Prolongation of Postembryonic Development in Experimental and Natural Cladoceran Populations

One of the methods for determining the duration of postembryonic development is the calculation method suggested by Gras and Saint-Jean (1978) for populations with continuous reproduction and stable age distribution. After inserting time-weighted means for instantaneous birth rates into the formula, it is possible to calculate the growth rates of the juveniles during each interval between obersvations for a non-stationary population. Estimated values were in a good agreement with those obtained from computer-constructed populations and determined directly from a natural cladoceran population. The duration of postembryonic development in cladoceran populations increases significantly during periods of food depletion caused by filtering activity of herbivorous zooplankton. This physiological response together with the decrease in age-specific fecundity permits effective regulation of population abundance through the birth rate.     

Effects of Daphnia longispina on rotifer populations in a natural environment: relative importance of food limitation and interference competition

To test the relative importance of exploitative and interferencecompetition from Daphnia limiting rotifer populations in Bermejalesreservoir, birth rates of rotifers, food abundance, zooplanktonbiomass and size distribution of Daphnia were analysed fromhigh frequency sampling at two depths. A depletion in food abundanceby Daphnia feeding should be reflected in the birth rates ofrotifers susceptible to exploitative competition, while interferenceshould produce direct negative relationships between the numberof individuals of the interacting species. Results show thatsignificant relationships between food (chlorophyll-a) and birthrates of rotifers are found when the ratio chlorophyll-a/herbivorouszooplankton biomass is used as a measure of food availability.In our study, Anuraeopsis fissa was only affected through exploitativecompetition by Daphnia, while only Synchaeta oblonga showedevidence of being suppressed through interference competitionby this cladoceran.     

Resource-mediated demographic variation during the midsummer succession of a cladoceran community

SUMMARY. 1. The midsummer succession of cladoceran zooplankton in Lake Texoma was examined by demographic characterization of lake populations and a parallel set of life table experiments in which the dominant cladoceran species were raised on naturally occurring lake phytoplankton at lake temperatures. Diaphanosoma leuchtenbergianum occurred throughout the study period (mid June-mid August 1981) but Daphnia parvula, D. galeata mendotae and Ceriodaphnia lacustris were rarely detected after 15 July.
2. Analyses of size structure and size-specific fecundity of the cladoceran populations showed that (1) size structure shifted to smaller individuals in mid July, (2) size-specific fecundity was relatively constant in the smaller size classes and was constant or declined in larger females of each species, and (3) size at maturation did not vary significantly during the study of any population.
3. Individual growth rates of the two Daphnia species and Ceriodaphnia in the life table experiments were significantly lower in mid July when populations were declining and when size structure of each population was more dominated by smaller Individuals. The reduction in individual growth rates was short-lived in the life table experiments; growth rates returned to pre-decline levels by the end of July.
4. Two effects of temporary reductions in individual growth rates when size-specific fecundity and size at maturation are constant are (1) that size structure is temporarily shifted to smaller individuals, and (2) the potential rate of population growth is reduced because of delays in reproduction. Because data on size structure and size-specific fecundity are commonly used to evaluate the relative effects of predators and resource changes on populations it is noteworthy that erroneous conclusions about the mechanism of population decline may be reached when individual growth rates vary.     

鄱阳湖水体淹没频率变化及其湿地植被的响应

湖水淹没频率是影响湿地植被生态系统的最重要的水文因素。基于地物波谱特征的MODIS混合像元分解模型,分析了2000—2015年退水期鄱阳湖水体淹没频率的时间变化和空间规律,并在此基础上探讨了湿地植被的空间响应。研究结果表明:(1)鄱阳湖退水期水体的淹没频率总体呈"南低北高",同时具有大小不一的"斑块式"空间分布特征;(2) 15年内湖水的淹没频率经历了先急剧缩减然后恢复到相对稳定的状态,并且不同空间段的变化差异明显:北部河道的淹没频率先急剧降低后回升,中部洲滩不如北部河道段剧烈但大面积的淹没频率下降,南部子湖泊的淹没频率则基本没变;(3)植被丰度对淹没频率具有密切的响应关系,两者呈中间高两边低的"n"形分布,当淹没频率为40%时高植被丰度的像元数最多。(4)淹没频率与植被丰度的关系指示着鄱阳湖湿生植被在空间上的积极演变。     

Competitive exclusion in Cladocera through elevated mortality of adults

The population dynamics of two cladocerans, Ceriodaphnia pulchellaand Diaphanosoma brachyurum competing under laboratory conditionsin lake water was analysed using cross-correlations. Both mixedand isolated populations of the two cladocerans showed delayeddensity-dependence in the death rates of juveniles and adultsas well as in fecundity rate. The regressions for each of thethree rates on total density of competitors were compared betweenthe two species. There were no significant differences in theslopes of regressions for fecundity rates and the death ratesof juveniles. However, in the inferior competitor (Diaphanosoma)which went extinct in all treatments, the death rate of adultsincreased with total density much more quickly than in the superiorcompetitor (Ceriodaphnia). The intraspecific comparisons indicatedthat while Ceriodaphnia adults survived better than juvenilesunder conditions of crowding, in Diaphanosoma, juveniles werebetter survivors than adults. These data suggest that the contentionof higher vulnerability of cladoceran juveniles than adultsto starvation and crowding may prove to be not a universal phenomenon.     

How important are trophic state,macrophyte and fish population effects on cladoceran community? A study in Lake Erhai

Environmental controls on cladoceran community structure in lake ecosystems are complex and may involve many environmental parameters including trophic state and fish populations. In Lake Erhai, a plateau lake located in southwest China, it was hypothesized that a combination of lake eutrophication and planktivorous fish introduction would increase the abundance of cladoceran, while also decreasing cladoceran size. To test this hypothesis, we examined temporal changes in cladoceran microfossils in the sediments of Lake Erhai over the past century. The influence of changing macrophyte coverage within the littoral region of the lake was also considered. Results demonstrated that cladoceran abundance (measured as flux of cladoceran fossils in the sediments) increased markedly accompanying eutrophication of the lake. In addition, there was a shift in the dominant cladoceran species from those species that prefer oligotrophic conditions to those that prefer mesotrophic and eutrophic conditions. A reduction in the ephippium length of Daphnia spp. was observed and attributed to the introduction of the planktivorous fish Neosalanx taihuensis. Our findings indicated that eutrophication and fish introduction were the main controls affecting cladoceran community structure during the recent decades, and predation by planktivorous fish had an important impact on Daphnia body size.     

Distribution patterns of Cladocera in subarctic Fennoscandian lakes and their potential in environmental reconstruction

Multivariate statistical techniques were used to examine the relationships between surface-sediment cladoceran assemblages and 28 physical and chemical variables in 53 small subarctic lakes from northern Fennoscandia. The lakes were distributed along a steep eco-climatic gradient, spanning boreal corniferous forest to treeless tundra. In general, the sites were small, oligotrophic, and bathymetrically simple, with little or no disturbance in their catchments. From the initial 53 localities, only 36 contained a sufficient number of cladoceran remains for reasonable quantification. From these, a total of 29 cladoceran taxa representing 19 genera were identified, comprising predominantly littoral chydorid species. A constrained redundancy analysis (RDA) and associated Monte Carlo permutation tests indicated that maximum lake depth, sediment organic content, epilimnetic summer temperature, lake perimeter, and lake catchment area made statistically significant (p le; 0.05) contributions to explaining the variance in the cladoceran taxon data. These five variables together accounted for 67.7% of the explained variance, and made a unique contribution of 26.8% to the total variance: all physical determinants independently captured 33.2% of the total variance. The significance of the most powerful explanatory variables is discussed in the paper in detail, and autecological information regarding the most common cladoceran taxa is given. To assess the potential of cladoceran assemblages in environmental reconstruction, quantitative inference models for mean July water and air temperatures were developed for the cladoceran assemblage using partial least squares (PLS) regression. The final prediction model yielded a root mean squared error of prediction (RMSEP). as assessed by jackknifing, of 1.19°C for Cladocera-water temperature data-set, whereas the cladoceran assemblages showed only very weak relationships to mean July air temperature. The overall results emphasize the role of physical factors in regulating species abundance and distributions in these environmentally sensitive ecotonal lakes.     

Zooplankton abundance and evidence for its reduction by macrophyte mats in two Orinoco floodplain lakes

Zooplankton populations were sampled over one annual cycle intwo floodplain lakes of the Orinoco River, Venezuela, in anattempt to establish the relationship between abundance patternsand the hydrology and morphometry of the lakes. One of the lakes(Tineo) is relatively large with a gently sloping basin; theother one (Aguilera) is smaller and channel-shaped. The hydraulicresidence time of Lake Aguilera during inundation by the riveris shorter (<1 day) than the minimum generation times ofcrustacean (4–12 days) and rotiferan (2.5 days) zooplankton.For Lake Tineo, residence time during inundation (7 days) islonger than generation times for all taxa except copepods. AlthoughLake Aguilera receives water from Lake Tineo during inundation,zooplankton densities were greatly reduced during passage througha large bed of the floating aquatic grass Paspalum repens locatednear the outlet of Lake Tineo. This retention was not size-selectiveand affected phytoplankton as well as zooplankton. In the Orinocofloodplain zooplankton densities are affected not only by hydraulicresidence times but also by passage of water between lakes,which exposes populations to large losses within macrophytebeds. Retention of plankton by floating macrophyte beds is potentiallyimportant to the trophic ecology of tropical floodplain lakesbecause it results in the concentration of planktonic productionin epiphytic and benthic habitats, where it can readily supportfood webs consisting of macroinvertebrates and fishes. Exportof plankton from floodplain waterbodies to the river is alsoreduced by this mechanism. ¹Present address: Department of Biological Sciences, Universityof California, Santa Barbara, CA 93106, USA     

Compensation in individual growth rates and its influence on lake trout population dynamics in the Michigan waters of Lake Superior

The role of compensatory mechanisms in the population dynamics of lake trout in the Michigan waters of Lake Superior was explored during three time periods: the pre-sea lamprey period, prior to 1950 when lake trout were at a relatively high abundance and the fishery was the primary source of lake trout mortality; the sea lamprey dominant period, from 1951 to 1961 when lake trout were at a very low abundance due to sea lamprey predation and overexploitation; and currently, from 1985 to 1993 when wild lake trout abundance was at a moderate level. The role of compensatory changes in growth and fecundity rates of lake trout in the Michigan waters of Lake Superior was evaluated using a life table approach. Individual growth and fecundity rates were calculated and compared between time periods. These rates were used to determine age-specific fecundity which, along with age-specific survival, were incorporated into a Leslie projection matrix to calculate the finite rate of population increase (λ). Individual growth rates and age-specific fecundity rates changed in response to the different levels of lake trout abundance during each of the study periods. Lake trout during the sea lamprey dominant period, which experienced the lowest abundance and highest mortality levels, exhibited the fastest individual growth rates and the highest age-specific fecundity. These high rates contributed to the relatively large compensatory scope exhibited by lake trout during the sea lamprey dominant period as compared to lake trout during the pre-sea lamprey or the current periods which are associated with higher levels of abundance.     

Advective effects of a reservoir flood on zooplankton abundance and dispersion

SUMMARY. 1. The diel vertical distribution and abundance of zooplankton in the Red River arm of Lake Texoma, Oklahoma-Texas, U.S.A., were examined between 25 January and 26 June 1982.
2. During periods of low river inflow, zooplankton vertical patchiness was related to wind stress. Zooplankton did not maintain distinct vertical patches under strong mixing.
3. In mid May heavy rainfall in the drainage basin increased discharge from the Red River and reduced water retention time in the reservoir. The Red River water mass entered the lake as a turbid, surface overflow plume. During this period of flooding most zooplankton populations declined and the distributions of remaining individuals deepened. Greatest population losses occurred between 0 and 7m, depths where most zooplankton had been concentrated prior to the flood.
4. A model of population dynamics based on depth specific rates of water exchange between the lake and the Red River, estimated from conductivity changes through time, accounted for the general pattern of change in zooplankton abundance and vertical dispersion.     

Demography of a natural population of Daphnia retrocurva in a lake with low food quality

The hypothesis was tested that Daphnia exhibit low populationrecruitment in a lake with phosphorus (P)-deficient food, whereDaphnia populations failed to increase in response to greatlylowered minnow density. Egg ratio analysis was performed onDaphnia retrocurva from L110 of the Experimental Lakes Area,Ontario, in 1994. L110 has high food abundance (seston carbon(C) 100 µM C), but the seston is P deficient (C:P atomic- 600). Chrysophytes dominated the algal community. The fishcommunity in this lake was manipulated in 1993 and 1994 by theaddition of northern pike, Esox lucius. Zooplanktivorous minnowswere greatly reduced after the piscivore addition, but the expectedincrease in abundance of the Daphnia to this altered predationregime was not observed, If food quality constrains the responseof the Daphnia to changed predation, there should be low recruitment in the relatively sparse Daphnia population in this lake.Birth rates estimated by standard egg ratio analysis were <0.1day^–1 for most of the sample period. In comparison toannual averages from the literature, recruitment in L110 wasmoderately, but not dramatically, low. Daphnia exhibited pronounced‘normal’ vertical migration (up at night, down duringthe day) all year, and a strongly declining size at first reproductionthrough the season. Population density and birth rates seemedto show much less short-term change than previously observedin other lakes. Although the demo graphic predictions for foodquality constraints seemed clear, in situ demography unfortunatelyneither supported nor strongly rejected the overall hypothesisof food quality limitation in this lake with very high C:P ratios.Possibly, direct demographic effects of low food quality willbe difficult to observe in nature.     

Some effects of enclosure on the zooplankton in a small lake

Observations on the effect of enclosure on zooplankton by introducing two experimental tubes, each holding some 18 000 m³ of water, into a small lake, showed that a limnetic community could be maintained within tubes of this capacity throughout a period of 22 months. Two species, the copepod Diaptomus gracilis and the cladoceran Daphnia hyalina were dominant both in the open lake and in each tube, but Diaptomus gracilis was relatively more abundant in the tubes than in the lake, whereas Daphnia hyalina, especially in spring and autumn, was more abundant in the lake than in the tubes. Several scarce species became relatively more abundant in the tubes than in the lake. These changes are more probably associated with reduced predation, especially by larvae of Chaoborus, than with artificially induced changes in the phytoplankton, changes only poorly correlated with changes in the zooplankton.     

Comparison of nets and pump sampling gears to assess zooplankton vertical distribution in stratified lakes

The efficiency of a cantilevered bridle net was tested in comparisonwith a Wisconsin net and a pumping system to sample zooplanktonorganisms in three water layers (epi-, meta- and hypolimnion)of three Canadian Shield lakes. Variations among samplers werecompared to variations due to within-lake vertical distributionof zooplankters and among lake variations. For each lake andwater layer, we also assessed the efficiency of the three methodsaccording to the catches of zooplanktonic taxa. The highestpercentages of variation were generally due to lake or water-layereffects; interaction between sampling gears and water layerswas above 50% for most taxa, except cladoceran. Sampling methodsexplained more variation than the lake effect for some zooplanktontaxa, indicating that using different sampling devices couldpotentially alter the among-lake variation interpretation ofzooplankton abundance. The pumping system captured higher densitiesof animals per taxa than the cantilever and the Wisconsin nets.The cantilever net generally captured mobile taxa more efficiently(Polyarthra vulgaris, copepods, Daphnia sp., Diaphanosoma brachyurumand chaoborids) than the Wisconsin net and the pumping system,but its efficiency varied among water layers.     

Prevalence and inferred effects of microsporidia of Holopedium gibberum (Crustacea:Cladocera) in a Canadian Shield lake

Two species of microsporidial parasites are reported from Holopediungibberum in a small Canadian Shield lake. Seasonal changes inprevalence of the parasites were not attributable to changesin water temperature or to changes in size distribution of hostsover the season. Seasonal changes in resistance of hosts toparasitism, related to food stress may account for the patternin prevalence but it was more likely a consequence of host andparasite population dynamics and interplay. An examination ofH.gibberum fecundity and size structure indicated that microsporidiosisreduced birth rates and may have decreased survival of Holopedium.     

Species succession and the development of a lacustrine fish community in an ephemeral lake

Here, we present a gillnet survey of Lake Liambezi a 370 km² shallow ephemeral floodplain lake situated in north-eastern Namibia, which is fed irregularly by the upper Zambezi and Kwando Rivers during years of high flooding. The lake dried up in 1985 and, with the exception of sporadic minor annual inundation events, remained dry until 2007. We describe the temporal succession of fish species over an 8 year period from initial inundation 2007 to maturation in 2014. The succession of the fish community did not follow the typical pattern of opportunistic strategists during colonisation, to periodic strategists that are eventually succeeded by equilibrium strategists. Instead, the evolution of the fish community was characterised by three distinct phases. The first phase involved the inundation and colonisation of the lake in 2007, followed by its decline until the floods that filled the lake in 2009. During this phase the lake was colonised by fishes from the adjacent upper Zambezi and Chobe River floodplains. Fish communities predominantly comprised floodplain specialists including the barbs Enteromius paludinosus and Enteromius poechii, the mormyrid Marcusenius altisambesi and catfishes Schilbe intermedius and Clarias gariepinus. The filling of the lake in the March 2009 floods marked the beginning of the second, successional phase. The barbs declined in abundance and the alestid Rhabdalestes maunensis underwent explosive population growth between 2009 and 2010, but populations crashed equally rapidly and were replaced by Brycinus lateralis which, together with S. intermedius went on to dominate the fish community 2011–2014. Larger, slower growing tilapiine cichlids increased steadily in abundance and became the dominant components in a 2700 t y^–1 artisanal fishery that developed on the lake. The fish community in the ephemeral Lake Liambezi is clearly influenced by numerous factors including connectivity, lake level fluctuations, competition and the effects of fishing, which may disrupt typical succession processes in floodplain ecosystems.     

Inferring a single variable from an assemblage with multiple controls: getting into deep water with cladoceran lake-depth transfer functions

Transfer functions have proved very useful for quantitative reconstruction of past environments. Inferring values of a single parameter based on changes in a community with multiple controls may result in unreliable inferences. To assess this unreliability cladoceran surface sediment assemblages from 53 lakes in Greenland, which have substantial variations in lake depth and fish abundance, both of which shape cladoceran communities, were analysed in this study. Redundancy analysis (RDA) revealed that maximum lake depth and either fish abundance or fish presence/absence exerted substantial and significant control on the cladoceran assemblage. Partial RDA showed that maximum lake depth and fish abundance uniquely explained 7.9 and 5.1%, respectively, with 5.3% variance being shared. A transfer function to infer lake depth from cladoceran sub-fossils was constructed and performed moderately well [coefficient of determination (r ²) = 0.65; root mean square error of prediction (RMSEP) = 0.32 log maximum depth] on the full dataset. When outliers, defined by a bootstrapped prediction error greater than 25% of the total depth gradient, were excluded, the model performed well (r ² = 0.74, RMSEP = 0.25 log maximum depth). The improved transfer function was then applied to sedimentary assemblage from a sediment core from Lake Bores?, in North-eastern Greenland, covering 9,000 years. A large increase in lake depth was inferred around 6250 bp. Whilst the climate was wetter at that time, the inferred changes in depth likely reflect the alteration of the food web, which resulted from the arrival of fish in the lake. This highlights the risks of using single-variable inference models for hindcasting change in lake physical and/or food web structure when there are other important co-variables.     

Evaluation of a remnant lake sturgeon population’s utility as a source for reintroductions in the Ohio River system

The selection of an appropriate source population may be crucial to the long-term success of reintroduction programs. Appropriate source populations often are those that originate from the same genetic lineage as native populations. However, source populations also should exhibit high levels of genetic diversity to maximize their capacity to adapt to variable environmental conditions. Finally, it is preferable if source populations are genetically representative of historical lineages with little or no contamination from non-native or domesticated stocks. Here, we use nuclear (microsatellite) and cytoplasmic (mitochondrial control region) markers to assess the genetic suitability of a potential source population inhabiting the White River in Indiana: the last extant lake sturgeon population in the Ohio River drainage. The White River population exhibited slightly lower levels of genetic diversity than other lake sturgeon populations. However, the population’s two private microsatellite alleles and three private haplotypes suggest a unique evolutionary trajectory. Population assignment tests revealed only two putative migrants in the White River, indicating the population has almost completely maintained its genetic integrity. Additionally, pairwise F _ST estimates indicated significant levels of genetic divergence between the White River and seven additional lake sturgeon populations, suggesting its genetic distinctiveness. These data indicate that the White River population may be the most suitable source population for future lake sturgeon reintroductions throughout the Ohio River drainage. Furthermore, the White River population appears to be a reservoir of unique genetic information and reintroduction may be a necessary strategy to ensure the persistence of this important genetic lineage.     

Effects of invading vendace (Coregonus albula L.) on species composition and body size in two zooplankton communities of the Pasvik River System, northern Norway

Species composition and body-size distribution were studiedin the crustacean zooplankton communities of two limnologicallysimilar lake localities situated 50 km apart in the Pasvik RiverSystem, northern Norway. A recent invasion and successive downstreamexpansion of vendace (Coregonus albula), a specialized zooplanktivorousfish, allowed comparisons between sites with different predationpressures. Vendace had established a high population densityand was the dominant fish species in the pelagic of the upperlocality, but had just invaded the lower locality with a smallnumber of individuals. Whitefish (Coregonus lavaretus), a closelyrelated but less specialized zooplanktivore species, dominatedthe native fish community of both lakes. The zooplankton communityof the upper locality was dominated in June and August by Bosminalongirostris, the smallest zooplankton species represented inthe water course, and in September by Daphnia cristata. Thelower locality was dominated by the larger Holopedium gibberumand Eudiaptomus graciloides in June, by D.cristata in August,and by D.cristata and B.longirostris in September. The meanbody size of the three most abundant cladoceran species wassignificantly smaller in the upper locality, compared to thelower locality. It was concluded that the invasion and establishmentof a dense vendace population in the upper locality had increasedthe predation pressure in the pelagic, resulting in a reductionof body size and a shift towards smaller species in the zooplanktoncommunity.     

Population Dynamics of Crustacean Zooplankton in a Mesotrophic Lake,with Emphasis on Boeckella hamata BREHM (Copepoda: Calanoida)

The crustacean zooplankton in Lake Mahinerangi, a polymictic, mesotrophic reservoir, were studied for 19 months. The cladocerans, Bosmina meridionalis and Ceriodaphnia dubia, had unimodal patterns of abundance with peak densities in summer; cyclopoids had a single peak of maximum abundance in autumn and Daphnia carinata showed a bimodal pattern with peak densities in early summer and early winter. The strong seasonality in abundance of zooplankton in Lake Mahinerangi distinguishes this lake from other temperate lakes in New Zealand and may reflect its cool winter temperatures (< 5 °C for 2 months). A calanoid, Boeckella hamata, bred throughout the year and was the dominant species numerically. Instar analysis indicated that there were at least three, and possibly four, generations per year. Instantaneous birth and death rates were low with annual mean values (0.036 and 0.057, respectively) that were 2-3.5 times less than those recorded in a population of the same species in Lake Pounui, but within the range of those recorded in calanoid populations elsewhere in New Zealand. The Boeckella population in Lake Mahinerangi appears to be controlled largely by temperature, parasitism and food, with predation having no, or a negligible, effect.     

Estimating cladoceran birth rate: use of the egg age distribution to estimate mortality of ovigerous females and eggs

The birth rate of natural cladoceran populations can change rapidly (during 2–3 days), reflecting rapid changes in their environment. If the egg ratio is calculated on the basis of egg age distribution, the birth rate can be estimated at short sampling intervals (shorter than egg stage duration) by modified Paloheimo's (1974) formula. When female size structure and age of eggs in clutches at the beginning and the end of a sampling interval are known, death rates of ovigerous females and eggs in separate size classes can be determined and incorporated in birth rate estimates. All these methods have been employed using the data on the population of Diaphanosoma brahyurum from the lake Obsterno (North-Western Belarus) in July–August, 1992. The birth rate values computed by the proposed methods and Poloheimo's formula differed significantly in many cases. The accuracy of birth rate estimations from various calculation methods was tested using a computer simulation. The model contains the essential features of cladoceran life history: distinct egg, juvenile and adult stages, development of eggs and reproduction. The population was divided into 25 age classes, each of 1 day duration. Durations of the egg, juvenile and adult stages were set at 3, 6 and 20 days, respectively. The embryogenesis was divided into three egg stages, each of 1 day duration. Survivorship was set from 0.2 up to 1.0 for each age class. The survivorship and brood size were changed through each of five time intervals (days) that allowed to simulate an increase or reduction of population density. Fecundity, survivorship and egg stage duration remained constant during each of 5 days that assumed stability of an environment (this does not occur in nature). Nevertheless, the egg ratio, proportion of juveniles and birth rates were variable even under these circumstances. Computer simulations showed that Poloheimo's formula evaluates birth rate with the relative error of 62% and usually overestimates its values. We propose methods to decrease errors of birth rate estimations by 3.5–5.5 times.