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.     

A note on separability and intra-household resource allocation in a collective household model

This paper shows that it is possible to track the changes in the distribution of power within a couple by focusing on the changes in the pattern of private consumption when the consumption decisions are efficient and private consumption is separable from public consumption in individual preferences. We first show that the separability of private consumption from public consumption at the individual level carries over to the household level. Hence, changes in public consumption only matters through a change in the residual budget available for private consumption. When the consumption decisions within the household is efficient, private consumption decisions can be modeled as the solution of a problem consisting in maximizing a weighted sum of the private-consumption sub-utility functions of the spouses under the residual budget, the weights being unique and representing the distribution of power over the allocation of private consumption. The model presented in this paper can be used to analyze the changes in the household resource allocation due to, for example, childbirth.     

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.     

The effects of spatial and temporal environmental heterogeneities on persistence in a laboratory experimental community

Among many stabilizing factors for community dynamics, spatial and temporal heterogeneities have been widely considered in recent years as two of the most important properties. However, the difference between the two types of heterogeneities have not been studied, except for Clark and Yoshimura (1993). We evaluated experimentally the effect of temporal and spatial heterogeneities on the persistence of a biological community. The experimental communities consisted of one parasitic wasp species, one bean weevil species, and two kinds of bean. Temporal and spatial heterogeneities of experimental communities were generated by kinds and timing of bean supply. Of all the experimental communities, the most persistent community was a temporally and spatially homogeneous community with Red Kidney bean as primary resource. Compared to spatially heterogeneous communities, temporally heterogeneous communities were more persistent. These results were easily explained by considering the attack rate of parasitic wasps and the difference between arithmetic and geometric means. In order to discuss the relative importance of environmental heterogeneity and the mode of biological interaction on community persistence, we have to measure the degree of environmental heterogeneity as the rate of change of the strength of interspecific interactions.     

The outbreak mechanisms of the green rice leafhopper,Nephotettix cincticeps Uhler, in northern Japan

Intraspecific regulatory processes keep the population ofNephotettix cincticeps stable at a low density in southern Japan. In northern Japan, however, the yearly population density of the insect fluctuates violently, and large outbreaks occasionally take place. To clarify the difference in the population dynamics between the two regions, we analyzed light-trap and sweep-net sampling records from prefectural and national agricultural experimental stations. The survival rate of the overwintering population decreased with increases in the period of continuous snow cover (PCSC) in the north, and initial population densities in the years of long PCSC were too low for populations to reach equilibrium density by the end of the active breeding season. This made yearly population fluctuations in the north much larger than in the south. The equilibrium density in the north was higher than in the south. The higher equilibrium density presumably permits the higher population density and larger yearly population fluctuations in the north. A major factor responsible for the difference in equilibrium densities between the two regions is the difference in heading dates of the host plant (rice). Qualitative differences among rice plant varieties, and among biotypes ofN. cincticeps, may also be important.     

Computer simulation study on the cyclicities ofTribolium population dynamics

Summary Under a set of assumptions, a mathematical model was constructed to investigate the effect of cannibalistic behavior and medium renewal schedule onTribolium population dynamics, and the results of simulation analyses were presented to show how modelling can contribute to a better understanding of experimental study. The analyses of the present model, the main concern of which is the cyclicity inTribolium population. showed that there are two distinct factors which create cyclicity, the cannibalistic behavior inTribolium itself, and the medium renewal schedule. Cannibalismper se does not necessarily cause cyclicity, but the combinations of cannibalistic behavior among various life stages and their relative intensities among them can cause cyclicity and can also determine the period of cycle. External factors also can generate cyclicity, but their interaction with cannibalistic behavior has a more significant effect in modifying the period of cycle. Some discrepancies between the model and experimental results were discussed.