Inter-specific competition between invasive ant Anoplolepis gracilipes and native.
Aim: Invasive species can affect the biodiversity of an invasive site by influencing native species populations through competition. Anoplolepis gracilipes is one of the most destructive invasive ants in the world. This study aims to identify the competitive relationship between A. gracilipes and a dominant indigenous ant species Oecophylla smaragdina in Xishuangbanna, southwestern China. Methods: By combining field investigation and the controlled experiment, the body size, the patterns of foraging activity outside the nest in cold fog season and rainy season, the foraging ability (foraging time and the maximum number of recruited workers within foraging time), the fighting behavior (attack intensity and mortality in different fighting combinations), and the starvation and thirst tolerance (the mean survival time and survival rate along time when no food and water were supplied) between A. gracilipes and O. smaragdina were observed and comparatively analyzed. Results: The body length of A. gracilipes workers (3.66±0.06 mm) was significantly smaller than that of O. smaragdina workers (8.27±0.16 mm). The foraging time of A. gracilipes was longer than that of O. smaragdina in the fog cold season, while the numbers of foraging individuals of both species decreased in the high temperature period of the afternoon in the rainy season. When three different foods (apple, bee honey and sausage) were used as the bait, A. gracilipes only needed 4-8 min to find food, while O. smaragdina needed 8-21 min to find food. After finding food, A. gracilipes workers had the ability to gather their companions faster than O. smaragdina. In the controlled experiments, no attack or low intensity attack occurred predominantly in the combination of one individual of A. gracilipes with one individual of O. smaragdina, and when the number of individuals of either of the two species increased to five, the fighting intensity increased significantly, and both species exhibited intraspecific cooperation. There was no significant difference in the average survival time of workers between the two species under starvation and thirst, but A. gracilipes could survive for 120 h, while O. smaragdina could only survive for 96 h. Conclusion: A. gracilipes exhibits stronger ability to forage and longer activity duration in the fog cold season than the indigenous ant species O. smaragdina in Xishuangbanna, suggesting that A. gracilipes may have strong temperature adaptability. It is necessary to intensify the research on this invasive species, and its population development in this area should be paid close attention to.