478 research outputs found
Ignorance can be evolutionarily beneficial
Information is increasingly being viewed as a resource used by organisms to
increase their fitness. Indeed, it has been formally shown that there is a
sensible way to assign a reproductive value to information and it is
non-negative. However, all of this work assumed that information collection is
cost-free. Here, we account for such a cost and provide conditions for when the
reproductive value of information will be negative. In these instances,
counter-intuitively, it is in the interest of the organism to remain ignorant.
We link our results to empirical studies where Bayesian behaviour appears to
break down in complex environments and provide an alternative explanation of
lowered arousal thresholds in the evolution of sleep.Comment: 5 pages, submitte
Loschmidt echo and fidelity decay near an exceptional point
Non-Hermitian classical and open quantum systems near an exceptional point
(EP) are known to undergo strong deviations in their dynamical behavior under
small perturbations or slow cycling of parameters as compared to Hermitian
systems. Such a strong sensitivity is at the heart of many interesting
phenomena and applications, such as the asymmetric breakdown of the adiabatic
theorem, enhanced sensing, non-Hermitian dynamical quantum phase transitions
and photonic catastrophe. Like for Hermitian systems, the sensitivity to
perturbations on the dynamical evolution can be captured by Loschmidt echo and
fidelity after imperfect time reversal or quench dynamics. Here we disclose a
rather counterintuitive phenomenon in certain non-Hermitian systems near an EP,
namely the deceleration (rather than acceleration) of the fidelity decay and
improved Loschmidt echo as compared to their Hermitian counterparts, despite
large (non-perturbative) deformation of the energy spectrum introduced by the
perturbations. This behavior is illustrated by considering the fidelity decay
and Loschmidt echo for the single-particle hopping dynamics on a tight-binding
lattice under an imaginary gauge field.Comment: 11 pages, 6 figures, to appear in Annalen der Physi
Duality and the vibrational modes of a Cooper-pair Wigner crystal
When quantum fluctuations in the phase of the superconducting order parameter
destroy the off-diagonal long range order, duality arguments predict the
formation of a Cooper pair crystal. This effect is thought to be responsible
for the static checkerboard patterns observed recently in various underdoped
cuprate superconductors by means of scanning tunneling spectroscopy. Breaking
of the translational symmetry in such a Cooper pair Wigner crystal may, under
certain conditions, lead to the emergence of low lying transverse vibrational
modes which could then contribute to thermodynamic and transport properties at
low temperatures. We investigate these vibrational modes using a continuum
version of the standard vortex-boson duality, calculate the speed of sound in
the Cooper pair Wigner crystal and deduce the associated specific heat and
thermal conductivity. We then suggest that these modes could be responsible for
the mysterious bosonic contribution to the thermal conductivity recently
observed in strongly underdoped ultraclean single crystals of YBCO tuned across
the superconductor-insulator transition.Comment: 14 pages; 3 figures; corrected the sample size value; version 3 to
appear in PR
Sex ratio distorting microbes exacerbate arthropod extinction risk in variable environments
Maternally-inherited sex ratio distorting microbes (SRDMs) are common among arthropod species. Typically, these microbes cause female-biased sex ratios in host broods, either by; killing male offspring, feminising male offspring, or inducing parthenogenesis. As a result, infected populations can experience drastic ecological and evolutionary change. The mechanism by which SRDMs operate is likely to alter their impact on host evolutionary ecology; despite this, the current literature is heavily biased towards a single mechanism of sex ratio distortion, male-killing. Furthermore, amidst the growing concerns surrounding the loss of arthropod diversity, research into the impact of SRDMs on the viability of arthropod populations is generally lacking. In this study, using a theoretical approach, we model the epidemiology of an understudied mechanism of microbially-induced sex ratio distortionâfeminisationâto ask an understudied questionâhow do SRDMs impact extinction risk in a changing environment? We constructed an individual-based model and measured host population extinction risk under various environmental and epidemiological scenarios. We also used our model to identify the precise mechanism modulating extinction. We find that the presence of feminisers increases host population extinction risk, an effect that is exacerbated in highly variable environments. We also identified transmission rate as the dominant epidemiological trait responsible for driving extinction. Finally, our model shows that sex ratio skew is the mechanism driving extinction. We highlight feminisers and, more broadly, SRDMs as important determinants of the resilience of arthropod populations to environmental change
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Insect herbivory on seedlings of rainforest trees: effects of density and distance of conspecific and heterospecific neighbours
Natural enemies of plants such as insect herbivores can contribute to structuring and maintaining plant diversity in tropical forests. Most research in this area has focused on the role of specialized enemies and the extent to which herbivory on individual plant species is densityâdependent. Relatively few insect herbivores specialize on a single host plant species. Insect herbivores that feed on more than one plant species may link the regeneration dynamics of their host species through âapparent competitionâ or âapparent mutualism.â We investigated herbivory and survival of seedlings of two tropical tree species (Cordia alliodora and Cordia bicolor) in the forests of Barro Colorado Island (Panama). We used experiments and observations to assess seedling fate in relation to the presence of conspecifics and heterospecifics across a range of spatial scales. Herbivory significantly increased seedling mortality and was highest at high local densities of C. alliodora seedlings. There was also evidence that high local densities of C. alliodora increased herbivory on coâoccurring C. bicolor seedlings. Synthesis. The elevated rates of seedling herbivory at high densities of conspecifics documented in our study are consistent with the predictions of the JanzenâConnell hypothesis, which explains how so many plant species can coexist in tropical forests. Our data also highlight the possibility that herbivoreâmediated densityâdependence, facilitated by herbivores that feed on multiple plant species, can also occur across plant species. Enemyâmediated indirect effects of this sort have the potential to structure plant communities
Sex ratio distorting microbes exacerbate arthropod extinction risk in variable environments
Maternally-inherited sex ratio distorting microbes (SRDMs) are common among arthropod species. Typically, these microbes cause female-biased sex ratios in host broods, either by; killing male offspring, feminising male offspring, or inducing parthenogenesis. As a result, infected populations can experience drastic ecological and evolutionary change. The mechanism by which SRDMs operate is likely to alter their impact on host evolutionary ecology; despite this, the current literature is heavily biased towards a single mechanism of sex ratio distortion, male-killing. Furthermore, amidst the growing concerns surrounding the loss of arthropod diversity, research into the impact of SRDMs on the viability of arthropod populations is generally lacking. In this study, using a theoretical approach, we model the epidemiology of an understudied mechanism of microbially-induced sex ratio distortionâfeminisationâto ask an understudied questionâhow do SRDMs impact extinction risk in a changing environment? We constructed an individual-based model and measured host population extinction risk under various environmental and epidemiological scenarios. We also used our model to identify the precise mechanism modulating extinction. We find that the presence of feminisers increases host population extinction risk, an effect that is exacerbated in highly variable environments. We also identified transmission rate as the dominant epidemiological trait responsible for driving extinction. Finally, our model shows that sex ratio skew is the mechanism driving extinction. We highlight feminisers and, more broadly, SRDMs as important determinants of the resilience of arthropod populations to environmental change
Predators reduce extinction risk in noisy metapopulations
Background
Spatial structure across fragmented landscapes can enhance regional population persistence by promoting local ârescue effects.â In small, vulnerable populations, where chance or random events between individuals may have disproportionately large effects on species interactions, such local processes are particularly important. However, existing theory often only describes the dynamics of metapopulations at regional scales, neglecting the role of multispecies population dynamics within habitat patches.
Findings
By coupling analysis across spatial scales we quantified the interaction between local scale population regulation, regional dispersal and noise processes in the dynamics of experimental host-parasitoid metapopulations. We find that increasing community complexity increases negative correlation between local population dynamics. A potential mechanism underpinning this finding was explored using a simple population dynamic model.
Conclusions
Our results suggest a paradox: parasitism, whilst clearly damaging to hosts at the individual level, reduces extinction risk at the population level
Assessing the potential of phytolith analysis to investigate local environment and prehistoric plant resource use in temperate regions:A case study from Williamsonâs Moss, Cumbria, Great Britain
Please note: this work is permanently embargoed in OpenBU. No public access is forecasted for this item. To request private access, please click on the locked Download file link and fill out the appropriate web form.First author draf
Cyclotron resonance lineshape in a Wigner crystal
The cyclotron resonance absorption spectrum in a Wigner crystal is
calculated. Effects of spin-splitting are modelled by substitutional disorder,
and calculated in the coherent potential approximation. Due to the increasing
strength of the dipole-dipole interaction, the results show a crossover from a
double-peak spectrum at small filling factors to a single-peak spectrum at
filling factors \agt 1/6. Radiation damping and magnetophonon scattering can
also influence the cyclotron resonance. The results are in very good agreement
with experiments.Comment: 4 pages REVTEX, attempt to append 3 figures that seem to have been
lost last tim
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