Foraging in agricultural fields: local ‘sit-and-move’ strategy scales up to risk-averse habitat use in a wolf spider

By making field observations on the movement pattern of the agrobiont wolf spider Pardosa agrestis at two spatiotemporal scales, we explored how fine-scale foraging movements scale up to medium-scale habitat use by the spiders. For fine-scale observations, we followed individuals for several metres and for up to 1-2 h. For medium-scale observations we used marking and recapture in live-trapping pitfall grids, which allowed us to detect movements up to 70 m and for 4 weeks. The analysis of fine-scale movement indicated that spiders followed a ‘sit-and-move’ foraging strategy, which consisted of variable periods of waiting (mean 2.5 min) and brief bouts of movements between the waiting sites. Spiders spent over 90% of the total observation time waiting. Prey capture (or capture attempts) was initiated only from waiting sites. Movement between consecutive waiting sites was more directional than predicted by the correlated random walk model. At medium (2-day) timescales the mean displacement of marked spiders was 7.4 m. Simulations suggested that such a displacement could be achieved if movement observed at the fine scale followed a random path for 2 days. We concluded that movement became less directional with increasing scale. Such a phenomenon might be related to avoidance of revisiting food patches locally and an efficient sampling of the habitat at higher scales. High movement activity in a species that is primarily adapted to ephemeral habitats might increase its likelihood of colonizing new habitat patches. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.