Population Size Structure Research Articles

Health impacts related to urban and transport planning: A burden of disease assessment

IntroductionUntil now, estimates of the Global Burden of Disease (GBD) have mainly been produced on national or regional levels. These general estimates, however, are less useful for city governments who have to take decisions on local scales. To address this gap, we focused on the city-level burden of disease (BD) due to exposures affected by urban and transport planning. We conducted a BD assessment using the Urban and Transport Planning Health Impact Assessment (UTOPHIA) tool to estimate annual preventable morbidity and disability-adjusted life-years (DALYs) under compliance with international exposure recommendations for physical activity (PA), exposure to air pollution, noise, heat, and access to green spaces in Barcelona, Spain. MethodsExposure estimates and morbidity data were available for 1,357,361 Barcelona residents ≥20years (2012). We compared recommended with current exposure levels to estimate the associated BD. We quantified associations between exposures and morbidities and calculated population attributable fractions to estimate the number of attributable cases. We calculated DALYs using GBD Study 2015 background DALY estimates for Spain, which were scaled to Barcelona considering differences in population size, age and sex structures. We also estimated annual health costs that could be avoided under compliance with exposure recommendations. ResultsNot complying with recommended levels for PA, air pollution, noise, heat and access to green spaces was estimated to generate a large morbidity burden and resulted in 52,001 DALYs (95% CI: 42,866–61,136) in Barcelona each year (13% of all annual DALYs). From this BD 36% (i.e. 18,951 DALYs) was due to traffic noise with sleep disturbance and annoyance contributing largely (i.e. 10,548 DALYs). Non-compliance was estimated to result in direct health costs of 20.10 million € (95% CI: 15.36–24.83) annually. ConclusionsNon-compliance of international exposure recommendations was estimated to result in a considerable BD and in substantial economic expenditure each year in Barcelona. Our findings suggest that (1) the reduction of motor traffic together with the promotion of active transport and (2) the provision of green infrastructure would result in a considerable BD avoided and substantial savings to the public health care system, as these measures can provide mitigation of noise, air pollution and heat as well as opportunities for PA promotion.

Rate of natural mortality in the sea starArchaster angulatus(Echinodermata: Asteroidea)

The population size structure from a total of 876 individuals, together with published values of growth rate, maximum size and size at age were used to estimate an instantaneous rate of natural mortality (M) of 0.46–0.59 year−1in a population of the sea starArchaster angulatusfrom south-western Australia. Peak abundance (17%) of all animals sampled was 105–109 mm arm radius (means of 4.2–4.8 years of age) and only one per cent of sea stars are predicted to live beyond 8 years in the population studied. There are few comparable studies on sea stars but when compared with rates of natural mortality in other echinoderms (sea urchins),A. angulatusis intermediate among species which exhibit the extremes of life history strategies, that is, those which grow very rapidly and may live just two years or less and those with very slow growth rates and which may live for decades.

No Significant Impact of Transgenic Cry1Ab/1Ac Cotton on Rhizosphere‐Soil Enzyme Activities and Bacterial Communities

Core Ideas The selected enzymatic activities were not significantly affected by the GK 12. The bacterial population size was not significantly affected by the GK 12. The bacterial community structure was not significantly affected by the GK 12. Transgenic Bt‐cotton (Gossypium hirsutum L.) GK 12 is commonly used for control of lepidopteran pests in China, but concerns exist regarding possible unintended effects on soil microbial communities. Bacterial population sizes and community structures in the rhizosphere soil under intensive cultivation of GK 12, its near‐isogenic parent Simian 3 and a conventional cotton DP 5415 were analyzed during 2009 to 2011 by quantitative polymerase chain reaction (qPCR) and denaturing gradient gel electrophoresis (DGGE). Dehydrogenase, urease, and phosphatase activities were also measured. It was found that these microbial‐related parameters were significantly influenced by variations due to the year and plant growth stage. There were occasional differences in bacterial population size and community structures at some growth stages, but they were not manifested throughout the growing cycle and were not considered meaningful. Generally no significant differences were found in selected enzymatic activities, and bacterial population sizes and community structures in the rhizosphere soil of GK 12 and Simian 3. Three different species or bands were unique to GK 12 and Simian 3, but they were unamplifiable. The resolvable band profile or annotatable species composition was not different between GK 12 and Simian 3. Therefore, the data of this study did not show any significant and permanent impacts of Bt‐insertion in GK 12 on selected enzymatic activities, bacterial population size, and community structures in the rhizosphere soil during 3‐yr tests in northern China.

Mating timing, dispersal and local adaptation in patchy environments

Dispersal is a life‐history trait that can evolve under various known selective pressures as identified by a multitude of theoretical and empirical studies. Yet only few of them are considering the succession of mating and dispersal. The sequence of these events influences gene flow and consequently affects the dynamics and evolution of populations. We use individual‐based simulations to investigate the evolution of the timing of dispersal and mating, i.e. mating before or after dispersal. We assume a discrete insect metapopulation in a heterogeneous environment, where populations may adapt to local conditions and only females are allowed to disperse. We run the model assuming different levels of species habitat tolerance, carrying capacity, and temporal environmental variability. Our results show that in species with narrow habitat tolerance, low to moderate dispersal evolves in combination with mating after dispersal (post‐dispersal mating). With such a strategy dispersing females benefit from mating with a resident male, as their offspring will be better adapted to the local habitat conditions. On the contrary, in species with wide habitat tolerance higher dispersal rates in combination with pre‐dispersal mating evolves. In this case individuals are adapted to the ‘average’ habitat where pre‐dispersal mating conveys the benefit of carrying relatives’ genes into a new population. With high dispersal rates and large population size, local adaptation and kin structure both vanish and the temporal sequence of dispersal and mating may become a (nearly) neutral trait.

Significance of Stump-Sprouting for the Population Size Structure and Spatial Distribution Patterns of Endangered Species, Magnolia cylindrical

Magnolia cylindrica Wils. is one of the third most-protected wild plants in China. To describe the size structure and dynamics of its population, field data were obtained from eight newly established sites, using a contiguous grid quadrate method in Jiulong Mountain of East China. The population size structure and spatial distribution pattern were discussed based on a theoretical distribution model and assembling intensity index. The population size structure showed a declining trend because of the lack of seedlings. The number of stump-sprouting, size class III (sapling trees) individuals was large enough to make up for the shortage of small seedlings and the complete regeneration of populations through sprouting. The distributions of M. cylindrica, both seedling populations (Group A) and overall populations (Group B), were mostly clumped. The spatial pattern intensities of the populations at different stages (mainly small trees, middle trees, and big trees) were higher for Group A than those for Group B. The two groups have the same tendency in that the pattern intensity declined from small trees to the larger ones. Group A and Group B differed in spatial pattern: small and middle trees were randomly distributed in seedling populations, but aggregated in overall populations. The populations of M. cylindrica (both group A and B) were characterized by the pattern scale between 16 to 32 m2, measured by Greig-Smith and Kershaw methods. These results suggest that sprouting should be seriously considered in population rehabilitation and forest tending management and the area of forest tending management should be close to the maximum intensity.

The effects of population density and lake characteristics on growth and size structure of brook trout Salvelinus fontinalis (Mitchill, 1815) in boreal forest lakes in Canada

This paper examines the effect of lake characteristics on population density and how this variation affects growth, mortality and population size structure of brook trout, Salvelinus fontinalis. The study was conducted on 17 recreationally fished, reproductively isolated boreal forest lakes in Newfoundland, Canada from 1993 to 2000. A standardized sampling program, the Fyke Littoral Index Netting program (FLIN) was used to collected data that describes brook trout population parameters and life history attributes. Regression analyses showed significant relationships between fish density and biomass and characteristics of the lakes. Variation in fish density and biomass was explained by lake surface area and littoral habitat area. Significant relationships were found when growth, mortality and size structure were regressed against density. The proportional stock distribution and theoretical maximum size of brook trout were negatively related to density, and natural mortality was positively related to density. The largest maximum length and highest proportional stock densities occurred at brook trout densities of less than 30 fish/ha. In general, the higher the proportion of littoral habitat area the higher the densities of brook trout, which correspondingly had important effects on growth, natural mortality and size structure of the brook trout populations. This information is critical to the development of management strategies aimed at altering size distribution to produce specific fisheries management outcomes.

Shifts in intertidal zonation and refuge use by prey after mass mortalities of two predators.

Recent mass mortalities of two predatory sea star species provided an unprecedented opportunity to test the effect of predators on rocky intertidal prey. Mass mortalities provide insight that manipulative experiments cannot because they alter ecosystems on a larger scale, for longer time periods, and remove both organisms and their cues from the environment. We examined shifts in population size structure, vertical zonation, and use of emersed refuge habitats outside tidepools by the abundant herbivorous black turban snail Tegula funebralis, both before and after the successive mortalities of two predatory sea stars. The small cryptic predator Leptasterias spp. suffered a localized but extreme mortality event in November 2010, followed by two mass mortalities of the keystone predator Pisaster ochraceus in August 2011 and autumn 2013. After the local extinction of Leptasterias, the population size of Tegula more than doubled. Also, since Leptasterias primarily inhabited only mid to low intertidal tidepools at this site, small and medium sized snails (which are preferred by Leptasterias) shifted lower in the intertidal and into tidepools after the mortality of Leptasterias. After the mortality of Pisaster in August 2011, large snails did not shift lower in the intertidal zone despite being preferred by Pisaster. Small and medium sized snails became denser in the higher zone and outside tidepools, which was not likely due to Pisaster mortality. Previous studies concluded that Pisaster maintained vertical size gradients of snails, but our data implicate the overlooked predator Leptasterias as the primary cause. This natural experiment indicated that (1) predators exert top-down control over prey population sizes and lower limits, (2) vertical zonation of prey are dynamic and controlled in part by prey behavior, and (3) predators exert the strongest effects on more vulnerable individuals, which typically inhabit stressful habitats higher on the shore or outside tidepools to avoid predation. Because the mass mortalities of two predators drastically reduced both the predation pressure and the chemical cues of predators in the environment, we were able to investigate both the effects of predators on prey populations and the effects on mobile prey behavior.

Population ecology of the snail Melampus bidentatus in changing salt marsh landscapes

We studied the population ecology of the snail Melampus bidentatus in relation to patch composition and landscape structure across several salt marsh systems in Connecticut, USA. These marshes have changed significantly over the past 40–50 years including loss of total area, increased areas of short Spartina alterniflora, and decreased areas and fragmentation of Spartina patens. These changes are consistent with tidal inundation patterns that indicate frequent flooding of high marsh areas. Melampus bidentatus densities were highly variable, both among different salt marsh systems and locations within specific marshes, but were generally similar among short Sp. alterniflora and Sp. patens patches within locations. Densities were lowest where the marsh was regularly inundated at high tide and only remnant Sp. patens patches remained. Almost no snails were found in bare patches. Areas that had large Sp. patens patches adjacent to short Sp. alterniflora supported the highest M. bidentatus densities. Population size-structure varied significantly among patch types, with higher proportions of large individuals in short Sp. alterniflora and hummocked Sp. patens patches than in large and remnant Sp. patens patches. This was likely due to size-selective predation and/or higher snail growth rates due to better food resource conditions in short Sp. alterniflora patches. Egg mass densities and the number of eggs per egg mass were highest in short Sp. alterniflora. Our results indicate that M. bidentatus is resilient to the level and patterns of salt marsh change evident at our study sites. Indeed, snail densities were significantly higher than reported in other field studies, suggesting that increased patch areas of short Sp. alterniflora and associated environmental conditions at our study sites may provide more favorable habitats than previously when marshes were dominated by extensive Sp. patens meadows. However, there may be threshold conditions that could overwhelm the ability of M. bidentatus to maintain itself within salt marsh systems where changes in hydrology, sedimentation and other factors lead to increased numbers of bare patches and ponds and loss of short Sp. alterniflora and Sp. patens. Studies of the responses of resident and transient fauna to salt marsh change are critically needed in order to better understand the implications for salt marsh ecosystem dynamics and services.

Population size structure of trees in a semi‐arid African savanna: Species differ in vulnerability to a changing environment and reintroduction of elephants

AbstractThe size structure of a plant population provides a snapshot of potential population trend and weak inference on past history. Size structure of 24 tree species was sampled in a savanna reserve in order to assess their potential vulnerability to local extirpation following the reintroduction of elephants. Regression of number per size class based on an expected reverse‐J structure for a healthy population was undertaken in order to classify trend of each species. On account of the weak realism of this expected structure in semi‐arid environments, log‐normal mixture models were also fitted to individual observations in order to identify states, whose distribution, size and shape can indicate potential population persistence. Population structure of 12 species approximated a reverse‐J, indicating potential future growth. Although regressions of seven species were not significant, suggesting vulnerable populations, mixture models of all except one showed multiple states, indicating variable regeneration and recruitment over time. A single state of adult plants indicates that Sclerocarya birrea was vulnerable to local extirpation if adult mortality escalates. Some apparently declining populations displayed multiple states of established individuals suggesting temporally varying regeneration and recruitment, attributed mainly to rainfall variation, but which were judged as likely to persist. Poor recent regeneration of most species was attributed to well below‐average rainfall for the preceding decade. Different savanna tree species apparently ensure persistence based on individualistic responses to population perturbations, but persistence of some following the reintroduction of elephants may be threatened if certain size classes experience escalated mortality. Subsequent monitoring has supported this concern.

Length Limits Fail to Restructure a Largemouth Bass Population: A 28‐Year Case History

AbstractLength limits have been implemented by fisheries management agencies to achieve population density, size structure, and angler satisfaction objectives. By redirecting harvest towards or away from particular length‐ or age‐groups, length limits rely on harvest by anglers to maintain a population at or near a desired state. The fish population changes that follow the implementation of harvest regulations may take several years to manifest, so long‐term monitoring may be needed to adequately evaluate length limits. We used an innovative application of cluster analysis to facilitate evaluation of the effects of three consecutive length limits on a population of Largemouth Bass Micropterus salmoides over a 28‐year period in Ross Barnett Reservoir, Mississippi. A 13–16‐in protected slot length limit (10 years), followed by a 15‐in minimum length limit (MLL; 11 years), followed by a 12‐in MLL (7 years) failed to restructure the Largemouth Bass population due to what we suggest was the expansion of a voluntary catch‐and‐release attitude that started in the first decade of the study period. Various population metrics shifted towards values expected in an unharvested population, and the observed shifts can be attributed to a harvest deficit created by the prevailing catch‐and‐release attitude. Largemouth Bass harvest regulations may no longer be relevant in many waters. The utility of regulations for restructuring Largemouth Bass populations is largely dependent on harvesting attitudes that vary geographically, depending on cultural characteristics and demographics.Received September 15, 2016; accepted March 15, 2017 Published online May 4, 2017

Impact of harvesting cleaner fish for salmonid aquaculture assessed from replicated coastal marine protected areas

ABSTRACTWrasse (Labridae) fisheries have increased markedly in Norway since 2010. Wrasse are being used as cleaner fish in salmonid aquaculture to control sea-lice infestations. However, fundamental knowledge on the demography and abundance of the targeted wrasse populations in Norwegian waters is lacking, and the consequences of harvesting at the current intensity have not been assessed. Here, we compared catch per unit effort (CPUE), size, age and sex ratio of goldsinny wrasse (Ctenolabrus rupestris) and corkwing wrasse (Symphodus melops) between marine protected areas (MPAs) and control areas open for fishing at four localities on the Skagerrak coast in Southern Norway. The CPUE of goldsinny larger than the minimum size limit was 33–65% higher within MPAs, while for corkwing three of four MPAs had higher CPUE with the relative difference between MPAs and control areas ranging from −16% to 92%. Moreover, corkwing, but not goldsinny, was significantly older and larger within MPAs than in control areas. Sex ratios did not differ between MPAs and control areas for either species. Our study suggests that despite its short history, the wrasse fisheries have considerable impacts on the target populations and, further, that small MPAs hold promise as a management tool for maintaining natural population sizes and size structure. Goldsinny, being a smaller-sized species, also seems to benefit from the traditional minimum size limit management tool, which applies outside MPAs.

Effects of habitat fragmentation on population structure of dune‐dwelling lizards

AbstractLandscape fragmentation alters biotic and abiotic characteristics of landscapes, variously affecting the size and demographic structure of species' populations. Fragmentation is predicted to negatively impact habitat specialists because of perturbations to their habitat, whereas generalists should be less sensitive to fragmentation. Differences in life history among the lizards in this community should partly explain some of the variation in generalist species' responses to fragmentation. During five seasons (2009–2013), we captured eight species of lizards on 27 independent trapping grids located in unfragmented (N = 18) and fragmented (N = 9) grids in the Mescalero‐Monahans Sandhills ecosystem in southeastern New Mexico. Using a two‐way ANOVA, we tested for effects of fragmentation and year on capture rates for each species. To test for effects of fragmentation on demographic structure, we used contingency tables with expected frequencies computed from the demographic structure on unfragmented grids. Capture rates of the endemic habitat specialist Sceloporus arenicolus (dunes sagebrush lizard) decreased to zero in fragmented sites. The demographic structure of S. arenicolus and Holbrookia maculata (common lesser earless lizard) was severely disrupted at fragmented sites, with proportions of juveniles, adult males, or adult females being over‐ or underrepresented during sample months. Variable responses of five generalist species could be attributed to life history patterns, habitat affinity, and breeding phenology. This is the first empirical study we are aware of that describes and quantifies the demographic effects of fragmentation on populations of multiple lizard species in a replicated study. Our findings lend important insights into how habitat specialization and differences in life history influence the susceptibility of species to the impacts of fragmentation.

Effects of invasion at two trophic levels on diet, body condition, and population size structure of Hawaiian red shrimp

AbstractWe examined the degree to which invasion by non‐native, nitrogen (N)‐fixing riparian trees and poeciliid fish alters diet of a common grazer/detritivore in brackish ponds on the dry coast of Hawai‛i Island. Because this shrimp, Halocaridina rubra (ʻōpaeʻula), displays a preference for autotrophic components of epilithon, we hypothesized that tree canopy would reduce their body condition and abundance, but that this would be moderated by nutrient quality of leaf litter (high‐quality, non‐native, nitrogen‐fixing tree vs. low‐quality, endemic non‐nitrogen‐fixing tree). We hypothesized that poeciliid invasion would reduce population size and body condition of H. rubra by direct predation and by inducing reductions in feeding rate. Analysis of stable isotopes (δD, δ13C, and δ15N) showed that direct consumption of leaf litter detritus supplemented H. rubra diet in ponds with canopy cover. In addition, epilithon in ponds with canopy cover was isotopically more similar to leaf litter than epilithon in ponds without canopy cover, and our evidence suggests this may be due to contributions of allochthonous nutrient sources to epilithon assemblages. However, canopy cover, whether native or invasive, did not decrease epilithon growth rates and had little effect on shrimp body condition or population size. In contrast, poeciliid invasion reduced daylight grazing on the benthos, and caused a reduction in body condition among larger shrimp. Our results indicate that primary succession by invasive trees may shift food web linkages in these ponds from autotrophic to heterotrophic support, without negative impacts on native grazer/detritivore communities. We suggest that poeciliid invasions have sub‐lethal effects on H. rubra as well as their direct predation effects, with potential long‐term implications for the ecosystem function of anchialine ponds and other coastal systems.

The population size structure of Aloe claviflora in the Wolwekraal Nature Reserve in the Prince Albert district

The population size structure of Aloe claviflora in the Wolwekraal Nature Reserve in the Prince Albert district

Evidence of clandestine harvest and failure of conservation policies for Argopecten purpuratus in the Rinconada Marine Reserve (Chile)

Abstract The study of Argopecten purpuratus reproduction, post‐larval settlement, stock size, and population size structure and shell growth was undertaken in the 2000s in the Rinconada marine reserve (Chile) to evaluate the effectiveness of scallop recruitment and self‐sustainability. The results highlight strong seasonal and inter‐annual variations of environmental conditions and scallop gonadosomatic index, spat collection, benthic distribution, total abundance and population size structure. The Von Bertalanffy growth parameters were L∞ = 120.12 mm and K = 0.9681; commercial size would be reached in about 17.2 months in the bay. Substrate availability, meteorological conditions, hydrodynamics and illegal harvesting explain spatial and temporal variations in scallop distribution and abundance. Recruitment strength depends on one main cohort from year to year. While recruitment made up 81% and 94% of total abundances in May 2002 and May 2003, respectively, there were no overall density‐dependent relationships between stock size and recruitment. Spawning asynchrony in the bay supports the hypothesis that multiple gamete releases form part of a reproductive strategy in response to environmental variability. The massive disappearance of large‐sized scallops during the study periods was direct evidence of overfishing owing to clandestine harvesting within the marine reserve. The failure of current legislation, strategies and policies for scallop conservation requires new regulations to restore scallop stock size, maintain its reproductive performance and limit illegal harvesting in the Rinconada. A scenario allowing harvesting regulated by stock‐dependent fishing quotas would more efficiently ensure stock recovery and self‐sustainability. The modalities of this new policy are discussed.

Keystone Species, Forest and Landscape: A Model to Select Protected Areas.

The selection of forest fragments for conservation is usually based on spatial parameters as forest size and canopy integrity. This strategy assumes that chosen fragments present high conservation status, ensuring biodiversity and ecological functions. We argue that a well-preserved forest fragment that remains connected by the landscape structure, does not necessarily hold attributes that ensure the presence of keystone species. We also discuss that the presence of keystone species does not always mean that it has the best conditions for its occurrence and maintenance. We developed a model to select areas in forest landscapes to be prioritized for protection based on suitability curves that unify and compare spatial indicators of three categories: forest fragment quality, landscape quality, and environmental conditions for the occurrence of a keystone species. We use a case study to compare different suitability degrees for Euterpe edulis presence, considered an important functional element in Atlantic Forest (São Paulo, Brazil) landscapes and a forest resource for local people. The results show that the identification of medium or advanced stage fragments as singular indicator of forest quality does not guarantee the existence or maintenance of this keystone species. Even in some well-preserved forest fragments, connected to others and with palm presence, the reverse J-shaped distribution of the population size structure is not sustained and these forests continue to be threatened due to human disturbances.

The ecology of the freshwater form of the Atlantic salmon Salmo salar L., the brown trout Salmo trutta L., and the freshwater pearl mussel Margaritifera margaritifera L. in Syuskyuyanyoki River (Basin of Lake Ladoga)

The locations and the area of the spawning–growing grounds have been assessed in the Syuskyuyanyoki River (the basin of Lake Ladoga), as has the population density of the juveniles of the freshwater form of the Atlantic salmon and the brown trout. The Atlantic salmon spawns at present on the rapids downstream of the hydroelectric power plant because of the insurmountable dam; the population density of this species has decreased dramatically. Only the landlocked form of the brown trout was found; the anadromous form was not. The brown trout has resettled along the major part of the river. We suggest that there are two subpopulations of the freshwater pearl mussel that differ with regard to the host for their larvae. The intensity of invasion of the juveniles of salmonids by the larvae of the freshwater pearl mussel and the survivability of glochidia did not depend on the host species. The growth rate of the mollusks and the age–size structure of the freshwater pearl mussel population have been assessed.

Population Status, Group Size, and Threat to Boutourlini’s Blue Monkeys (Cercopithecus mitis boutourlinii) in Jibat Forest, Ethiopia

The present study was conducted to determine population and group size, and identify major conservation challenges to the blue monkey (Cercopithecus mitis boutourlinii) in Jibat forest. Data were collected from July 2012 to April 2013 through direct field observation, focus group discussion, interview, and questionnaire survey. Individual count was used to determine the current population size, seasonal distribution, and sex and age structure of blue monkey. Data were analyzed using descriptive statistics. Chi-square test was used to compare the sex and age ration, and their distribution among the counting blocks. The mean estimated population of Boutourlini’s blue monkeys in the study area was 188 individuals. Of which, adult males and adult females comprised 18.61% and 33.77%, respectively. There was statistical difference between the number of adult males and adult females (χ2=8.495, df=1, p 0.05). The sex ratio of adult males to adult females was 1:1.81, and adult female to infant was 1:1.65. Blue monkeys in the study area were seen mostly in groups and occasionally in pairs. The range of troop size varied from 2 to 21 with mean of 11 individuals of various sex and age categories. Major threats for blue monkey recorded in the study area were deforestation, poaching, agricultural land expansion, overgrazing, human encroachment, tree cutting and cultivation. Increasing human population density with the absence of participatory forest management has accelerated deforestation of the natural ecosystem and loss of wildlife.

Managing for naturalness alone is not an effective way to preserve all the valuable natural features of the Białowieża Forest – a reply to Jaroszewicz et al.

AbstractCurrently, Brzeziecki et al. 2016 (Journal of Vegetation Science 27: 460–467.) are using data from permanent study plots established in 1936 in Białowieża National Park (NE Poland) to develop theoretical equilibrium tree size distributions and to then compare modelled and actual distributions with a view to assessing the population dynamics of the species involved. As part of their discussion, the authors address the question of possible consequences for the overall diversity of forest ecosystems under strict protection if long‐term trends relating to tree population densities and size structures are maintained. In the overall context of the above, the goal of the present paper is to respond to Jaroszewicz et al. (Journal of Vegetation Science 28: 218–222.) who suggest that the paper of Brzeziecki et al. (2016) is not representative for the whole Białowieża National Park, and that – in this connection – strict protection should not be seen as a cause for concern. In this paper, we show that the data analysed by Brzeziecki et al. (2016) adequately characterize conditions in the wider Park. We also point out that the thorough scientific understanding of the long‐term dynamics of woodland communities under strict protection should indeed be taken into account as efforts are made to arrive at an effective conservation strategy capable of ensuring that the uniquely valuable features of the Białowieża Forest are retained.

The Effect of the Dual Household Registration System on the Population Risk in China

In order to understand the factors influencing the population risks accurately, this paper analyzes the influence mechanism of China’s dual household registration system on population risks. It is found that the China’s dual household registration system combined with specific employment, welfare and social security system and family planning policy, and caused the differences of population risks between the urban and rural. The dual household registration system affects the fertility level, the sex ratio at births and mortality, then affecting the urban and rural population size risks and structure risks. The differences of welfare and social security level between the urban and rural residents binding in the dual household registration system affect the size and structure of rural-urban migrants, thus affecting the size risks and structure risks of urban and rural population. The welfare and the urban-rural differences of social security level generate social exclusion, thus the dual household registration system affects the risks of social exclusion in cities.