Yoshito Mitsuo

Beak marks on the wings of butterflies and predation pressure in the field

Beak marks on butterfly wings have been used as an indicator of predation pressure. The relationship between butterflies and their predators in the field was examined to evaluate the beak mark rate as an indicator of predation pressure. Transect censuses were conducted to measure the beak mark rate on butterflies from May to November, 2010, in Shiga Prefecture, Japan. A total of 1216 butterflies of 42 species from five families were observed during the study period. The beak mark rate in the Papilionidae was significantly higher than those of all other families. Analysis of the monthly fluctuations in the beak mark rate and relative abundance of predators revealed that the higher beak mark rates observed for two butterfly families (Papilionidae and Nymphalidae) were significantly and positively related to predation pressure, while no significant relationship was found for other families (Lycaenidae, Pieridae and Hesperiidae). Beak marks in larger butterflies (Papilionidae and Nymphalidae) can be used as an indicator to evaluate the relative intensity of predation pressure in the field.

Predicting patterns of intentional introduction of non-native largemouth bass into farm ponds in northeastern Japan

Non-native species are difficult to eradicate or control once established. Thus, the prevention of invasions is a high priority for conserving native ecosystems. Our objective was to determine the factors that influence illegal introductions of non-native largemouth bass (Micropterus salmoides) and to develop a model that could be used to predict the pattern of future illegal introduction by anglers. We used generalized linear modeling (GLM) to evaluate the relationship between landscape and environmental factors and the presence of bass in farm ponds. Our results suggest that the occurrence of bass was primarily associated with pond size, distance of ponds from the urban center, and the proportion of the pond shoreline covered with a concrete revetment. We conclude that introductions occurred in ponds that were: easier to locate on a map, closer to anglers’ residential areas, and more easily accessible to the pond shore. Last, we suggest our predictive model could be used for preventive measures, such as identifying other ponds most at risk of future illegal introduction of non-native bass.

Studying the contribution of two types of landlocked Ayu fish in Lake Biwa to the next generation using nitrogen-stable isotope ratio analysis

Contribution of amphidromous (Ooayu) and lake types (Koayu) of the landlocked Ayu (Plecoglossus altivelis altivelis) fish population in Lake Biwa to the next generation was investigated by isotopic approaches. δ15N values of eggs in adult ovaries distinctively differed between the two types. Contribution of Koayu, calculated using δ15N values of spawned Ayu eggs, was much greater than that of Ooayu in general, as previously reported. Ooayu spawned more eggs in the upper area of the spawning ground and did so late in the season. These results show the potential of isotopic approaches for identifying maternal life-history types of spawned eggs of migratory animals.