Minami-rinkan, Japan
Minami-rinkan, Japan

Tokyo Keizai University is a private university in Tokyo, Japan. Wikipedia.


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Nakata K.,Nagasaki Institute of Applied Science | Nakata K.,Tokyo Keizai University | Zschokke S.,University of Basel
Proceedings of the Royal Society B: Biological Sciences | Year: 2010

Almost all spiders building vertical orb webs face downwards when sitting on the hubs of their webs, and their webs exhibit an up-down size asymmetry, with the lower part of the capture area being larger than the upper. However, spiders of the genus Cyclosa, which all build vertical orb webs, exhibit inter-and intraspecific variation in orientation. In particular, Cyclosa ginnaga and C. argenteoalba always face upwards, and C. octotuberculata always face downwards, whereas some C. confusa face upwards and others face downwards or even sideways. These spiders provide a unique opportunity to examine why most spiders face downwards and have asymmetrical webs. We found that upward-facing spiders had upside-down webs with larger upper parts, downward-facing spiders had normal webs with larger lower parts and sideways-facing spiders had more symmetrical webs. Downward-facing C. confusa spiders were larger than upward-and sideways-facing individuals. We also found that during prey attacks, downward-facing spiders ran significantly faster downwards than upwards, which was not the case in upwardfacing spiders. These results suggest that the spider's orientation at the hub and web asymmetry enhance its foraging efficiency by minimizing the time to reach prey trapped in the web. © 2010 The Royal Society.


Zschokke S.,University of Basel | Nakata K.,Nagasaki Institute of Applied Science | Nakata K.,Tokyo Keizai University
Naturwissenschaften | Year: 2010

Orb-web building spiders (Araneae: Araneoidea, Uloboridae) can be considered as territorial central place foragers. In territorial central place foragers, the optimal foraging arena is circular, with the forager sitting in its centre. In orb webs, the spider's orientation (head up or head down) whilst waiting for prey on the hub of its web and the downwards-upwards asymmetry of its running speeds are the probable causes for the observed deviation of the hub from the web's centre. Here, we present an analytical model and a more refined simulation model to analyse the relationships amongst the spider's running speeds, its orientation whilst waiting for prey and the vertical asymmetry of orb webs. The results of our models suggest that (a) waiting for prey head down is generally favourable because it allows the spider to reach the prey in its web on average quicker than spiders waiting head up, (b) the downwards-upwards running speed asymmetry, together with the head-down orientation of most spiders, are likely causes for the observed vertical asymmetry of orb webs, (c) waiting head up can be advantageous for spiders whose downwards-upwards running speed asymmetry is small and who experience high prey tumbling rates and (d) spiders waiting head up should place their hub lower than similar spiders waiting head down. © 2009 Springer-Verlag.


Enoki M.,Tokyo Keizai University | Ishiyama T.,University of Tsukuba | Kobayashi M.A.R.,Ehime University | Nagashima M.,Nagasaki University | Nagashima M.,Bunkyo University
Astrophysical Journal | Year: 2014

Recent observations show that the space density of luminous active galactic nuclei (AGNs) peaks at higher redshifts than that of faint AGNs. This downsizing trend in the AGN evolution seems to be contradictory to the hierarchical structure formation scenario. In this study, we present the AGN space density evolution predicted by a semi-analytic model of galaxy and AGN formation based on the hierarchical structure formation scenario. We demonstrate that our model can reproduce the downsizing trend of the AGN space density evolution. The reason for the downsizing trend in our model is a combination of the cold gas depletion as a consequence of star formation, the gas cooling suppression in massive halos, and the AGN lifetime scaling with the dynamical timescale. We assume that a major merger of galaxies causes a starburst, spheroid formation, and cold gas accretion onto a supermassive black hole (SMBH). We also assume that this cold gas accretion triggers AGN activity. Since the cold gas is mainly depleted by star formation and gas cooling is suppressed in massive dark halos, the amount of cold gas accreted onto SMBHs decreases with cosmic time. Moreover, AGN lifetime increases with cosmic time. Thus, at low redshifts, major mergers do not always lead to luminous AGNs. Because the luminosity of AGNs is correlated with the mass of accreted gas onto SMBHs, the space density of luminous AGNs decreases more quickly than that of faint AGNs. We conclude that the anti-hierarchical evolution of the AGN space density is not contradictory to the hierarchical structure formation scenario. © 2014. The American Astronomical Society. All rights reserved..


Okubo N.,Tokyo Keizai University | Onuma A.,Keio University
Ecosystem Services | Year: 2015

The deterioration of coral reefs in Japan is a serious environmental problem. Conventional conservation policies for terrestrial ecosystems are sometimes difficult to apply to coral reef protection because of the large number of stakeholders involved. In what seems to be an interesting attempt to solve this problem, tourist divers in Okinawa, Japan have begun to transplant coral fragments onto deteriorated coral reefs, by participating in a tour provided by diving shops. However, the problem here is that when the transplanted fragments have been taken out from the natural coral colonies, it tends to cause a host of potential problems such as decreasing fecundity of donor colonies, negative effects on the surrounding environment of the exploited corals and low species diversity of transplanted fragments. In this paper, we examine the merits of commercial coral transplantation in marine ecosystem conservation, and to suggest some reforms that could help to mitigate the problems encountered when using sexually propagated coral transplants. Finally, we discuss how the commercial transplantation in Okinawa could be applied to the conservation of other marine ecosystem. © 2014 Elsevier B.V.


Nakata K.,Tokyo Keizai University | Mori Y.,Teikyo University of Science & Technology
Animal Behaviour | Year: 2016

Complex behaviour may incur a cost. We assumed here that web-building behaviour for two species of orb-web spider, Cyclosa argenteoalba and Eriophora sagana, was more complex when their webs were asymmetric from top to bottom than when their webs were symmetric. The rationale for this assumption was that, while spiders have to adjust their spiral building behaviour in different web sectors to build asymmetric webs, they do not have to make these adjustments for symmetric webs. To estimate the costs involved in building more asymmetric webs, we measured the time taken for spiders to build orb-webs with various up-down size asymmetries and used this as a measure of the complexity of web-building behaviour. The results showed that the spiders required more time to lay the spiral threads as their webs became more asymmetric even when the length of spiral threads was the same, suggesting a time cost of processing complex information. Furthermore, we found that spiders built more symmetric webs when they perceived a risk of predation, perhaps to reduce the web-building time during which they are more vulnerable. This suggests that the cost of behavioural complexity may mediate the outcome of interspecific interactions and thus may be ecologically important. © 2016 The Association for the Study of Animal Behaviour


Yamauchi I.,Chiyoda Corporation | Nagaoka S.,Tokyo Keizai University
Research Policy | Year: 2015

This paper investigates the effects of outsourcing of prior art search on the efficiency of patent examination, using a large scale Japanese patent examination data. Outsourcing may increase examination quality by expanding the scope of prior art search, while it may have a negative effect if the synergy between search and examination is important. Controlling for the endogeneity of outsourcing decision as well as the changes in the time resources available for an examiner, we find that the outsourcing of prior art search significantly decreases the frequency of appeals against both examiners' rejections and grant decisions and reduces the length of examination duration. At the same time we find that the prior art search of complex inventions is not outsourced. These results suggest that the opportunity for exploiting external knowledge and capability can increase the quality as well as the speed of examination. © 2015 Elsevier B.V. All rights reserved.


Nakata K.,Tokyo Keizai University
Naturwissenschaften | Year: 2010

Most orb web spiders face downward on the web hub, and their webs are vertically asymmetrical, that is, the lower part of the web is larger than the upper part and the ratio of the lower part to the whole web area increases as the spider grows. This phenomenon may reflect biogenetic law such that young animals exhibit a general ancestral trait whereas adults exhibit specific and derived traits. An alternative explanation is that vertical asymmetry may arise from the difference in time required by spiders to move up or down the web to capture prey. The present study tested these two hypotheses for Eriophora sagana. Subadults of this species build their webs with reverse asymmetry in that the upper part of the web area is larger than the lower part. In both subadults and adults, the upper proportion decreased with spider weight, and adult spiders built more symmetric webs. These results support the capture time difference hypothesis. Copyright © Springer-Verlag 2010.


Nakata K.,Tokyo Keizai University
Proceedings of the Royal Society B: Biological Sciences | Year: 2010

Focusing attention is a way for animals to search for and to obtain food efficiently. This study examines whether a sit-and-wait forager, the orb-web spider Cyclosa octotuberculata, focuses its attention on limited foraging areas. Video records of foraging activity revealed that the spiders detected prey trapped in the west and east sectors of their web less frequently than prey trapped in the north and south sectors. Comparison of photos of the web hub area with and without spiders present revealed that the spiders pulled radii towards the centre when waiting for prey. Radius pulling is stronger in the north and south web sectors than in the west and east sectors, possibly causing more tension in radii running vertically. Experimental manipulation indicated that the spiders responded to prey quicker when thread tension was increased. The results suggest that C. octotuberculata focus their attention on the web areas above and below the spider by adjusting the tension in web threads; and this causes higher prey detection rates in these areas. © 2009 The Royal Society.


The order Scleractinia includes two distinct groups, which are termed "complex" and "robust" as indicated by the molecular phylogeny of mitochondrial 16S ribosomal gene sequences. Since this discovery, coral taxonomists have been seeking morphological characters for grouping this deep division in the order Scleractinia. Recently, morphological characteristics during embryogenesis that facilitate grouping the two clades as "complex" and "robust" were reported, thus clarifying a deep division in the Scleractinia. In the present report, I establish two new suborders, Refertina and Vacatina, on the basis of the embryogenetic morphological characteristics, molecular data, and new observations of Tubastraea coccinea and Cyphastrea serailia embryogenesis. In particular, the embryo of T. coccinea has a possible fertilization membrane that was first observed in the phylum Cnidaria. The new suborder Refertina consists of the families that belong to the "complex" clade and have no or little blastocoel. The new suborder Vacatina is composed of the families that fall into the "robust" clade and have an apparent blastocoel. © 2016 Zoological Society of Japan.


Nakata K.,Tokyo Keizai University
Animal Behaviour | Year: 2012

Orb webs built by spiders are an extended phenotype, and spiders can modify their morphology when rebuilding them. Internal and external environmental conditions can affect how spiders rebuild. Most spiders that build vertical orb webs wait for prey at the web hub and orient downwards. Moreover, their webs exhibit up-down size asymmetry; specifically, the area below the hub is larger than the area above it. However, some spiders reverse this asymmetry in their webs. To examine the relationship between phenotypic plasticity and web asymmetry reversal and whether spiders elongate their webs upwards in response to prey capture in the upper web, I manipulated prey capture location in two closely related spider species. Cyclosa octotuberculata build webs with typical asymmetry (larger area below the web hub). Cyclosa argenteoalba build webs with reversed asymmetry, a derived phenotype, and wait in a reversed orientation, facing upwards. I found that, when spiders fed in the lower part of the web, both species elongated their webs downwards and that C. argenteoalba webs lost their asymmetry and became symmetrical. In contrast, webs were not elongated in the upward direction when spiders of either species were fed in the upper part of the web. These results provided evidence that the up-down asymmetry of Cyclosa webs is a plastic trait regardless of whether spiders build webs with typical or reversed asymmetry. However, no significant upward elongation of webs indicates that there is no evidence of a relationship between plasticity in the extended phenotype and web asymmetry reversal. © 2012 The Association for the Study of Animal Behaviour.

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