A Population Dynamics Approach to the Distribution of Space Debris in Low Earth Orbit

The presence of the debris in the Earth’s orbit poses a significant risk to human activity in outer space.This debris population continues to grow due to ground launches,the loss of external parts from space ships,and uncontrollable collisions between objects.A computationally feasible continuum model for the growth of the debris population and its spatial distribution is therefore critical.Here we propose a diffusion-collision model for the evolution of the debris density in the low-Earth orbit and its dependence on the ground-launch policy.We parametrize this model and test it against data from publicly available object catalogs to examine timescales for the uncontrolled growth.Finally,we consider sensible launch policies and cleanup strategies and how they reduce the future risk of collisions with active satellites or space ships.

Model fitting of the seasonal population dynamics of the soybean aphid, Aphis glycines Matsumura, in the field

The soybean aphid, Aphis glycines Matsumura(Hemiptera: Aphididae), is one of the greatest threats to soybean production, and both trend analysis and periodic analysis of its population dynamics are important for integrated pest management(IPM). Based on systematically investigating soybean aphid populations in the field from 2018 to 2020, this study adopted the inverse logistic model for the first time, and combined it with the classical logistic model to describe the changes in seasonal population abundance from colonization to extinction in the field. Then, the increasing and decreasing phases of the population fluctuation were divided by calculating the inflection points of the models, which exhibited distinct seasonal trends of the soybean aphid populations in each year. In addition, multifactor logistic models were then established for the first time, in which the abundance of soybean aphids in the field changed with time and relevant environmental conditions. This model enabled the prediction of instantaneous aphid abundance at a given time based on relevant meteorological data. Taken as a whole, the successful approaches implemented in this study could be used to build a theoretical framework for practical IPM strategies for controlling soybean aphids.

Factors regulating population dynamics of the amphipod Ampithoe valida in a eutrophic subtropical coastal lagoon

Year-round investigations were carried out to address the population dynamics of amphipod Ampithoe val- ida and its potential regulating factors in the Yundang Lagoon （a eutrophic subtropical coastal lagoon in Xiamen City, China） from October 2007 to October 2008. The results show that A. valida population was largely composed of juveniles and reached a peak abundance （12.02× 10^3 ind./m2） in March, but sharply shrunk in July. The monthly variation pattern ofA. valida seemed to follow that of Ulva lactuca which is the main food resource for A. valida, indicating a strong influence of food availability on A. valida popu- lation dynamics. Life cycle studies in laboratory indicate that A. valida adopted an r-selected life strategy, e.g., rapid growth rate （0.216-0.302 mm/d）, consecutive breeding （4-10 times）, short reproductive rhythm （9-17 d） and huge fecundity （24-192 eggs or 6-94 juveniles per brood）, which contributed to the fast pop- ulation growth ofA. valida from January to March. Although temperature may also be a significant cause, A. valida could grow quickly and show normal reproductive traits （i.e., the timing of sexual differentiation or maturity, the reproductive rhythm, the number of broods all through its lifespan and offspring produc- tion） in temperature between 15-30~ C. Therefore, the temperature variation in the lagoon water should not account for the sharp variation of A. valida population by affecting the survival, growth and reproduction of the amphipod. However, negative correlation between water temperature and U. lactuca biomass in the lagoon suggested that temperature could have indirectly affected the population dynamics ofA. ualida by affecting its food availability. The authors conclude that, in the Yundang Lagoon, the population dynamics ofA. validawas mainly controlled by the food availability rather than water temperature.

Potential influence of carbohydrate and amino acid intake by adults on the population dynamics of Cnaphalocrocis medinalis(Lepidoptera: Crambidae)

Cnaphalocrocis medinalis is a key lepidopteran pest of rice. However, little is known about the nutritional requirements of the adult or the effects of adult-derived nutrients on reproduction. The aim of the present study was to evaluate the effects of carbohydrates and amino acids on the reproductive and demographic parameters of C. medinalis. Different feeding solutions significantly influenced adult survival and reproduction. All the sources of carbohydrates used in the treatments(fructose, glucose, and sucrose) were sufficient to increase adult longevity and fecundity, and benefited the development of ovaries in the adult stage. The positive impact of carbohydrates on lifetime fecundity was due to the prolonged oviposition period and the increased daily fecundity. The intrinsic rate of increase(rm) of C. medinalis increased from 0.103 in waterfed individuals to approximately 0.138 when adults were fed with solutions containing carbohydrates. In contrast, amino acid intake by adult insects exhibited no effect on the longevity, fecundity, ovarian development or population growth, even showing an impact of decreasing longevity of females. As nectar secreted by the flowering plant is generally rich in sugars, the potential effects of nectar on the adults of C. medinalis and other pests have to be considered during the development of biological control by applying flowering plants as a microhabitat and food source for natural enemies in rice fields.

Population dynamics modelling with spatial heterogeneity for yellow croaker(Larimichthys polyactis)along the coast of China

As one of the top four commercially important species in China,yellow croaker(Larimichthys polyactis)with two geographic subpopulations,has undergone profound changes during the last several decades.It is widely comprehended that understanding its population dynamics is critically important for sustainable management of this valuable fishery in China.The only two existing population dynamics models assessed the population of yellow croaker using short time-series data,without considering geographical variations.In this study,Bayesian models with and without hierarchical subpopulation structure were developed to explore the spatial heterogeneity of the population dynamics of yellow croaker from 1968 to 2015.Alternative hypotheses were constructed to test potential temporal patterns in yellow croaker’s population dynamics.Substantial variations in population dynamics characteristics among space and time were found through this study.The population growth rate was revealed to increase since the late 1980s,and the catchability increased more than twice from 1981 to 2015.The East China Sea’s subpopulation witnesses faster growth,but suffers from higher fishing pressure than that in the Bohai Sea and Yellow Sea.The global population and two subpopulations all have high risks of overfishing and being overfished according to the MSY-based reference points in recent years.More conservative management strategies with subpopulation considerations are imperative for the fishery management of yellow croaker in China.The methodology developed in this study could also be applied to the stock assessment and fishery management of other species,especially for those species with large spatial heterogeneity data.

Studies on ecological characteristics variation and population dynamics of four lizardfishes in the southern Taiwan Straits

The ecological characteristics of four lizardfishes, Trachinocephalus myops, Saurida undosquamis, Saurida tumbil and Saurida elongata, were studied from specimens （910 T. myops, 454 S. un-dosquamis, 686 S. tumbil and 744 S. elongata） collected monthly in the southern Taiwan Straits from April 2005 to March 2006. The population dynamics of the four lizardfishes was also discussed by the comparison with the previous studies. All being composed of 7 a classes; the dominant group of T. myops and S. tumbil was 1–2 a, while S. undosquamis and S. elongate were 2–3 a. The total mortality coefficient Z and the fishing mortality F were at high as indicated by the exploitation ratio E（0.5）, and a large number of by-caught juvenile and young fishes showing that the stock of lizardfishes in this area was overexploited and the fishing gear was irrational. Compared with the previous studies, the maximum and mean fork length, body mass and age of the four lizard- fishes declined gradually, the lizardfishes populations were younger in age and smaller in size. The asymptotic fork length L ∞ decreased while increasing growth coefficient k, and age at the inflexion point of mass t r was younger compared with the previous studies. The declining of older ones has moderated the feeding competition and the younger ones grew faster. The larger mortality param-eters Z, M and F have revealed higher fishing pressure. The smaller change of the first mature fork length of female T . myops and the change from K selection pattern to r selection pattern of S. tumbil have indicated a more vulnerable fishery ecosystem in this area. The changes of ecological characteristics and population dynamics may be caused by over-exploitation of demersal fishes such as the lizardfishes, especially a large number of juvenile and young fishes by-catch by the current fishing gears and methods. Therefore, in addition to the traditional fishery management approach such as the minimum length-limit, ecosystem approach to fisheries management （EAF） should be taken to improve the practical marine ecosystem management, including increased fishing intensity of the non-economic species especially the feeding competitors of the lizardfishes and the conservation of the pelagic fishery population in the fisheries ecosystem, in order to restore the fishery population and achieve the sustainable use of the fishery stocks.

OPTIMAL HARVESTING CONTROL PROBLEM FOR LINEAR AGE-DEPENDENT POPULATION DYNAMICS

An optimal harvesting problem for linear age-dependent population dynamics is investigated.By Mazur's Theorem,the existence of solutions of the optimal control problem (OH) is demonstrated.The first order necessary conditions of optimality for problem (OH) is obtained by the conception of normal cone. Finally,under suitable assumptions,the uniqueness of solutions of the optimal control problem (OH) is given.The results extend some known criteria.

Population dynamics of Piscicola geometra (Hirudinea: Rhynchobdellida) on Oreochromis Niloticus (Cichlidae) cultured in a rainforest fish pond, South Eastern Nigeria

The distribution, abundance and intensity of the annelid worm, Piscicola geometra (leeches) infecting Oreochromis niloticus cultured in a rainforest fish pond, South Eastern Nigeria was studied over a 12 months period. Three hundred fish were examined of which 48.3% were infected. Infection occurred throughout the year, with a peak in February. Female fish had a significantly higher intensity of infection( P < 0.05) than males. There was a clear seasonal periodicity in the degree of infection and the distribution of the parasite exhibited an aggregated or contagious model of dispersion. There was a significant positive correlation between the size of the fish and worm burden.

The Abundance and Population Dynamics of Leptocybe invasa (Hymenoptera:Eulophidae) Galls on Eucalyptus spp.in China

The blue gum chalcid, Leptocybe invasa Fisher ＆ La Salle, invaded China in 2007 and has subsequently caused substantial damage to eucalyptus trees. In the current paper, we investigated the susceptibility of 10 Eucalyptus spp. and Eucahetus dunnii to L. invasa in the field, determined the density of galls as well as the gall volume on these tree species, and monitored the population dynamics of wasps in Hainan and Guangdong provinces of China. The order of susceptibility to L. invasa was Eucalyptus urophyllaxEucalyptus camaldulensis〉E, urophylla （coppices）〉Eucalyptus exserta〉 Eucalyptus grandisxE, urophylla in Hainan, and Eucalyptus propinqua〉Eucalyptus saligna〉E, exserta〉Eucalyptus microcorys〉Eucahetus dunnii〉E, camaldulensis〉Eucalyptus tereticornis〉Eucalyptus robust in Guangdong, China. Although L. invasa generally damages the midribs and petioles of young leaves and the tender bark of twigs of eucalyptus, galls were not observed on leaves of E. microcorys, E. camaldulensis, or E. dunnii. Gall volume significantly differed among the tree species, and gall volume and wasp number were positively correlated. In Dongfang, Hainan Province, the overwintering period of L. invasa emergencing through the year was from the end of December to March of the next year, and the number of population was the greatest on E. urophylla^E, camaldulensis, and the smallest on E. grandis E. urophylla. In Guangzhou, Guangdong Province, L. invasa hardly emerged in winter from December to June of the next year, and the population was the greatest on E. propinqua, and the smallest on E. microcorys.

Effect of UV-B radiation on the population dynamics of the rotifer Brachionus urceus

The effect of UV-B radiation enhancement at experimental doses of 0.00,0.24,0.48,0.72,0.96,and 1.20 kJ/m 2 on the population dynamics of the rotifer Brachionus urceus feeding on the alga Chlorella sp.was studied under controlled laboratory conditions using clonal culture and life-table techniques.The results show that UV-B radiation treatment significantly shortened the survival time of the rotifer （P 0.05）： The longest survival time （336 h） occurred in the control （0.00 kJ/m 2 ） while the shortest （222 h） occurred when exposed to the highest UV-B radiation treatment （1.20 kJ/m 2 ）.The fecundity of the rotifer B.urceus was enhanced by the lower UV-B radiation treatment （0.24 and 0.48 kJ/m 2 ） but inhibited by the higher treatments （0.96 and 1.20 kJ/m 2 ）.Life expectancy also was obviously affected by UV-B radiation （P 0.05）.The highest life expectancy occurred in the control （0.00 kJ/m 2 ）,and it became shorter with increasing doses of UV-B radiation.The resutls in the present study indicate that the life expectancy of the rotifer B.urceus can be used as an indicator for UV-B radiation enhancement.

Population dynamics and condition index of natural stock of blood cockle,Tegillarca granosa(Mollusca,Bivalvia,Arcidae)in the Marudu Bay,Malaysia

The population parameters of blood cockles,Tegillarca granosa in the intertidal zone of Marudu Bay,Sabah,Malaysia were investigated based on monthly length-weight frequency data(July 2017 to June 2018).A total of 279 cockle individuals with shell length and weight ranging from 27.7 mm to 82.2 mm and 13.11 g to 192.7 g were subjected to analysis.T.granosa in Marudu Bay showed a consistent moderately high condition index 4.98±0.86 throughout the year.The exponent b of the length-weight relationship was 2.6 demonstrating negative allometric growth.The estimated asymptotic length(L_(∞)),growth coefficient(K)and growth performance(Ф)of the T.granosa population in Marudu Bay were estimated at 86.68 mm,0.98 a^(-1) and 3.87,respectively.The observed maximum shell length was 82.55 mm and the predicted maximum shell length was 84.44 mm with estimated maximum life span(t_(max))of 3.06 years.The estimated mean lengths at the end of 2,4,6,8,10 and 12 months of age were 21.31 mm,31.16 mm,39.53 mm,46.63 mm,52.67 mm and 57.79 mm.Total,natural,and fishing mortalities were estimated at 2.39 a^(-1),1.32 a^(-1) and 1.07 a^(-1).The exploitation level(E)was 0.45.Results of the current study also demonstrated that T.granosa in the Marudu Bay has two major recruitment peaks;one in March and another in October.The exploitation level revealed that natural stock of T.granosa in the Marudu Bay was approaching the maximum exploitation level.If such trend continues or demand for T.granosa is increasing,coupled with no effective fisheries management in place,possibility of the T.granosa population in the Marudu Bay to collapse is likely to elevate.

Population dynamics of Acartia pacifica (Copepoda:Calanoida):the importance of benthic-pelagic coupling

The seasonal occurrence of Acartia pacifica （ Copepoda： Calanoida） and their resting eggs in the sediment of Xiamen Bay were documented between October 2002 and September 2003. The numher of viable eggs in the sediment increased from January to May with the increase in the numher of planktonic females. When the population ofA. pacifica disappeared from the water cohinm, the number of eggs in the sediment began to decrease and reached a low value due to lack of input. The peak of nauplii abundance occurred when the hatching potential of eggs from the sediment was high under the natural environment from February to June. The hatching of resting eggs of A. pacifica was essentially temperature-dependent after suspension, while photoperied regimes had no significant effect on the hatching. The mean density of subitaneeus eggs was 1. 122 0 g/cm^3 with a standard deviation （SD） of 0. 000 2 g/cm^3. The mean density of diapause eggs was 1. 151 2 g/cm^3 with a SD of 0.000 1 g/cm^3. The sinking rates of subitaneons eggs ranged from 19.55 to 26.17 m/d, while those of diapause eggs ranged from 30.29 to 31.28 m/d. The comparison of the egg deposition time and egg hatching time suggested that in most cases virtually all subitaneous eggs of A. pacifica would settle to the bottom before their hatching even though the eggs have high potential to hatch. The evidence was provided that the seasonal dynamics of A. pacifica is accompanied by benthic-pelagic coupling.

The Influence of Fence on Body Mass and Population Dynamics of Plateau Pika

To determine the influence of the fence on plateau pika (Ochotona curzoniae), we measured the body mass, breeding status, population densities, using live-trapping and line-transect sampling in April and September 2006. In April, body mass of both male and female plateau pika inside of fence were significant higher than that outside of fence (♀: F = 6.583, df = 1.20, p = 0.019;♂: F = 6.49, df = 1.17, p = 0.021). The ratio of spermary drop of an adult male was also higher (92.31% vs 57.14%). In September, body mass of adult male in both study sites showed no significant difference (F = 0.001, df = 1.23, p = 0.975), but were all significant higher than that of April (F = 121.713, df = 1.22, p < 0.001;F = 105.819, df = 1.20, p < 0.001). In April, the population densities of both study sites showed on significant difference (F = 2.388, df = 1.38, p = 0.131), but the population density inside of fence was much higher than that outside of fence (F = 7.534, df = 1.38, p = 0.009) in September. Our results show that the changes of quality and quantity of food that available to plateau pika in winter, can depress the range of reducing body mass of plateau pika, make breeding season ahead, and then promote the increase of population.

Smart energy management system framework for population dynamics modelling and suitable energy trajectories identification in islanded micro-grids

In an increasingly electrified and connected world,renewable energy production and robust distribution as well as sobriety paradigm,both for the individual and the society,will most likely play a central role regarding global systems stability.Consequently,while being able to conceive efficient storage systems coupled with robust energy management strategies present significant interests,a number of related studies often consider the human behaviour factor separately.While not decisive in large industrial factories,human demeanor impact cannot be overlooked in residential areas.As such,this work proposes an innovative and flexible dynamic population model,inspired from epidemiological methods,that allows simulation of a vast spectrum of social scenarios.By pairing this formalization with a smart energy management strategy,a complete framework is proposed.In particular,beyond the theoretical identification of sustainable parameters in a wide diversity of configurations,our experiments demonstrate the relevance of reinforcement learning agents as efficient energy management policies.Depending on the scenario,the trained agent enables an increase of the sustainability areas over baseline strategies up to 200%,thus hinting at ultimately softer societal impact.

Microbial population dynamics and changes in main nutrients during the acidification process of pig manures

This study evaluated the impact of pig manure acidification on anaerobic treatment and composition of the fecal microbial community. According to the different chemical oxygen demand （COD） in the anaerobic treatment processes, pig manure was diluted 4 times （×4）, 16 times （×16）, or 64 times （×64） and subjected to acidification. During the acidification process, pH, soluble chemical oxygen demand （SCOD）, volatile fatty acids （VFAs）, nitrogen （N）, phosphorus （P） and potassium （K） were determined along with microbial population dynamics. The pH of the three dilutions first declined, and then slowly increased. The total VFAs of x4 and xl6 dilutions peaked on day 15 and 20, respectively. The content of acetic acid, propanoic acid, butanoic acid and valeric acid of the × 4 dilution were 23.6, 11.4, 8.8 and 0.6 g/L respectively, and that of the xl6 dilution was 5.6, 2.3, 0.9 and 0.2 g/L respectively. Only acetic acid was detected in the ×64 dilution, and its level peaked on day 10. The results showed that the liquid pig manure was more suitable to enter the anaerobic methanogenic hioreactors after two weeks of acidification. During the acidification process, total P concentration increased during the first ten days, then dropped sharply, and rose again to a relatively high final concentration, while total N concentration rose initially and then declined. Based on the analysis of denaturing gradient gel electrophoresis （DGGE） and 16S rRNA gene clone library, we concluded that the acidification process reduced the number of pathogenic bacteria species in pig manure.

Population dynamics of Amur tigers(Panthera tigris altaica)in Sikhote-Alin Biosphere Zapovednik:1966–2012

In 2010,the world’s tiger(Panthera tigris)range countries agreed to the goal of doubling tiger numbers over 12 years,but whether such an increase is biologically feasible has not been assessed.Long-term monitoring of tigers in Sikhote-Alin Biosphere Zapovednik(SABZ),Russia provided an opportunity to determine growth rates of a recovering population.A 41-year growth phase was followed by a rapid decline in tiger numbers.Annual growth rates during the growth phase averaged 4.6%,beginning near 10%in the earliest years but quickly dropping below 5%.Sex ratio(females per male)mirrored growth rates,declining as population size increased.The rapid decline from 2009 to 2012 appeared to be tied to multiple factors,including poaching,severe winters and disease.Reproductive indicators of this population are similar to those of Bengal tiger populations,suggesting that growth rates may be similar.These results suggest that,first,tiger populations likely in general grow slowly:3–5%yearly increases are realistic and larger growth rates are likely only when populations are highly depressed,mortality rates are low and prey populations are high relative to numbers of adult females.Second,while more research is needed,it should not be assumed that tiger populations with high prey densities will necessarily grow more quickly than populations with low prey densities.Third,while growth is slow,decline can be rapid.Fourth,because declines can happen so quickly,there is a constant need to monitor populations and be ready to respond with appropriate and timely conservation interventions if tiger populations are to remain secure.Finally,an average annual growth rate across all tiger populations of 6%,required to reach the Global Tiger Initiative’s goal of doubling tiger numbers in 12 years,is a noble but unlikely scenario.

Long-term patterns in Iberian hare population dynamics in a protected area(Doñana National Park)in the southwestern Iberian Peninsula:Effects of weather conditions and plant cover

The Iberian hare(Lepus granatensis)is a widely distributed endemic species in the Iberian Peninsula.To improve our knowledge of its population dynamics,the relative abundance and population trends of the Iberian hare were studied in the autumns of 1995-2012 in a protected area(Doñana National Park)by spotlighting in 2 different habitats:marshland and ecotones.The average relative abundance was 0.38 hare/km(SD=0.63)in the marshland and 3.6 hares/km(SD=4.09)in ecotones.The Iberian hare population exhibited local interannual fluctuations and a negative population trend during the study period(1995-2012).The results suggest that its populations are in decline.The flooding of parts of the marshland in June,July and October favor hare abundance in the ecotone.Hare abundance in the marshland increases as the flooded surface area increases in October.These effects are more pronounced if the rains are early(October)and partially flood the marsh.By contrast,when marsh grasses and graminoids are very high and thick(as measured using the aerial herbaceous biomass[biomass marshland]as a proxy),the abundance of hares decreases dramatically as does the area of the marsh that is flooded(in November).

Mining hourly population dynamics by activity type based on decomposition of sequential snapshot data

The dynamic population distributions by activity type(e.g.working,shopping or in-home)are vital for resource allocation,urban planning and epidemic containment.Although studies have incorporated individual-level human mobility data to map population distribution by activity type,access to such data is hindered due to privacy issues and they rely on auxiliary data to provide priori activity knowledge.This paper presents a method for generating the population dynamics by activity type.We first introduce more readily available sequential snapshot data to construct the population mixture model,then decompose the population mixture,and finally estimate the dynamic population size for each activity.We test the method in the central districts of Guangzhou city,China,based on real-time Tencent user density data.Correlation analysis and accuracy assessment prove that our method can accurately estimate hourly distributions for populations engaging in working,stay-at-home,and socializing activities.The temporal distribution of the working population reproduces the regular work scenarios and socializing population displays complex spatial patterns.We also find that there is an underlying relationship between a region’s function and its dynamic population structure.The presented method has great potential for application and could provide new insight for studying urban dynamic functions.

Population dynamics inside cancer biomass driven by repeated hypoxia-reoxygenation cycles

A computational analysis of genome-scale transcriptomic data collected on -1,700 tissue samples of three cancer types： breast carcinoma, colon adenocarcinoma and lung adenocarcinoma, revealed that each tissue consists of （at least） two major subpopulations of cancer cells with different capabilities to handle fluctuating Oz levels. The two populations have distinct genomic and transcriptomic characteristics, one accelerating its proliferation under hypoxic conditions and the other proliferating faster with higher O2 levels, referred to as the hypoxia and the reoxygenation subpopulations, respectively. The proportions of the two subpopulations within a cancer tissue change as the average 02 level changes. They both contribute to cancer development but in a complementary manner. The hypoxia subpopulation tends to have higher proliferation rates than the reoxygenation one as well as higher apoptosis rates; and it is largely responsible for the acidic environment that enables tissue invasion and provides protection against attacks from T-cells. In comparison, the reoxygenation subpopulation generates new extracellular matrices in support of further growth of the tumor and strengthens cell-cell adhesion to provide scaffolds to keep all the cells connected. This subpopulation also serves as the major source of growth factors for tissue growth. These data and observations strongly suggest that these two major subpopulations within each tumor work together in a conjugative relationship to allow the tumor to overcome stresses associated with the constantly changing Oz level due to repeated growth and angiogenesis. The analysis results not only reveal new insights about the population dynamics within a tumor but also have implications to our understanding of possible causes of different cancer phenotypes such as diffused versus more tightly connected tumor tissues.