Dispersal of the lycaenid Plebejus argus in response to patches of its mutualist ant Lasius niger.

We examined the movement rates of individuals of an obligate myrmecophilous butterfly, Plebejus argus (Lycaenidae: Lepidoptera), in relation to a patch of its mutualist ant, Lasius niger. Marked male and female P. argus from local (resident), fragmented and continuous populations were released into and away from (>100m) a patch of L. niger, and subsequently searched for in a 500×500 m area. Recaptures of males and females from all populations were strongly associated with the target patch of mutualist ants. First day recapture displacements were significantly higher for releases away from the target patch for males, but not for females. Mutualist ant presence was shown to be more important than nectar source density in determining persistence of P. argus in release squares. There was no significant difference in displacement distances or recapture frequencies (standardised for search effort) in the target patch of individuals from local (resident of target patch), fragmented and continuous populations. The recapture frequency in the target patch of males from the local population released outside the target patch was greater than expected from a null model of random straight line movement, suggesting non-random (systematic or orientated) search behaviour. The number of males remaining in the target patch following release into the target patch was greater than expected from a simple diffusion model, suggesting a behavioural response to patch boundaries or other cues related to the patch. [ABSTRACT FROM AUTHOR]