Aerial dispersal plasticity under different wind velocities in a salt marsh wolf spider

Dispersal can be regarded as a process operating both betweenand within patches of suitable habitat. For uncontrolled dispersalprocesses, the risk of crossing the borders of the habitat patchand arriving in the unsuitable landscape matrix will increasewith decreasing patch area, in particular when the distancebetween isolated habitat patches is larger than the species'average dispersal capacity. Ballooning dispersal in spiderscan be considered as a passive dispersal process, in which disperseddistances depend on the prevalent wind velocity. We executeda reaction norm analysis to analyze how dispersal propensityof the salt marsh wolf spider Pardosa purbeckensis dependedon population characteristics (patch size) and the environment(wind velocity). Dispersal propensity was affected by the interactionbetween wind velocity and maternal patch size. Ballooning propensitiesdecreased with decreasing salt marsh size. Interestingly, genotypesfrom large salt marshes show higher ballooning propensitiesunder higher wind velocities, whereas those from small habitatpatches show their highest dispersal propensity under low windvelocities. Crossing reaction norms and subsequently stronggenotype x environment interaction variation was observed inall populations but tended to be lower in genotypes from largesalt marshes. It is likely that this pattern results from differencesin wind velocity–related costs of within-habitat dispersalin salt marshes of different sizes.