered MMF, and the fringe contrast of the interference spectrum can increase by 2.3 times. The response of the collected interference spectra from the sapphire fiber EFPI using tapered MMF was tested when ambient pressure and temperature was changed from 0.1 MPa to 6.1 MPa and 17 °C to 302°C respectively. The results validate that tapered MMF can provide a high stability against environmental pressure and temperature variations.

Increasing temporal variance leads to stable species range limits.

What prevents populations of a species from adapting to the novel environments outside the species' geographic distribution? Previous models highlighted how gene flow across spatial environmental gradients determines species expansion versus extinction and the location of species range limits. However, space is only one of two axes of environmental variation-environments also vary in time, and we know temporal environmental variation has important consequences for population demography and evolution. We used analytical and individual-based evolutionary models to explore how temporal variation in environmental conditions influences the spread of populations across a spatial environmental gradient. We find that temporal variation greatly alters our predictions for range dynamics compared to temporally static environments. When temporal variance is equal across the landscape, the fate of species (expansion versus extinction) is determined by the interaction between the degree of temporal autocorrelation in environmental fluctuations and the steepness of the spatial environmental gradient. When the magnitude of temporal variance changes across the landscape, stable range limits form where this variance increases maladaptation sufficiently to prevent local persistence. These results illustrate the pivotal influence of temporal variation on the likelihood of populations colonizing novel habitats and the location of species range limits.

Time series aggregation-based design and operation optimization of a solar-driven organic Rankine cycle incorporating variation of environmental temperature and solar radiation

The efficient utilization of renewable energy, e.g., solar energy, has become a major requirement to build a clean and efficient energy system and achieve the goal of carbon neutrality. Organic Rankine cycle (ORC) is one of the most promising technologies for converting solar energy into power. However, life-span low operation performance is still a barrier to the wide-spread application of ORC. Design and off-design operation optimization is significant in improving the life-span performance of ORC. In the routine methods, the ORC system is usually designed under a specific rated condition. However, the ORC mostly operates under off-design conditions. The conventional method separates the off-design operation process from the design process and typically loses solution optimality. In the present study, the off-design operation conditions are incorporated into the design process. A time series aggregation-based method for design and operation optimization of a solar driven ORC is proposed. K-means algorithm is applied to achieve the optimal aggregation operating points for the environmental temperature and solar radiation. The design and operation optimization model incorporating the off-design component performance is developed. The optimal design and operating schemes are achieved based on the aggregated operating points, and the effectiveness of the proposed method is validated. The results indicate that the ORC obtained by the proposed method features a 37.37% lower electricity production cost compared with the conventional method.

ANALISIS PRODUKSI BIOGAS SEBAGAI ENERGI ALTERNATIF PADA KOMPOR BIOGAS MENGGUNAKAN CAMPURAN KOTORAN SAPI DAN AMPAS TAHU

Biogas decomposes organic waste by bacteria through an anaerobic fermentation process that produces manageable methane gas. The purpose of this study was to determine the temperature, pressure, mass and flame duration of biogas produced from a mixture of cow dung and tofu waste liquid waste using a batch type digester. The digester uses a volume capacity of 30 liters with a volume of stuffing raw material as much as of the volume of the digester. This study uses three variations of the volume ratio of the mixture of cow dung and tofu waste liquid waste, namely S1 (50%: 50%), S2 (70%: 30%), and S3 (90%: 10%) with the addition of 2.5 liters of water for each variation. Data collection was carried out for 30 days at 11.00 WITA and 17.00 WITA. Based on the results of the study, it is known that the mixed variation of 50%: 50% is the best variation compared to the variations of 70%: 30%, and 90%: 10%. The results of the daily average environmental temperature variation of the S1 mixture are 30.19°C, and the average substrate temperature are 27.06°C. The average daily yield of biogas pressure are 0.039 bar with a total mass of biogas are 57.8 grams. Based on the measurement results of biogas flame duration comparasion with LPG on the total mass of biogas with the variation of the S1 mixture, it is obtained that biogas flame duration are 4.38 minutes while the combustion of LPG gas with the same total mass are 49 seconds.

Effects of breeding resource and environmental temperature on adult locomotor activity in cactophilic Drosophila

The evolution of insects inhabiting arid environments is heavily shaped by resource scarcity and temperature. Ecological interdependence could be tight and complex as in the model cactus–yeast–Drosophila. Cactophilic species of Drosophila (Diptera: Drosophilidae) differ in their preference for the type of breeding resources and life‐history traits that respond to variation in environmental temperature. Adult flies feed and breed on rotting cacti but they are physiologically limited to cope with temperature changes. However, flies can behaviourally avoid such stressful conditions by actively seeking benign microhabitats. We investigate how alternative breeding resources (cactus species) and thermal environment affect the spontaneous adult locomotor activity in two species, Drosophila buzzatii Patterson & Wheeler and Drosophila koepferae Fontdevila & Wasserman, adapted to semi‐arid environments. Locomotor activity of D. buzzatii was more affected by the breeding resource, whereas D. koepferae showed a clear ‘bell shape’ activity curve in response to a wide range of temperatures, independent of the breeding resource. These idiosyncratic responses suggest that the selective pressures that shaped life‐history evolution in these Drosophila species were different, with the breeding resource and environmental temperature contributing to the development of diverging survival strategies in arid environments.

Temperature drift compensation of fiber strapdown inertial navigation system based on GSA-SVR

The fiber strapdown inertial navigation system (INS) has been widely utilized in aircraft, autonomous driving, robotics, and other fields due to the rapid growth of fiber technology. The core components of INS, the fiber optic gyroscope (FOG) and quartz flexible accelerometer (QFA), are prone to affected by the environmental temperature variation. The traditional temperature drift compensation method requires a considerable time to calibrate each inertial sensor individually. But after the six inertial sensors are integrated, the temperature environment inside the INS will become more complex. As a result, this device-level method has an unsatisfactory effect in the practical application of INS. Furthermore, the traditional method ignores the fact that the temperature drift characteristics of FOG are not the same at different working states. To solve the above problems, we propose a novel temperature drift compensation method of INS based on gravitational search algorithm (GSA) tuning support vector regression (SVR). The startup state and stable working state are modeled independently based on the FOG's features. Without adding additional thermometers to the inertial sensors, the temperature field is constructed by making full use of the information provided by the built-in thermometer of six inertial sensors. The experimental results verify the effectiveness of our method during different working states. And compared with the traditional polynomial fitting method, our method has better performance in the navigation experiment, the navigation accuracy increased by more than 50%.

How the storage effect and the number of temporal niches affect biodiversity in stochastic and seasonal environments.

Temporal environmental variations affect diversity in communities of competing populations. In particular, the covariance between competition and environment is known to facilitate invasions of rare species via the storage effect. Here we present a quantitative study of the effects of temporal variations in two-species and in diverse communities. Four scenarios are compared: environmental variations may be either periodic (seasonal) or stochastic, and the dynamics may support the storage effect (global competition) or not (local competition). In two-species communities, coexistence is quantified via the mean time to absorption, and we show that stochastic variations yield shorter persistence time because they allow for rare sequences of bad years. In diverse communities, where the steady-state reflects a colonization-extinction equilibrium, the actual number of temporal niches is shown to play a crucial role. When this number is large, the same trends hold: storage effect and periodic variations increase both species richness and the evenness of the community. Surprisingly, when the number of temporal niches is small global competition acts to decrease species richness and evenness, as it focuses the competition to specific periods, thus increasing the effective fitness differences.

Spatial and temporal variability and connectivity of the marine environment of the South Sandwich Islands, Southern Ocean

The South Sandwich Islands form the eastern boundary to the highly biologically productive Scotia Sea in the southwest Atlantic sector of the Southern Ocean and are part of a large Marine Protected Area. The South Sandwich Islands have a complex marine environment that is influenced by both the Antarctic Circumpolar Current and the Weddell Gyre, and seasonal sea ice. Here we investigate the local and regional dynamics and variability of the ocean and sea ice to inform management of the region. Remotely sensed sea surface temperature (SST), sea ice concentration and chlorophyll a data from 2009 to 2021 are used to define the mean seasonal cycle in the environment and the associated temporal and spatial variability. While sea surface temperature and sea ice have a clearly defined seasonality, local chlorophyll blooms are irregular in timing, location and magnitude. Interannual variability in summer SST is strongly positively correlated along the island arc. The islands experience very different winter sea ice conditions from year to year, with marked variability in sea ice distribution and duration. Surface chlorophyll blooms develop in most years close to the island arc, but there is little spatial consistency and there are years where blooms are not observed. The timing and pattern of sea ice retreat appears to be a key driver in the formation of chlorophyll blooms, with their propagation affected by local circulation, but additional local processes are also important. Trajectories of near-surface satellite tracked surface buoys and Argo floats, together with an analysis of sea surface height output from a global reanalysis product, demonstrate the connectivity of the South Sandwich Islands to the wider regional marine system. Enhanced current flows around and between the South Sandwich Islands are likely to affect the transport and exchange of material along the island arc. The South Sandwich Islands are connected with the Scotia and Weddell seas, with contribution from the different regions varying according to latitude along the island arc. There are also connections with islands downstream including Bouvet, Crozet and Kerguelen Islands and seamounts, with possible return flow via the Weddell Gyre. Our analyses indicate that accounting for the complexity and variability in the South Sandwich Islands marine environment will be crucial in the development of conservation and fisheries management procedures.

A High Reliability Damage Imaging Method Under Environmental Temperature Variations

Abstract In Lamb wave-based structural health monitoring (SHM), the environmental temperature variations can easily affect Lamb wave monitoring signals and seriously reduce the reliability of final damage detection results. To resolve the temperature effect problem, a temperature compensation method of improved baseline signal stretch (IBSS) is presented and applied for high reliability damage imaging under large environmental temperature variations in this paper. After the basic principle of IBSS is analyzed, the realization of IBSS is discussed. Then, a IBSS-based high reliability damage imaging method under temperature variation situation is developed. An experimental study is finally arranged.

Thermal evolution of CRTS Ⅱ slab track under various environmental temperatures: Experimental study

The environmental temperature plays an important role in thermal performance of materials and structure in CRTS Ⅱ ballastless slab track under operational condition. In this paper, two 1:4 geometric scaled models of five CRTS Ⅱ slab tracks on a simply-supported box girder under three environmental temperatures rising and dropping cases were conducted in a large-scale environmental simulation testing chamber, respectively. In order to study the effect of constraint conditions on the bond of cement asphalt mortar (CAM), the internal temperature distribution, stress and displacement of two scaled models with constraint and freedom boundary conditions are also compared. Results show that the internal temperatures, longitudinal stresses and displacements of the track structure increase nonlinearly within an increase of the environmental temperature. Accordingly, these same responses decrease linearly within a temperature decrease. Most importantly, when the environmental temperature variation is + 26.5℃, the testing axial force at the two ends of the prototype track structure reaches 2,849kN, and the relative longitudinal displacement between the track slab and base plate become larger with a decrease of the environmental temperature, especially for the lowest temperature of −20℃. Moreover, fixed constraint condition decelerates the temperature transfer of the track slab to CAM, since it leads to the larger absolute temperatures and stresses of the track structure compared to the free constraint.

Effect of ambient temperature on growth performances, carcass traits and meat quality of pigs

ABSTRACT Pigs are sensitive to high environmental temperature due to difficulties in eliminating excess body heat. The present study was undertaken to evaluate the effects of ambient temperature on growth performances, carcass traits and meat quality of pigs. This trial was carried out at the Experimental Center of Livestock at Sunchon National University, South Korea. A total of 40 three-way crossbred pigs (initial body weight 38.50 ± 0.55 kg) were assigned into four groups: group 1 (12°C to 19°C), group 2 (19°C to 25°C), group 3 (25°C to 31°C) and group 4 (31°C to 37°C). Pigs were offered ad libitum diet and free access to drinking water. Weight gain and feed intake were significantly enhanced in groups 1 and 2, respectively. The lowest weight gain, feed intake, back-fat thickness and cholesterol content was observed in group 4 (P < 0.05). Temperature variation exerted no significant effect on TBARS, pH during the storage period and water holding capacity, shear force and meat colour. The total microbial content was significantly enhanced in group 1 compared to other groups (P < 0.05). We therefore conclude that pigs respond differently to environmental temperature variations, with respect to growth performances, carcass traits and meat quality.

High discharge intensified low net ecosystem productivity, hypoxia, and acidification at three outlets of the Pearl River Estuary, China

Clarifying the influence of hydrological variations on ecological function is a topic of considerable interest in watershed ecological flow assessment and water resource management. Net ecosystem productivity (NEP) is a useful composite indicator of ecosystem function, reflecting material cycling and energy flow. However, the effects of hydrological variations on NEP, especially the influence mechanism, remain unclear due to the complex environmental characteristics in estuaries. We analysed the spatial–temporal variability of the aquatic environment and NEP through in-situ monitoring and field sampling from December 2018 to January 2020 at three outlets (Humen, Jiaomen, and Hongqimen) with different hydrological conditions in the Pearl River Estuary (PRE), China, and explored the influence mechanism of hydrological variation on NEP. The 155 groups of effective metabolism values were estimated using Odum's open-water method. The daily ecosystem respiration (ER) was higher than the gross primary production (GPP); therefore, water bodies were dominated by net heterotrophy at the three outlets. The daily NEP (–4.34 ± 1.40 mg O2 L–1d–1), O2 concentration (5.2 ± 1.02 mg L–1), and pH (7.53±0.24) were lowest at Humen, which also had the largest discharge and tide volume, deepest water depth, and widest channel. Seasonally, the NEP in the summer (–3.30 ± 1.39 mg O2 L–1d–1) and autumn (–3.19 ± 1.60 mg O2 L–1d–1) was lower than those in the spring (–1.56 ± 1.92 mg O2 L–1d–1) and winter (–2.17 ± 1.50 mg O2 L–1d–1). The inhibitory effect of increased discharge on the metabolic rate exceeded the stimulation provided by seasonal factors, such as increased temperature and solar radiation. The scour and dilution effect caused by discharge increase reduced chlorophyll a concentration; meanwhile, the increase in turbidity resulted in a decrease in the photosynthetic rate and GPP. ER was stimulated by heterotrophic microorganisms and high total suspended solids, resulting in a decrease in O2 and endogenous organics, thus causing the low NEP, hypoxia, and acidification phenomenon. Our results suggest that lengthening the discharge pulse period in summer and autumn will further decrease NEP and increase the area of hypoxia and acidification at the three outlets in the PRE.

Heterogeneous environmental seascape across a biogeographic break influences the thermal physiology and tolerances to ocean acidification in an ecosystem engineer

AbstractAimUnderstanding how spatio‐temporal environmental variability influences stress tolerance, local adaptation and phenotypic variation among populations is a key challenge for evolutionary ecology and climate change biology. Coastal biogeographic breaks are natural laboratories to explore this fundamental research question due to the contrasting environmental conditions experienced by natural populations across these regions.LocationIn the South East Pacific (SEP) coast, a major break (30º‐32ºS) is characterized by extreme natural variability in sea surface temperature (SST) and carbonate chemistry parameters related to temporal and spatial dynamics in upwelling events. Calcifying organisms inhibiting this zone are exposed to marked fluctuations and clines in SST that together with naturally acidified waters can impact their metabolism, calcification and fitness, making them particularly prone to the effects of climate change (e.g. ocean acidification, OA). We investigated to what extent the spatial and temporal environmental variability (in SST and seawater carbonate conditions) that characterizes the biogeographic break in the SEP influences intra‐specific differences in the thermal ecology and the tolerances to OA of the limpet Scurria araucana.MethodsDuring two years, we conducted field surveys of limpet populations at sites across the SEP break (27ºS, 30ºS and 32ºS). We collected individuals from each population to test for geographic differences in morphometric (e.g. total buoyancy weight, shell length) and physiological (e.g. oxygen consumption rate, cardiac activity and thermal performance curves; TPC) responses to local environmental conditions (Tº and pH/pCO2) and to simulated OA scenarios.ResultsPopulations of S. Araucana exhibit high tolerance to OA with no signal of geographic influence on this attribute. However, inter‐population differences in thermal physiology (metabolic rates and performances) were found across the biogeographic break in the SEP coast. Limpets from the central part of the break (30ºS) exhibit higher thermal performance compared to limpets from populations at both sides of the break.Main conclusionsVariation in SST has a greater effect shaping inter‐population differences in thermal physiology of the limpet S. araucana. These physiological differences are aligned the thermal heterogenous seascape along the biogeographic break in the SEP. Contrarily, temporal and spatial variation in seawater carbonate conditions does not influence inter‐population differences in phenotypic response populations, but an overall high tolerance to OA.

Assessing the short-term response of fish assemblages to damming of an Amazonian river

The enormous biodiversity of tropical freshwater combined with a considerable increase in the construction of reservoirs urges to understand the ecological effects caused by damming. Using rarely available data obtained before (one year) and after (four years) the filling of a hydroelectric plant on the Teles Pires River (Amazon River basin), the effects on abundance, biomass, and diversity of the fish assemblage were evaluated using two complementary approaches: a BACI (before-after-control-impact) design with mixed models and analyses of covariance. Significant Before-After × Control-Impact interactions in abundance, biomass, and species richness were observed, with decreases of abundance and species richness and more stable biomass after filling. Some abundant species, such as Jupiaba polylepis, Jupiaba acanthogaster, Knodus cf. heteresthes, and Moenkhausia lepidura among others, declined in abundance or disappeared from the impact sites. However, temporal and particularly spatial variation independent of damming explained more variation in all the response variables analyzed, including species composition, and analyses of covariance demonstrated general negative trends irrespective of damming. This study illustrates the usefulness of BACI designs to assess the effects of damming but also that other statistical approaches are complementary, given the difficulty of identifying control sites and the short length of most ecological time series. The results also suggest that preserving tributaries upstream of reservoirs and natural regimes of spatial and temporal environmental variation might help to mitigate the impacts of damming in tropical ecosystems.

Evolution of polygenic traits under global vs local adaptation.

Observations about the number, frequency, effect size, and genomic distribution of alleles associated with complex traits must be interpreted in light of evolutionary process. These characteristics, which constitute a trait’s genetic architecture, can dramatically affect evolutionary outcomes in applications from agriculture to medicine, and can provide a window into how evolution works. Here, I review theoretical predictions about the evolution of genetic architecture under spatially homogeneous, global adaptation as compared with spatially heterogeneous, local adaptation. Due to the tension between divergent selection and migration, local adaptation can favor “concentrated” genetic architectures that are enriched for alleles of larger effect, clustered in a smaller number of genomic regions, relative to expectations under global adaptation. However, the evolution of such architectures may be limited by many factors, including the genotypic redundancy of the trait, mutation rate, and temporal variability of environment. I review the circumstances in which predictions differ for global vs local adaptation and discuss where progress can be made in testing hypotheses using data from natural populations and lab experiments. As the field of comparative population genomics expands in scope, differences in architecture among traits and species will provide insights into how evolution works, and such differences must be interpreted in light of which kind of selection has been operating.