Estimating the functional form for the density dependence from life history data

Two contrasting approaches to the analysis of population dynamics are currently popular: demographic approaches where the associations between demographic rates and statistics summarizing the population dynamics are identified; and time series approaches where the associations between population dynamics, population density, and environmental covariates are investigated. In this paper, we develop an approach to combine these methods and apply it to detailed data from Soay sheep (Ovis aries). We examine how density dependence and climate contribute to fluctuations in population size via age- and sex-specific demographic rates, and how fluctuations in demographic structure influence population dynamics. Density dependence contributes most, followed by climatic variation, age structure fluctuations and interactions between density and climate. We then simplify the density-dependent, stochastic, age-structured demographic model and derive a new phenomenological time series which captures the dynamics better than previously selected functions. The simple method we develop has potential to provide substantial insight into the relative contributions of population and individual-level processes to the dynamics of populations in stochastic environments

Assessing and ensuring patient safety during breath-holding for radiotherapy

OBJECTIVE: While there is recent interest in using repeated deep inspiratory breath-holds, or prolonged single breath-holds, to improve radiotherapy delivery, breath-holding has risks. There are no published guidelines for monitoring patient safety, and there is little clinical awareness of the pronounced blood pressure rise and the potential for gradual asphyxia that occur during breath-holding. We describe the blood pressure rise during deep inspiratory breath-holding with air and test whether it can be abolished simply by pre-oxygenation and hypocapnia. METHODS: We measured blood pressure, oxygen saturation (SpO(2)) and heart rate in 12 healthy, untrained subjects performing breath-holds. RESULTS: Even for deep inspiratory breath-holds with air, the blood pressure rose progressively (e.g. mean systolic pressure rose from 133 ± 5 to 175 ± 8 mmHg at breakpoint, p < 0.005, and in two subjects, it reached 200 mmHg). Pre-oxygenation and hypocapnia prolonged breath-hold duration and prevented the development of asphyxia but failed to abolish the pressure rise. The pressure rise was not a function of breath-hold duration and was not signalled by any fall in heart rate (remaining at resting levels of 72 ± 2 beats per minute). CONCLUSION: Colleagues should be aware of the progressive blood pressure rise during deep inspiratory breath-holding that so far is not easily prevented. In breast cancer patients scheduled for breath-holds, we recommend routine screening for heart, cardiovascular, renal and cerebrovascular disease, routine monitoring of patient blood pressure and SpO(2) during breath-holding and requesting patients to stop if systolic pressure rises consistently >180 mmHg and or SpO(2) falls <94%. ADVANCES IN KNOWLEDGE: There is recent interest in using deep inspiratory breath-holds, or prolonged single breath-holding techniques, to improve radiotherapy delivery. But there appears to be no clinical awareness of the risks to patients from breath-holding. We demonstrate the progressive blood pressure rise during deep inspiratory breath-holds with air, which we show cannot be prevented by the simple expedient of pre-oxygenation and hypocapnia. We propose patient screening and safety guidelines for monitoring both blood pressure and SpO(2) during breath-holds and discuss their clinical implications

Using evolutionary demography to link life history theory, quantitative genetics and population ecology

1. There is a growing number of empirical reports of environmental change simultaneously influencing population dynamics, life history and quantitative characters. We do not have a well-developed understanding of links between the dynamics of these quantities

Ageing in a variable habitat: environmental stress affects senescence in parasite resistance in St Kilda Soay sheep

Despite widespread empirical evidence for a general deterioration in the majority of traits with advancing age, it is unclear whether the progress of senescence is chronologically determined, or whether factors such as environmental conditions experienced over the lifespan are more important. We explored the relative importance of &lsquo;chronological&rsquo; and &lsquo;environmental&rsquo; measures of age to changes in parasite resistance across the lifespan of free-living Soay sheep. Our results show that individuals experience an increase in parasite burden, as indicated by gastrointestinal helminth faecal egg count (FEC) with chronological age. However, chronological age fails to fully explain changes in FEC because a measure of environmental age, cumulative environmental stress, predicts an additional increase in FEC once chronological age has been accounted for. Additionally, we show that in females age-specific changes are dependent upon the environmental conditions experienced across individuals' life histories: increases in FEC with age were greatest among individuals that had experienced the highest degree of stress. Our results illustrate that chronological age alone may not always correspond to biological age, particularly in variable environments. In these circumstances, measures of age that capture the cumulative stresses experienced by an individual may be useful for understanding the process of senescence

Sexual dimorphism in postcranial skeletal shape suggests male‐biased specialization for physical competition in anthropoid primates

Sexual dimorphism often arises as a response to selection on traits that improve a male's ability to physically compete for access to mates. In primates, sexual dimorphism in body mass and canine size is more common in species with intense male–male competition. However, in addition to these traits, other musculoskeletal adaptations may improve male fighting performance. Postcranial traits that increase strength, agility, and maneuverability may also be under selection. To test the hypothesis that males, as compared to females, are more specialized for physical competition in their postcranial anatomy, we compared sex‐specific skeletal shape using a set of functional indices predicted to improve fighting performance. Across species, we found significant sexual dimorphism in a subset of these indices, indicating the presence of skeletal shape sexual dimorphism in our sample of anthropoid primates. Mean skeletal shape sexual dimorphism was positively correlated with sexual dimorphism in body size, an indicator of the intensity of male–male competition, even when controlling for both body mass and phylogenetic relatedness. These results suggest that selection on male fighting ability has played a role in the evolution of postcranial sexual dimorphism in primates

The Role of Mesotocin on Social Bonding in Pinyon Jays

The neuropeptide oxytocin influences mammalian social bonding by facilitating the building and maintenance of parental, sexual, and same‐sex social relationships. However, we do not know whether the function of the avian homologue mesotocin is evolutionarily conserved across birds. While it does influence avian prosocial behavior, mesotocin\u27s role in avian social bonding remains unclear. Here, we investigated whether mesotocin regulates the formation and maintenance of same‐sex social bonding in pinyon jays (Gymnorhinus cyanocephalus), a member of the crow family. We formed squads of four individually housed birds. In the first, “pair‐formation” phase of the experiment, we repeatedly placed pairs of birds from within the squad together in a cage for short periods of time. Prior to entering the cage, we intranasally administered one of three hormone solutions to both members of the pair: mesotocin, oxytocin antagonist, or saline. Pairs received repeated sessions with administration of the same hormone. In the second, “pair‐maintenance” phase of the experiment, all four members of the squad were placed together in a large cage, and no hormones were administered. For both phases, we measured the physical proximity between pairs as our proxy for social bonding. We found that, compared with saline, administering mesotocin or oxytocin antagonist did not result in different proximities in either the pair‐formation or pair‐maintenance phase of the experiment. Therefore, at the dosages and time frames used here, exogenously introduced mesotocin did not influence same‐sex social bond formation or maintenance. Like oxytocin in mammals, mesotocin regulates avian prosocial behavior; however, unlike oxytocin, we do not have evidence that mesotocin regulates social bonds in birds

Grandparental Child Care in Europe : Evidence for Preferential Investment in More Certain Kin

Peer reviewe

Egg investment in response to helper presence in cooperatively breeding Tibetan ground tits

Life-history theory predicts a trade-off between current and future reproduction to maximize lifetime fitness. In cooperatively breeding species, where offspring care is shared between breeders and helpers, helper presence may influence the female breeders' egg investment, and consequently, survival and future reproductive success. For example, female breeders may reduce egg investment in response to helper presence if this reduction is compensated by helpers during provisioning. Alternatively, female breeders may increase egg investment in response to helper presence if helpers allow the breeders to raise more or higher quality offspring successfully. In the facultatively cooperative-breeding Tibetan ground tit Pseudopodoces humilis, previous studies found that helpers improve total nestling provisioning rates and fledgling recruitment, but have no apparent effects on the number and body mass of fledglings produced, while breeders with helpers show reduced provisioning rates and higher survival. Here, we investigated whether some of these effects may be explained by female breeders reducing their investment in eggs in response to helper presence. In addition, we investigated whether egg investment is associated with the female breeder's future fitness. Our results showed that helper presence had no effect on the female breeders' egg investment, and that egg investment was not associated with breeder survival and reproductive success. Our findings suggest that the responses of breeders to helping should be investigated throughout the breeding cycle, because the conclusions regarding the breeders' adjustment of reproductive investment in response to being helped may depend on which stage of the breeding cycle is considered

Averaging in Cosmology

In this paper we discuss the effect of local inhomogeneities on the global expansion of nearly FLRW universes, in a perturbative setting. We derive a generic linearized averaging operation for metric perturbations from basic assumptions, and we explicify the issue of gauge invariance. We derive a gauge invariant expression for the back-reaction of density inhomogeneities on the global expansion of perturbed FLRW spacetimes, in terms of observable quantities, and we calculate the effect quantitatively. Since we do not adopt a comoving gauge, our result incorporates the back-reaction on the metric due to scalar velocity and vorticity perturbations. The results are compared with the results by other authors in this field.Comment: 24 pages, Latex, accepted for publication in Phys. Rev.