Adaptive dynamics of cooperation may prevent the coexistence of defectors and cooperators and even cause extinction

It has recently been demonstrated that ecological feedback mechanisms can facilitate the emergence and maintenance of cooperation in public goods interactions: the replicator dynamics of defectors and cooperators can result, for example, in the ecological coexistence of cooperators and defectors. Here we show that these results change dramatically if cooperation strategy is not fixed but instead is a continuously varying trait under natural selection. For low values of the factor with which the value of resources is multiplied before they are shared among all participants, evolution will always favour lower cooperation strategies until the population falls below an Allee threshold and goes extinct, thus evolutionary suicide occurs. For higher values of the factor, there exists a unique evolutionarily singular strategy, which is convergence stable. Because the fitness function is linear with respect to the strategy of the mutant, this singular strategy is neutral against mutant invasions. This neutrality disappears if a nonlinear functional response in receiving benefits is assumed. For strictly concave functional responses, singular strategies become uninvadable. Evolutionary branching, which could result in the evolutionary emergence of cooperators and defectors, can occur only with locally convex functional responses, but we illustrate that it can also result in coevolutionary extinction.     

Why people punish defectors. Weak conformist transmission can stabilize costly enforcement of norms in cooperative dilemmas

In this paper, we present a cultural evolutionary model in which norms for cooperation and punishment are acquired via two cognitive mechanisms: (1) payoff-biased transmission-a tendency to copy the most successful individual; and (2) conformist transmission-a tendency to copy the most frequent behavior in the population. We first show that if a finite number of punishment stages is permitted (e.g. two stages of punishment occur if some individuals punish people who fail to punish non-cooperators), then an arbitrarily small amount of conformist transmission will stabilize cooperative behavior by stabilizing punishment at some n -th stage. We then explain how, once cooperation is stabilized in one group, it may spread through a multi-group population via cultural group selection. Finally, once cooperation is prevalent, we show how prosocial genes favoring cooperation and punishment may invade in the wake of cultural group selection.     

Optimising the success of random destructive searches: Lévy walks can outperform ballistic motions

We re-evaluate the long standing and widely held belief that ballistic movements (i.e. straight-lines movements) outperform Lévy walks when searching for targets that once located are not revisited. The belief stems from the results of analyses of one-dimensional searches, analyses which have not accounted for the fact that target numbers can be continually depleted during the search process. This is a crucial oversight because continual depletion promotes the searching efficiencies of some Lévy walks above that of ballistic motion. The continual depletion effect is not so important for two- and three-dimensional searches. Nevertheless, we show that Lévy walks and ballistic movements can be equally or almost equally effective when searching within two- and three-dimensional environments for randomly and sparsely distributed targets or when searching for targets that are occasionally concealed. We also show that Lévy walks are advantageous when searching for targets that can occasionally evade capture. These situations represent common predator–prey interactions in which predators are involved in ‘imperfect destructive’ searches. Our model suggests that accounting for coevolutionary arms races at the predator–prey detection/reaction scales can explain to some extent Lévy walk searching patterns of predators at larger scales. This result provides new insights into the Lévy walk movement patterns of some destructive foragers.     

On classifying observations when one population is a mixture of normals

Some simple models for the mixture of distribution problems are considered. Two possible alternatives to the rather complex optimal discriminant function rule are mentioned. The performance of the BC method is never as satisfactory as the QDF method and in some cases it is far worse than the QDF method. The QDF can be used whenever sufficient numbers of observations are available to provide reasonably good estimates of means and covariances.     

Group beneficial norms can spread rapidly in a structured population

Group beneficial norms are common in human societies. The persistence of such norms is consistent with evolutionary game theory, but existing models do not provide a plausible explanation for why they are common. We show that when a model of imitation used to derive replicator dynamics in isolated populations is generalized to allow for population structure, group beneficial norms can spread rapidly under plausible conditions. We also show that this mechanism allows recombination of different group beneficial norms arising in different populations.     

The free energy of a liquid when viewed as a population of overlapping clusters

The expression of the free energy of a liquid in terms of an explicit decomposition of the particle configurations into local coordination clusters is examined. We argue that the major contribution to the entropy associated with structural fluctuations arises from the local athermal constraints imposed by the overlap of adjacent coordination shells. In the context of the recently developed Favoured Local Structure model [Soft Matt. 11, 3322 (2015)], we derive explicit expressions for the structural energy and entropy in the high-temperature limit, compare this approximation with simulation data and consider the extension of this free energy to the case of spatial inhomogeneity in the distribution of local structures.     

Consequences of ignoring spatial variation in population trend when conducting a power analysis

Long‐term, large‐scale monitoring programs are becoming increasingly common to document status and trends of wild populations. A successful program for monitoring population trend hinges on the ability to detect the trend of interest. Power analyses are useful for quantifying the sample size needed for trend detection, given expected variation in the population. Four components of variation (within‐year variation at a given site, interannual variation within a site, variation among sites in the interannual variation, and variation among sites in mean abundance or density) are commonly considered in power analyses for population trend, but a fifth is rarely considered: variation among sites in the local trend. Spatial variation in trend is expected to reduce statistical power, but the magnitude of this reduction has not been fully explored. We used computer simulations to evaluate the consequences of ignoring spatial variation in trend under a variety of sampling designs and wide ranges of other components of variation. The effect of spatial variation in trend on power was minor when other input parameters took extreme values that made the trend either very difficult or very easy to detect. However, at moderate values of the other parameters, spatial variation in trend had a strong effect, reducing statistical power by up to 60%. In some cases, ignoring spatial variation in trend resulted in an 80% probability of a type I error (falsely detecting a trend in a stable population). Spatial variation in trend is therefore an important consideration when designing a long‐term monitoring program for many species, especially those affected by local conditions at sites that are repeatedly surveyed. If variation in trend is ignored, as in many previous power analyses, the recommended sampling design will likely be insufficient to detect the trend of interest and lead to potentially false conclusions of a stable population.     

Sexual harassment in heterogeneous landscapes can mediate population regulation in a grasshopper

Population regulation has been related to differences in thequality among habitats, which mediate differences in vital ratessuch that in poor habitats reproductive rates are lower thanthose in high-quality habitats. The spatial distribution ofanimals in such habitats depends on their preferences and thedegree to which individuals have a free choice of a particularhabitat. The identified mechanisms that lead to a particularspatial distribution and eventually to regulation mainly includeforaging-related interference, for example, ideal free distribution,or simple selection of available high-quality habitats, thatis, site-dependent habitat selection. However, in insect speciesthese mechanisms might not be applicable, but density-dependenthabitat selection still occurs. We therefore suggest a mechanismthat refers to the nearly universal observation that matingsalso bear fitness costs. Although these costs have been investigatedon the individual level in many insect species, their consequencesfor population dynamics have not yet been addressed. In thegrasshopper species Stenobothrus lineatus, females in a nonreceptivemating status escape sexually approaching males by undirectedjumps. By including such avoidance behavior in a spatially-explicitsimulation model, we investigated its potential to result inprogressive use of low-quality habitats at increasing populationdensities. In particular, we show that (1) such behavior changeshabitat selection, (2) altered habitat selection results inpopulation regulation, and (3) the degree of habitat heterogeneityinfluences regulation such that (4) heterogeneous habitats showfine-tuned regulation and homogeneous habitats tend to supportlarge fluctuations.     

Enrichment can damp population cycles: a balance of inflexible and flexible interactions

Destabilization of one predator–one prey systems with an increase in nutrient input has been viewed as a paradox. We report that enrichment can damp population cycles by a food‐web structure that balances inflexible and flexible interaction links (i.e. specialist and generalist predators). We modeled six predator–prey systems involving three or four species in which the predators practice optimal foraging based on prey profitability determined by handling time. In all models, the balance of interaction links simultaneously decreased the amplitude of population oscillations and increased the minimum density with increasing enrichment, leading to a potential theoretical resolution of the paradox of enrichment in non‐equilibrium dynamics. The stabilization mechanism was common to all of the models. Important previous studies on the stability of food webs have also demonstrated that a balance of interaction strengths stabilizes systems, suggesting a general rule of ecosystem stability.     

Simple sleep questions can predict 12-year mortality in a rural population

Sleep and Biological Rhythms - There is apt evidence in favor of a significant association between sleep and mortality. So far, most studies examine sleep problems using comprehensive,...     

The evolution of cytoplasmic incompatibility or when spite can be successful

It is proposed that the phenomena of cytoplasmic incompatibility is explicable in terms of the selfish interests of the prokaryotic symbionts associated with the phenomena. It is hypothesized that in males the symbionts produce a product, termed wolbachin, which is carried in sperm and has the capability of inhibiting zygotic development if not neutralized. Symbionts are capable of neutralizing wolbachin. If this is the correct mechanism then the symbionts by killing eggs incapable of neutralizing wolbachin are acting spitefully. A simple model demonstrates that spiteful symbionts can invade a population of non-spiteful symbionts. The resulting population of spiteful symbionts is capable of resisting invasion by other spiteful symbionts even if the invaders have more efficient vertical transmission. Spite is successful in this system because all of the costs of being spiteful are inflicted on the host and not on the symbionts. This is in contrast to other systems of spite.     

Epstein-Barr virus can establish infection in the absence of a classical memory B-cell population

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that persists in the body for life after primary infection. The primary site of EBV persistence is the memory B lymphocyte, but whether the virus initially infects na?ve or memory B cells is still disputed. We have analyzed EBV infection in nine cases of X-linked hyper-immunoglobulin M (hyper-IgM) syndrome who, due to a mutation in CD40 ligand gene, do not have a classical, class-switched memory B-cell population (IgD(-) CD27(+)). We found evidence of EBV infection in 67% of cases, which is similar to the infection rate found in the general United Kingdom population (60 to 70% for the relevant age range). We detected EBV DNA in peripheral blood B cells and showed in one case that the infection was restricted to the small population of nonclassical, germinal center-independent memory B cells (IgD(+) CD27(+)). Detection of EBV small RNAs, latent membrane protein 2, and EBV nuclear antigen 3C expression in peripheral blood suggests full latent viral gene expression in this population. Analysis of EBV DNA in serial samples showed variability over time, suggesting cycles of infection and loss. Our results demonstrate that short-term EBV persistence can occur in the absence of a germinal center reaction and a classical memory B-cell population.     

Estimating the area under the ROC curve when transporting a prediction model to a target population

We propose methods for estimating the area under the receiver operating characteristic (ROC) curve (AUC) of a prediction model in a target population that differs from the source population that provided the data used for original model development. If covariates that are associated with model performance, as measured by the AUC, have a different distribution in the source and target populations, then AUC estimators that only use data from the source population will not reflect model performance in the target population. Here, we provide identification results for the AUC in the target population when outcome and covariate data are available from the sample of the source population, but only covariate data are available from the sample of the target population. In this setting, we propose three estimators for the AUC in the target population and show that they are consistent and asymptotically normal. We evaluate the finite-sample performance of the estimators using simulations and use them to estimate the AUC in a nationally representative target population from the National Health and Nutrition Examination Survey for a lung cancer risk prediction model developed using source population data from the National Lung Screening Trial.     

Heterorhizy can lead to underestimation of fine-root production when using mesh-based techniques

This study investigates the relationship between fine-root morphology and net mesh size in fine-root production (FRP) measurements (ingrowth core and net method). The data collected show that when a fine root has an apical diameter equal or bigger than the mesh size, the degree of difficulty in passing through the net determines a response that arrests growth or deviation from the initial direction of growth. Both reactions prevent the root from crossing the net and induce the fine root to produce new laterals with thinner diameters. The investment in biomass necessary to form the new laterals is smaller than that needed to support the parental fine root and this leads to determines an underestimation of FRP. In particular, a considerable reduction of fine-root biomass in the area outside the netting was detected with a mesh size below 1.5 mm. The choice of net mesh size to be used for FRP measurement cannot be arbitrary, but should be evaluated through a preliminary analysis of fine-root morphology of experimental species prior to net installation.     

Increased coupling between subpopulations in a spatially structured environment can lead to population outbreaks

Destruction and fragmentation of habitats is widely considered as a major threat to biological diversity. A theoretical framework aimed at understanding and predicting species responses to these destructive processes is still lacking, however. In this paper, the species dynamics in a spatially structured, two-habitat, patchy environment is considered subject to changes in individual migration intensity, i.e. coupling between the habitats. The subpopulation dynamics inside each habitat is assumed to be bistable but with different parameter values. By using space-discrete/continuous metapopulation dynamic models and computer simulations, we show that there can be two principally different regimes of metapopulation dynamics. With increasing intensity in the interplay between subpopulations, the total abundance can either gradually decrease or experience a sudden burst-like increase. This result is shown to be robust to the choice of mathematical models (discrete or continuous). Particularly, both the "self-excitation" and "self-inhibition" regimes of the metapopulation system are robust to variation in habitat size; however, when one of the habitats is much smaller than the other, the "self-excitation" regime can give way to the "self-inhibition" regime and vice versa.