FOOD-DEPENDENT AND DENSITY-DEPENDENT DISPERSAL - EVIDENCE FROM A SOIL COLLEMBOLAN

1. Dispersal in a fungivore species of Collembola, Onychiurus armatus, in a homogeneous soil was theoretically approached as a deterministic compartmental process, in which the movement of animals between discrete patches could be described by a series of differential equations or by the discrete geometric probability distribution, assuming a constant probability to move from one patch to the next. 2. Experiments were designed for a release of collembolans in two types of soil in a physical arrangement of distinct patches represented by vials connected by tubings to cover a distance of 40 cm. Dispersal distances of individuals were determined, and theoretical and observed distributions compared. 3. Dispersal rates, estimated from transfer rate constants, ranged from 0.020 to 1.42 day-1, suggesting that an average O. armatus moved less than 10 cm day-1. The probability to leave a patch varied between 0.10 and 0.50. 4. Dispersal was dependent on population density, soil type and length of fungal mycelium; it was almost twice as high at a high than at a low density (90 000 and 30 000 individuals m-2) in a mor soil and four times as high in a sandy compared with a mor soil. Dispersal rate decreased as the mycelial length increased, especially in a sandy soil. 5. Collembolans in a feeding phase had a higher tendency to disperse than those that were moulting. 6. Enriching the soil patch at 40 cm distance from the release point with a favoured food item, the fungal species Mortierella isabellina, increased dispersal rate by more than four times in a mor soil, suggesting that fungal odour can attract collembolans from a large distance and enhance their rate of movement more than a three-fold increase of their population density does.