The population of Myrmica ants, which is most abundant in high altitudinal areas in South Korea, is expected to decrease significantly due to climatic warming, whereas Aphaenogaster japonica population is expected to increase in these areas. The two ant groups are similar in shape, size, and ecology, indicating intensive competition in overlapping areas. To determine the competitions between the two groups, I investigated the ants at a high mountain (Mt. Gaebangsan) during two ant foraging seasons (2010 and 2011) using pitfall traps and bait traps along altitudinal gradients. Two Myrmica species (kotokui and kurokii) were present between 800 m to 1577 m, whereas A. japonica appeared up to 1200 m. Fights between ants were observed 22 times and fights between these two ant groups were most frequently found. Although a competitive hierarchy was not apparent, A. japonica appears to be dominant over Myrmica species in food competition when considering the more timid behavior of Myrmica species and my unpublished data. However, food discovery speed is greater in Myrmica species than in A. japonica, indicating a dominance-discovery tradeoff. The food discovery capability of A. japonica was greatly reduced at 1050 m elevation, which is around the elevational limit. This elevational suppression of food discovery capability was not found in Myrmica species.

In South Korea, ants are predicted to shift their distributions northwards and upwards. It was predicted that ant fauna will be changed dramatically in highlands due to the range shifts. The Mymica ants which are most abundant in high altitudinal areas in South Korea will be nearly disappeared there in 2050s, and replaced by Aphaenogaster japonica which is abundant in lowlands. It was recently found that A. japonica shifted upwards in Mt. Hanla in Jeju island, South Korea. Interestingly, A. japonica is similar in shape and size with the Myrmica species, which indicate niche overlap and resulting intensive competition. To find elevational change of competitions between two specie, we investigated ants during two ant foraging periods (2010 and 2011) in a high mountain (Mt. Gaebang) using pitfall traps and bait traps along elevational gradients. Ten ant species were collected from a.s.l. 800 m to a.s.l. 1577 m. Myrmica sp. 1 was most abundant (35% of total ants) and collected at all elevations. Myrmica sp. 2 (19.7%) occurred from 1000 m to 1577 m. Meanwhile, A. japonica occurred up to 1200 m. Fights between ants were observed 22 times; fights between these two species were most frequently found. Although, competitive hierarchy was not recognized due to a low frequency of interspecific encounters, A. japonica is likely to be superior over Myrmica species in food competition when considering the slower and more timid behavior of Myrmica species compared with A. japonica. Therefore, it is likely that A. japonica would replace easily Myrmica species in Korean highlands when thermal barrier (i.e., cold climate in high elevations) will be removed due to climate warming.