Changes in spider diversity and community structure along abandonment and vegetation succession in rice paddy ecosystems

Field abandonment is a new threat to the biodiversity of agricultural land, but its impacts on arthropod communities remain unclear. We investigated how field abandonment influences spider abundance and diversity in rice paddy ecosystems. We collected spiders in paddy fields and six types of abandoned fields with different combinations of vegetation successional stage (early, middle, or late) and soil water content (wet or dry) in Ibaraki Prefecture, Japan. The abundance and species richness of cursorial spiders were higher in the abandoned fields than in the paddy fields, but there was no difference in the case of orb-weavers. Total spider abundance decreased with increasing successional stage, but the responses differed between orb-weavers and cursorial spiders: the abundance of orb-weavers decreased in the middle stage, whereas that of cursorial spiders decreased in the late stage. Soil water content affected only the abundance of orb-weavers: abundance was higher on wet soil than on dry soil. Species richness was not affected by either vegetation succession or soil water content. On the other hand, an individual-based species-accumulation curve showed that rarefied species richness tended to be greater in abandoned fields at the late stage. Ordination analysis showed that species composition clearly differed among paddy and abandoned fields at different successional stages. Our findings suggest that spider abundance and diversity are higher in abandoned fields than in cultivated fields, and that species composition varies depending on field abandonment and succession. Therefore, maintaining cultivated fields and abandoned fields at different successional stages can maintain a high diversity of spiders across rice paddy ecosystems.