Statistical analysis of the influence of conspecifics
on the dispersal of a soil Collembola}

GÖRAN BENGTSSON*, TOBIAS RYDÉN**, MARIA SJÖGREN ÖHRN* AND MAGNUS WIKTORSSON**


*Department of Ecology, Lund University, Sölvegatan 37, SE-223 62 Lund, Sweden

**Centre for Mathematical Sciences, Lund University, Box 118, SE-221 00 Lund, Sweden


Abstract

The evidence for dispersal activity among soil-living invertebrates
comes mainly from observations of their movement on artificial
substrates or of colonisation of defaunated soils in the field. In an
attempt to elucidate the dispersal pattern of soil collembolans in the
presence of conspecifics,
statistical analyses were undertaken to describe and simulate the
movement of groups of the species \textit{Onychiurus armatus} released in trays
of homogeneous soil. A $\chi^2$ test was used to reject the null
hypothesis that individuals moved independently of each other and
uniformly in all directions. The mean radial distance moved (1--2 cm
day${}^{-1}$) and the radial standard deviation varied temporally and
with the density of conspecifics. To capture the interaction between
the moving individuals, four dispersal models, pure diffusion,
diffusion with drift interaction, drift interaction and synchronized
diffusion, and drift interaction and behavioural mood, were formulated
as stochastic differential equations. The parameters of the models
were estimated by minimising the deviance between the observed
replication and replications that were simulated using the models. The
dynamics of movement were best described by modelling the drift
interaction as dependent on whether individuals were in a social or
asocial mood. 

Key words: migration, movement, stochastic differential equation,
social behaviour.