Atsugi Children’s Wood Park is located in Nakaogino, Atsugi, Kanagawa Prefecture. Since 2015, two alien species, African clawed frogs (
Xenopus laevis) and American bullfrogs (
Lithobates catesbeianus), have been found in ponds and waterways that were newly created in this park, an area previously occupied by disused rice-fields. These new ponds are important habitats for several rare endemic species, including two odonatans, the Siberian winter damselfly (
Sympecma paedisca) and the Four-spotted chaser dragonfly (
Libellula quadrimaculata). The primary threat posed by the two alien frog species is considered to be predation, and we therefore examined the stomach contents of individual frogs trapped in this park. The results indicate that the diet of
Xenopus laevis is dominated by aquatic arthropods, especially larval Odonata, although a Japanese Eight-barbel loach (
Lefua echigonia), an Endangered IB species in the Red data book of Kanagawa Prefecture, was also identified.
Lithobates catesbeianus, on the other hand, preyed on various arthropods, more than half of which were terrestrial species. However,
L. catesbeianus fed less frequently on aquatic species than
X. laevis, larval odonatans were again dominant among its aquatic prey. The predation pressure exerted by the two alien species on
Sympecma paedisca and
Libellula quadrimaculata could not be determined decisively in this study, given the number of sampled individuals and the limited sampling-period. However, as the artificial ponds are small, with few places to escape from predators, the alien species could be threat to any vertebrate or invertebrate living there. The invasion of alien species into newly built ponds in the Atsugi Children’s Wood Park has continued, despite continued monitoring. Active control of alien species is crucial for conservation of rare endemic species in this area.
View full abstract