Movement patterns and displacement of a soil insect

Movement and dispersal are important determinants of the spatial distribution and persistence of animal populations in a heterogeneous environment. I studied the small-scale movement pattern of a soil-living insect, Protaphorura armata (Collembola) by using a video-equipment. I added chemical cues, food and conspecifics to their environment and evaluated the effects of external cues on the movement pattern and on displacement at a larger scale. P. armata walked in loops combined with more irregular walks in an environment without known cues. Loops indicate that the direction of the step taken now depends on the direction of the step/steps taken in the past. A mathematical (autoregressive) model was used to describe the looping behaviour. P. armata walked more straightened out and faster in presence of attractive or repellent chemical cues. The result was an increased displacement either towards or away from the source. Chemical cues from live conspecifics were attractive to P. armata while chemical cues from dead conspecifics and from dead individuals of two closely related species were repellent. The repellence is interpreted as an avoidance of areas with a high probability of being killed by e.g. predation. Free linoleic acid present in crushed individuals was shown to be at least partly responsible for the observed repellence. P. armata changed its movement pattern and the displacement decreased in presence of both food and conspecifics. The turning rate increased in individuals moving in an attractive area, which is common in animals and will increase the probability to stay within an area and also increase the search intensity of the area. P. armata is predicted to aggregate in areas with food due to odour attraction and a decreased displacement. The presence of other individuals in areas with food will further contribute to the aggregation. However, it is known from previous results that food of Collembola attracts their predators as well and attractive areas may turn repellent to P. armata as predation occurs and linoleic acid is released.