Patterns in the distribution of two wolf spiders (Araneae: Lycosidae) in two soybean agroecosytems

We studied the distribution of 2 wolf spider species in 2 soybean, Glycine max (L.), agroecosystems in southwestern Ohio, USA. We used replicated 0.42-ha soybean fields maintained under 2 different tillage regimes (conservation tillage and conventional tillage) and 2 wolf spider species [Hogna helluo (Walckenaer) and Pardosa milvina Hentz]. We censused the spiders over 4 field seasons (1994-1997) and found a tendency for there to be more of both species in the conservation tillage plots, although this difference was not statistically significant in most years. There were also more P. milvina than H. helluo on most census dates. P. milvina had 2 population peaks in the years we censused for the whole season (1995-1997), which may be explained by a bivoltine life cycle in the fields. We also found that the conservation-tilled fields had more vegetative debris on the soil surface and more standing weeds than the conventionally tilled fields. The conservation-tilled fields also had a greater prey biomass than the tilled fields overall. These differences in habitat structure and prey availability were positively correlated with differences in the abundances of the 2 wolf spider species. The results of substratum-choice experiments conducted in the field and laboratory indicate that the greater vegetative debris on the soil surface in the conservation tillage fields may explain the greater densities of both specks in these fields.