• Journal of Marine Life Science
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• v.4 no.2
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• pp.53-62
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• 2019

Heterotrophic bacteria are a major member of the microbial loop in the marine ecosystem and play an important role in the biogeochemical cycle decomposing organic matter. Therefore study of bacterial variation is important to understand the material cycle and energy flow of marine ecosystems. We investigated the monthly variations of bacteria and environmental factors in the Youngsan River estuary, and the correlation between bacteria and phytoplankton biomass (chlorophyll-a) including size-structure. As a result, bacteria of the Youngsan River estuary were higher in the surface than in the bottom layer, and higher in the summer than in winter. And the closer to the dike, the abundance increased, and it increased to the peaks in August, September, and June 2019 at the station closest to the dike. The chlorophyll-a also increases at the stations and time when the bacterial abundance was high and they correlates positively displaying no difference between size fractions. The results indicate that organic matter derived from phytoplankton has an effect on bacterial variation but no size-dependent effects. In addition, the seasonal pattern of bacteria increasing in proportion to the water temperature suggests the effect of water temperature on the growth of bacteria. No association of bacterial abundance variation with nutrient supply due to freshwater input was observed. In this study, dissolved oxygen was depleted and hypoxia was observed for a short time when a strong stratification was not developed. This may be resulted from the supply of organic matter from phytoplankton and the consumption of oxygen due to bacterial decomposition.

• Korean Journal of Ecology and Environment
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• v.45 no.1
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• pp.123-128
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• 2012

We aimed to estimate the accumulated degree days required for the development of $Cloeon$ $dipterum$ (Ephemeroptera: Baetidae) in an experimental tub under field conditions from August 7 to October 10 in 2011. After 4 days in a tub setting, a dead female adult was found on the water surface at which oviposition had presumably occurred. Adults emerged from 39 days to 61 days after the oviposition date. The total number of emerged adults was 229, and the sex ratio (number of females : total population) was 0.45, although not statistically significant ($p$ >0.05). The males generally emerged earlier than females. Assuming that the basal temperature ($T_b$) value is $0^{\circ}C$, we estimated the number of accumulated degree days required for the development of $C.$ $dipterum$ to be $1,221.8{\pm}116.0$ DD (mean${\pm}$SD). Since the annual number of accumulated degree days in the reference wetland was measured to be 5,650.0 DD, we estimated that $C.$ $dipterum$ is multivoltine, with a maximum of 4 cohorts in 1 year in natural habitats.

• Korean journal of applied entomology
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• v.58 no.4
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• pp.347-354
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• 2019

Temperature-dependent traits of Laodelphax striatellus, rice stripe virus vector, were investigated at 10 constant temperatures (12.5, 15.0, 17.5, 20.0, 22.5, 25.0, 27.5, 30.0, 32.5, and 35.0 ± 1℃) under a fixed photoperiod (14/10-hr light/dark cycle). Unit functions for the oviposition model were estimated and implemented into a population dynamics model using DYMEX. The longevity of L. striatellus adults decreased with increasing temperature (56.0 days at 15.0℃ and 17.7 days at 35.0℃). The highest total fecundity (515.9 eggs/female) was observed at 22.5℃, while the lowest (18.6 eggs/female) was observed at 35.0℃. Adult developmental rates, temperature-dependent fecundity, age-specific mortality rates, and age-specific cumulative oviposition rates were estimated. All unit equations described adult performances of L. striatellus accurately (r² =0.94~0.97). After inoculating adults, the constructed model was tested under pot and field conditions using the rice-plant hopper system. The model output and observed data were similar up to 30 days after inoculation; however, there were large discrepancies between observed and estimated population density after 30 days, especially for 1^st and 2^nd instar nymph densities. Model estimates were one or two nymphal stages faster than was observed. Further refinement of the model created in this study could provide realistic forecasting of this important rice pest.

• Korean Journal of Environment and Ecology
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• v.33 no.4
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• pp.402-407
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• 2019

In this study, we investigated the habitat characteristics of a reservoir in Gyeongju City, Gyeongbuk, in which a large group of Mauremys reevesii (endangered species Class II and natural monument No. 453 in Korea) was discovered. We examined the biotic and abiotic factors that directly and indirectly threaten the survival of M. reevesii within the habitat. The reservoir where M. reevesii was discovered was built for agriculture and surrounded by submerged trees, dam, forests, reeds, and farmland (paddy field). All of the M. reevesii were found only in the submerged trees on the north side of the reservoir. We found 28 M. reevesii (8 juveniles) and 21 M. reevesii (16 juveniles) from field surveys on May 10th and August 9th, 2018, respectively. A number of red-eared sliders (Trachemys scripta elegans) and American bullfrogs (Rana catesbeiana), which threaten the survival of M. reevesii, were also found in and around the reservoir. Moreover, there were signs of excavation of cultural asset, chemical fertilizer, and household garbage, all of which are considered to be major threats to the survival of M. reevesii, all over the reservoir. Newborn turtles in this year were not observed. However, we estimated that natural breeding had sufficiently occurred since we observed many young turtles in the reservoir. Furthermore, the presence of young T. s. elegans individuals can be a persistent problem for M. reevesii as they are competing species. In conclusion, in-situ conservation method should be considered for protecting the endangered turtle and their habitat.

• Korean Journal of Poultry Science
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• v.44 no.2
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• pp.83-92
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• 2017

The purpose of this study was to estimate the inbreeding level and effective population size of Korean indigenous chickens. In the study, two variables were considered to evaluate the pedigree completeness: (1) the proportion (%) of animals with complete pedigree, and (2) the proportion of animals with inbreeding coefficients greater than zero. In the proportion of animals having complete pedigree, all strains reached almost 100% completeness in 1~2 years. In the proportion of animals with inbreeding coefficients greater than zero, all strains reached almost 100% completeness in 5~6 years. We considered that the pedigree recoding system is well managed and that the inbreeding coefficient is a reliable measure. Over the past 20 years, the increase of inbreeding coefficients in Korean indigenous chicken strains has been 7.6~10.9%. The S strain showed the most rapid increase of inbreeding coefficient of 8.2% in 10 years. The reason for this rapid increase is considered to be associated with the fact that the numbers of sires and dams involved in reproduction was 115 and 91, respectively, which are lower than those of the other strains. According to average rates of increase in inbreeding coefficients (${\Delta}F$), all strains have ${\Delta}F$ values of 0.39~0.85%, which is lower than 1%, and the effective population size is above 50. The results showed that inbreeding levels were within the acceptable range and that Korean indigenous chicken population scan be regarded as safe from the threat of extinction.

• Korean Journal of Ecology and Environment
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• v.53 no.3
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• pp.275-285
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• 2020

Two specimens presumed to be hybrids of Rhodeus pseudosericeus and R. notatus were collected from the Sangcheon Stream of the Han River, Korea. The body color of natural hybrid individuals was yellowish brown, showing the intermediate characteristics of R. pseudosericeus and R. notatus, but overall, the characteristics of R. notatus were similar. Meristic and morphometric characters, the number of dorsal fin rays, anal fin rays and longitudinal row scales showed a hybrid index (HI) of 0, indicating the characters of R. notatus. The hybrid index of predorsal length (HI=74.6), preanal length (HI=75.3), and preventral length (HI=77.6) were similar to the characters of the R. pseudosericeus. Also four characters were appeared to have intermediate characters between R. pseudosericeus and R. notatus; number of gill rakers (HI=55.3), body depth (HI=67.9), snout length (HI=43.4), and inter orbital width (HI=44.8). The rest of 14 characters deviated between 0 and 100, showing unique characteristics of hybrid individuals. Recombination activating gene 1 (RAG1) analysis, hybrids were identified as natural hybrids due to the overlapping peaks of their parent species. Also, as a result of analysis using the cytochrome b gene (COB), one individual was derived from R. pseudosericeus, while the other was derived from R. notatus.

• Korean Journal of Environment and Ecology
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• v.29 no.6
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• pp.873-883
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• 2015

From August 2012 to April 2013, the ichthyofauna and post-restoration properties of Yangjae stream were investigated. A total of 1,503 fish of 2 forms, 16 species and 5 families were studied during the survey period. A survey of the distribution of freshwater fish inhabiting Yangjae stream after restoration of the stream showed large populations of Zacco platypus and Rhynchocypris oxycephalus. From the frequency distribution of the total length for the Zacco platypus population inhabiting Yangjae stream, it was estimated that there are 4 distinct age groups, with an abundance of the 27-63 mm (Age $0^+$) category accounting for 51.3% of the population. The regression coefficient (b) for the length-weight relationship in Zacco platypus was 3.27, while the slope of the condition factor was positive, demonstrating that stable growth conditions are being maintained. Analysis of tolerance and trophic guilds showed a decrease in the numbers of sensitive species and insectivore species further downstream, and an increase in tolerant species and omnivore species. Principal component analysis using community indices and indices of biotic integrity (IBI) showed that there were differences according to the survey time: the first and second surveys showed major changes on certain single species populations while during the third survey, it was analyzed that the populations of various types of fish had established balance.

• The Korean Journal of Ecology
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• v.28 no.6
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• pp.375-382
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• 2005

The American bullfrog, Rana catesbeiana was imported from Japan for farming for the human consumption in 1970's and introduced populations were a great threat to native habitats in the pond and lake ecosystem. However, it is thought that the population of bullfrog has rapidly declined for past years in Korea. In this study, we investigated the intra-genetic diversity of R. catesbeiana habitated in Korea. The nucleotide sequences of 1,215bp mitochondrial ND1/tRNA region in bullfrogs sampled from 5 sites in Jeollanamdo were analyzed and compared to the original sequence of R. catesbeiara reported in Genbank. The nucleotide similarity between Korean and North American bullfrog was ranged from 98.7% to 100% based on kimura-2-parameter distance. In addition, bullfrogs analyzed in this study were clustered into two groups with one including Jangheung and the other including Gwangju populations in the neighbor-joining tree. North American R. catesbeiana was grouped in Jangheung cluster, indicating that there is the very low genetic difference between Korean and North American populations. The maximum parsimony tree in which North American R. catesbeiana was set as an outgroup suggests that Jangheung group represents the introduced population to Korea. Taken together, the results indicate that the population of R. catesbeiana in Korea has not segregated geographically yet, after the introduction.

• Journal of Embryo Transfer
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• v.29 no.3
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• pp.289-296
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• 2014

The pedigree information and race records of 1,000 m finishing time of Jeju race horses at KRA were used to study the effect of amount of pedigree information and parental misidentification on the estimates of genetic parameters. The modified data sets were made at the range of 2.5 to 25% parental misidentifications or loss of parental information of individuals with an increment of 2.5 percent. For each incremental level, 20 randomly replicated data sets were obtained and analyzed by single-trait analysis with a DF-REML(AI) algorithm. As the rate of misidentification increased or the amount of pedigree information decreased, the estimates of fraction of additive genetics variance component gradually decreased almost linearly (p<0.05), while the estimated fractions of error variance and permanent environmental variance components gradually increased for the finishing time. Regression coefficients of the percentage amount of both parents' information loss and incorrect pedigree information on additive genetic variances were -0.079 and -0.114, respectively (p<0.01). The estimate of heritability decreased by 0.92% for one percent loss of both parents' information and 1.39% for one percent increase of both parental misidentifications of progeny (p<0.01). For the consideration of probable incorrect and missing parent information of progeny in this early population of Jeju horses, the estimates of additive genetic parameters would be biased downward about ten percent. This results indicate that the amount of pedigree information loss and misidentification of progeny would severely affect estimates of genetic parameters and would reduce genetic gains for selection in Jeju horse population.

• Korean Journal of Environment and Ecology
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• v.30 no.4
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• pp.658-675
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• 2016

The environmental characteristics of the habitats, the population structures, ecological niche, life traits and the population demography are used as an essential informations to the effective conservation plans about the target species. We first confirmed a total of 37 populations through 12 years of investigation on the extents, and investigated the environmental factors of habitats and the population structures of the 25 cohorts in 12 regions among them. And, we investigated the population dynamics targeting at 8 cohorts in the population of Daegwanryeong-myeon, Pyeongchang-gun, Gangwon-do. Along with this, we conducted 4 years of cultivation experiments and how pollinators affect the success of reproduction. The results shows that the Paeonia obovata Maxim. was found in a relatively wide range of habitats. For the population structures of the 25 cohorts, there were considerable differences among cohorts, including a case which showed relative stable structure and an extreme case in which only adults were found. The factor that affected the population dynamics during the investigation was thought as a forest gap created in the tree layer. In the cultivation experiment, seedlings grew well in a less soil organic matter. The seed setting rate and the number of seeds generated by visiting pollinators were higher trends. In conclusion, to understand the distribution of the Paeonia obovata Maxim., there needs to be investigated on the other factors that are involved in dispersal factors other than environmental factors, and thus we suggest the necessity of the research on the dispersal vectors. The current Paeonia obovata Maxim. population was thought as a process of expansion after the rapid reduction of the extents in the past. For the effective conservation of the Paeonia obovata Maxim., an endangered plant, we recommend to understand the species through the spatio-temporal expansion, and maintain the health of the ecosystem based on it.