• Journal of the Korea Society for Simulation
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• v.19 no.3
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• pp.37-43
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• 2010

In field, one can observe without difficulties that two flocks are intersected or combined with each other. For example, a fish flock in a stream separates into two part by obstacles (e.g. stone) and rejoins behind the obstacles. The dynamics of two flocks guided by their leader were studied in the situation where the flocks cross each other with a crossing angle, ${\theta}$, between their moving directions. Each leader is unaffected by its flock members whereas each member is influenced by its leader and other members. To understand the dynamics, I investigated the order parameter, ${\phi}$, defined by the absolute value of the average unit velocity of the flocks' members. When the two flocks were encountered, the first peak in ${\phi}$ was appeared due to the breaking of the flocks' momentum balance. When the flocks began to separate, the second peak in ${\phi}$ was observed. Subsequently, erratic peaks were emerged by some individuals that were delayed to rejoin their flock. The amplitude of the two peaks, $d_1$ (first) and $d_2$ (second), were measured. Interestingly, they exhibited a synchronized behavior for different ${\theta}$. This simulation model can be a useful tool to explore animal behavior and to develop multi-agent robot systems.

• Korean Journal of Agricultural and Forest Meteorology
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• v.12 no.2
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• pp.122-131
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• 2010

This paper introduces the concept of a virtual ecosystem and reports the following three mathematical approaches that could be widely used to construct such an ecosystem, along with examples: (1) a molecular dynamics simulation approach for animal flocking behavior, (2) a stochastic lattice model approach for termite colony behavior, and (3) a rule-based cellular automata approach for biofilm growth. The ecosystem considered in this study consists of artificial organisms and their environment. Each organism in the ecosystem is an agent that interacts autonomously with the dynamic environment, including the other organisms within it. The three types of model were successful to account for each corresponding ecosystem. In order to accurately mimic a natural ecosystem, a virtual ecosystem needs to take many ecological variables into account. However, doing so is likely to introduce excess complexity and nonlinearity in the analysis of the virtual ecosystem's dynamics. Nonetheless, the development of a virtual ecosystem is important, because it can provide possible explanations for various phenomena such as environmental disturbances and disasters, and can also give insights into ecological functions from an individual to a community level from a synthetic viewpoint. As an example of how lower and higher levels in an ecosystem can be connected, this paper also briefly discusses the application of the second model to the simulation of a termite ecosystem and the influence of climate change on the termite ecosystem.

• Korean Journal of Environmental Biology
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• v.31 no.4
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• pp.322-332
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• 2013

This study was conducted to understand the control mechanism of Sika deer (Cervus nippon taiouanus) populations which are adapted to the natural forest areas and the semi-natural forest areas of Korea. We monitored and analyzed the behaviour patterns and habitat characteristics of Sika deers. After we released 12 Sika deers (male 3, female 9) each at the two study areas in and around Seoul under the approval of Korean government, we monitored them through our survey researchers' naked eyes from May 2011 to January 2012. We discriminated their habitat patterns to 4 major places - eating food place, drinking water place, daytime rest place, and nighttime rest place. Our results showed that Sika deer preferred the open grassland habitats for feeding and resting in daytime but the closed bushland for their protection and sleep. We also found the recommended sex ratio of adult male to female in a herd was 1 : 4~9 for breeding and they had few cubs in a herd. The average amount of food for 1 adult deer was 391.62 kg of fresh grasses and 286.90 kg of hay per year. Our results suggest that the amount of drinking water required for a deer when grazed on grasses during spring and summer seasons is 256.8 L and when a deer feeds on dry food during autumn and winter seasons, 209.8 L of water is required. From these results, we observe that the amount of drinking water was affected substantially by the moisture content of their food. This observational study must be very valuable for land managers to judge the number of deers that should be released in natural areas without high risk and to ascertain the sex ratio of large mammals including Sika deer. Therefore, we conclude that this population control mechanism study consists of efficient basic data and their values must be very effective for various purposes.

• Journal of the Korean Society of Marine Environment & Safety
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• v.16 no.3
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• pp.241-248
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• 2010

Hypoxic(oxygen-deficient) water masses are a key threat to the ecosystem of shallow marine coastal areas worldwide. The phenomena of hypoxia occurred at Gamak Bay, on the southeast coast of Korea, in late June 2007. In this paper, the physicochemical characteristics of seawater were surveyed for a period of hypoxic water mass disappearance. The hypoxic water mass was located between Sunso and the northwestern area of the inner bay. The dissolved oxygen(DO) concentrations of surface and bottom water were $1.3mgL^{-1}$ and less than $2mgL^{-1}$, respectively, in the hypoxic water masses, and $4.5{\sim}6.8mgL^{-1}$ and $3.8{\sim}6.0mgL^{-1}$ at the other oxygen-rich sample sites, respectively. Chlorophyll a concentrations were $4.9{\sim}25.3{\mu}gL^{-1}$ at the surface, $2.3{\sim}23.1{\mu}gL^{-1}$ in the middle, and $1.9{\sim}9.0{\mu}gL^{-1}$ at the bottom of the hypoxic water masses. When the hypoxic water mass appeared in Gamak Bay, it formed three different vertical types. The first type occurred throughout the water depth around Sunso. The second type developed from the bottom. The third type of hypoxic water mass was formed in the middle water layer when the inversion of water temperature occurred. The third type of phenomena appeared at only St. 9, St. 14 and St. 21 sites near the Hodo coast. Aquatic surface respiration of bottom-dwelling fishes such as the oriental goby(Acanthogobius flavimanus) was observed and many crustaceans were seen along the adjacent shore of the hypoxic water mass area. About 3,000 oriental gobies as well as many crustaceans died due to this event in Gamak Bay. The results of this study could provide fundamental data for the mechanism of hypoxic water masses in Gamak Bay.