Abstract
BackgroundIn Japan, invasive raccoons cause severe ecological and social problems by transmitting pathogens to humans, livestock, and native species, causing substantial crop damage, and competing with native species. Possible competition between invasive raccoons and native raccoon dogs is of concern in Japan because Japanese raccoon dogs have a limited distribution and are native only to Japan and the two species have similar characteristics. We assessed potential competition between raccoons and raccoon dogs by comparing feeding habits and habitat use.ResultsBoth species were captured in Hokkaido, Japan from 2004 to 2017. More raccoons were captured close to agricultural land at the forest periphery (70.1%, 358/511); conversely, more raccoon dogs were captured in the forest core (74.9%, 253/338). Feeding habits were then examined by fecal analysis and stable isotope analyses. Fecal analysis revealed both species to be opportunistic omnivores that consumed easily found food items. However, raccoon feces contained more crops, whereas raccoon dog feces contained more insects, reflecting the different locations in which the species were trapped. Moreover, stable isotope ratios were significantly higher in raccoons than raccoon dogs (Corn has the highest carbon stable isotope (δ13C) value, and amphibians and reptiles are high in nitrogen stable isotope (δ15N); forest resources such as insects and wild fruits are low in δ13C and δ15N).ConclusionsWe conclude that both species ate similar food types, but their food preferences appeared to differ. Raccoon and raccoon dog habitat use also differed, possibly because the two species inhabited areas where they could easily obtain their preferred foods. Therefore, the current feeding habits and habitat use of raccoons do not appear to overlap sufficiently with those of raccoon dogs to impact the latter. The results of this study, particularly the stable isotope data, may provide a useful precedent for future studies of competition in medium-sized mammals, particularly canids.
Highlights
In Japan, invasive raccoons cause severe ecological and social problems by transmitting pathogens to humans, livestock, and native species, causing substantial crop damage, and competing with native species
We examined the potential impact of raccoons on raccoon dogs by comparing their habitat use and feeding habits
Our study provides novel information regarding the potential competition between an invasive species and a native species in an isolated forest
Summary
In Japan, invasive raccoons cause severe ecological and social problems by transmitting pathogens to humans, livestock, and native species, causing substantial crop damage, and competing with native species. Native species become extinct or decline in population size and are replaced by the invasive species. A system for classifying alien taxa based on the magnitude of environmental impacts was developed by Blackburn et al [10] This classification system uses five semiquantitative scenarios that describe the different levels of impact of a species—ranging from massive to minimal—with assignment corresponding to the highest level of associated deleterious impacts. Massive competition results in replacement or local extinction of one or several native species, and changes in community composition are irreversible. Major competition results in local or population extinction of at least one native species, which leads to changes in community composition, but changes are reversible when the alien species is removed. Moderate competition results in a decline of population size of at least one native species, but no changes in community composition. Raccoons have not been classified in Japan according to competition risk
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