ABSTRACT
Contrary to the standard lore, there is mounting observational evidence that feedback from active galactic nuclei (AGN) may also play a role at the low-mass end of the galaxy population. We ...investigate this using the cosmological simulation suite fable, with a particular focus on the dwarf regime (Mstellar < 109.5 M⊙). We find that overmassive black holes (BHs), with respect to the mean scaling relations with their host galaxies, drive hotter and faster outflows and lead to significantly reduced gas mass fractions. They are also more likely to display a kinematically misaligned ionized gas component in our mock MaNGA velocity maps, although we caution that cosmic inflows and mergers contribute to misalignments as well. While in the local Universe the majority of AGN in dwarfs are much dimmer than the stellar component, for z ≥ 2 there is a significant population that outshines their hosts. These high-redshift overmassive BHs contribute to the quenching of dwarfs, whereas at late cosmic times supernova (SN) feedback is more efficient. While our results are overall in good agreement with X-ray observations of AGN in dwarfs, the lack of high-luminosity X-ray AGN in fable at low redshifts highlights an interesting possibility that SN feedback could be too strong in fable’s dwarfs, curtailing AGN growth and feedback. We predict that future observations may uncover many more AGN in dwarfs with lower luminosities and at higher redshifts.
Collapsing population cycles Ims, Rolf A.; Henden, John-André; Killengreen, Siw T.
Trends in ecology & evolution (Amsterdam),
02/2008, Volume:
23, Issue:
2
Journal Article
Peer reviewed
During the past two decades population cycles in voles, grouse and insects have been fading out in Europe. Here, we discuss the cause and implication of these changes. Several lines of evidence now ...point to climate forcing as the general underlying cause. However, how climate interacts with demography to induce regime shifts in population dynamics is likely to differ among species and ecosystems. Herbivores with high-amplitude population cycles, such as voles, lemmings, snowshoe hares and forest Lepidoptera, form the heart of terrestrial food web dynamics. Thus, collapses of these cycles are also expected to imply collapses of important ecosystem functions, such as the pulsed flows of resources and disturbances.
ABSTRACT
We study the gas and stellar mass content of galaxy groups and clusters in the fable suite of cosmological hydrodynamical simulations, including the evolution of their central brightest ...cluster galaxies (BCGs), satellite galaxies, and intracluster light (ICL). The total gas and stellar mass of fable clusters are in good agreement with observations and show negligible redshift evolution at fixed halo mass for $M_{500} \gtrsim 3 \times 10^{14} \, \mathrm{M}_{\odot }$ at z ≲ 1, in line with recent findings from Sunyaev–Zel’dovich (SZ)-selected cluster samples. Importantly, the simulations predict significant redshift evolution in these quantities in the low-mass ($M_{500} \sim 10^{14} \, \mathrm{M}_{\odot }$) regime, which will be testable with upcoming SZ surveys such as SPT-3G. Whilst the stellar masses of fable BCGs are in reasonable agreement with observations, the total stellar mass in satellite galaxies is lower than observed and the total mass in ICL is somewhat higher. This may be caused by enhanced tidal stripping of satellite galaxies due to their large sizes. BCGs are characterized by moderate stellar mass growth at z < 1 coincident with a late-time development of the ICL. The level of BCG mass growth is in good agreement with recent observations; however, we caution that the inferred growth depends sensitively on the mass definition. We further show that in situ star formation contributes more than half the mass of a BCG over its lifetime, the bulk of which is gained at z > 1 where star formation rates are highest. The stellar mass profiles of the BCG+ICL component are similar to observed profiles out to ∼100 kpc at z ≈ 0 and follow a close to power law shape out to several hundred kpc. We further demonstrate that the inferred size growth of BCGs can be severely biased by the choice of parametric model and the outer radius of the fit.
Abstract
We study the redshift evolution of the X-ray and Sunyaev–Zel’dovich (SZ) scaling relations for galaxy groups and clusters in the fable suite of cosmological hydrodynamical simulations. Using ...an expanded sample of 27 high-resolution zoom-in simulations, together with a uniformly sampled cosmological volume to sample low-mass systems, we find very good agreement with the majority of observational constraints up to z ∼ 1. We predict significant deviations of all examined scaling relations from the simple self-similar expectations. While the slopes are approximately independent of redshift, the normalizations evolve positively with respect to self-similarity, even for commonly used mass proxies such as the YX parameter. These deviations are due to a combination of factors, including more effective active galactic nuclei feedback in lower mass haloes, larger binding energy of gas at a given halo mass at higher redshifts, and larger non-thermal pressure support from kinetic motions at higher redshifts. Our results have important implications for cluster cosmology from upcoming SZ surveys such as SPT-3G, ACTpol, and CMB-S4, as relatively small changes in the observable–mass scaling relations (within theoretical uncertainties) have a large impact on the predicted number of high-redshift clusters and hence on our ability to constrain cosmology using cluster abundances. In addition, we find that the intrinsic scatter of the relations, which agrees well with most observational constraints, increases at lower redshifts and for lower mass systems. This calls for a more complex parametrization than adopted in current observational studies to be able to accurately account for selection biases.
We present the Feedback Acting on Baryons in Large-scale Environments suite of cosmological hydrodynamical simulations of galaxies, groups, and clusters. The simulations use the AREPO moving-mesh ...code with a set of physical models for galaxy formation based on the successful Illustris simulation, but with updated active galactic nucleus (AGN) and supernovae feedback models. This allows us to simultaneously reproduce the observed redshift evolution of the galaxy stellar mass function together with the stellar and gas mass fractions of local groups and clusters across a wide range of halo masses. Focusing on the properties of groups and clusters, we find very good agreement with a range of observed scaling relations, including the X-ray luminosity–total mass and gas mass relations as well as the total mass–temperature and Sunyaev–Zel’dovich flux–mass relations. Careful comparison of our results with scaling relations based on X-ray hydrostatic masses as opposed to weak-lensing-derived masses reveals some discrepancies, which hint towards a non-negligible X-ray mass bias in observed samples. We further show that radial profiles of density, pressure, and temperature of the simulated intracluster medium are in very good agreement with observations, in particular for r > 0.3 r500. In the innermost regions however we find too large entropy cores, which indicates that a more sophisticated modelling of the physics of AGN feedback may be required to accurately reproduce the observed populations of cool-core and non-cool-core clusters.
To improve understanding and management of the consequences of current rapid environmental change, ecologists advocate using long‐term monitoring data series to generate iterative near‐term ...predictions of ecosystem responses. This approach allows scientific evidence to increase rapidly and management strategies to be tailored simultaneously. Iterative near‐term forecasting may therefore be particularly useful for adaptive monitoring of ecosystems subjected to rapid climate change. Here, we show how to implement near‐term forecasting in the case of a harvested population of rock ptarmigan in high‐arctic Svalbard, a region subjected to the largest and most rapid climate change on Earth. We fitted state‐space models to ptarmigan counts from point transect distance sampling during 2005–2019 and developed two types of predictions: (1) explanatory predictions to quantify the effect of potential drivers of ptarmigan population dynamics, and (2) anticipatory predictions to assess the ability of candidate models of increasing complexity to forecast next‐year population density. Based on the explanatory predictions, we found that a recent increasing trend in the Svalbard rock ptarmigan population can be attributed to major changes in winter climate. Currently, a strong positive effect of increasing average winter temperature on ptarmigan population growth outweighs the negative impacts of other manifestations of climate change such as rain‐on‐snow events. Moreover, the ptarmigan population may compensate for current harvest levels. Based on the anticipatory predictions, the near‐term forecasting ability of the models improved nonlinearly with the length of the time series, but yielded good forecasts even based on a short time series. The inclusion of ecological predictors improved forecasts of sharp changes in next‐year population density, demonstrating the value of ecosystem‐based monitoring. Overall, our study illustrates the power of integrating near‐term forecasting in monitoring systems to aid understanding and management of wildlife populations exposed to rapid climate change. We provide recommendations for how to improve this approach.
Iterative near‐term forecasting based on long‐term monitoring data may be particularly useful for adaptive management of ecosystems subjected to rapid climate change. We used this approach to explain and forecast population dynamics of ptarmigan in the high‐Arctic Archipelago of Svalbard, a region experiencing profound warming. We found that a recent increasing trend in the Svalbard rock ptarmigan population can be attributed to major changes in winter climate, especially in terms of increased temperature. Moreover, our model yielded good forecasts of next‐year ptarmigan population density even if based on a relatively short time series.
Increasing populations of mesopredators are suspected to cause declines in vulnerable wildlife to the extent that mesopredator decimation actions (culling) have become commonplace. Design ...constraints, especially a lack of spatial replication, often hamper the assessment of the impact of such actions. However, extensive temporal replication (i.e. time series) and accounting for potentially confounding variables may alleviate this problem.
In alpine‐arctic tundra, the red fox Vulpes vulpes is increasing, while many bird species are declining, likely due to increased predation. Here, we assessed the impact of a long‐term (12‐year) and spatially extensive (~3,500 km2) red fox culling action on the red‐listed willow ptarmigan Lagopus lagopus in the Norwegian Arctic. Ptarmigan populations were monitored annually in the impact area and in an adjacent no‐action area, including a 5‐year period before the action commenced. While logistical constraints prohibited monitoring of red fox population densities, the number of culled foxes and three influential food web covariates were monitored after the onset of the culling action.
A Before‐After‐Control‐Impact‐Paired‐Series (BACIPS) analysis without food web covariates indicated that red fox culling curbed the decline of the population in the impact area, and that ptarmigan population density became ~25% higher than in the reference area.
Spatially and temporally variable drivers within the food web confounded the simple BACIPS analysis. Accounting for three food web drivers as covariates in a linear mixed model after the onset of action, yielded a more unbiased impact estimate that amounted to ~40% higher ptarmigan population density (4.3 more ptarmigan/km2) in the red fox impact area.
Synthesis and applications. We provide the first evidence of the role of the recent expansion of red fox in the decline of bird populations in tundra. We also show that red fox culling may be able to curb such declines, given that management actions are large scale and long term. As mesopredator culling campaigns are often expensive and controversial, it is important that their impacts are accurately assessed. We demonstrate that the accuracy of impact assessments can be profoundly increased by monitoring drivers of food web dynamics that impinge on the target species so that such drivers can be included as covariates in the analysis. This applies in particular to declining bird populations in boreal and arctic food webs ruled by strong multi‐annual interaction cycles.
We provide the first evidence of the role of the recent expansion of red fox in the decline of bird populations in tundra. We also show that red fox culling may be able to curb such declines, given that management actions are large scale and long term. As mesopredator culling campaigns are often expensive and controversial, it is important that their impacts are accurately assessed. We demonstrate that the accuracy of impact assessments can be profoundly increased by monitoring drivers of food web dynamics that impinge on the target species so that such drivers can be included as covariates in the analysis. This applies in particular to declining bird populations in boreal and arctic food webs ruled by strong multi‐annual interaction cycles.
Assessing the effectiveness of conservation actions to halt population declines is challenging when confounded by other factors. We assessed whether culling of red fox, a predator currently ...increasing in number in the sub‐Arctic, contributed to recent recovery of the critically endangered Fennoscandian population of Lesser White‐fronted Goose Anser erythropus, while controlling for potentially confounding food web dynamics.
Using 19 years of data, 10 before and 9 after the implementation of annual red fox culling, we estimated the effect of this action on annual performance of the goose population. We corrected for the potentially confounding effects of cyclic rodent dynamics and semi‐domestic reindeer carrion abundance, both of which are expected to trigger predator functional and numerical responses, as well as for annual variation in spring phenology.
Goose reproductive success fluctuated in synchrony with the rodent cycle and was negatively related to abundant carrion. When accounting for these aspects of food web dynamics, there was no evidence for an effect of red fox culling on reproductive success. There was, however, a tendency for fox culling to increase adult survival.
Our analysis suggests that goose performance in their breeding area is influenced by fluctuating offspring predation, mediated by mainly natural (rodents) and partly anthropogenic (semi‐domestic reindeer) dynamic components of the food web.
Synthesis and applications. The effect of a decade‐long red fox culling on goose reproductive success and survival is currently uncertain, despite predation driving reproductive success through changes in rodent and reindeer carrion abundance. New management actions may consist of regulation of reindeer herd sizes and/or removal of carcasses to reduce the subsidizing effect of reindeer carrion on mesopredators. Getting robust evidence regarding the impact of red fox culling on population recovery depends on continuing research to disentangle food web dynamics and efficiency of management actions.
The effect of a decade‐long red fox culling on goose reproductive success and survival is currently uncertain, despite predation driving reproductive success through changes in rodent and reindeer carrion abundance. New management actions may consist of regulation of reindeer herd sizes and/or removal of carcasses to reduce the subsidizing effect of reindeer carrion on mesopredators. Getting robust evidence regarding the impact of red fox culling on population recovery depends on continuing research to disentangle food web dynamics and efficiency of management actions.
Graft-versus-host disease (GVHD) in the gastrointestinal (GI) tract is the principal determinant of lethality following allogeneic bone marrow transplantation (BMT). Here, we examined the mechanisms ...that initiate GVHD, including the relevant antigen-presenting cells. MHC class II was expressed on intestinal epithelial cells (IECs) within the ileum at steady state but was absent from the IECs of germ-free mice. IEC-specific deletion of MHC class II prevented the initiation of lethal GVHD in the GI tract. MHC class II expression on IECs was absent from mice deficient in the TLR adaptors MyD88 and TRIF and required IFNγ secretion by lamina propria lymphocytes. IFNγ responses are characteristically driven by IL-12 secretion from myeloid cells. Antibiotic-mediated depletion of the microbiota inhibited IL-12/23p40 production by ileal macrophages. IL-12/23p40 neutralization prevented MHC class II upregulation on IECs and initiation of lethal GVHD in the GI tract. Thus, MHC class II expression by IECs in the ileum initiates lethal GVHD, and blockade of IL-12/23p40 may represent a readily translatable therapeutic strategy.
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•The microbiota influences MHC class II expression on IECs in the ileum•MHC class II expression on IECs requires an IL-12-IFNγ cytokine axis•MHC class II+ IECs present antigen, activate CD4+ T cells, and initiate lethal gut GVHD•IL-12/23p40 neutralization pretransplant prevents the initiation of lethal GVHD
Graft-versus-host disease in the gastrointestinal tract is the principal determinant of lethality following allogeneic bone marrow transplantation. Koyama et al. find that MHC class II-dependent antigen presentation by ileal intestinal epithelial cells (IECs) is critical for the initiation of lethal GVHD in the gut, define the requirements for IEC MHC class II expression, and propose IL-12 neutralization as a therapeutic strategy for GVHD.
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