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Rozowski M, Palumbo J, Bisen J, Bi C, Bouhrara M, Czaja W, Spencer RG. Input layer regularization for magnetic resonance relaxometry biexponential parameter estimation. Magn Reson Chem 2022; 60:1076-1086. [PMID: 35593385 PMCID: PMC10185331 DOI: 10.1002/mrc.5289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 04/22/2022] [Accepted: 05/17/2022] [Indexed: 05/17/2023]
Abstract
Many methods have been developed for estimating the parameters of biexponential decay signals, which arise throughout magnetic resonance relaxometry (MRR) and the physical sciences. This is an intrinsically ill-posed problem so that estimates can depend strongly on noise and underlying parameter values. Regularization has proven to be a remarkably efficient procedure for providing more reliable solutions to ill-posed problems, while, more recently, neural networks have been used for parameter estimation. We re-address the problem of parameter estimation in biexponential models by introducing a novel form of neural network regularization which we call input layer regularization (ILR). Here, inputs to the neural network are composed of a biexponential decay signal augmented by signals constructed from parameters obtained from a regularized nonlinear least-squares estimate of the two decay time constants. We find that ILR results in a reduction in the error of time constant estimates on the order of 15%-50% or more, depending on the metric used and signal-to-noise level, with greater improvement seen for the time constant of the more rapidly decaying component. ILR is compatible with existing regularization techniques and should be applicable to a wide range of parameter estimation problems.
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Affiliation(s)
- Michael Rozowski
- Applied Mathematics and Statistics, and Scientific Computation, University of Maryland, College Park, Maryland, USA
- Department of Mathematics, University of Maryland, College Park, Maryland, USA
| | - Jonathan Palumbo
- National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Jay Bisen
- National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Chuan Bi
- National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Mustapha Bouhrara
- National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Wojciech Czaja
- Department of Mathematics, University of Maryland, College Park, Maryland, USA
| | - Richard G. Spencer
- National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
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Harborne AR, Kochan DP, Esch MM, Fidler RY, Mitchell MD, Butkowski DW, González-Rivero M. Drivers of fine-scale diurnal space use by a coral-reef mesopredatory fish. J Fish Biol 2022; 100:1009-1024. [PMID: 35099815 DOI: 10.1111/jfb.15006] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 01/27/2022] [Accepted: 01/29/2022] [Indexed: 06/14/2023]
Abstract
The habitat preferences of many reef fishes are well established, but the use of space within these habitats by non-site-attached species is poorly studied. The authors examined the space use of a functionally important mesopredator, graysby (Cephalopholis cruentata), on six patch reefs in the Florida Keys. A 1 m2 -scale grid was constructed on each reef and 16 individual C. cruentata were tracked diurnally in situ to identify space use. At the patch reef scale, larger C. cruentata were more active and had larger observed home ranges, although home ranges were also affected by fish density and the abundances of prey and predators. The total time in each 1 m2 grid cell was regressed against a range of fine-scale biotic variables, including multiple variables derived from structure-from-motion three-dimensional digital reconstructions of each reef. Nonetheless, time in grid cells (preferred microhabitats) was only significantly positively correlated with the height of carbonate structures, likely because the cavities they enclose are particularly suitable for predator avoidance, resting and ambushing prey. The ongoing flattening of reefs in the region caused by negative carbonate budgets is thus likely to have significant effects on the abundance and space use of C. cruentata. In addition to examining spatial patterns, we analysed C. cruentata waiting times in each grid cell before moving. These times were best approximated by a truncated power-law (heavy-tailed) distribution, indicating a "bursty" pattern of relatively long periods of inactivity interspersed with multiple periods of activity. Such a pattern has previously been identified in a range of temperate ambush predators, and the authors extend this move-wait behaviour, which may optimize foraging success, to a reef fish for the first time. Understanding how C. cruentata uses space and time is critical to fully identify their functional role and better predict the implications of fishing and loss of reef structure.
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Affiliation(s)
- Alastair R Harborne
- Institute of Environment, Department of Biological Sciences, Florida International University, North Miami, Florida, USA
| | - David P Kochan
- Institute of Environment, Department of Biological Sciences, Florida International University, North Miami, Florida, USA
| | - Melanie M Esch
- Institute of Environment, Department of Biological Sciences, Florida International University, North Miami, Florida, USA
| | - Robert Y Fidler
- Institute of Environment, Department of Biological Sciences, Florida International University, North Miami, Florida, USA
| | - Matthew D Mitchell
- Institute of Environment, Department of Biological Sciences, Florida International University, North Miami, Florida, USA
- Marine Biology Lab, Division of Science, New York University, Abu Dhabi, UAE
| | - Drew W Butkowski
- Institute of Environment, Department of Biological Sciences, Florida International University, North Miami, Florida, USA
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Abstract
Efficient foraging depends on decisions that account for the costs and benefits of various activities like movement, perception, and planning. We conducted a virtual foraging experiment set in the foothills of the Himalayas to examine how time and energy are expended to forage efficiently, and how foraging changes when constrained to a home range. Two hundred players foraged the human-scale landscape with simulated energy expenditure in search of naturally distributed resources. Results showed that efficient foragers produced periods of locomotion interleaved with perception and planning that approached theoretical expectations for Lévy walks, regardless of the home-range constraint. Despite this constancy, efficient home-range foraging trajectories were less diffusive by virtue of restricting locomotive search and spending more time instead scanning the environment to plan movement and detect far-away resources. Altogether, results demonstrate that humans can forage efficiently by arranging and adjusting Lévy-distributed search activities in response to environmental and task constraints.
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Affiliation(s)
- Ketika Garg
- Department of Cognitive and Information Sciences, University of California, Merced, CA, 95343, USA.
| | - Christopher T Kello
- Department of Cognitive and Information Sciences, University of California, Merced, CA, 95343, USA
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Abstract
A wide variety of animals become completely immobile after initial contact with a potential predator. This behaviour is considered to be a last-ditch escape strategy. Here, we test the hypothesis that such immobility should have an extremely unpredictable duration. We find that it spans more than three orders of magnitude in antlion larvae. We also analyse the second period of immobility that follows the first bout of immobility, and consider the distributions of both first and second immobility periods within the context of the intermittence that characterizes the movement of most organisms. Both immobility durations were fitted best by exponential distributions. Therefore, both were characterized by high variability and hence, unpredictability. The immobility half-life, its mean duration and standard deviation were greater for the first than the second immobility. Furthermore, individual consistency was weak or absent in repeated measures of the first immobility and between the first and second immobilities. Our quantitative approach can be replicated across taxa and would help link an understanding of immobility after an initial predator contact in both vertebrates and invertebrates. To facilitate this, we contend that the terminology should be simplified, and we advocate the use of the term post-contact immobility (PCI).
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Affiliation(s)
- Ana B Sendova-Franks
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Alan Worley
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Nigel R Franks
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
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Meyer X, MacIntosh AJJ, Chiaradia A, Kato A, Ramírez F, Sueur C, Ropert‐Coudert Y. Oceanic thermal structure mediates dive sequences in a foraging seabird. Ecol Evol 2020; 10:6610-6622. [PMID: 32724536 PMCID: PMC7381582 DOI: 10.1002/ece3.6393] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 04/07/2020] [Accepted: 04/14/2020] [Indexed: 11/11/2022] Open
Abstract
Changes in marine ecosystems are easier to detect in upper-level predators, like seabirds, which integrate trophic interactions throughout the food web.Here, we examined whether diving parameters and complexity in the temporal organization of diving behavior of little penguins (Eudyptula minor) are influenced by sea surface temperature (SST), water stratification, and wind speed-three oceanographic features influencing prey abundance and distribution in the water column.Using fractal time series analysis, we found that foraging complexity, expressed as the degree of long-range correlations or memory in the dive series, was associated with SST and water stratification throughout the breeding season, but not with wind speed. Little penguins foraging in warmer/more-stratified waters exhibited greater determinism (memory) in foraging sequences, likely as a response to prey aggregations near the thermocline. They also showed higher foraging efficiency, performed more dives and dove to shallower depths than those foraging in colder/less-stratified waters.Reductions in the long-term memory of dive sequences, or in other words increases in behavioral stochasticity, may suggest different strategies concerning the exploration-exploitation trade-off under contrasting environmental conditions.
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Affiliation(s)
- Xavier Meyer
- CNRSIPHC UMR7178Université de StrasbourgStrasbourgFrance
- Kyoto University Primate Research InstituteInuyamaJapan
| | | | - Andre Chiaradia
- Conservation DepartmentPhillip Island Nature ParksCowesVicAustralia
| | - Akiko Kato
- Centre d'Etudes Biologiques de ChizéCNRS UMR 7372Université de La RochelleVilliers‐en‐BoisFrance
| | - Francisco Ramírez
- Departament de Biologia EvolutivaEcologia i Ciènces AmbientalsUniversitat de BarcelonaBarcelonaSpain
| | - Cédric Sueur
- CNRSIPHC UMR7178Université de StrasbourgStrasbourgFrance
| | - Yan Ropert‐Coudert
- Centre d'Etudes Biologiques de ChizéCNRS UMR 7372Université de La RochelleVilliers‐en‐BoisFrance
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Le Guen C, Kato A, Raymond B, Barbraud C, Beaulieu M, Bost CA, Delord K, MacIntosh AJJ, Meyer X, Raclot T, Sumner M, Takahashi A, Thiebot JB, Ropert-Coudert Y. Reproductive performance and diving behaviour share a common sea-ice concentration optimum in Adélie penguins (Pygoscelis adeliae). Glob Chang Biol 2018; 24:5304-5317. [PMID: 29957836 DOI: 10.1111/gcb.14377] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Accepted: 05/29/2018] [Indexed: 06/08/2023]
Abstract
The Southern Ocean is currently experiencing major environmental changes, including in sea-ice cover. Such changes strongly influence ecosystem structure and functioning and affect the survival and reproduction of predators such as seabirds. These effects are likely mediated by reduced availability of food resources. As such, seabirds are reliable eco-indicators of environmental conditions in the Antarctic region. Here, based on 9 years of sea-ice data, we found that the breeding success of Adélie penguins (Pygoscelis adeliae) reaches a peak at intermediate sea-ice cover (ca. 20%). We further examined the effects of sea-ice conditions on the foraging activity of penguins, measured at multiple scales from individual dives to foraging trips. Analysis of temporal organisation of dives, including fractal and bout analyses, revealed an increasingly consistent behaviour during years with extensive sea-ice cover. The relationship between several dive parameters and sea-ice cover in the foraging area appears to be quadratic. In years of low and high sea-ice cover, individuals adjusted their diving effort by generally diving deeper, more frequently and by resting at the surface between dives for shorter periods of time than in years with intermediate sea-ice cover. Our study therefore suggests that sea-ice cover is likely to affect the reproductive performance of Adélie penguins through its effects on foraging behaviour, as breeding success and most diving parameters share a common optimum. Some years, however, deviated from this general trend, suggesting that other factors (e.g. precipitation during the breeding season) might sometimes become preponderant over the sea-ice effects on breeding and foraging performance. Our study highlights the value of monitoring fitness parameters and individual behaviour concomitantly over the long-term to better characterize optimal environmental conditions and potential resilience of wildlife. Such an approach is crucial if we want to anticipate the effects of environmental change on Antarctic penguin populations.
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Affiliation(s)
- Camille Le Guen
- Centre d'Etudes Biologiques de Chizé, UMR7372 CNRS-Université La Rochelle, Villiers en Bois, France
| | - Akiko Kato
- Centre d'Etudes Biologiques de Chizé, UMR7372 CNRS-Université La Rochelle, Villiers en Bois, France
| | - Ben Raymond
- Australian Antarctic Division, Department of the Environment, Australian Government, Kingston, Tasmania, Australia
| | - Christophe Barbraud
- Centre d'Etudes Biologiques de Chizé, UMR7372 CNRS-Université La Rochelle, Villiers en Bois, France
| | - Michaël Beaulieu
- Zoological Institute & Museum, University of Greifswald, Greifswald, Germany
- German Oceanographic Museum, Stralsund, Germany
| | - Charles-André Bost
- Centre d'Etudes Biologiques de Chizé, UMR7372 CNRS-Université La Rochelle, Villiers en Bois, France
| | - Karine Delord
- Centre d'Etudes Biologiques de Chizé, UMR7372 CNRS-Université La Rochelle, Villiers en Bois, France
| | | | - Xavier Meyer
- CNRS, Institut Pluridisciplinaire Hubert Curien UMR7178, Université de Strasbourg, Strasbourg, France
| | - Thierry Raclot
- CNRS, Institut Pluridisciplinaire Hubert Curien UMR7178, Université de Strasbourg, Strasbourg, France
| | - Michael Sumner
- Australian Antarctic Division, Department of the Environment, Australian Government, Kingston, Tasmania, Australia
| | - Akinori Takahashi
- National Institute of Polar Research, Tachikawa, Tokyo, Japan
- Department of Polar Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, Japan
| | | | - Yan Ropert-Coudert
- Centre d'Etudes Biologiques de Chizé, UMR7372 CNRS-Université La Rochelle, Villiers en Bois, France
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Reynolds AM, Paiva VH, Cecere JG, Focardi S. Lévy patterns in seabirds are multifaceted describing both spatial and temporal patterning. Front Zool 2016; 13:29. [PMID: 27366198 PMCID: PMC4928295 DOI: 10.1186/s12983-016-0160-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2016] [Accepted: 06/17/2016] [Indexed: 11/10/2022] Open
Abstract
Background The flight patterns of albatrosses and shearwaters have become a touchstone for much of Lévy flight research, spawning an extensive field of enquiry. There is now compelling evidence that the flight patterns of these seabirds would have been appreciated by Paul Lévy, the mathematician after whom Lévy flights are named. Here we show that Lévy patterns (here taken to mean spatial or temporal patterns characterized by distributions with power-law tails) are, in fact, multifaceted in shearwaters being evident in both spatial and temporal patterns of activity. Results We tested for Lévy patterns in the at-sea behaviours of two species of shearwater breeding in the North Atlantic Ocean (Calonectris borealis) and the Mediterranean sea (C. diomedea) during their incubating and chick-provisioning periods. We found that distributions of flight durations, on/in water durations and inter-dive time-intervals have power-law tails and so bear the hallmarks of Lévy patterns. Conclusions The occurrence of these statistical laws is remarkable given that bird behaviours are strongly shaped by an individual’s motivational state and by complex environmental interactions. Our observations could take Lévy patterns as models of animal behaviour to a new level by going beyond the characterisation of spatial movements to characterise how different behaviours are interwoven throughout daily animal life.
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Affiliation(s)
| | - Vitor H Paiva
- MARE - Marine and Environmental Sciences Centre, Department of Life Sciences, University of Coimbra, Coimbra, 3004-517 Portugal
| | - Jacopo G Cecere
- ISPRA, Ozzano dell'Emilia, 40064 Italy ; LIPU, Conservation Department, Parma, 43100 Italy
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Reynolds A. Venturing beyond the Lévy flight foraging hypothesis: Reply to comments on "Liberating Lévy walk research from the shackles of optimal foraging". Phys Life Rev 2015; 14:115-9. [PMID: 26283073 DOI: 10.1016/j.plrev.2015.07.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 07/20/2015] [Indexed: 01/18/2023]
Affiliation(s)
- Andy Reynolds
- Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK.
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