Bank-firm credit network in Japan. An analysis of a bipartite network

We present an analysis of the credit market of Japan. The analysis is performed by investigating the bipartite network of banks and firms which is obtained by setting a link between a bank and a firm when a credit relationship is present in a given time window. In our investigation we focus on a community detection algorithm which is identifying communities composed by both banks and firms. We show that the clusters obtained by directly working on the bipartite network carry information about the networked nature of the Japanese credit market. Our analysis is performed for each calendar year during the time period from 1980 to 2011. Specifically, we obtain communities of banks and networks for each of the 32 investigated years, and we introduce a method to track the time evolution of these communities on a statistical basis. We then characterize communities by detecting the simultaneous over-expression of attributes of firms and banks. Specifically, we consider as attributes the economic sector and the geographical location of firms and the type of banks. In our 32 year long analysis we detect a persistence of the over-expression of attributes of clusters of banks and firms together with a slow dynamics of changes from some specific attributes to new ones. Our empirical observations show that the credit market in Japan is a networked market where the type of banks, geographical location of firms and banks and economic sector of the firm play a role in shaping the credit relationships between banks and firms.Comment: 9 pages, 4 figures, 2 Table

Diversity, Generalization, and Specialization in Plant-Pollinator Networks of Montane Meadows, Western Cascades, Oregon

Despite the importance of plant-pollinator interactions for ecological communities, few long-term observational studies have been conducted of plant-pollinator networks. Using four years of plant-pollinator interaction data from 18 meadows in the Willamette National Forest, Oregon, this thesis examined how meadow size, the amount of nearby meadow habitat, weather, degree days, and soil moisture are related to the frequency of plant-pollinator interactions. Spatial and temporal turnover of plant and pollinator assemblages (based on the Jaccard dissimilarity index) were compared between meadows in a given year and within a meadow in different years. The degree distributions of these plant-pollinator networks were constructed, and analyses were conducted to determine the prevalence of generalization in the component species, and the possible presence of modularity in some of the meadows. Pollinator assemblages varied little in space: pollinator communities were very similar in the 18 study meadows in a given year, but pollinator communities differed dramatically between years. In contrast, plant assemblages had high turnover: plants differed dramatically between nearby meadows in the same year, and plant turnover was also high within meadows between years. Network structures were dominated by species that were very well connected, and they contained more well-connected species than would occur in a randomly-assembled network. Plant and pollinator assemblages in interaction networks also were dominated by generalist species. Some evidence of modularity occurred in small meadows in the network. The results of this study are consistent with many published studies that have found that generalization in plant-pollinator networks promotes their resilience over time in spite of the high component species turnover occurring between growing seasons. These results provide little support for the hypothesis that pollinator networks in fragmented habitats are fragile and highly sensitive to the loss of individual species. However, the high spatial heterogeneity among the meadows in this study, shown by dissimilarity in flowering plants, and the high permeability of the forest separating the meadow habitats, shown by the similarity among pollinators, both contribute to the generalization and resilience of these networks. Future work on plant-pollinator networks should focus on naturally fragmented, heterogeneous habitats, and continue to observe long-term changes in pollinator assemblages