Yuki G. Baba

A macro-scale perspective on within-farm management: how climate and topography alter the effect of farming practices

Organic farming has the potential to reverse biodiversity loss in farmland and benefit agriculture by enhancing ecosystem services. Although the mixed success of organic farming in enhancing biodiversity has been attributed to differences in taxa and landscape context, no studies have focused on the effect of macro-scale factors such as climate and topography. This study provides the first assessment of the impact of macro-scale factors on the effectiveness of within-farm management on biodiversity, using spiders in Japan as an example. A multilevel modelling approach revealed that reducing pesticide applications increases spider abundance, particularly in areas with high precipitation, which were also associated with high potential spider abundance. Using the model we identified areas throughout Japan that can potentially benefit from organic farming. The alteration of local habitat-abundance relations by macro-scale factors could explain the reported low spatial generality in the effects of organic farming and patterns of habitat association.

Adjustment of web-building initiation to high humidity: a constraint by humidity-dependent thread stickiness in the spider Cyrtarachne

Cyrtarachne is an orb-weaving spider belonging to the subfamily Cyrtarachninae (Araneidae) which includes triangular-web-building Pasilobus and bolas spiders. The Cyrtarachninae is a group of spiders specialized in catching moths, which is thought to have evolved from ordinary orb-weaving araneids. Although the web-building time of nocturnal spiders is in general related to the time of sunset, anecdotal evidence has suggested variability of web-building time in Cyrtarachne and its closely related genera. This study has examined the effects of temperature, humidity, moonlight intensity, and prey (moths) availability on web-building time of Cyrtarachne bufo, Cyrtarachne akirai, and Cyrtarachne nagasakiensis. Generalized linear mixed model (GLMM) have revealed that humidity, and not prey availability, was the essential variable that explained the daily variability of web-building time. Experiments measuring thread stickiness under different humidities showed that, although the thread of Cyrtarachne was found to have strong stickiness under high humidity, low humidity caused a marked decrease of thread stickiness. By contrast, no obvious change in stickiness was seen in an ordinary orb-weaving spider, Larinia argiopiformis. These findings suggest that Cyrtarachne adjusts its web-building time to favorable conditions of high humidity maintaining strong stickiness, which enables the threads to work efficiently for capturing prey.

Spatio-temporal dynamics of generalist predators (Tetragnatha spider) in environmentally friendly paddy fields

Earlier studies showed environmentally friendly farming (EFF) increased the populations of various organisms in agricultural landscapes, but the mechanisms of these increases were not well studied, due to a lack of knowledge on their temporal dynamics. Here, we examined spatio-temporal dynamics of Tetragnatha spiders, natural enemies of rice pests, in EFF and conventional farming (CF). Field surveys were conducted in 15 paddy fields under CF and 18 under EFF during three seasons in Tochigi Prefecture, central Japan. The results showed that Tetragnatha spiders were more abundant in paddy fields than in ditches during the growing season, but this tendency was reversed during the non-crop season. Thus, complementary utilization of ditches and paddy fields during different seasons appeared to maintain Tetragnatha populations. Both Tetragnatha spider and flying insect abundance increased in paddy fields under only EFF when the surrounding forest cover was high. There was a significant positive correlation between the density of flying insects and the population growth rate of Tetragnatha spiders, suggesting a bottom-up effect of flying insects emerging from paddy fields. We concluded that the high potential productivity in paddy fields, coupled with the presence of ditches as important habitats, maintained the high abundance of Tetragnatha spiders in paddy-dominated landscapes.

Complex latitudinal variation in the morphology of the kleptoparasitic spider Argyrodes kumadai associated with host use and climatic conditions

We examined complex geographical patterns in the morphology of a kleptoparasitic spider, Argyrodes kumadai, across its distributional range in Japan. To disentangle biotic and abiotic factors underlying morphological variation, latitudinal trends were investigated in two traits, body size and relative leg length, across separate transition zones for host use and voltinism. Statistical analyses revealed complex sawtooth clines. Adult body size dramatically changed at the transition zones for host use and voltinism, and exhibited a latitudinal decline following the converse to Bergmann’s cline under the same host use and voltinism in both sexes. A similar pattern was observed for relative leg length in females but not in males. A genetic basis for a part of observed differences in morphology was supported by a common-garden experiment. Our data suggest that local adaptation to factors other than season length such as resource availability (here associated with host use) obscures underlying responses to latitude.

Dead or alive? Sexual conflict and lethal copulatory interactions in long-jawed Tetragnatha spiders

Yuki G. Baba,a, Akio Tanikawa,b Mayura B. Takada,c and Kyoko Futamid aInstitute for Agro-Environmental Sciences NARO, 3-1-3 Kannondai, Tsukuba-shi, 305–8604 Ibaraki, Japan, bLaboratory of Biodiversity Science, School of Agriculture and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113–8657, Japan, cInstitute for Sustainable Agro-ecosystem Services, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Midoricho, Nishitokyo, Tokyo 188-0002, Japan, and dInstitute of Tropical Medicine, Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852–8523, Japan

Specimen records of spiders (Arachnida: Araneae) by monthly census for 3 years in forest areas of Yakushima Island, Japan

Abstract Background Spiders (Arachnida: Araneae) are a classic indicator taxon for evaluating the health of natural environments. However, studies of spiders’ responses to forest succession under natural and anthropogenic disturbance regimes are lacking. Yakushima Island in southwestern Japan has a unique forest ecosystem, and part of the island is designated as a world natural heritage site by UNESCO. Approximately 90% of Yakushima is covered by forest, including both plantations and natural forests. New information We made an inventory of spiders on Yakushima Island by collecting specimens in five forests (two plantations and three natural forests) with Malaise and window traps from 2006 to 2008 (a total of 637 traps). We collected 3487 specimens, representing 31 families and 165 species or morphotypes, including undescribed and unidentified species. All specimens were preserved in 70% ethanol, and all data were gathered into a Darwin Core Archives as sample event data. The data set is available from the GBIF network (http://www.gbif.org/dataset/f851fd75-32b2-4a23-8046-9c8ae7013a3c). Because there have been no spider inventories based on such a systematic trapping survey in Japan, this data set provides new insight into the biodiversity on Yakushima Island.