Is movement behavior of riparian wolf spiders guided by external or internal information?

Orientation is an essential process preceding movement behavior. Information necessary for orientation toward suitable habitat can be gathered by acute and internal information. The former comprises directly detectable, external stimuli, whereas internal information includes earlier experienced environmental cues and inherited information related to an individual's origin. In habitats that can suddenly be disturbed (such as river banks), an accurate orientation is of prime importance for successful movement toward safe habitat. In a common-garden field experiment, we studied between-population variation in movement responses toward safe winter habitat (dike vegetation) of two sympatric riparian wolf spiders, the stenotopic riparian species Pardosa agricola (Thorell 1856) and the generalist P. amentata (Clerck 1757). Both responses to direct visual cues and orientation toward home habitat were investigated on an unfamiliar river bank upstream from the original populations. Movement toward safe habitat was mainly controlled by previously collected information on the riverbank location in the stenotopic species and additionally influenced by visual cues and the prevailing weather conditions. Movements in P. amentata were flexible and not systematically guided by either internal information or direct visual cues. Experience on the location of safe habitat consequently guided orientation in the stenotopic species. Internal information is therefore hypothesised to favor the stenotopic wolf spider by restricting unnecessary movements when sudden threatening situations emerge. Generalist species have less experience with the specific disturbance and do not show pronounced orientation capabilities toward safe habitat