A Measurement of Dispersal in the Grasshopper Podisma Pedestris (Orthoptera: Acrididae)

Abstract

The dispersal rate of the grasshopper Podisma pedestris has been measured, with the aim of interpreting the width of a chromosomal cline. 171 adults were marked individually, and released within the cline. 169 movements were seen over three subsequent scorings; the distribution of distances, after correction for the loss of long distance dispersants, was close to a normal curve, but there was an initial shift of ten metres, perhaps towards a better habitat. The linear variance increased at about 21·4 m2 day-1, which corresponds to a standard deviation of 20·7 m gen-1/2 over a 20 day life span. Statistical uncertainty in this estimate can be expressed using a distribution-free maximum likelihood method, which gives support limits of 18·6-27·0 m gen-1/2. However, the main errors come from extrapolating from this experiment to the cline as a whole. © 1982 The Genetical Society of Great Britain.