An interactive key to Central European species of the Pteromalus albipennis species group and other species of the genus (Hymenoptera: Chalcidoidea: Pteromalidae), with the description of a new species

Parasitoid wasps of the genus Pteromalus play an important role in biological pest control, however, the genus includes a large number of cryptic species, which makes reliable identification difficult. The latest identification key dates back to Graham (1969) and since then many new species have been described and nomenclatural changes proposed.Here we present an interactive and fully illustrated identification key in Xper3 for 27 species of the Pteromalus albipennis species group as well as for 18 similar species. In addition to qualitative traits, a large set of body measurements is incorporated in the key. We also explored a new set of qualitative features on the propodeum and metasternum. During field work, a new species of the P. albipennis species group, P. capito Baur sp. n., could be reared from flower heads of Asteraceae, which is described here. It looks very similar to P. albipennis and P. cingulipes, however, several qualitative characters and body ratios distinguish it clearly from the most similar species

Validating a continental European charcoal calibration dataset

Large-scale training sets enabling quantitative reconstructions of past fire parameters are needed to better assess potential effects of increased fire hazard under global warming conditions. The aim of this article is to validate recently developed continental regression equations for the reconstruction of fire number, intensity and size. These transfer functions were built by linking satellite data and charcoal collected in annually sampled sediment traps. We apply these European regression equations to four annually layered lakes located on a North-South gradient in Europe. Down-core annual microscopic charcoal (MIC) and macroscopic charcoal (MAC) influx values were compared with satellite-derived time series of fire number, fire intensity and area burned. Results show that the match between predicted and observed values improves when the overall mean and median of sampled years (12 and 9 years) are considered. Especially, the comparisons of median values show a very good agreement between charcoal-inferred and satellite-observed fire-regime parameters. MIC-based predictions underestimate the variability of the observed fire parameters and MAC-based predictions overestimate it. Our results imply that median values of the fire parameters can be reconstructed well by using MIC and MAC, while it is more difficult to infer the variability of fire-regime parameters. However, when MIC- and MAC-based predictions are pooled together, the fit between observed and predicted values increases for both medians and variability. This finding suggests that MIC and MAC are complementary proxies, thus best sedimentary fire reconstructions may be achieved when they are used together. We conclude that sediment traps can be used for the construction of continental-scale training sets and that their results can be applied to Holocene sedimentary charcoal sequences

Density effects of two hemiparasitic Melampyrum species on grassland plant diversity

Hemiparasitic plants can reduce interspecific competition by parasitizing competitive species or by reducing the density of dominant plants. However, effects of hemiparasites have been suggested to be density dependent and to follow an optimum curve, with the highest diversity values occurring at intermediate hemiparasite densities. As a proof of principle, we tested whether this holds true for the two hemiparasitic species Melampyrum arvense and M. nemorosuni. We conducted vegetation surveys in thermophilous fringe communities on the island of Saaremaa (Estonia) and tested how the local species richness of all vascular plants, and (orbs and graminoids separately, vary along density gradients of the two hemiparasitic species. In total, we investigated four spatially separated populations of M. arvense, and six separated populations of M. nemorosum. Within each population, we placed nine subplots along a Melampyrum density gradient. Using random slope, mixed-effects models, we found significant hump-shaped relationships of total vascular plant species richness with relative cover of arvense and M. nemorosum, with the highest richness values occurring at 13% and 40% cover, respectively. Starting at relatively low densities (> 29.7%) of M. arvense and relatively high densities (> 81.8%) of M. nemorosum, species richness was even lower than in plots without these hemiparasites. In contrast to results for total species richness, we found no significant effect of hemiparasite density when looking at graminoid and forb species separately. Our results help fill an important knowledge gap and underline the generality of density-dependent hemiparasite effects on local species richness. Our findings also clearly support the use of the density-gradient approach when the aim is to explore relationships between hemiparasites and species richness.Hemiparasitische Pflanzenarten betreiben Photosynthese, bilden aber Haustorien an den Wurzeln anderer Arten und entziehen so ihren Wirten Wasser, Nährstoffe, Assimilate und sekundäre Verbindungen (ADLER 2000, CAMERON & SEEL 2007, TĔŠITEL et al. 2010, WESTWOOD et al. 2010). Sie können dadurch die interspezifische Konkurrenz in Pflanzengemeinschaften reduzieren, indem sie die Dichte dominanter Pflanzen verringern und generell die Produktivität verringern. Auf diese Weise können sie die Koexistenz erleichtern und die Stabilität von Pflanzengemeinschaften fördern (PHOENIX & PRESS 2005). Einjährige hemiparasitische Arten können zudem die Etablierung von Keimlingen anderer Arten fördern, indem sie nach dem Absterben Lücken schaffen (JOSHI et al. 2000). Die Auswirkungen von hemiparasitischen Arten auf die Diversität von Pflanzengemeinschaften sind jedoch umstritten. Die Tatsache, dass sowohl positive, negative als auch neutrale Effekte von Hemiparasiten auf die lokale Diversität gefunden wurden (GIBSON & WATKINSON 1992, AMELOOT et al. 2005, FIBICH et al. 2016), kann auf den am häufigsten verwendeten methodischen Ansatz zurückgeführt werden, d. h. den Vergleich von Standorten mit und ohne Hemiparasiten ("Alles-oder-Nichts-Ansatz"; z. B. GIBSON & WATKINSON 1992, FIBICH et al. 2016). Entgegen der intuitiven Erwartung einer rein linearen negativen Beziehung zwischen einer dominanten Pflanzenart und dem Artenreichtum einer Pflanzengemeinschaft hat sich jedoch gezeigt, dass Effekte von Hemiparasiten höchstwahrscheinlich dichteabhängig sind und einer Optimumskurve folgen, wobei die höchste Diversität bei mittleren Hemiparasitendichten auftreten (z. B. gezeigt für Rhinanthus alectorolophus (Scop.) Pollich; HEER et al. 2018). Dies legt nahe, dass der "Alles-oder-Nichts"-Ansatz für die Untersuchung von Hemiparasiten-Effekten auf den Artenreichtum irreführend sein kann, da dieser den Dichtegradienten von Hemiparasiten nicht erfasst. Ob diese Zusammenhänge auch für andere Hemiparasiten als Rhinanthus spp. gelten, wie Melampyrum spp., wurde jedoch bislang noch nicht untersucht. Um diese Wissenslücke zu schließen, untersuchten wir die Vegetation an zehn Standorten in zwei Regionen auf der Insel Saaremaa (Estland). Wir testeten, wie der lokale Artenreichtum von (1) allen Gefäßpflanzen und (2) Kräutern und Grasartigen separat, entlang von Dichtegradienten der beiden Hemiparasiten Melampyrum arvense und M. nemorosum variier

SI_Adolf_et_al_The_Holocene – Supplemental material for Validating a continental European charcoal calibration dataset

<p>Supplemental material, SI_Adolf_et_al_The_Holocene for Validating a continental European charcoal calibration dataset by Carole Adolf, Fabienne Doyon, Fabian Klimmek and Willy Tinner in The Holocene</p

Hemiparasite-density effects on grassland plant diversity, composition and biomass

Hemiparasitic plants are considered ecosystem engineers because they can modify the interactions between hosts and other organisms. Thereby, they may affect vegetation structure, community dynamics and facilitate coexistence as they are able to reduce interspecific competition by parasitizing selectively on competitive species and promote subordinate ones. In agri-environmental schemes, introducing the hemiparasite Rhinanthus has therefore been suggested as a low-cost method to increase grassland plant diversity, which is still subject to debate. The majority of previous studies simply compared sites with and without hemiparasites. However, as hemiparasite effects are most likely density-dependent, we present a novel approach assessing the effect of Rhinanthus alectorolophus density on grassland plant diversity, yield and community biomass quality. Moreover, we investigated whether functional plant composition and community mean traits are affected by Rhinanthus density, which has been largely neglected in previous studies. The relationship between species richness and relative Rhinanthus biomass followed an optimum curve with highest values at 31 relative Rhinanthus biomass. At this Rhinanthus-biomass level, species richness was increased by 12 and yield decreased by 26 compared with plots without Rhinanthus. At relative Rhinanthus biomass >60, species richness was even lower than in plots without Rhinanthus. Overall, the biomass of grasses and the cumulative cover of legumes decreased linearly with increasing relative Rhinanthus biomass. Community mean trait analysis revealed that an increasing Rhinanthus density shifts the community composition towards smaller plant species. Biomass quality was not affected by increasing relative Rhinanthus biomass. In summary, our results of increased plant diversity - in line with a slightly lower yield but similar community biomass quality - indicate that Rhinanthus is a suitable biological tool for grassland restoration