Masahiko Kitahara

Biodiversity and community structure of temperate butterfly species within a gradient of human disturbance : an analysis based on the concept of generalist vs. specialist strategies

We monitored nine butterfly communities with varying degrees of human disturbance by conducting a census twice a month during 1980 by the line transect method in and around Tsukuba City, central Japan. We analyzed the biodiversity and community structures using the generalist/specialist concept. The site (community) order based on decreasing human disturbance was positively correlated with butterfly species diversity (H′), species richness (the total number of species), and the number of specialist species in a community, but not with the number of generalist species. The number of generalist species was rather constant, irrespective of the degree of human disturbance. Thus, both the butterfly species diversity and species richness were more dependent on the specialists than the generalists. Our analyses also showed that the generalist species were distributed widely over the communities, and they maintained high population densities, resulting in high rank status in abundance in a community, with more spatial variation in density per species. Specialist species showed the opposite trends. These results demonstrate that the generalist/specialist concept is a powerful tool applicable to analyse the biodiversity and structure of natural communities.

Patterns in the structure of grassland butterfly communities along a gradient of human disturbance: further analysis based on the generalist/specialist concept.

Abstract Kitahara and Fujii, in 1994, analyzed the butterfly communities along a gradient of human disturbance by applying the generalist/specialist concept. Butterfly species were classified into generalist or specialist species based on their voltinism (seasonal time dimension) and potential larval resource breadth (food dimension). The community structure and species composition showed the systematic changes along the gradient. To verify the generality of those trends, we monitored five grassland butterfly communities with varying degrees of human disturbance twice a month during 1985 by the line transect method at the foot of Mt. Fuji, central Japan, and analyzed their structure in a manner similar to that employed by Kitahara and Fujii. Most results were consistent with the patterns recognized by Kitahara and Fujii. The route (community) order based on increasing human disturbance was strongly and negatively correlated with butterfly species richness but with neither butterfly species diversity (H′) nor evenness (J′). Also, the degree of human disturbance was significantly and negatively correlated with the number of specialist species, but not with that of generalists, in a community. Butterfly species richness was more strongly correlated with the number of specialist species than with that of generalists. Our analyses also showed that the generalist species were distributed more widely over the communities than were the specialists. However, in contrast to the trend revealed by Kitahara and Fujii, there was no significant difference in the population densities and in the spatial population variability between the two species groups. As a whole, our analyses confirmed the consistency of most community patterns detected by Kitahara and Fujii. The causes of the inconsistencies in some patterns were thought to be mainly the present habitat conditions with a relatively short growing season at high altitudes.

Relationship of butterfly diversity with nectar plant species richness in and around the Aokigahara primary woodland of Mount Fuji, central Japan

We examined the relationships between the diversities of vegetation, adult nectar plants, and butterflies in and around the Aokigahara primary woodland on the northwestern footslopes of Mount Fuji, central Japan. The results showed that the nectar resource utilization by adult butterflies was significantly biased to herbaceous plants, especially to perennials, compared to woody species, although most of the study area was in and near a primary woodland. There were greater nectar plant species in sites with greater plant species richness. Among the butterfly community indices analyzed, the strongest correlation was detected between butterfly species richness and nectar plant species richness at each site. Another close correlation was detected between the species richness of nectar plants and herbaceous plants at each site. These results suggest that herbaceous plant species richness in a habitat plays a central role in its nectar plant species richness, and the nectar plant richness is a highly important factor supporting its adult butterfly species richness. Consequently, we propose that the maintenance and management of herbaceous plant species richness in a butterfly habitat, which lead to those of its nectar plant species richness, are very important for conservation of butterfly diversity even in and around woodland landscapes of temperate regions.

Butterfly community composition and conservation in and around a primary woodland of Mount Fuji, central Japan

A study was conducted in and around the Aokigahara primary woodland of Mount Fuji, central Japan, to clarify butterfly community structure along the environmental gradients of human disturbance, shade, and plant species richness, with a view to formulating conservation strategies for the community. The composition and abundance of butterfly species were recorded during 1999 along transects in three habitats: woodland, woodland edge and open land. Two sites were selected for each habitat. Canonical correspondence analysis (CCA) showed that community structure was correlated with both disturbance and shade. However, neither relationship was significant when disturbance and shade were analyzed as covariables (partial CCA), suggesting that the combined effect of the two variables played an important role in determining community structure. In contrast, CCA showed no significant relationships between butterfly community structure and plant or hostplant species richness. Correlation analyses between species characteristics and the CCA scores showed that species occurring in more disturbed habitats were more voltine, had a wider hostplant range and were associated with lower shade tolerance than those occurring in less disturbed habitats, and species occurring in darker habitats with higher shade tolerance. Generally, the structure and characteristics of the butterfly community could be understood well in terms of the habitat templet theory. To conserve endangered species on the Red List of Japan, and to maintain butterfly diversity in and around the woodland, this study suggests a need not only to conserve the primary woodland area, but most importantly to maintain the surrounding forest edge including areas of semi-natural grassland.

An island biogeographical approach to the analysis of butterfly community patterns in newly designed parks

We analyzed the butterfly communities in the newly designed city parks (area C), “newly opened habitat islands”, of Tsukuba City, central Japan. The area constituted a natural ecological experiment on the mainland for clarifying the pattern and process of faunal immigration. We compared butterfly communities in area C with those in two other areas in the light of the theory of island biogeography and the concept of generalist/specialist. Our results showed the following: (1) Fewer species were found in area C than in other areas, due largely to the absence of many specialist types, restricted and habitat specialists, and/or low density species in the area. Generalist types, widespread and habitat generalists, and/or high density species predominated in area C. (2) The difference in the species numbers among the three sections within area C could be explained by the habitat structure in and around the respective sections. (3) The densities of many species were low in area C, probably due to its man-modified habitat structure. In particular, several species occurred at extremely low densities in area C, but at high densities in other areas. (4) The internal structure of the habitat island butterfly community in area C was almost perfectly consistent with that of “quasi-equilibrium” communities that appear during the colonization of an island. Our results demonstrate that the synergetic application of the generalist/specialist concept and the island biogeography theory is effective for the understanding of the patterns and structures of habitat island communities.

Seasonal fluctuations in butterflies and nectar resources in a semi-natural grassland near Mt. Fuji, central Japan

We investigated seasonal fluctuation patterns in species and individuals of adult butterflies and flowering plants providing nectar in a semi-natural grassland in central Japan. We considered their interrelationships and implications for conservation. The semi-natural grassland included different vegetation structures and management regimes, including: (1) firebreaks where the grass was mowed and removed, (2) plantation areas that were mowed, (3) unpaved roads with mowed banks, (4) abandoned grassland, (5) scattered scrub forest, and (6) the surrounding forest. The sites with management (e.g., firebreaks), plantations and banks of the unpaved road sustained a larger number of butterflies and flowers than sites without management, such as the abandoned grassland, scrub forest and surrounding forest. The number of butterflies increased in the firebreak in June and at all sites in August and September. The firebreak sustained flowers in the spring, and the plantation area and banks of the unpaved road sustained flowers primarily in August and September, which was correlated with the distribution of butterflies. The different treatments such as mowing or mowing with removal of grass induced different numbers of flowers of each species affecting the habitat of adult butterflies through a season. On the other hand, the shrub tree species composing the scrub forest were host plants for the larvae of certain butterfly species. Our results suggest that heterogeneous environments with different human management or different vegetation structure or both could support habitat for various butterfly species, depending on the season and the seral stage.

Analysis and understanding of butterfly community composition based on multivariate approaches and the concept of generalist/specialist strategies

We analyzed butterfly community composition using multivariate analyses. The results of principal components analysis showed that the butterfly community was composed mainly of two species groups. This species grouping was also supported by the results of the cluster analysis (unweighted pair‐group method using arithmetic average). Comparing the present results with species classification based on the generalist/specialist concept, the butterfly community was found to be composed of five species groups differing  from  each  other  in  their  ecological  characteristics:  a  specialist  group,  two  intermediate  groups and two generalist groups. By comparison of their characteristics, it was suggested that, in the butterfly community, the positions of the specialist group and one of the generalist groups are the endpoints on the generalist/specialist selection spectrum, and the three other groups are positioned between these two extremes. The multivariate analyses showed that the species grouping with the generalist/specialist concept based only on voltinism and larval diet breadth was not sufficient to classify both intermediate and generalist groups, and also succeeded in extracting a typical generalist group from the butterfly community. From these results, we propose and recommend the synergetic application of the generalist/specialist concept and multivariate approaches to the detailed analysis and deeper understanding of community structure and composition.

The role of linear mown firebreaks in conserving butterfly diversity: Effects of adjacent vegetation and management: Linear firebreak as a butterfly habitat

Semi‐natural grasslands are vital for maintaining grassland butterflies in Japan, as well as in Europe. However, severe decline in these grassland environments has recently attracted attention to linear grasslands, such as firebreaks and power‐line corridors, as alternative habitats for grassland insects. We surveyed butterflies in an abandoned grassland and nearby linear mown firebreaks adjacent to different vegetation at the northern foot of Mt. Fuji, central Japan, over 5 successive years, particularly focusing on species on the 2012 Japanese Red List of Threatened Species (“red‐list” species). We found that the firebreaks were consistently higher in species richness and abundance of butterflies than the long‐term abandoned grassland, and that species composition differed among the firebreaks depending on conditions of the adjacent vegetation. The firebreaks surrounded by forests were mainly utilized by forest and edge species, whereas the firebreaks adjacent to the grassland were essential for conserving red‐list grassland species. Thus, only the mown firebreaks adjacent to the grassland were regarded as a high‐quality alternative habitat for many grassland butterflies, but the area was limited. Therefore, creating heterogeneity in the abandoned grassland by infrequent mowing could help conserve grassland butterflies, including red‐list species.

Effects of fragmentation of secondary broadleaf deciduous forests on populations of the near-threatened butterfly, Sasakia charonda (Lepidoptera, Nymphalidae), in central Japan.

We examined the effects of fragmentation of secondary broadleaf deciduous forests (secondary forests) on populations of the near-threatened butterfly, Sasakia charonda, in central Japan. Regression analyses revealed that the number of overwintering larvae per host tree significantly increased when the area of secondary forest patches and the Isolation Index of the forest patch increased and the distance from secondary forest patches containing the focal host trees to the nearest secondary forest patch decreased. There was a significantly positive correlation between the number of overwintering larvae and the number of host trees in the neighborhood. The host trees were primarily distributed at the edges of secondary forests. From the results of the backward elimination method of multiple linear regression analysis, independent variables other than patch area were eliminated, and the standardized partial regression coefficient of the patch area was significant. This result suggested that a contiguous distribution of large secondary forest patches with many host trees is very important to conserving this butterfly species.