科研之友
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摘要
A permanent snow cover for several months is typical for lame parts of Norway, Sweden and Finland Snow layers thicker than about 20 cm insulate the soil surface and stabilize the ground temperature close to 0 degrees C Many ground-living invertebrates are active at this temperature in the subnivean an space From this "base camp", some invertebrates migrate upwards to use the snow as a subsume The intranivean fauna consists of springtails (Collembola) and mites (Acari) that are small enough to move within the narrow pores between snow crystals The supianvean fauna consists of various invertebrates that ale active on the snow surface Some of them are Collembola that have migrated through the snow layers However, most of them are larger insects and spiders which migrate between the subnivean and supranivean habitats following air channels which are naturally created along tree stems, bushes etc penetrating the snow Likewise, certain Chironomidae and Plecoptera, hatching from winter-open rivers and brooks, are active on the snow surface The supranivean arthropod fauna has the following characteristics I It is a weather dependent assemblage of species. coming and going with changes in air temperature, cloud cover, and wind Below ea -6 degrees C animals are absent, but at temperatures around of above zero, many groups can be simultaneously active on snow. 2 The snow surface fauna shows pheno-logical changes throughout the winter, as certain species and groups are mainly active during certain months 3 Some invertebrates are highly specialized and take advantage of the snow surface as an arena in their life cycle Examples are Hypogastrura social's (Collembola), and the two wingless insects Chionea sp (Diptera Limoniidae) and Boreus sp (Mecoptera) They use the smooth snow sui face for efficient migration Chioea sp and Boreus sp lay their cuss during the snow-covered period. while H social's migrates to mate new colonies The cold tolerant spider Bolephthyphantes index is unique in constructing webs in small depressions on the snow, to catch migrating Collembola Various adaptations for using the snow as a substrate are discussed Besides physiological and morphological adaptations, snow surface arthiopods show special behavioural adaptations Most conspicuous is the ability of several Collembola species to navigate during migiation, using the position of the sun for orientation Furthermore, in Collembola and Mecoptera, jumping as an original mechanism to escape predators has independently evolved into a migrating mechanism An evolutionary potential exists for more invertebrate groups to take advantage of snow as a substrate in their life cycle For instance, several more cold tolerant spiders mid-it evolve the ability to catch migrating Collembola on snow
- 出版日期2010
