Temporal variation in the population density and structure of the Eurasian BullfinchPyrrhula pyrrhulain the Iberian Peninsula

Intraspecific competition and food shortage due to high population density during early life can have a profound effect on adult fitness. Organisms often mitigate negative effects of high population density by adjusting resource allocation to adult morphological and life-history traits. In Lepidoptera with short-lived adults that do not feed, it is predicted that females developed from dense larval aggregations invest more in reproduction and traits linked to offspring survival. Here, we investigated the effects of larval population density on adult morphology and life-history traits in the female Mediterranean flour moth, Ephestia kuehniella by raising larvae at a range of population densities. Adults from high population density (16 larvae per g of food) had smaller head, thorax, and forewing compared to other densities. The allometric slope of forewing length with body mass did not differ among population densities, indicating no changes in adult wing morphology at high population density. However, we found that females emerged from larvae at high population density had bigger abdomens relative to body mass, indicating resource investment in reproduction, probably to mitigate the negative effects of crowding on egg production. Ovipositor length did not differ among population densities, indicating conservation of resources to structures with egg-laying function that affect offspring survival. Taken together, these results suggest that female E. kuehniella responding to high larval population density invest relatively more in reproduction, a life-history strategy that could alleviate negative effects of population density on fitness. This study also highlights the importance of a species' reproductive strategy in its adaptive response to environmental conditions, which is relevant to many capital breeders dependent on larval resources for reproduction.

Juveniles of chum salmon (Oncorhynchus keta) held at high population density were apparently smaller than those held at medium and low population densities. The effects of high population density on pituitary growth hormone (GH) cells in juvenile chum salmon were examined using immunocytochemical and in situ hybridization techniques. The ratio of GH-immunoreactive (ir) area to the whole pituitary was almost constant in all of the high, medium and low population density groups, although the number and sizes of GH-ir cells were decreased in the high population density group. Image-analysis of GH-ir cells indicated the presence of a population of heterogenous cells, in which medium or rather strongly stained smaller cells and as extreme weakly stained larger cells. The medium or rather strongly stained smaller cells predominated in the high population density group, while weakly stained larger cells in the low population density group. In situ hybridization study showed somewhat different distributions and intensities of hybridization signals for mRNAs encoding GH I and II precursors. The area showing signals for GH II mRNA in the high population density group was significantly smaller than those in the medium and low population density groups. In contrast, the sizes of areas showing signals for GH I mRNA did not differ among the groups, although the intensity was slightly higher in the high population density group. These results indicate that high population density decreased the number of weakly immunoreactive larger GH cells, and also suppressed expression of the gene encoding GH II precursor, which may result in retarded somatic growth.

Assessing the impact of emergency measures in varied population density areas during a large dengue outbreak

Group living can select for increased immunity, given the heightened risk of parasite transmission. Yet, it also may select for increased male reproductive investment, given the elevated risk of female multiple mating. Trade-offs between immunity and reproduction are well documented. Phenotypically, population density mediates both reproductive investment and immune function in the Indian meal moth, Plodia interpunctella. However, the evolutionary response of populations to these traits is unknown. We created two replicated populations of P.interpunctella, reared and mated for 14 generations under high or low population densities. These population densities cause plastic responses in immunity and reproduction: at higher numbers, both sexes invest more in one index of immunity [phenoloxidase (PO) activity] and males invest more in sperm. Interestingly, our data revealed divergence in PO and reproduction in a different direction to previously reported phenotypic responses. Males evolving at low population densities transferred more sperm, and both males and females displayed higher PO than individuals at high population densities. These positively correlated responses to selection suggest no apparent evolutionary trade-off between immunity and reproduction. We speculate that the reduced PO activity and sperm investment when evolving under high population density may be due to the reduced population fitness predicted under increased sexual conflict and/or to trade-offs between pre- and post-copulatory traits.

In Russia, socio-demographic, health care management, climatic and environmental TB risk factors such as population density, intensity of social contacts, availability of medical care, seasonal climate changes, environmental issues affecting quality of public health have been holding the leading place while a life standard elevates, and epidemic situation becomes improved. However, the magnitude of specific population density-related TB risk factors in the Russian regions has not been examined yet. The study aim was to assess structured TB risk factors in the Russian regions with high and low population densities decreasing public health quality. Materials and methods. There was conducted a study using sociological, cluster-quota approaches, with respondent-based sample and a face-to-face distribution questionnaire provided by 2500 subjects, of which 1497 were from the North Ossetia-Alania Republic with a high population density, 1003 — from the Republic of Karelia with a low population density. A significance of differences was assessed by using exact criterion Fisher using a contingency table. Results. In the Republic of Karelia, compared with North Ossetia-Alania Republic, despite a higher gross regional product (527.8 thousand rubles vs 293.4 thousand rubles, p 0.000), social and behavioral TB risk factors were significantly elevated: fewer respondents with high education (18.4% vs 33.6%, p 0.000), higher divorced (18.7% vs 26.9%, p 0.022), higher number of those living in apartment buildings (65.0% vs 39.5%, p 0.000), more hired and seasonal workers, unemployed, pensioners due to age and disability (55.0% vs 32.3%, p 0.000), more alcohol abusers (67.4% vs 34.3%, p 0.000), “heavy” smokers (20.8% vs 7.2%, p 0.000), more subjects with chronic diseases (43.7% vs 32.1%, p 0.02); more issues related to accessibility to medical care: municipal policlinics are less available (42.7% vs 85.6%, p 0.000), the distant location of medical facilities (21.4% vs 2.7%, p 0.000), lack of transport links (15.7% vs 8.5%, p 0.000), poor roads (5.9% vs 16.9%, p 0.000) and few medical specialists (60.9% vs 16,8%, p 0.000) are more often noted. In the North Ossetia-Alania Republic vs the Republic of Karelia, respondents had more frequent social contact with TB patients (66.9% vs 34.8%, p 0.000). Conclusion. The epidemiological TB factors in the Russian regions with high population density hold a lead place; in regions with low population density, social, behavioral and accessibility to medical care factors remain relevant, which should be taken into account while developing measures for efficient management of epidemic process.

Effects of high density on spacing behaviour and reproduction in Akodon azarae: A fencing experiment

The productivity of maize may be increased by using maize hybrid ideotype (erect leaves and small leaf angles) which is adaptive under high plant population density. The hybrids maize was desirable in increasing the plant density due to better light interception and space so that it can increase the yield per unit area. The aim of the research was to assess S3 lines that had good combining ability and to determine the traits associated with high yields under high plant population density (83.333 plants/ha). A total of 242 hybrids (F1) were examined from a crossed combination of 121 lines x 2 tester were evaluated with three commercial hybrid varieties such as Bisi 18, P 27, and P 36. The evaluation was carried under high plant population density (83,333 plants/ha) in the rainy season (November 2020 – February 2021). The research used an alpha lattice design with three replications. The results showed that the inbred lines had a greater effect on the yield character and yield components, while the leaf angle and leaf orientation effected by the tester. The lines that had good general combining ability for high yielding were M3B11P27T3-11-3-1, P27M3B11T3-1-4-2, P27M3B11T3-1-2-1, M3B11P27T3-8-4-1, P27M3B11T1-7-1-1, M3B11P27T1-1-1-3. The yield range of the hybrids were 8.43-9.90 t/ha, significantly higher than Bisi 18, P 27, P 36 varieties were 7.13 t/ha. Traits such as small leaf angle, erect leaf, root and stem lodging resistance, stem diameter, leaf length, ear diameter, and kernel row number were significantly correlated with high yield under high plant population density.

Population density can influence all three phases of natal dispersal: departure from the place of birth, searching the landscape, and selecting a new site in which to settle. The direction of the effect of density on dispersal should be affected by the relative costs and benefits of living in an area with high population density. Animals may benefit from high population density due to mate availability and predator risk dilution, but may also face increased competition in high density areas. These conflicting mechanisms should influence the pattern of change in population density between pre‐ and post‐dispersal locations: do dispersing individuals choose to move to areas of higher or lower population density than that at their natal site? We examined the influence of density on dispersal in brush mice (Peromyscus boylii). We documented pre‐ and post‐dispersal locations of individuals using both radio telemetry and live‐trapping, and used a spatially explicit capture–recapture model to estimate density across the landscape. We also tested for a relationship between dispersal distance and local population density at the natal site. Animals tended to settle in areas with higher population densities than where they were born. This pattern held when landscape‐level changes in population density were incorporated: the magnitude of change in local population density between the pre‐ and post‐dispersal locations of a given individual tended to be greater than would be explained by increasing population density across the landscape alone. Further, dispersal distances were shorter when local natal population density was higher.

For decades, the continuous advance of urbanization has led to the continuous expansion of urban land and rapid increase in the total area of cities. The phenomenon of urban land expansion faster than population growth has become widespread. High population density can lead to problems such as traffic congestion and exacerbated air pollution and can hinder sustainable development, affecting the quality of life of urban residents. China is currently in a phase of rapid urbanization, with high urban population density and rapid decline in urban population density. The decrease in urban population density is conducive to promoting sustainable urban development. This study selected 34 cities in China as sample cities and analyzed the spatial expansion and population density changes using land use and population density data from 2000, 2005, 2010, 2015, and 2020 in order to provide reference for controlling population density and promoting sustainable urban development. The conclusions of the study are as follows: In the 34 sample cities, the average urban radius was only 11.61 km in 2000, but reached 17.98 km in 2020, with an annual growth rate of 2.5%. There were significant spatial differences in urban expansion. Beijing and Shanghai, as the most developed cities in China, had urban radii exceeding 40 km, while the less developed cities of Liaoyang and Suzhou had urban radii of only 9 km. Although the population density decreased in most cities, the population density values in first-tier cities in China, such as Tianjin, Beijing, and Shanghai, continued to rise. Cities with loose spatial expansion patterns had faster decreases in population density than compact-type cities. The rate of urban spatial expansion was negatively correlated with changes in population density, with cities that had faster urban spatial expansion also having faster declines in artificial ground density.

The objective of this work was to evaluate the effects of the population density of Typha angustifolia plants in the anatomical and physiological characteristics. Plants were collected from populations of high density (over 50% of colonization capacity) and low density (less than 50% of colonization capacity) and cultivated under controlled greenhouse conditions. Plants from both populations were grown in plastic trays containing 4 L of nutritive solution for 60 days. At the end of this period, the relative growth rate, leaf area ratio, net assimilatory rate, root/shoot ratio, leaf anatomy, root anatomy, and catalase and ascorbate peroxidase activities were evaluated. Plants from high density populations showed increased growth rate and root/shoot ratio. Low density populations showed higher values of stomatal index and density in leaves, as well as increased palisade parenchyma thickness. Root epidermis and exodermis thickness as well as the aerenchyma proportion of high density populations were reduced, these plants also showed increased vascular cylinder proportion. Only catalase activity was modified between the high and low density populations, showing increased values in low density populations. Therefore, different Typha angustifolia plants show differences in its anatomy and physiology related to its origins on high and low density conditions. High density population plants shows increased growth capacity related to lower apoplastic barriers in root and this may be related to increased nutrient uptake capacity.

BackgroundPhysical activity among children and adolescents (collectively, youth) is important to ensure adult health. Population density is a factor that affects physical activity via various environmental factors. However, the relationship between population density and physical activity among youth is not fully understood, especially in extremely high density area. The aim of this study was to examine the relationship between population density and physical activity of youth using pedometer-determined step data.MethodsA total of 13,688 youth between 6 to 15 years of age were identified from the 2011 Tokyo Metropolitan Survey of Physical Fitness, Physical Activity and Lifestyle. Participants were divided into five subgroups according to the population density of their municipality of residence. The population density’s fixed effects on in-school, out-of-school, and daily total step count adjusted for gender and school grade were estimated.ResultsThe lowest (< 2500 people/km2) and highest (> 10,000 people/km2) population density subgroups had significantly lower daily total step count and out-of-school step count than those of the reference population (5000–7500 people/km2). In contrast, in-school step count did not significantly differ according to population density.ConclusionsBoth low population density and also high population density were related to lower step count. Low physical activity in high density areas has not been well documented in previous research. Considering population growth in urbanized area globally, these results suggest the importance of continued research of physical activity determinants in high population density areas.

Parasite resistance mechanisms can be costly to maintain. We would therefore predict that organisms should invest in resistance only when it is likely to be required. Insects that show density-dependent phase polyphenism, developing different phenotypes at high and low population densities, have the opportunity to match their levels of investment in resistance with the likelihood of exposure to pathogens. As high population densities often precipitate disease epidemics, the high-density form should be selected to invest relatively more in resistance. We tested this prediction in larvae of the noctuid Spodoptera exempta. Larvae reared at a high density were found to be considerably more resistant to a nuclear polyhedrosis virus than those reared in isolation. A conspicuous feature of the high-density phase of S. exempta and other phase-polyphenic Lepidoptera is cuticular melanization. As melanization is controlled by the phenoloxidase enzyme system, which is also involved in the immune response, this suggests a possible mechanism for increased resistance at high population densities. We demonstrated that melanized S. exempta larvae were more resistant than non-melanized forms, independent of rearing density. We also found that haemolymph phenoloxidase activity was correlated with cuticular melanization, providing further evidence for a link between melanization and immunity. These results suggest that pathogen resistance in S. exempta is phenotypically plastic, and that the melanized cuticles characteristic of the high-density form may be indicative of a more active immune system.

Mangrove soils provide many important ecosystem services such as carbon sequestration, yet they are vulnerable to the negative impacts brought on by anthropogenic activities. Research in recent decades has shown a progressive loss of blue carbon in mangrove forests as they are converted to aquaculture, agriculture, and urban development. We seek to study the relationship between human population density and soil carbon stocks in urban mangrove forests to quantify their role in the global carbon budget. To this end, we conducted a global analysis, collecting mangrove soil carbon data from previous studies and calculating population density for each study location utilizing a recent database from the European Commission. Results indicate population density has a negative association with mangrove soil carbon stocks. When human population density reaches 300 people km−2, which is defined as ‘urban domains’ in the European Commission database, mangrove soil carbon is estimated to be lower than isolated mangrove forests by 37%. Nonetheless, after accounting for climatic factors in the model, we see the negative relationship between population density and soil carbon is reduced and is even non-significant in mixed effects models. This suggests population density is not a good measure for the direct effects of humans on mangrove ecosystems and further implies mangrove ecosystems in close proximity to very high population density can still possess valuable carbon stocks. Our work provides a better understanding of how soil carbon stocks in existing mangrove forests correlate with different levels of population density, underscores the importance of protecting existing mangroves and especially those in areas with high human population density, and calls for further studies on the association between human activities and mangrove forest carbon stocks.

Plant-parasitic nematodes (PPNs), also known as phyto-parasitic or plant-destructive nematodes are microscopic, translucent, bilaterally symmetrical, pseudocoelomic, multicellular worm-like organisms which feed on plant root mostly, and seldom on other vegetative parts. Although these PPNs have been reported to constitute threat to rice production, documentation of their spatial distribution and densities in major rice-producing areas of Benue state, Nigeria is absent. Using multi-stage sampling procedure, surveillance for PPNs, their densities and community analyses were conducted in six major rice-producing local government areas (LGAs) of Benue. The LGAs included Agatu, Apa, Gwer West, Guma, Kwande and Makurdi LGAs and a total of 108 samples were collected comprising 54 soil and 54 root samples. Nine plant-parasitic nematode genera which included Criconemoides, Tylenchorhynchus, Trichodorus, Hirschmanniella, Xiphinema, Helicotylenchus, Scutellonema, Pratylenchus and Meloidogyne were recovered. In order of ranking, Meloidogyne sp., P. zeae and H. oryzeae had the highest population densities across all LGAs included in the study. The highest density of PPN was recorded in Kwande (ca. 133 PPNs/10mL of nematode suspension) while lowest population density was recorded in Makurdi (ca. 77 PPNs/10mL of suspension). Although Meloidogyne sp. recorded the highest average population density in all LGA except in Gwer West LGA where H. oryzae recorded the highest average population density of approximately 13 PPNs/10mL of suspension. Community analysis also revealed that Meloidogyne sp. was the most spatially distributed PPN closely followed by P. zeae and H. oryzae with prominence values of 37.78, 21.84 and 20.91, respectively. However, in the soil, the highest prominence value was recorded in H. oryzae making it the most spatially distributed PPN in the soil.

SummaryReproductive properties of the oriental chinch bug, Cavelerius saccharivorus, were investigated for three types of female adults: brachypters produced in both high and low density populations and macropters produced in high density populations. With respect to egg‐laying potential in terms of clutch size, clutch number, and total fecundity, macropters were superior to brachypters produced in the same high density population, although inferior to brachypters produced in the low density population. The mean fecundity of female adults in each type was positively correlated with mean body length.Macropterous females markedly prolonged their initiation of both copulation and oviposition and had a much longer life span compared with both types of brachypters. However, there was no fundamental difference in reproductive schedules between the two types of brachypters.