DROUGHT STRESS AS A MORTALITY FACTOR IN 2 PAIRS OF SYMPATRIC SPECIES OF COLLEMBOLA AT SPITSBERGEN, SVALBARD

Desiccation resistance was investigated experimentally in two species pairs of Collembola: Hypo-gastrura viatica and H. longispina, and Fols omia sexoculata and F. quadrioculata. A previous field study in Ny-(A) over circle>lesund, Svalbard, showed clear habitat segregation between the species, related to two concomitant gradients of habitat cover an d soil moisture. H. longispina and F. sexoculata inhabit areas with hi gh habitat cover and soil moisture, whereas F. quadrioculata is mainly found in drier areas with high cover and H. viatica exploits the whol e range of humidities;habitat cover. The desiccation experiments were aimed at testing if drought is likely to be a limiting factor for the distribution of H. longispina and F. sexoculata. Drought was induced e xperimentally by testing different temperatures at a constant relative humidity. Temperature recordings from the field showed that temperatu res within the range tested in the experiments occur naturally. H. lon gispina was highly drought sensitive compared to H. viatica, and desic cation stress probably acts as a limiting factor for its distribution in the area. F. sexoculata, was, however, much more resistant to desic cation than F. quadrioculata. For F. sexoculata, resistance to desicca tion may show a trade-off in favour of tolerating a wider range of hum idities, or be the result of a cuticular adaptation related to long di spersal distances and/or tolerance to submergence. For F. quadrioculat a, desiccation may be an important mortality factor (but not limiting) , contributing to high between-population variability in density and d emography.