Abstract / Introduction / Summary:
In this survey (2021) a total of 31 ant species belonging to 20 genera in 4 subfamilies were collected from 4 types of lava of different ages on the Sakurajima volcano (one site of around 200 m2 for each lava type was surveyed), each with a different vegetation: 13 species from Showa lava (ejecta of 1946 eruption), 12 from Taisho lava (1914–15), 17 from An-ei lava (1779–80), 21 from Bunmei lava (1471–78). Four species, Camponotus bishamon, Proceratium itoi, Crematgaster vagula and Vollenhovia benzai were newly found on these lavas. A total of 52 species have so far been recorded from all over Sakurajima; this figure corresponds to 47.3% of the around 110 ant species recorded on mainland Kagoshima.
The total number of species from the four different lavas combined was rather constant from 1985 to 2021, ranging from 31 to 36. The species number for the An-ei and Bunmei lavas ranged between 17 and 29 and was constantly higher than that for the Showa and Taisho lavas (7–19). No obvious tendency in the similarity in species composition among the four lavas and among years was detected, though in 1985 and 2006 the Showa and Taisho lavas had similar species compositions and the An-ei and Bunmei lavas had also very similar species compositions except in 1985. Strangely, Lasius japonicus, very common through 1985 to 2006 everywhere and one of the top-three dominant species on the Showa lava in 1985 and 2006 and on the Bunmei lava in 1985, drastically decreased from 2016 and completely disappeared in 2021.
Among the top-three dominant species (ground surface foragers only) on the Showa and Taisho lavas in the four survey years (14 species) eight (57%) were inhabitants of open land. On the other hand, all the top-three dominant species found on the An-ei and Bunmei lavas were inhabitants of forest and forest edge. The ratio of ponerine species was higher on the An-ei and Bunmei lavas than on the other lavas. Proceratiinae ants were collected only on the Bunmei lava.Among the 52 species so far recorded from Sakurajima eight species (15.4%) are aliens, mostly found on the Showa and Taisho lavas. However, on the Taisho lava the ratio of alien species drastically decreased from 25% to 8.3% between 2016 and 2021, probably due to the recent forest development. The important tramp ant Technomyrmex brunneus was confirmed in 2006 for the first time on Sakurajima outside our survey sites (residential area in Shirahama). In 2021 the authors found numerous colonies in western part of Sakurajima, e.g., Kyôryû Park, Yôgan-Nagisa Park etc.