The Morphological Changes of Moths on Nakajima Island, Hokkaido, Japan.

Overgrazing by large mammalian herbivores has led to significant adverse impacts on ecosystems globally. Insects are often a key taxon affected by large herbivores because the plants that are grazed provide crucial food and habitat. By changing vegetation, overgrazing by herbivores could affect aspects of insect morphology, including through changes to larval development due to reduced food availability, and adult dispersal ability due to habitat fragmentation. We investigated the wing morphology of moth species in two contrasting sites at Lake Toya in Hokkaido, Japan. We compared moths on Nakajima Island where deer are overabundant, with moths from the lakeshore 3 km away where deer are far less abundant. We compared forewing size and aspect ratio (length/width) of 13 moth species from both lakeshore and island sites. Four species, three of which were herb-feeding generalists, had significantly smaller wings on the island compared with the lakeshore. Seven species demonstrated a reduction in wing aspect ratio, whereas one species, the largest we measured, showed an increase in wing aspect ratio. We suggest that these morphological changes could be induced by overgrazing by deer (i.e., a reduction in moth host plant biomass and quality) and/or the isolation of moth populations on Nakajima Island. Further work is needed to reveal how these confounded but potentially interacting effects contribute to the morphological changes we found in the moths on the island. Our results show that habitat isolation and overabundance of deer populations can affect moth wing morphology, with potential implications for their population dynamics and community structure.

Increasing sika deer population density may change resource use by larval dung beetles.

Because animal feces contain organic matter and plant seeds, dung beetles (Scarabaeinae) are important for the circulation of materials and secondary seed dispersal through burying feces. Dung beetles are usually generalists and use the feces of various mammals. Additionally, the larval stages have access to feces from only one mammal species leaving them susceptible to changes in animal fauna and variations in animal populations. Here, we explain the effects of resource availability changes associated with sika deer (Cervus nippon) overabundance on dung beetle larvae feeding habits in Japan. δ15N values were notably higher in raccoon dog and badger dung than in that of other mammals. A dung beetle breeding experiment revealed that the δ15N values of dung beetle exoskeletons that had fed on deer feces during their larval stage were significantly lower than those of beetles that had fed on raccoon dog feces. The δ15N values of the adult exoskeleton were significantly lower in a deer high-density area than in a low-density area in large dung beetles only. It is possible that the high-quality feces, such as those of omnivores, preferred by the large beetles decrease in availability with an increase in deer dung; large beetles may therefore be unable to obtain sufficient high-quality feces and resort to using large amounts of low-quality deer feces. Small dung beetles may use the easily obtained feces that is in high abundance and they may also use deer feces more frequently with increases in deer density. These findings suggest that a larval resource shift associated with deer overabundance may affect ecosystem functions such as soil nutrient cycling and seed dispersal.