98 research outputs found
Multilayer network analysis : new opportunities and challenges for studying animal social systems
M.J.H. is supported by a European Research Council H2020 grant (#638873) awarded to Ellouise Leadbeater. M.J.S is funded by the University of Exeter.Peer reviewedPublisher PD
Understanding animal social structure: exponential random graph models in animal behaviour research
M.J.S. is funded by a NERC grant NE/M004546/1. D.N.F. is funded by the Natural Sciences and Engineering Research Council of Canada. We thank Jared Wilson-Aggarwal for helpful discussions and two anonymous referees for constructive comments that improved the article.Peer reviewedPublisher PD
The use of multilayer network analysis in animal behaviour
Network analysis has driven key developments in research on animal behaviour
by providing quantitative methods to study the social structures of animal
groups and populations. A recent formalism, known as \emph{multilayer network
analysis}, has advanced the study of multifaceted networked systems in many
disciplines. It offers novel ways to study and quantify animal behaviour as
connected 'layers' of interactions. In this article, we review common questions
in animal behaviour that can be studied using a multilayer approach, and we
link these questions to specific analyses. We outline the types of behavioural
data and questions that may be suitable to study using multilayer network
analysis. We detail several multilayer methods, which can provide new insights
into questions about animal sociality at individual, group, population, and
evolutionary levels of organisation. We give examples for how to implement
multilayer methods to demonstrate how taking a multilayer approach can alter
inferences about social structure and the positions of individuals within such
a structure. Finally, we discuss caveats to undertaking multilayer network
analysis in the study of animal social networks, and we call attention to
methodological challenges for the application of these approaches. Our aim is
to instigate the study of new questions about animal sociality using the new
toolbox of multilayer network analysis.Comment: Thoroughly revised; title changed slightl
Cosmic Evolution of Black Holes and Spheroids. II: Scaling Relations at z=0.36
We combine Hubble Space Telescope images of a sample of 20 Seyfert galaxies
at z=0.36 with spectroscopic information from the Keck Telescope to determine
the black hole mass - spheroid luminosity relation (M-L), the Fundamental Plane
(FP) of the host galaxies and the M-sigma relation. Assuming pure luminosity
evolution, we find that the host spheroids had smaller luminosity and stellar
velocity dispersion than today for a fixed M. The offsets correspond to Delta
log L_B,0=0.40+-0.11+-0.15 (Delta log M = 0.51+-0.14+-0.19) and Delta log sigma
= 0.13+-0.03+-0.05 (Delta log M = 0.54+-0.12+-0.21), respectively for the M-L
and M-sigma relation. A detailed analysis of known systematic errors and
selection effects shows that they cannot account for the observed offset. The
data are inconsistent with pure luminosity evolution and the existence of
universal and tight scaling relations. To obey the three local scaling
relations by z=0 the distant spheroids have to grow their stellar mass by
approximately 60% (\Delta log M_sph=0.20+-0.14) in the next 4 billion years.
The measured evolution can be expressed as M/ M_sph ~ (1+z)^{1.5+-1.0}. Based
on the disturbed morphologies of a fraction of the sample (6/20) we suggest
collisional mergers with disk-dominated systems as evolutionary mechanism.Comment: 17 pages, 10 figures; accepted for publication in the Astrophysical
Journa
Diversity in Valuing Social Contact and Risk Tolerance Lead to the Emergence of Homophily in Populations Facing Infectious Threats
How self-organization leads to the emergence of structure in social
populations remains a fascinating and open question in the study of complex
systems. One frequently observed structure that emerges again and again across
systems is that of self-similar community, i.e., homophily. We use a game
theoretic perspective to explore a case in which individuals choose affiliation
partnerships based on only two factors: the value they place on having social
contacts, and their risk tolerance for exposure to threat derived from social
contact (e.g., infectious disease, threatening ideas, etc.). We show how
diversity along just these two influences are sufficient to cause the emergence
of self-organizing homophily in the population. We further consider a case in
which extrinsic social factors influence the desire to maintain particular
social ties, and show the robustness of emergent homophilic patterns to these
additional influences. These results demonstrate how observable
population-level homophily may arise out of individual behaviors that balance
the value of social contacts against the potential risks associated with those
contacts. We present and discuss these results in the context of outbreaks of
infectious disease in human populations. Complementing the standard narrative
about how social division alters epidemiological risk, we here show how
epidemiological risk may deepen social divisions in human populations.Comment: 17 pages, 4 figure
Multilayer and multiplex networks: an introduction to their use in veterinary epidemiology
This is the final version. Available from Frontiers Media via the DOI in this record.Contact network analysis has become a vital tool for conceptualizing the spread of pathogens in animal populations and is particularly useful for understanding the implications of heterogeneity in contact patterns for transmission. However, the transmission of most pathogens cannot be simplified to a single mode of transmission and, thus, a single definition of contact. In addition, host-pathogen interactions occur in a community context, with many pathogens infecting multiple host species and most hosts being infected by multiple pathogens. Multilayer networks provide a formal framework for researching host-pathogen systems in which multiple types of transmission-relevant interactions, defined as network layers, can be analyzed jointly. Here, we provide an overview of multilayer network analysis and review applications of this novel method to epidemiological research questions. We then demonstrate the use of this technique to analyze heterogeneity in direct and indirect contact patterns amongst swine farms in the United States. When contact among nodes can be defined in multiple ways, a multilayer approach can advance our ability to use networks in epidemiological research by providing an improved approach for defining epidemiologically relevant groups of interacting nodes and changing the way we identify epidemiologically important individuals such as superspreaders.Biotechnology and Biological Sciences Research Council (BBSRC)NIFA-NSF-NIH Ecology and Evolution of Infectious Disease awardAgriculture and Food Research InitiativeSwine Health Information Center (SHIC)University of MinnesotaUniversity of Exete
Evaluating Bayesian stable isotope mixing models of wild animal diet and the effects of trophic discrimination factors and informative priors
Funding information University of Exeter; CONICYT, Grant/ Award Number: 3190800; ERC, Grant/ Award Number: 310820Peer reviewedPublisher PD
Resolving the Formation of Protogalaxies. II. Central Gravitational Collapse
Numerous cosmological hydrodynamic studies have addressed the formation of
galaxies. Here we choose to study the first stages of galaxy formation,
including non-equilibrium atomic primordial gas cooling, gravity and
hydrodynamics. Using initial conditions appropriate for the concordance
cosmological model of structure formation, we perform two adaptive mesh
refinement simulations of ~10^8 M_sun galaxies at high redshift. The
calculations resolve the Jeans length at all times with more than 16 cells and
capture over 14 orders of magnitude in length scales. In both cases, the dense,
10^5 solar mass, one parsec central regions are found to contract rapidly and
have turbulent Mach numbers up to 4. Despite the ever decreasing Jeans length
of the isothermal gas, we only find one site of fragmentation during the
collapse. However, rotational secular bar instabilities transport angular
momentum outwards in the central parsec as the gas continues to collapse and
lead to multiple nested unstable fragments with decreasing masses down to
sub-Jupiter mass scales. Although these numerical experiments neglect star
formation and feedback, they clearly highlight the physics of turbulence in
gravitationally collapsing gas. The angular momentum segregation seen in our
calculations plays an important role in theories that form supermassive black
holes from gaseous collapse.Comment: Replaced with accepted version. To appear in ApJ v681 (July 1
Variability of Moderate Luminosity Active Galactic Nuclei at z=0.36
We monitored 13 moderate luminosity active galactic nuclei at z=0.36 to
measure flux variability, explore feasibility of reverberation mapping, and
determine uncertainties on estimating black hole mass from single-epoch data.
Spectra and images were obtained with approximately weekly cadence for up to 4
months, using the KAST spectrograph on the 3-m Shane Telescope. In broad band
we detect peak-to-peak variations of 9-37% and rms variations of 2-10%. The
observed flux variability in the g' band (rest-frame 2800-4000\AA) is
consistent with that in the r' band (rest-frame 4000-5200\AA), but with larger
amplitude. However, after correcting for stellar light dilution, using Hubble
Space Telescope images, we find nuclear variability of 3-24% (rms variation)
with similar amplitudes in the g' and r' bands within the errors. Intrinsic
flux variability of the H line is also detected at the 3-13% level,
after accounting for systematic errors on the spectrophotometry. This
demonstrates that a reverberation mapping campaign beyond the local universe
can be carried out with a 3-m class telescope, provided that sufficiently long
light curves are obtained. Finally, we compare the H FWHM measured from
mean spectra with that measured from single-epoch data, and find no bias but an
rms scatter of 14%, mostly accounted for by the uncertainty on FWHM
measurements. The propagated uncertainty on black hole mass estimates, due to
the FWHM measurement errors using low S/N (10--15 per pixel) single-epoch
spectra, is 30%.Comment: 12 pages, 7 figures, accepted by Ap
Associations between abundances of free-roaming gamebirds and common buzzards Buteo buteo are not driven by consumption of gamebirds in the buzzard breeding season
Releasing gamebirds in large numbers for sport shooting may directly or indirectly influence the abundance, distribution and population dynamics of native wildlife. The abundances of generalist predators have been positively associated with the abundance of gamebirds. These relationships have implications for prey populations, with the potential for indirect impacts of gamebird releases on wider biodiversity. To understand the basis of these associations, we investigated variation in territory size, prey provisioning to chicks, and breeding success of common buzzards Buteo buteo, and associations with variation in the abundances of free- roaming gamebirds, primarily pheasants Phasianus colchicus, and of rabbits Oryctolagus cuniculus and field voles Microtus agrestis, as important prey for buzzards. The relative abundance of game-birds, but not those of rabbits or voles, was weakly but positively correlated with our index of buzzard territory size. Gamebirds were rarely brought to the nest. Rabbits and voles, and not gamebirds, were provisioned to chicks in proportion to their relative abundance. The number of buzzard chicks increased with provisioning rates of rabbits, in terms of both provisioning frequency and biomass, but not with provisioning rates for gamebirds or voles. Associations between the abundances of buzzards and gamebirds may not be a consequence of the greater availability of gamebirds as prey during the buzzard breeding season. Instead, the association may arise either from habitat or predator management leading to higher densities of alternative prey (in this instance, rabbits), or from greater availability of gamebirds as prey or carrion during the autumn and winter shooting season. The interactions between gamebird releases and associated practices of predator control and shooting itself require better understanding to more effectively intervene in any one aspect of this complex social-ecological system
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