De Harkwesp in de kustduinen. Bedreigd door begrazing en recreatie?

Data on nesting densities of Bembix rostrata, a digger wasp inhabiting dynamic coastal dunes,were used to document the detrimental effects of trampling by cattle and vacationers. Both types of disturbance resulted in similar sand displacement and prey availability. Nesting densities of Europe’s largest digger wasp declined dramatically with increasing trampling, probably below the critical population size. Hence, additional human disturbance, although resulting in similar environmental conditions compared to natural disturbance, significantly affected local population sizes.As a result, anthropogenic disturbance in order to restore or conserve natural dynamics has to be avoided and efforts to restore natural dynamics in a more natural way should be promoted. Although this is here only documented for one large specialised invertebrate, the application of traditional management techniques, such as grazing by large herbivores, within newly evolved landscapes may introduces new pressures that affect pre-adapted species to natural disturbances negatively within short time spans

Inbreeding depresses short and long distance dispersal in three congeneric spiders

Dispersal is one of the most important precopulatory inbreeding avoidance mechanisms and subject to landscape related selection pressures. In small populations, inbreeding within and between populations may strongly affect population dynamics if it reduces fitness and gene-flow. While inbreeding avoidance is generally considered to be a key evolutionary driver of dispersal, potential effects of inbreeding on the dispersal process, are poorly known. Here, I document how inbreeding within a population, so by mating among relatives, affects the survivorship and the dispersal behaviour of three congeneric spider Erigone species (Araneae: Linyphiidae) that differ in habitat preference and regional rarity. The three species were chosen as a model because they allow the assessment of both long and short distance dispersal motivation (respectively ballooning and rappelling) under laboratory conditions. Inbreeding reduced both long and short distance dispersal modes in the three congeneric species. Because survival was depressed after inbreeding, with a tendency of reduced survival loss in the rare and highly stenotopic species, energetic constraints are likely to be the underlying mechanism. Inbreeding consequently depresses silk-related dispersal in three related spiders. This may induce an inbreeding depression vortex with important consequences for range expansion and metapopulation dynamics of aerially dispersing species from highly fragmented landscapes

Ongewervelden in de Vlaamse duinen: Waarom 5 doelsoorten meer zeggen dan 1

We analysed the patterns of occupancy of five threatened invertebrates in a highly fragmented dynamic grey dune landscape. During two years (2003-2004), 133 dune patches between Nieuwpoort (Belgium) and Bray-Dunes (France) varying in area, connectivity, eolian sand dynamics and trampling disturbance were sampled for five focal species: two spiders (Alopecosa fabrilis and Xysticus sabulosus), two butterflies (Issoria lathonia and Hipparchia semele) and one grasshopper (Oedipoda caerulescens). Overall diversity was highest in large and well connected patches that were characterised by high eolian sand dynamics and an intermediate trampling intensity. Patch occupancy differed greatly among species: all species significantly occurred more often in large and connected patches. High trampling intensity (by cattle and/or tourists) negatively affected the two ground dwelling spiders, but not the grasshopper or the butterfly species. High eolian sand dynamics positively affected the presence of the spider X.sabulosus, the grasshopper O. caerulescens and the butterfly H. semele, but had no significant effect on both other species. Colonization was mainly explained by connectivity and never by patch area, while extinction events in H. semele were explained by small patch area. We discuss the implications of using a suite of focal species for management and restoration purposes in the highly fragmented dune area in Belgium and we promote the use of a multispecies approach for evaluating and monitoring conservation efforts in general

Life history, habitat use and dispersal of a dune wolf spider (<i>Pordosa monticola</i> (Clerck, 1757) Lycosidae, Araneae) in the Flemish coastal dunes (Belgium)

Pardosa monticola (Araneae, Lycosidae) is a rare spider in Flanders. It is restricted to thermophilic mesotrophic (dune and heath) grasslands. Its life cycle and its habitat preference in the coastal dunes were analysed by interpreting data of more than 200 year-round pitfall-samplings. Viable populations are found in short dune grasslands (grazed by rabbits) and in mown young dune slacks. The life cycle is mixed annual-biannual and hibernation takes place in the juvenile or sub-adult instars. In short grasslands, the species overwinters in the rough neighbouring vegetation, in dune slacks, in litter accumulations. In the latter, the species survives submerging during winter inundation. Dispersal between suitable habitats can occur by male terrestrial movements via xerophylic habitats and dense grassland vegetation. Aeronautic dispersal is a rare phenomenon in the first instars that takes place only in periods of food shortage. Although a low proportion of the population exhibits this behaviour, this kind of dispersal can be of great importance for gene exchange between distant or strongly isolated populations. The implications and the importance of these data are discussed in relation to contemporary nature management

Search for the Tunguska event in the Antarctic snow

The Tunguska explosion in 1908 is supposed to have been produced by the impact of a small celestial body. The absence of any identifiable crater together with the huge energy released by the event suggest that the impactor exploded in midair and that its material was widely spread over the Earth. The short term contribution of such exceptional events to the total accretion rate of extraterrestrial material by the Earth could be significant. Samples were chosen in a core electromechanically drilled in 1984 near South Pole Station. There, the low temperatures, preventing melting all year long, and the nearly regular snow fall rate provide good conditions for a reliable continuous record of any infalling material. In many samples Ir was below the detection limit of the instrumentation. The iridium infall averaged over 45 samples is given. In a few samples the iridium content is significantly higher than the average: the frequency and amplitude of such fluctuations can be explained by the presence on some filters of finite size cosmic particles. No significant systematic increase above the average level is observed in the part of the core corresponding to the Tunguska event. The two major results of this study are: (1) The presence of Tunguska explosion debris in the Antarctic snow is not confirmed; and (2) The estimate of the average iridium infall, is an order of magnitude lower than the Ganapathy's background but is close to the values measured in Antarctic snow and atmospheric samples by Takahashi et al. The results are also consistent with the flux of micrometeoroids deduced from optical and radar observations or derived from the study of Greenland cosmic dust collection but are lower than the flux at mid-latitude measured in paleocene-oligocene sediments from the central part of the Pacific Ocean