The role of group size and environmental factors on survival in a cooperatively breeding tropical passerine

1. Variation in survival, a major determinant of fitness, may be caused by individual or environmental characteristics. Furthermore, interactions between individuals may influence survival through the negative feedback effects of density dependence. Compared to species in temperate regions, we have little knowledge about population processes and variation in fitness in tropical bird species. 2. To investigate whether variation in survival could be explained by population size or climatic variables we used capture-recapture models in conjunction with a long-term data set from an island population of the territorial, cooperatively breeding Seychelles warbler (Acrocephalus sechellensis). The lack of migration out of the study population means that our results are not confounded by dispersal. 3. Annual survival was high, both for adults (84%) and juveniles (61%), and did not differ between the sexes. Although there was significant variation in survival between years, this variation could not be explained by overall population size or weather variables. 4. For territorial species, resource competition will work mainly on a local scale. The size of a territory and number of individuals living in it will therefore be a more appropriate measure of density than overall population density. Consequently, both an index of territory quality per individual (food availability) and local density, measured as group size, were included as individual covariates in our analyses. 5. Local density had a negative effect on survival; birds living in larger groups had lower survival probabilities than those living in small groups. Food availability did not affect survival. 6. Our study shows that, in a territorial species, although density-dependent effects might not be detectable at the population level they can be detected at the individual territory level - the scale at which individuals compete. These results will help to provide a better understanding of the small-scale processes involved in the dynamics of a population in general, but in particular in tropical species living in relatively stable environments.     

Huisartsgeneeskundige zorg in het verzorgingshuis

Dutch GP's (General Practitioners) take care of people living in homes for the elderly. The population of these homes is selected on the basis of poor functioning on ADL (activities of daily living). We expected to find a group of elderly people within these homes that need more complex primary care. We describe the characteristics of care for an institutionalized elderly population and compare these to the care provided to their independently living peers. The design of this study is a matched case-control study in a Dutch General Practice in the study period 1/1/1998 to 1/7/2004. Our main results show that the rate of cognitive problems is two times, the prevalence of depression even three times higher in older people living in a home for the elderly than in those who live independently. Locomotory problems are a frequent problem in homes for the elderly. Rates of chronic pulmonary problems, atherosclerosis-related diseases and urinary tract infection are higher, whereas no significant differences for CVA, diabetes and cancer were found. Institutionalized older patients use more different types of medication. GP's do not have more contacts with people living in a home for the elderly than with older people living independently. We conclude that people living in homes for the elderly have complex problems, and need special attention for their specific vulnerability. Differences in care are not primarily explained by chronic disease but by problems with mobility, confusion, depression and cognition.     

Genetic studies on the Asmat population (Irian-Jaya, Indonesia)

The Asmat are a population of about 35,000 people living on the South-West coast of Irian-Jaya (Indonesia; New Guinea). This paper presents the results of enzyme group and serum protein group typings in a sample of Asmats living in the coastal region around Agats. Red cell enzyme polymorphisms (EaP, PGM1, 6-PGD, EsD, ADA and AK) could be typed in 154 blood samples, serum protein polymorphisms (Ge, alpha 1-AT, PLG, Tf and Hp) in 160 blood samples. The results of this study are discussed in detail.     

Positive solutions of an elliptic system arising from a model in evolutionary ecology

We give sufficient and almost necessary conditions for the existence of positive solutions to an elliptic system satisfying various Dirichlet boundary conditions. The elliptic system consists of the steady-state equations of a parabolic system used to model the growth and spread of a particular gene and population living in a bounded region. The model takes into account the fact that the fitness of the individuals in the population may depend on the population size. Some non-existence results are also included.Research partially supported by NSF grant no. DMS-8801968     

Comments on size dispersion in living systems

The use of a size dispersion term in population balance analyses of living systems is discussed. Results show that the use of the term with a constant dispersion coefficient results in the prediction that some members of the population should shrink in size at later times. It is argued, therefore, that, if the use of the term is fundamentally correct and represents a real phenomenon, the coefficient must decrease with time, as the population reaches its terminal average size. In the final analysis more work is needed to clearly understand the appropriate use of the size dispersion term for living systems.     

Rapid recovery of a population of the cryptic and evolutionarily distinct Hochstetter's Frog,Leiopelma hochstetteri,in a pest‐free environment

New Zealand's native frogs (genus Leiopelma) display a very high degree of endemism and belong to a distinctive and ancient evolutionary lineage. All four extant species are considered to be threatened or endangered, but the mechanisms behind their decline are poorly understood. Many of the potential factors causing population declines are confounded for the two species living on the mainland; in particular, habitat degradation and the presence of introduced mammalian pests have been difficult to disentangle in the past. Here we present data on a population of Hochstetter's Frog (Leiopelma hochstetteri) living in a pest‐free mainland sanctuary, the 3363‐ha Maungatautari Ecological Island. Survey data from this population shows a fourfold increase in numbers between 2009 and 2012 from a very low initial density. Our results suggest that for Hochstetter's Frog at least, and possibly the other mainland species of Leiopelma, introduced mammals are a major driving factor in population declines. Given that the frog population at Maungatautari was discovered by serendipity when planning for the pest‐free sanctuary was already well underway, this also highlights the conservation value of large pest‐free areas and ecosystem‐level management.     

Population dynamical consequences of gregariousness in a size-structured consumer-resource interaction

Many animal species live in groups. Group living may increase exploitation competition within the group, and variation among groups in intra-group competition intensity could induce life-history variability among groups. Models of physiologically structured populations generally predict single generation cycles, driven by exploitation competition within and between generations. We expect that life-history variability and habitat heterogeneity induced by group living may affect such competition-driven population dynamics. In this study, we vary the gregariousness (the tendency to aggregate in groups) of a size-structured consumer population in a spatially explicit environment. The consumer has limited mobility, and moves according to a probabilistic movement process. We study the effects on the population dynamics, as mediated through the resource and the life-history of the consumer. We find that high gregariousness leads to large spatial resource variation, and highly variable individual life-history, resulting in highly stochastic population dynamics. At reduced gregariousness, life-history of consumers synchronizes, habitat heterogeneity is reduced, and single generation cycles appear. We expect this pattern to occur for any group living organism with limited mobility. Our results indicate that constraints set by population dynamical feedback may be an important aspect in understanding group living in nature.     

The evolution of social discounting in hierarchically clustered populations

The expression of a social behaviour may affect the fitness of actors and recipients living in the present and in the future of the population. When there is a risk that a future reward will not be experienced in such a context, the value of that reward should be discounted; but by how much? Here, we evaluate social discount rates for delayed fitness rewards to group of recipients living at different positions in both space and time than the actor in a hierarchically clustered population. This is a population where individuals are grouped into families, families into villages, villages into clans, and so on, possibly ad infinitum. The group-wide fitness effects are assumed to either increase or decrease the fecundity or the survival of recipients and can be arbitrarily extended in space and time. We find that actions changing the survival of individuals living in the future are generally more strongly discounted than fecundity-changing actions for all future times and that the value of future rewards increases as individuals live longer. We also find that delayed fitness effects may not only be discounted by a constant factor per unit delay (exponential discounting), but that, as soon as there is localized dispersal in a population, discounting per unit delay is likely to fall rapidly for small delays and then slowly for longer delays (hyperbolic discounting). As dispersal tends to be localized in natural populations, our results suggest that evolution is likely to favour individuals that express present-biased behaviours and that may be time-inconsistent with respect to their group-wide effects.     

The effect of supplementary feeding upon the sizes of the home ranges of woodmice Apodemus sylvaticus living on a system of maritime sand-dunes

The woodmouse is primarily a woodland species but it also occurs on maritime sand-dunes. The home ranges of mice living on the sand-dunes are much larger than those of animals living in woodlands. Here we test the hypothesis that this difference is due to the fact that woodland provides substantially more food than do sand-dunes. Our experimental approach was to provide supplementary food in the form of wheatgrain to a sand-dune population and to compare range sizes with a control population. Range sizes on the supplemented area were significantly smaller than the controls and essentially similar to those of woodmice living in deciduous woodland.     

Genomic signatures of evolution in Nautilus—An endangered living fossil

Living fossils are survivors of previously more diverse lineages that originated millions of years ago and persisted with little morphological change. Therefore, living fossils are model organisms to study both long‐term and ongoing adaptation and speciation processes. However, many aspects of living fossil evolution and their persistence in the modern world remain unclear. Here, we investigate three major aspects of the evolutionary history of living fossils: cryptic speciation, population genetics and effective population sizes, using members of the genera Nautilus and Allonautilus as classic examples of true living fossils. For this, we analysed genomewide ddRAD‐Seq data for all six currently recognized nautiloid species throughout their distribution range. Our analyses identified three major allopatric Nautilus clades: a South Pacific clade, subdivided into three subclades with no signs of admixture between them; a Coral Sea clade, consisting of two genetically distinct populations with significant admixture; and a widespread Indo‐Pacific clade, devoid of significant genetic substructure. Within these major clades, we detected five Nautilus groups, which likely correspond to five distinct species. With the exception of Nautilus macromphalus, all previously described species are at odds with genomewide data, testifying to the prevalence of cryptic species among living fossils. Detailed F_ST analyses further revealed significant genome‐wide and locus‐specific signatures of selection between species and differentiated populations, which is demonstrated here for the first time in a living fossil. Finally, approximate Bayesian computation (ABC) simulations suggest large effective population sizes, which may explain the low levels of population differentiation commonly observed in living fossils.     

ANCIENT URBANIZATION PREDICTS GENETIC RESISTANCE TO TUBERCULOSIS

A link between urban living and disease is seen in recent and historical records, but the presence of this association in prehistory has been difficult to assess. If the transition to urban living does result in an increase in disease‐based mortality, we might expect to see evidence of increased disease resistance in longer‐term urbanized populations, as the result of natural selection. To test this, we determined the frequency of an allele (SLC11A1 1729 + 55del4) associated with natural resistance to intracellular pathogens such as tuberculosis and leprosy. We found a highly significantly correlation with duration of urban settlement—populations with a long history of living in towns are better adapted to resisting these infections. This correlation remains strong when we correct for autocorrelation in allele frequencies due to shared population history. Our results therefore support the interpretation that infectious disease loads became an increasingly important cause of human mortality after the advent of urbanization, highlighting the importance of population density in determining human health and the genetic structure of human populations.     

If a population crashes in prehistory, and there is no paleodemographer there to hear it, does it make a sound?

Catastrophic episodes (e.g., epidemics, natural disasters) strike with only limited regard for age. A large percentage of catastrophic mortality in a population can lead to a death distribution that resembles the living distribution, which includes greater numbers of older children, adolescents, and young adults than typical mortality profiles. This paper examines both the population implications of a large catastrophic mortality event, based on the Black Death as it ravaged medieval Europe, and its long-term effects on age-at-death distributions. An increased prevalence of epidemic disease is a common feature of reconstructions of the shift to agriculture and the rise of urban centers. The model begins with a hypothetical Medieval living population. This population is stable and characterized by slow growth. It has fertility and mortality rates consistent with a natural-fertility, agrarian population. The effects of catastrophic episodes are simulated by projecting the model population and subjecting it to one large (30% mortality) catastrophic episode as part of a 100-year population projection. A pair of Leslie matrices forms the basis of the projection. The catastrophic episode has important, long-term effects on both the living population and the cumulative distribution of death. The living population fails to recover from plague losses; at the end of the projection, population is still less than 75% its pre-plague level. The age-at-death distribution takes on the juvenile-young adult-heavy profile characteristic of many archaeological samples. The cumulative death profile based on the projection differs from that produced by the stable model significantly (P < 0.05) for 25-50 years after the plague episode, depending on sample size.     

The evolution of dispersal in random environment

In this paper we introduce a stochastic model for a population living and migrating between s sites without distinction in the states between residents and immigrants. The evolutionary stable strategies (ESS) is characterized by the maximization of a stochastic growth rate. We obtain that the expectation of reproductive values, normalized by some random quantity, are constant on all sites and that the expectation of the normalized vector population structure is proportional to eigenvector of the dispersion matrix associated to eigenvalue one, which are, in some way, analogous to the results obtained in the deterministic case.     

Calcium and phosphorous in teeth from children with and without cystic fibrosis

The objective of this study is to analyze the percentage of Ca and P in teeth from children with and without cystic fibrosis with respect to different variables, namely, gender, age, type of teeth, area, fluoridation of water supply, term of pregnancy, and maternal smoking and drinking habits. The method of analysis is proton-induced X-ray emission and proton-induced gamma emission on tooth-crown samples. T-test results show less Ca in the teeth of the population of CF + NT (cystic fibrosis+ nontetracycline antibiotics) than in that of NCF (noncystic fibrosis) for incisors and the total tooth population. It also shows greater Ca for incisors than for nonincisors for NCF. Teeth from urban CF + NT have less Ca than those from urban NCF. This holds for the total area population. Both Ca and P in teeth of NCF population living in fluoridated areas are greater than in those living in nonfluoridated area. Ca is depleted in the teeth of CF + NT children whose mothers smoke and P is depleted in the teeth of NCF children whose mothers drink. High and low Ca and P values for individual teeth are reported.     

How Spanish primary school students interpret the concepts of population and species

This article presents research concerning the way in which primary school pupils in southern Spain interpret the concepts of population and species. The results show that, for the concept of population, there was an intense anthropocentrism in pupils’ responses, while for the concept of species, only animals were considered as living creatures. These interpretations influence the vision that the students will develop of ecosystems and biodiversity, as well as their respect and care for living beings. We propose some suggestions in order to improve the teaching of these concepts in primary education.     

羊草种群的热值及其能量贮藏特点

为了获得有关中国东北羊草草原生态系统能量学方面的基础数据,作者对该草原的建群植被——羊草种群进行了热值含量的测定,在此基础上,对单位面积上的羊草种群热值含量进行了计算,以便分析在自然条件下,羊草种群的能量贮藏特点。研究结果表明,羊草(Leymus Chinensis)种群的果穗与其各器官相比,具有最高的热值含量,为4898.28cal/gDW,其活枝条与羊草种群的各部分相比,具有最高的热值含量,为4711.86cal/gDW。羊草种群将其截获的绝大部分太阳辐射能贮藏在地下部分以便为种群的安全越冬和第二年生长季节开始对其地上部分的萌发提供充足的能量。     

Stress associated with group living in a long-lived bird

Many long-lived avian species adopt life strategies that involve a gregarious way of life at juvenile and sub-adult stages and territoriality during adulthood. However, the potential associated costs of these life styles, such as stress, are poorly understood. We examined the effects of group living, sex and parasite load on the baseline concentration of faecal stress hormone (corticosterone) metabolites in a wild population of common ravens (Corvus corax). Corticosterone concentrations were significantly higher in non-breeding gregarious ravens than in territorial adults. Among territorial birds, males showed higher stress levels than their mates. Parasite burdens did not affect hormone levels. Our results suggest a key role of the social context in the stress profiles of the two population fractions, and that group living may be more energetically demanding than maintaining a territory. These findings have implications for understanding hormonal mechanisms under different life styles and may inspire further research on the link between hormone levels and selective pressures modulating gregarious and territorial strategies in long-lived birds.     

Feedbacks, thresholds and synergies in global change: population as a dynamic factor

The role of feedbacks, thresholds, and synergies in environmental science, and their implications for environmental degradation under a growing human population, are reviewed. A detailed analysis of the impacts of climate change on water resources is used to elucidate mechanisms by which nonlinearities arise in environmental science. Additional examples are drawn from analysis of soil degradation and non-climate related degradation of water resources. The often-assumed notion that impacts will grow in proportion to population size is shown to be overly optimistic. In particular, feedbacks, thresholds, and synergies among multiple threats, tend to amplify risk and cause environmental impacts to grow considerably faster than linearly in population size, even when the per-capita living standard and the technological systems deployed to achieve that living standard are assumed to remain constant.