Drought stress as a mortality factor in two pairs of sympatric species of Collembola at Spitsbergen, Svalbard

Abstract

Desiccation resistance was investigated experimentally in two species pairs of Collembola: Hypogastrura viatica and H. longispina, and Folsomia sexoculata and F. quadrioculata. A previous field study in Ny-Ålesund, Svalbard, showed clear habitat segregation between the species, related to two concomitant gradients of habitat cover and soil moisture. H. longispina and F. sexoculata inhabit areas with high habitat cover and soil moisture, whereas F. quadrioculata is mainly found in drier areas with high cover and H. viatica exploits the whole 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 experimentally by testing different temperatures at a constant relative humidity. Temperature recordings from the field showed that temperatures within the range tested in the experiments occur naturally. H. longispina was highly drought sensitive compared to H. viatica, and desiccation stress probably acts as a limiting factor for its distribution in the area. F. sexoculata, was, however, much more resistant to desiccation than F. quadrioculata. For F. sexoculata, resistance to desiccation may show a trade-off in favour of tolerating a wider range of humidities, or be the result of a cuticular adaptation related to long dispersal distances and/or tolerance to submergence. For F. quadrioculata, desiccation may be an important mortality factor (but not limiting), contributing to high between-population variability in density and demography.