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.

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 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.

Population Interaction Dynamics Analysis of an Algae-Fish System

In this paper, before the implementation of ecological laboratory experiments, the population interaction dynamics of an algae-fish system were studied mathematically and numerically. The purpose of this study was to explore how filter-feeding fish population affects the growth dynamics of the algae population. Mathematically theoretical works have been pursuing the investigation of some key conditions for stability of the equilibrium and existence of Hopf bifurcation. Numerical simulation works have been parsing the discovery of the growth dynamics of the algae population in view of population interaction dynamics, which in turn could prove the feasibility of the theoretical derivation and reveal the relationship between filter-feeding fish abundance and algal biomass in fish-drift algae communiyua. Furthermore, it was successful to show that the filter-feeding fish population may be a crucial factor in controlling the proliferation of the algae population, which could also directly grasp the evolution of community dynamics. All these results were expected to be useful in the study of community dynamics and laboratory elimination experiment of the algae population.

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.

Modeling the dynamics of a spruce forest and dwarf mistletoe population:a coupled system

The parasitic plant dwarf mistletoe(Arceuthobium) is currently one of the most threatening infestations of coniferous forests worldwide,especially in Eurasia and North America,but its population dynamics in relation to one of its hosts(spruce) remain unclear.Here,toward understanding the population dynamics,differential equations were used to construct a life history model for the two populations,and two relatively independent subsystems,host and parasite,were generated from their symbiotic relationships.A suspected-infection model was used to couple them.The resulting models were used to analyze structural changes in the forest.When each infected spruce was assumed to support 1000 parasite shoots,the spruce population first increased rapidly,then slows.When 2000 parasite shoots were assumed,the forest declined dramatically,slipping to zero in the 10 th year,and the spruce seedlings were unable to regenerate.Parasite shoot population curves transformed from exponential J-shapes to logistic S-shapes,reaching population limitations as germination rates changed.These results provide important clues to understanding developmental trends of the present parasite population and will assist in reconstructing invasion histories.

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.

Population,Environment Dynamics,Poverty and Quality of Life in China

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Fractional Order Nonlinear Bone Remodeling Dynamics Using the Supervised Neural Network

This study aims to solve the nonlinear fractional-order mathematical model(FOMM)by using the normal and dysregulated bone remodeling of themyeloma bone disease(MBD).For themore precise performance of the model,fractional-order derivatives have been used to solve the disease model numerically.The FOMM is preliminarily designed to focus on the critical interactions between bone resorption or osteoclasts(OC)and bone formation or osteoblasts(OB).The connections of OC and OB are represented by a nonlinear differential system based on the cellular components,which depict stable fluctuation in the usual bone case and unstable fluctuation through the MBD.Untreated myeloma causes by increasing the OC and reducing the osteoblasts,resulting in net bone waste the tumor growth.The solutions of the FOMM will be provided by using the stochastic framework based on the Levenberg-Marquardt backpropagation(LVMBP)neural networks(NN),i.e.,LVMBPNN.The mathematical performances of three variations of the fractional-order derivative based on the nonlinear disease model using the LVMPNN.The static structural performances are 82%for investigation and 9%for both learning and certification.The performances of the LVMBPNN are authenticated by using the results of the Adams-Bashforth-Moulton mechanism.To accomplish the capability,steadiness,accuracy,and ability of the LVMBPNN,the performances of the error histograms(EHs),mean square error(MSE),recurrence,and state transitions(STs)will be provided.

Sex-specific facilitation and reproduction of the gynodioecious cushion plant Arenaria polytrichoides on the Himalaya-Hengduan mountains,SW China

When benefiting other beneficiaries,cushion plants may reciprocally receive feedback effects.The feedback effects on different sex morphs,however,remains unclear.In this study,taking the gynodioecious Arenaria polytrichiodes as a model species,we aimed to assess the sex-specific facilitation intensity of cushion plant by measuring the beneficiary cover ratio,and to assess the potential costs in cushion reproductive functions by measuring the flower and fruit cover ratios.The total beneficiary cover ratio was similar between females and hermaphrodites.Females produced much less flowers but more fruits than hermaphrodites.These results suggested that females and hermaphrodites possess similar facilitation intensity,and female cushion A.polytrichoides may allocate more resources saved from pollen production to seed production,while hermaphrodites possibly allocate more resources to pollen production hence reducing seed production.The surface areas covered by beneficiaries produced less flowers and fruits than areas without beneficiaries.In addition,strong negative correlations between beneficiary cover and flower cover were detected for both females and hermaphrodites,but the correlation strength were similar for these two sex morphs.However,the correlation between beneficiary cover and fruit cover was only significantly negative for females,suggesting that beneficiary plants negatively affect fruit reproduction of females while have neutral effects on hermaphrodites.All the results suggest that to facilitate other beneficiaries can induce reproductive costs on cushion A.polytrichoides,with females possibly suffering greater cost than hermaphrodites.Such differentiation in reproductive costs between sex morphs,in long-term perspective,may imply sex imbalance in population dynamics.

Density and Seasonal Dynamics of Bemisia tabaci(Gennadius) Mediterranean on Common Crops and Weeds Around Cotton Fields in Northern China

The density seasonal dynamics of Bemisia tabaci MED were evaluated over two years in a cotton-growing area in Langfang, Hebei Province, northern China on cotton （Gossypium hirsutum L.） and six other co-occurring common plants, common ragweed （Ambrosia artemisiifolia L.）, piemarker （Abutilon theophrasti Medicus）, sunflower （Helianthus annuus L.）, sweet potato （Ipomoea batatas L.）, soybean （Glycine max L.）, and maize （Zea mays L.）. The whitefly species identity was repeatedly tested and confirmed; seasonal dynamics on the various host plants were standardized by the quartile method. B. tabaci MED appeared on weeds （the common ragweed and piemarker） about 10 days earlier than on cotton, or the other cultivated plants. The peak population densities were observed over a span of 2 to 3 weeks on cotton, starting in early （2010） or mid-August （2011）. The common ragweed growing adjacent to cotton supported the highest B. tabaci densities （no. on 100 cm2 leaf surface）, 12-22 fold higher than on cotton itself. Sunflower supported more B. tabaci than the other plants, and about 1.5-2 fold higher than cotton did, Our results indicate that weeds （esp. the common ragweed） around cotton fields could increase the population density of B. tabaci MED on cotton, while sunflower could act as a trap crop for decreasing pest pressure on cotton.