Print PageIn Japan, paddy landscape includes grassland networks on the banks between paddy fields and along irrigation channels. Such grasslands have sustained rich biological diversity compared to large-scale monoculture of terrestrial crops in North America and Europe. We investigated the food web of arthropod communities in various types of grasslands left in/around paddy fields, crop fields, riparian zones and parks along urban-rural gradient in Japan. It is probable that food web structure of arthropod communities in grassland becomes more complex according to the disturbance levels. Our research objectives were (1) to compare the guild structure of food webs among various types of grasslands, and (2) to determine the importance of landscape types and vegetation properties on the guild structure of arthropod food webs. In 27 research sites, arthropods were collected by sweeping along a 2 m × 15 m transect in two seasons during 2010. We classified all arthropod individuals into 12 guild types based on the combination of food type (carnivore, herbivore, omnivore and detritivore) and body size (small, middle, large and larger). The relationships among landscape types, vegetation properties, and abundance of guild types in each food web were analyzed using principle component analysis.
Small omnivores were abundant in sites surrounded by urbanized areas. Abundance of larger herbivores increased as proportion of agricultural lands in urban landscape increased. The vegetation of such sites was covered by Setaria viridis which is commonly found in margins of crop fields characterized by urbanized disturbance with infrequent mowing. Abundance of various guild types (i.e. small and middle size carnivores, small to large herbivores, and small and middle size detritivores) increased as proportion of grasslands in agricultural landscape increased. The vegetation of such sites was covered by Lespedeza juncea which is dominant in riparian zones that are occasionally disturbed by the river. Large and lager carnivores and middle size omnivores were abundant in grasslands surrounded by small agricultural lands and large forests. These grasslands were dominated by Miscanthus sinensis and Pueraria lobata which is usually managed with infrequent mowing and is not urbanized. In conclusion, food chains in arthropod food webs became longer in rural landscapes compared to urban landscapes because the abundance of larger carnivores, i.e., the highest trophic level, became higher. These trends are highly affected by mowing and urbanization because both landscape characteristics and plant composition represented the disturbance levels.
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