Imperial College London

Dr Samraat Pawar

Faculty of Natural SciencesDepartment of Life Sciences (Silwood Park)

Reader in Theoretical Ecology
 
 
 
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Contact

 

+44 (0)20 7594 2213s.pawar CV

 
 
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Location

 

2.4KennedySilwood Park

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Summary

 

Publications

Publication Type
Year
to

70 results found

Christensen AK, Piggott MD, van Sebille E, van Reeuwijk M, Pawar Set al., 2022, Investigating microscale patchiness of motile microbes under turbulence in a simulated convective mixed layer., PLoS Comput Biol, Vol: 18

Microbes play a primary role in aquatic ecosystems and biogeochemical cycles. Spatial patchiness is a critical factor underlying these activities, influencing biological productivity, nutrient cycling and dynamics across trophic levels. Incorporating spatial dynamics into microbial models is a long-standing challenge, particularly where small-scale turbulence is involved. Here, we combine a fully 3D direct numerical simulation of convective mixed layer turbulence, with an individual-based microbial model to test the key hypothesis that the coupling of gyrotactic motility and turbulence drives intense microscale patchiness. The fluid model simulates turbulent convection caused by heat loss through the fluid surface, for example during the night, during autumnal or winter cooling or during a cold-air outbreak. We find that under such conditions, turbulence-driven patchiness is depth-structured and requires high motility: Near the fluid surface, intense convective turbulence overpowers motility, homogenising motile and non-motile microbes approximately equally. At greater depth, in conditions analogous to a thermocline, highly motile microbes can be over twice as patch-concentrated as non-motile microbes, and can substantially amplify their swimming velocity by efficiently exploiting fast-moving packets of fluid. Our results substantiate the predictions of earlier studies, and demonstrate that turbulence-driven patchiness is not a ubiquitous consequence of motility but rather a delicate balance of motility and turbulent intensity.

Journal article

Kordas RL, Pawar S, Kontopoulos D-G, Woodward G, O'Gorman EJet al., 2022, Metabolic plasticity can amplify ecosystem responses to global warming, NATURE COMMUNICATIONS, Vol: 13

Journal article

Phillips JA, Soto JSV, Pawar S, Koprivnikar J, Benesh DP, Molnar PKet al., 2022, The effects of phylogeny, habitat and host characteristics on the thermal sensitivity of helminth development, PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 289, ISSN: 0962-8452

Journal article

Huxley PJ, Murray KA, Pawar S, Cator LJet al., 2022, Competition and resource depletion shape the thermal response of population fitness in Aedes aegypti, COMMUNICATIONS BIOLOGY, Vol: 5

Journal article

Woodward G, Morris O, Barquin J, Belgrano A, Bull C, de Eyto E, Friberg N, Guobergsson G, Layer-Dobra K, Lauridsen RB, Lewis HM, McGinnity P, Pawar S, Rosindell J, O'Gorman EJet al., 2021, Using food webs and metabolic theory to monitor, model, and manage Atlantic salmon - a keystone species under threat, Frontiers in Ecology and Evolution, Vol: 9, ISSN: 2296-701X

Populations of Atlantic salmon are crashing across most of its natural range: understanding the underlying causes and predicting these collapses in time to intervene effectively are urgent ecological and socioeconomic priorities. Current management techniques rely on phenomenological analyses of demographic population time-series and thus lack a mechanistic understanding of how and why populations may be declining. New multidisciplinary approaches are thus needed to capitalize on the long-term, large-scale population data that are currently scattered across various repositories in multiple countries, as well as marshaling additional data to understand the constraints on the life cycle and how salmon operate within the wider food web. Here, we explore how we might combine data and theory to develop the mechanistic models that we need to predict and manage responses to future change. Although we focus on Atlantic salmon—given the huge data resources that already exist for this species—the general principles developed here could be applied and extended to many other species and ecosystems.

Journal article

Cook J, Pawar S, Endres R, 2021, Thermodynamic constraints on the assembly and diversity of microbial ecosystems are different near to and far from equilibrium, PLOS COMPUTATIONAL BIOLOGY, Vol: 17, ISSN: 1553-734X

Journal article

Ho H-C, Pawar S, Tylianakis JM, 2021, Less is worse than none: ineffective adaptive foraging can destabilise food webs

<jats:title>Abstract</jats:title><jats:p><jats:list list-type="order"><jats:list-item><jats:p>Consumers can potentially adjust their diet in response to changing resource abundances, thereby achieving better foraging payoffs. Although previous work has explored how such adaptive foraging scales up to determine the structure and dynamics of food webs, consumers may not be able to perform perfect diet adjustment due to sensory or cognitive limitations. Whether the effectiveness of consumers’ diet adjustment alters food-web consequences remains unclear.</jats:p></jats:list-item><jats:list-item><jats:p>Here, we study how adaptive foraging, specifically the effectiveness (i.e. rate) with which consumers adjust their diet, influences the structure, dynamics, and overall species persistence in synthetic food webs.</jats:p></jats:list-item><jats:list-item><jats:p>We model metabolically-constrained optimal foraging as the mechanistic basis of adaptive diet adjustment and ensuing population dynamics within food webs. We compare food-web dynamical outcomes among simulations sharing initial states but differing in the effectiveness of diet adjustment.</jats:p></jats:list-item><jats:list-item><jats:p>We show that adaptive diet adjustment generally makes food-web structure resilient to species loss. Effective diet adjustment that maintains optimal foraging in the face of changing resource abundances facilitates species persistence in the community, particularly reducing the extinction of top consumers. However, a greater proportion of intermediate consumers goes extinct as optimal foraging becomes less-effective and, unexpectedly, slow diet adjustment leads to higher extinction rates than no diet adjustment at all. Therefore, food-web responses cannot be predicted from species’ responses in isolation, as even less-effective adaptive foraging benefits i

Journal article

Kenna D, Pawar S, Gill R, 2021, Thermal flight performance reveals impact of warming on bumblebee foraging potential, Functional Ecology, Vol: 35, Pages: 2508-2522, ISSN: 0269-8463

1. The effects of environmental temperature on components of insect flight determine life history traits, fitness, adaptability, and ultimately, organism ecosystem functional roles. Despite the crucial role of flying insects across landscapes, our understanding of how temperature affects insect flight performance remains limited.2. Many insect pollinators are considered under threat from climatic warming. Quantifying the relationship between temperature and behavioural performance traits allows us to understand where species are operating in respect to their thermal limits, helping predict responses to projected temperature increases and/or erratic weather events.3. Using a tethered flight mill, we quantify how flight performance of a widespread bumblebee, Bombus terrestris, varies over a temperature range (12-30oC). Given that body mass constrains insect mobility and behaviour, bumblebees represent a useful system to study temperature-mediated size-dependence of flight performance owing to the large intra-colony variation in worker body size they exhibit..4. Workers struggled to fly over a few hundred metres at the lowest tested temperature of 12oC, however flight endurance increased as temperatures rose, peaking around 25oC after which it declined. Our findings further revealed variation in flight capacity across the workforce, with larger workers flying further, longer, and faster than their smaller nestmates. Body mass was also positively related with the likelihood of flight, although importantly this relationship became stronger as temperatures cooled, such that at 12oC only the largest workers were successful fliers. Our study thus highlights that colony foraging success under variable thermal environments can be dependent on the body mass distribution of constituent workers, and more broadly suggests smaller-bodied insects may benefit disproportionately more from warming than larger-bodied ones in terms of flight performance.5. By incorporating both flight e

Journal article

Lechon-Alonso P, Clegg T, Cook J, Smith TP, Pawar Set al., 2021, The role of competition versus cooperation in microbial community coalescence, PLOS COMPUTATIONAL BIOLOGY, Vol: 17, ISSN: 1553-734X

Journal article

Kordas R, Pawar S, Woodward G, O'Gorman Eet al., 2021, Metabolic plasticity can amplify ecosystem responses to global warming

<jats:title>Abstract</jats:title> <jats:p>Organisms have the capacity to alter their physiological response to warming through acclimation or adaptation, but empirical evidence for this metabolic plasticity across species within food webs is lacking, and a generalisable framework does not exist for modelling its ecosystem-level consequences. Here we show that the ability of organisms to raise their metabolic rate following chronic exposure to warming decreases with increasing body size. Chronic exposure to higher temperatures also increases the sensitivity of organisms to short-term warming, irrespective of their body size. A mathematical model parameterised with these findings shows that metabolic plasticity could account for an additional 60% of ecosystem energy flux with just +2 °C of warming. This could explain why ecosystem respiration continues to rise in long-term warming experiments and highlights the need to embed metabolic plasticity in predictive models of global warming impacts on ecosystems.</jats:p>

Journal article

Christensen A, Piggott M, Sebille EV, Reeuwijk MV, Pawar Set al., 2021, Investigating microscale patchiness of motile microbes driven by the interaction of turbulence and gyrotaxis in a 3D simulated convective mixed layer.

<jats:title>Abstract</jats:title> <jats:p>Microbes play a primary role in aquatic ecosystems and biogeochemical cycles. Spatial patchiness is a critical factor underlying these activities, influencing biological productivity, nutrient cycling and dynamics across trophic levels. Incorporating spatial dynamics into microbial models is a long-standing challenge, particularly where small-scale turbulence is involved. Here, we combine a fully 3D direct numerical simulation of convective mixed layer turbulence, with an individual-based microbial model to test the key hypothesis that the coupling of gyrotactic motility and turbulence drives intense microscale patchiness. The fluid model simulates turbulent convection caused by heat loss through the fluid surface, for example during the night, during autumnal or winter cooling or during a cold-air outbreak. We find that under such conditions, turbulence-driven patchiness is depth-structured and requires high motility: Near the fluid surface, intense convective turbulence overpowers motility, homogenising motile and non-motile microbes approximately equally. At greater depth, in conditions analogous to a thermocline, highly motile microbes can be over twice as patch-concentrated as non-motile microbes, and can substantially amplify their swimming velocity by efficiently exploiting fast-moving packets of fluid. Our results substantiate the predictions of earlier studies, and demonstrate that turbulence-driven patchiness is not a ubiquitous consequence of motility but rather a delicate balance of motility and turbulent intensity.</jats:p>

Journal article

Smith TP, Clegg T, Bell T, Pawar Set al., 2021, Systematic variation in the temperature dependence of bacterial carbon use efficiency, ECOLOGY LETTERS, Vol: 24, Pages: 2123-2133, ISSN: 1461-023X

Journal article

Jackson MC, Pawar S, Woodward G, 2021, The temporal dynamics of multiple stressor effects: from individuals to ecosystems, Trends in Ecology and Evolution, Vol: 36, Pages: 402-410, ISSN: 0169-5347

Multiple stressors, such as warming and invasions, often occur together and have nonadditive effects. Most studies to date assume that stressors operate in perfect synchrony, but this will rarely be the case in reality. Stressor sequence and overlap will have implications for ecological memory - the ability of past stressors to influence future responses. Moreover, stressors are usually defined in an anthropocentric context: what we consider a short-term stressor, such as a flood, will span multiple generations of microbes. We argue that to predict responses to multiple stressors from individuals to the whole ecosystem, it is necessary to consider metabolic rates, which determine the timescales at which individuals operate and therefore, ultimately, the ecological memory at different levels of ecological organization.

Journal article

Huxley PJ, Murray KA, Pawar S, Cator LJet al., 2021, The effect of resource limitation on the temperature-dependence of mosquito population fitness, Proceedings of the Royal Society B: Biological Sciences, Vol: 288, ISSN: 0962-8452

Laboratory-derived temperature dependencies of life history traits are increasingly being usedto make mechanistic predictions for how climatic warming will affect vector-borne diseasedynamics, partially by affecting abundance dynamics of the vector population. Thesetemperature-trait relationships are typically estimated from juvenile populations reared onoptimal resource supply, even though natural populations of vectors are expected toexperience variation in resource supply, including intermittent resource limitation. Usinglaboratory experiments on the mosquito Aedes aegypti, a principal arbovirus vector,combined with stage-structured population modelling, we show that low-resource supply inthe juvenile life stages significantly depresses the vector’s maximal population growth rateacross the entire temperature range (22–32°C) and causes it to peak at a lower temperaturethan at high-resource supply. This effect is primarily driven by an increase in juvenilemortality and development time, combined with a decrease in adult size with temperature atlow-resource supply. Our study suggests that most projections of temperature-dependentvector abundance and disease transmission are likely to be biased because they are based ontraits measured under optimal resource supply. Our results provide compelling evidence forfuture studies to consider resource supply when predicting the effects of climate and habitatchange on vector-borne disease transmission, disease vectors and other arthropods.

Journal article

Cook J, Pawar S, Endres RG, 2021, Thermodynamic constraints on the assembly and diversity of microbial ecosystems are different near to and far from equilibrium

<jats:title>Abstract</jats:title><jats:p>Non-equilibrium thermodynamics has long been an area of substantial interest to ecologists because most fundamental biological processes, such as protein synthesis and respiration, are inherently energy-consuming. However, most of this interest has focused on developing coarse ecosystem-level maximisation principles, providing little insight into underlying mechanisms that lead to such emergent constraints. Microbial communities are a natural system to decipher this mechanistic basis because their interactions in the form of substrate consumption, metabolite production, and cross-feeding can be described explicitly in thermodynamic terms. Previous work has considered how thermodynamic constraints impact competition between pairs of species, but restrained from analysing how this manifests in complex dynamical systems. To address this gap, we develop a thermodynamic microbial community model with fully reversible reaction kinetics, which allows direct consideration of free-energy dissipation. This also allows species to interact via products rather than just substrates, increasing the dynamical complexity, and allowing a more nuanced classification of interaction types to emerge. Using this model, we find that community diversity increases with substrate lability, because greater free-energy availability allows for faster generation of niches. Thus, more niches are generated in the time frame of community establishment, leading to higher final species diversity. We also find that allowing species to make use of near-to-equilibrium reactions increases diversity in a low free-energy regime. In such a regime, two new thermodynamic interaction types that we identify here reach comparable strengths to the conventional (competition and facilitation) types, emphasising the key role that thermodynamics plays in community dynamics. Our results suggest that accounting for realistic thermodynamic constraints is vital fo

Journal article

Smith TP, Mombrikotb S, Ransome E, Kontopoulos D-G, Pawar S, Bell Tet al., 2021, Latent functional diversity may accelerate microbial community responses to environmental fluctuations, Publisher: Cold Spring Harbor Laboratory

Whether and how whole ecological communities can respond to climate change remains an open question. With their fast generation times and abundant functional diversity, microbes in particular harbor great potential to exhibit community-level adaptation through a combination of strain-level adaptation, phenotypic plasticity, and species sorting. However, the relative importance of these mechanisms remains unclear. Here, through a novel laboratory experiment, we show that bacterial communities can exhibit a remarkable degree of community-level adaptability through a combination of phenotypic plasticity and species sorting alone. Specifically, by culturing soil communities from a single location at six temperatures between 4°C and 50°C, we find that multiple strains well adapted to different temperatures can be isolated from the community, without immigration or strain-level adaptation. This is made possible by the ability of strains with different physiological and life history traits to “switch on” under suitable conditions, with phylogenetically distinct K-specialist taxa favoured under cooler conditions, and r-specialist taxa in warmer conditions. Our findings provide new insights into microbial community adaptation, and suggest that microbial community function is likely to respond rapidly to climatic fluctuations, through changes in species composition during repeated community assembly dynamics.

Working paper

Padfield D, O'Sullivan H, Pawar S, 2021, rTPC and nls.multstart: A new pipeline to fit thermal performance curves in r, METHODS IN ECOLOGY AND EVOLUTION, Vol: 12, Pages: 1138-1143, ISSN: 2041-210X

Journal article

Zheng JX, Pawar S, Goodman DFM, 2021, Further towards unambiguous edge bundling: Investigating power-confluentdrawings for network visualization, IEEE Transactions on Visualization and Computer Graphics, Vol: 27, Pages: 2244-2249, ISSN: 1077-2626

Bach et al. [1] recently presented an algorithm for constructing confluentdrawings, by leveraging power graph decomposition to generate an auxiliaryrouting graph. We identify two problems with their method and offer a singlesolution to solve both. We also classify the exact type of confluent drawingsthat the algorithm can produce as 'power-confluent', and prove that it is asubclass of the previously studied 'strict confluent' drawing. A descriptionand source code of our implementation is also provided, which additionallyincludes an improved method for power graph construction.

Journal article

Ho H-C, Tylianakis JM, Pawar S, 2020, Behaviour moderates the impacts of food-web structure on species coexistence, Ecology Letters, Vol: 24, Pages: 298-309, ISSN: 1461-023X

How species coexistence (mathematical ‘feasibility’) in food webs emerges from species' trophic interactions remains a long‐standing open question. Here we investigate how structure (network topology and body‐size structure) and behaviour (foraging strategy and spatial dimensionality of interactions) interactively affect feasibility in food webs. Metabolically‐constrained modelling of food‐web dynamics based on whole‐organism consumption revealed that feasibility is promoted in systems dominated by large‐eat‐small foraging (consumers eating smaller resources) whenever (1) many top consumers are present, (2) grazing or sit‐and‐wait foraging strategies are common, and (3) species engage in two‐dimensional interactions. Congruently, the first two conditions were associated with dominance of large‐eat‐small foraging in 74 well‐resolved (primarily aquatic) real‐world food webs. Our findings provide a new, mechanistic understanding of how behavioural properties can modulate the effects of structural properties on species coexistence in food webs, and suggest that ‘being feasible’ constrains the spectra of behavioural and structural properties seen in natural food webs.

Journal article

Kontopoulos D-G, Smith TP, Barraclough TG, Pawar Set al., 2020, Adaptive evolution shapes the present-day distribution of the thermal sensitivity of population growth rate, PLoS Biology, Vol: 18, ISSN: 1544-9173

Developing a thorough understanding of how ectotherm physiology adapts to different thermal environments is of crucial importance, especially in the face of global climate change. A key aspect of an organism's thermal performance curve (TPC)-the relationship between fitness-related trait performance and temperature-is its thermal sensitivity, i.e., the rate at which trait values increase with temperature within its typically experienced thermal range. For a given trait, the distribution of thermal sensitivities across species, often quantified as "activation energy" values, is typically right-skewed. Currently, the mechanisms that generate this distribution are unclear, with considerable debate about the role of thermodynamic constraints versus adaptive evolution. Here, using a phylogenetic comparative approach, we study the evolution of the thermal sensitivity of population growth rate across phytoplankton (Cyanobacteria and eukaryotic microalgae) and prokaryotes (bacteria and archaea), 2 microbial groups that play a major role in the global carbon cycle. We find that thermal sensitivity across these groups is moderately phylogenetically heritable, and that its distribution is shaped by repeated evolutionary convergence throughout its parameter space. More precisely, we detect bursts of adaptive evolution in thermal sensitivity, increasing the amount of overlap among its distributions in different clades. We obtain qualitatively similar results from evolutionary analyses of the thermal sensitivities of 2 physiological rates underlying growth rate: net photosynthesis and respiration of plants. Furthermore, we find that these episodes of evolutionary convergence are consistent with 2 opposing forces: decrease in thermal sensitivity due to environmental fluctuations and increase due to adaptation to stable environments. Overall, our results indicate that adaptation can lead to large and relatively rapid shifts in thermal sensitivity, especially in microbes f

Journal article

Kontopoulos D-G, Patmanidis I, Barraclough TG, Pawar Set al., 2020, Higher temperatures worsen the effects of mutations on protein stability

<jats:title>Abstract</jats:title><jats:p>Understanding whether and how temperature increases alter the effects of mutations on protein stability is crucial for understanding the limits to thermal adaptation by organisms. Currently, it is generally assumed that the stability effects of mutations are independent of temperature. Yet, mutations should become increasingly destabilizing as temperature rises due to the increase in the energy of atoms. Here, by performing an extensive computational analysis on the essential enzyme adenylate kinase in prokaryotes, we show, for the first time, that mutations become more destabilizing with temperature both across and within species. Consistent with these findings, we find that substitution rates of prokaryotes decrease nonlinearly with temperature. Our results suggest that life on Earth likely originated in a moderately thermophilic and thermally fluctuating environment, and indicate that global warming should decrease the per-generation rate of molecular evolution of prokaryotes.</jats:p>

Journal article

Cator L, Johnson LR, Mordecai EA, El Moustaid F, Smallwood TRC, LaDeau SL, Johansson MA, Hudson PJ, Boots M, Thomas MB, Power AG, Pawar Set al., 2020, The role of vector trait variation in vector-borne disease dynamics, Frontiers in Ecology and Evolution, Vol: 8, ISSN: 2296-701X

Many important endemic and emerging diseases are transmitted by vectorsthat are biting arthropods. The functional traits of vectors can affect pathogen transmission ratesdirectly andalso through their effect on vector population dynamics. Increasing empirical evidence shows that vector traits vary significantlyacross individuals, populations, and environmental conditions, andat time scales relevant to disease transmission dynamics. Here, we review empirical evidence for variation invector traits and how this trait variation is currentlyincorporated into mathematical modelsof vector-borne disease transmission. We argue that mechanistically incorporating trait variationinto these models, by explicitly capturingits effects on vector fitness and abundance, can improve the reliability oftheir predictions in a changing world. We provide a conceptual framework for incorporating trait variation into vector-borne disease transmission models,and highlight key empirical and theoretical challenges.This framework provides a means to conceptualize how traits can be incorporated in Vector Borne Disease systems,and identifies key areas in which trait variation can be explored. Determining when and to what extent it is important to incorporate trait variation into vector borne disease models remainsan important, outstanding question.

Journal article

Kontopoulos D, van Sebille E, Lange M, Yvon-Durocher G, Barraclough TG, Pawar Set al., 2020, Phytoplankton thermal responses adapt in the absence of hard thermodynamic constraints, Evolution, Vol: 74, Pages: 775-790, ISSN: 0014-3820

To better predict how populations and communities respond to climatic temperature variation, it is necessary to understand how the shape of the response of fitness‐related rates to temperature evolves (the thermal performance curve). Currently, there is disagreement about the extent to which the evolution of thermal performance curves is constrained. One school of thought has argued for the prevalence of thermodynamic constraints through enzyme kinetics, whereas another argues that adaptation can—at least partly—overcome such constraints. To shed further light on this debate, we perform a phylogenetic meta‐analysis of the thermal performance curves of growth rate of phytoplankton—a globally important functional group—, controlling for environmental effects (habitat type and thermal regime). We find that thermodynamic constraints have a minor influence on the shape of the curve. In particular, we detect a very weak increase of maximum performance with the temperature at which the curve peaks, suggesting a weak “hotter‐is‐better” constraint. Also, instead of a constant thermal sensitivity of growth across species, as might be expected from strong constraints, we find that all aspects of the thermal performance curve evolve along the phylogeny. Our results suggest that phytoplankton thermal performance curves adapt to thermal environments largely in the absence of hard thermodynamic constraints.

Journal article

Rabeling SC, Lim JL, Tidon R, Neff JL, Simpson BB, Pawar Set al., 2019, Seasonal variation of a plant-pollinator network in the Brazilian Cerrado: implications for community structure and robustness, PLoS One, Vol: 14, ISSN: 1932-6203

Seasonal variation in the availability of floral hosts or pollinators is a key factor influencing diversity in plant-pollinator communities. In seasonally dry Neotropical habitats, where month-long periods of extreme drought are followed by a long rainy season, flowering is often synchronized with the beginning of precipitation, when environmental conditions are most beneficial for plant reproduction. In the Brazilian Cerrado, a seasonally dry ecosystem considered one of the world's biodiversity hotspots for angiosperms, plants with shallow root systems flower predominantly during the rainy season. Foraging activity in social bees however, the major pollinators in this biome, is not restricted to any particular season because a constant supply of resources is necessary to sustain their perennial colonies. Despite the Cerrado's importance as a center of plant diversity, the influence of its extreme cycles of drought and precipitation on the dynamics and stability of plant-pollinator communities is not well understood. We sampled plant-pollinator interactions of a Cerrado community weekly for one year and used network analyses to characterize intra-annual seasonal variation in community structure. We also compared seasonal differences in community robustness to species loss by simulating extinctions of plants and pollinators. We find that the community shrinks significantly in size during the dry season, becoming more vulnerable to disturbance due to the smaller pool of floral hosts available to pollinators during this period. Major changes in plant species composition but not in pollinators has led to high levels of turnover in plant-pollinator associations across seasons, indicated by in interaction dissimilarity (<3% of shared interactions). Aseasonal pollinators, which mainly include social bees and some solitary specialized bees, functioned as keystone species, maintaining robustness during periods of drastic changes in climatic conditions.

Journal article

Smith T, Thomas TJH, Garcia-Carreras B, Sal S, Yvon-Durocher G, Bell T, Pawar Set al., 2019, Community-level respiration of prokaryotic microbes may rise with global warming, Nature Communications, Vol: 10, ISSN: 2041-1723

Understanding how the metabolic rates of prokaryotes respond to temperature is fun-damental to our understanding of how ecosystem functioning will be altered by climatechange, as these micro-organisms are major contributors to global carbon efflux. Ecologicalmetabolic theory suggests that species living at higher temperatures evolve higher growthrates than those in cooler niches due to thermodynamic constraints. Here, using a globalprokaryotic dataset, we find that maximal growth rate at thermal optimum increases withtemperature for mesophiles (temperature optima.45◦C), but not thermophiles (&45◦C).Furthermore, short-term (within-day) thermal responses of prokaryotic metabolic rates aretypically more sensitive to warming than those of eukaryotes. Because climatic warmingwill mostly impact ecosystems in the mesophilic temperature range, we conclude that asmicrobial communities adapt to higher temperatures, their metabolic rates and therefore,biomass-specific CO2production, will inevitably rise. Using a mathematical model, weillustrate the potential global impacts of these findings.

Journal article

Ho H-C, Tylianakis JM, Zheng JX, Pawar Set al., 2019, Predation risk influences food-web structure by constraining species diet choice, Ecology Letters, Vol: 22, Pages: 1734-1745, ISSN: 1461-023X

The foraging behaviour of species determines their diet and, therefore, also emergent food-web structure. Optimal foraging theory (OFT) has previously been applied to understand the emergence of food-web structure through a consumer-centric consideration of diet choice. However, the resource-centric viewpoint, where species adjust their behaviour to reduce the risk of predation, has not been considered. We develop a mechanistic model that merges metabolic theory with OFT to incorporate the effect of predation risk on diet choice to assemble food webs. This 'predation-risk-compromise' (PR) model better captures the nestedness and modularity of empirical food webs relative to the classical optimal foraging model. Specifically, compared with optimal foraging alone, risk-mitigated foraging leads to more-nested but less-modular webs by broadening the diet of consumers at intermediate trophic levels. Thus, predation risk significantly affects food-web structure by constraining species' ability to forage optimally, and needs to be considered in future work.

Journal article

Zheng JX, Pawar S, Goodman DFM, 2019, Graph drawing by stochastic gradient descent, IEEE Transactions on Visualization and Computer Graphics, Vol: 25, Pages: 2738-2748, ISSN: 1077-2626

A popular method of force-directed graph drawing is multidimensional scaling using graph-theoretic distances as input. We present an algorithm to minimize its energy function, known as stress, by using stochastic gradient descent (SGD) to move a single pair of vertices at a time. Our results show that SGD can reach lower stress levels faster and more consistently than majorization, without needing help from a good initialization. We then show how the unique properties of SGD make it easier to produce constrained layouts than previous approaches. We also show how SGD can be directly applied within the sparse stress approximation of Ortmann et al. [1], making the algorithm scalable up to large graphs.

Journal article

Kontopoulos D-G, Smith TP, Barraclough TG, Pawar Set al., 2019, Adaptive evolution shapes the present-day distribution of the thermal sensitivity of population growth rate, Publisher: Cold Spring Harbor Laboratory

<jats:title>Abstract</jats:title><jats:p>Developing a thorough understanding of how ectotherm physiology adapts to different thermal environments is of crucial importance, especially in the face of global climate change. A key aspect of an organism’s thermal performance curve—the relationship between fitness-related trait performance and temperature—is its thermal sensitivity, i.e., the rate at which trait values increase with temperature within its typically-experienced thermal range. For a given trait, the distribution of thermal sensitivities across species, often quantified as “activation energy” values, is typically right-skewed. Currently, the mechanisms that generate this distribution are unclear, with considerable debate about the role of thermodynamic constraints vs adaptive evolution. Here, using a phylogenetic comparative approach, we study the evolution of the thermal sensitivity of population growth rate across phytoplankton (Cyanobacteria and eukaryotic microalgae) and prokaryotes (bacteria and archaea), two microbial groups that play a major role in the global carbon cycle. We find that thermal sensitivity across these groups is moderately phylogenetically heritable, and that its distribution is shaped by repeated evolutionary convergence throughout its parameter space. More precisely, we detect bursts of adaptive evolution in thermal sensitivity, increasing the amount of overlap among its distributions in different clades. We obtain qualitatively similar results from evolutionary analyses of the thermal sensitivities of two physiological rates underlying growth rate: net photosynthesis and respiration of plants. Furthermore, we find that these episodes of evolutionary convergence are consistent with two opposing forces: decrease in thermal sensitivity due to environmental fluctuations and increase due to adaptation to stable environments. Overall, our results indicate that adaptation can lead to large a

Working paper

Pawar S, Dell AI, Lin T, Wieczynski DJ, Savage VMet al., 2019, Interaction dimensionality scales up to generate bimodal consumer-resource size-ratio distributions in ecological communities, Frontiers in Ecology and Evolution, Vol: 7, ISSN: 2296-701X

Understanding constraints on consumer-resource body size-ratios is fundamentally important from both ecological and evolutionary perspectives. By analyzing data on 4,685 consumer-resource interactions from nine ecological communities, we show that in spatially complex environments—where consumers can forage in both two (2D, e.g., benthic zones) and three (3D, e.g., pelagic zones) spatial dimensions—the resource-to-consumer body size-ratio distribution tends toward bimodality, with different median 2D and 3D peaks. Specifically, we find that median size-ratio in 3D is consistently smaller than in 2D both within and across communities. Furthermore, 2D and 3D size (not size-ratio) distributions within any community are generally indistinguishable statistically, indicating that the bimodality in size-ratios is not driven simply by a priori size-segregation of species (and therefore, interactions) by dimensionality, but due to other factors. We develop theory that correctly predicts the direction and magnitude of these differences between 2D and 3D size-ratio distributions. Our theory suggests that community-level size-ratio bimodality emerges from the stronger scaling of consumption rate with size in 3D interactions than in 2D which both, maximizes consumer fitness, and allows coexistence, across a larger range of size-ratios in 3D. We also find that consumer gape-limitation can amplify differences between 2D and 3D size-ratios, and that for either dimensionality, higher carrying capacity allows coexistence of a wider range of size-ratios. Our results reveal new and general insights into the size structure of ecological communities, and show that spatial complexity of the environment can have far reaching effects on community structure and dynamics across scales of organization.

Journal article

Rund SSC, Braak K, Cator L, Copas K, Emrich SJ, Giraldo-Calderón GI, Johansson MA, Heydari N, Hobern D, Kelly SA, Lawson D, Lord C, MacCallum RM, Roche DG, Ryan SJ, Schigel D, Vandegrift K, Watts M, Zaspel JM, Pawar Set al., 2019, MIReAD, a minimum information standard for reporting arthropod abundance data, Scientific Data, Vol: 6, ISSN: 2052-4463

Arthropods play a dominant role in natural and human-modified terrestrial ecosystem dynamics. Spatially-explicit arthropod population time-series data are crucial for statistical or mathematical models of these dynamics and assessment of their veterinary, medical, agricultural, and ecological impacts. Such data have been collected world-wide for over a century, but remain scattered and largely inaccessible. In particular, with the ever-present and growing threat of arthropod pests and vectors of infectious diseases, there are numerous historical and ongoing surveillance efforts, but the data are not reported in consistent formats and typically lack sufficient metadata to make reuse and re-analysis possible. Here, we present the first-ever minimum information standard for arthropod abundance, Minimum Information for Reusable Arthropod Abundance Data (MIReAD). Developed with broad stakeholder collaboration, it balances sufficiency for reuse with the practicality of preparing the data for submission. It is designed to optimize data (re)usability from the “FAIR,” (Findable, Accessible, Interoperable, and Reusable) principles of public data archiving (PDA). This standard will facilitate data unification across research initiatives and communities dedicated to surveillance for detection and control of vector-borne diseases and pests.

Journal article

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