Phenology of High-Arctic Arthropods: Effects of Climate on Spatial, Seasonal, and Inter-Annual Variation

The short summers of the High Arctic pose a strong time constraint on the annual cycle of all organisms in this region. Although arctic arthropods can complete their development at very low temperatures, the predicted climatic changes may shift their phenology outside its normal range. Hence, arctic arthropods may become exposed to conditions to which they are not adapted. On the basis of long-term data from several plots of pitfall and window traps at Zackenberg in high-arctic Northeast Greenland, we document that the timing of emergence is closely related to date of snowmelt in nine taxa of common surface-active and flying arthropods. Average air temperature seemed to play a lesser role, although the duration from snowmelt to the date when 50% of the individuals in the season were caught (date50) was negatively related to the average daily air temperature during the same time interval in three of the nine taxa. Since short-term weather fluctuations appeared to have a small eVect on capture numbers in pitfall and window traps, we suggest that timing of snowmelt is a good predictor of the phenology ofmost arthropods in high-arctic Greenland. The spatial synchrony of capture numbers between individual traps within plots was high. However, among pairs of plots, the spatial synchrony varied between taxa and habitats and declined with distance between plots for surface-dwelling taxa and with diVerence in timing of snowmelt for the most abundant families of Diptera (Muscidae and Chironomidae). Detritus feeders (collembolans,mites andmost larvae of Diptera) and predators (spiders of the families Linyphiidae and Lycosidae) were abundant throughout the summer season. In contrast, the abundance ofmore specialized groups, like butterflies (e.g., Nymphalidae) and parasitoid wasps (e.g., Ichneumonidae), was restricted to a narrow seasonal time window in the warmest part of the summer. Because of their narrow phenological range and their host specialization, these taxa may be most vulnerable to trophicmismatch. Furthermore, snowmelt is predicted to become more variable, and this may aVect organisms in areas of late snowmelt most severely.