In the Nylsvley Nature Reserve, in the South African savanna, the spider community in 320 abandoned mammal burrows was investigated. Three species, Agelena ocellata (Agelenidae), Euprosthenops proximus (Pisauridae) and Smeringopus pallidus (Pholcidae), coexisted in the burrows. The number of individuals and the number of species inhabiting the burrows increased with burrow size. Gerbil burrows were apparently too small to provide space for more than one individual of any of the three species. Only the burrows of springhares, warthogs, and antbears contained more than one spider. When artificial burrows were provided a rapid increase in settlement resulted. Competition for space therefore seems to be the determining factor influencing the population size. A relatively low number of prey items (136, in 119 webs) were found in agelenid webs only. Kleptoparasitic ants were observed stealing prey items from the webs.
During a 3-year-experiment on strip-management a population of the spider Dictyna arundinacea (L.) was released in a winter wheat field. D. arundinacea built its webs with high preference at the ears of the wheat and 26-28 % of the released spiders were rediscovered at the marked first web-sites some weeks later. Enclosure studies and prey samples from several sub-populations showed that D. arundinacea caught almost exclusively wheat pest insects, with Oscinellafrit (L.), cereal aphids [Sitobion avenae (F.) and Rhopalosiphum padi (L.) ; mainly winged specimens] and thysanopterans as main prey groups. D. arundinacea moved from the release site into adjacent successional strips, where it survived the harvest and successfully overwintered. From here, a repopulation of the wheat-strips in the next year occurred but the total abundance was so low that after this two-fold habitat change no high population density was reached. The ability of spiders, as unspecialized predators, to prey on wheat pest insects and the suitability of successional strips to preserve high spider densities by habitat change during harvest or other critical events are discussed.
The orchid species Dactylorhiza majalis is endangered by continuing habitat destruction and fragmentation. This requires more detailed information with respect to its sexual reproduction, which is especially relevant for Germany, where from 10 % to 30 % of the worldwide remaining populations grow. In the present study, we determined both the numbers of growing and flowering individuals per stand with regard to D. majalis at 12 localities of Upper Lusatia, Saxony, Germany, during the season 2014. For up to 25 plants per stand, sexual reproduction was assessed by checking over the numbers of blossoms and fruits per inflorescence and by calculating percentages of seed fertilities from embryo-viability stains. Applying pair-wise statistical analyses, we found correlations between two of the above-mentioned traits as well as among the above-cited population-specific reproduction parameters and four out of six Ellenberg's indicator values, which have been calculated to characterize local site conditions. We furthermore recorded both very poor and enhanced seed fertilities, clustering into two groups which were associated with the Ellenberg's indicator value thermal continentality. Lower seed fertilities were generally detected in the northern lowlands, whereas D. majalis is probably able to compensate the unpleasant environments of the southern highlands by bearing more fertile seeds. Conducting genetic inventories with three nuclear microsatellites, the sampled seed-producing mother plants of both fertility groups differed by the opposite frequency distribution of two prominent genotypes DD and EE at locus ms14. These findings indicate a genetic selection due to adaptation to climatical stresses. Based on the additionally detected aberrant megasporogenesis, we propose that mother plants of homozygous genotype EE and their germ-cells are less affected by both aneuploidy and large deletions on the remaining chromosomes, and we assume that a linkage disequilibrium exists between such advantageous karyotypes and the studied microsatellite locus. Regarding the challenges of global warming, repeated inventories are finally recommended at all 12 stands in order to validate the long-term indicative properties of the discovered findings.
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