Net primary production and light use efficiency in a mixed coniferous forest in Sweden

Simple light use efficiency (ɛ) models of net primary production (NPP) have recently been given great attention (NPP = ɛ × absorbed photosynthetically active radiation). The underlying relationships have, however, not been much studied on a time step less than a month. In this study daily NPP was estimated as the sum of net ecosystem exchange (NEE) and heterotrophic respiration (R_h) of a mixed pine and spruce forest in Sweden. NEE was measured by eddy correlation technique and R_h was estimated from measurements of forest floor respiration (R_f) and the root share of R_f. The total yearly NPP was on average 810 g C m⁻² year⁻¹ for 3 years and yearly ɛ was between 0.58 and 0.71 g C MJ⁻¹, which is high in comparison with other studies. There was a seasonal trend in ɛ with a relatively constant level of approximately 0.90 g C MJ⁻¹ from April to September Daily NPP did not increase for daily intercepted radiation above 6 MJ m⁻² d⁻¹, indicating that between-years variation in NPP is not directly dependent on total Q_i. The light was most efficiently used at an average daytime temperature of around 15 °C. At daytime vapour pressure deficit above 1400 Pa ɛ was reduced by approximately 50%.     

Understanding the toad code: Behavioural responses of cane toad (Chaunus marinus) larvae and metamorphs to chemical cues

Abstract Larvae of many anuran taxa display strong behavioural responses to chemical cues, including alarm signals from injured conspecific tadpoles. We exposed tadpoles and metamorphs from an Australian population of the invasive cane toad (Chaunus[Bufo] marinus) to a range of chemical stimuli and quantified their responses both in the laboratory and in the field. Filtered fluids containing scent cues from crushed conspecifics elicited strong avoidance from tadpoles, whereas other cues (e.g. scent of food, of native‐range fish or urodele predators, and thermal stimuli) did not. Apparent aggregation of tadpoles in response to scent cues proved to be an artifact of tank design, and was an indirect consequence of avoidance of those cues. Field trials confirmed that free‐ranging toad tadpoles and metamorphs avoided chemical cues from crushed conspecifics, suggesting that the chemicals inducing this response might provide an opportunity to develop targeted control methods for this invasive species.     

Additive effects of predator diversity on pest control caused by few interactions among predator species

1. Studies of the impact of predator diversity on biological pest control have shown idiosyncratic results. This is often assumed to be as a result of differences among systems in the importance of predator–predator interactions such as facilitation and intraguild predation. The frequency of such interactions may be altered by prey availability and structural complexity. A direct assessment of interactions among predators is needed for a better understanding of the mechanisms affecting prey abundance by complex predator communities. 2. In a field cage experiment, the effect of increased predator diversity (single species vs. three‐species assemblage) and the presence of weeds (providing structural complexity) on the biological control of cereal aphids were tested and the mechanisms involved were investigated using molecular gut content analysis. 3. The impact of the three‐predator species assemblages of aphid populations was found to be similar to those of the single‐predator species treatments, and the presence or absence of weeds did not alter the patterns observed. This suggests that both predator facilitation and intraguild predation were absent or weak in this system, or that these interactions had counteracting effects on prey suppression. Molecular gut content analysis of predators provided little evidence for the latter hypothesis: predator facilitation was not detected and intraguild predation occurred at a low frequency. 4. The present study suggests additive effects of predators and, therefore, that predator diversity per se neither strengthens nor weakens the biological control of aphids in this system.     

Studies on the mechanism of resistance to Bipolaris sorokiniana in the barley lesion mimic mutant bst1

The Bipolaris sorokiniana tolerant 1 ( bst1 ) barley mutant is derived from fast neutron-irradiated seeds of wild-type Bowman( Rph3 ). The induced mutation was genetically localized to a position on chromosome 5HL distal to the centromere using amplified fragment length polymorphism markers. In addition, the defence responses and related gene expression in the bst1 mutant after fungal challenge were compared with those occurring in wild-type plants. Hydrogen peroxide generation, determined by 3,3-diaminobenzidine staining, revealed a clearly reduced level of bst1 , compared with the wild-type, during the entire experimental time: 8–120 h post-inoculation (hpi). At 48 hpi, the wild-type samples displayed twice as much fungal mass and three times greater H₂O₂ production than bst1 . At the same time, staining of B. sorokiniana showed less fungal growth in the spontaneous lesions of bst1 compared with the wild-type. Monitoring of defence-related genes at 48 hpi demonstrated strong expression of PR-1a , PR-2 , PR-5 and PR-10 in bst1. A gene coding for a unique oxidoreductase enzyme, designated as HCP1 , was expressed at much higher levels in inoculated leaves of the bst1 mutant than in those of the wild-type plant. Taken together, the results suggest that the defence to B. sorokiniana largely relies on salicylic acid-responsive pathogenesis-related ( PR ) genes, as well as selected reactive oxygen species and unknown HCP1 -associated factors.     

Quasimodoana, a new Holarctic genus of eucoiline wasps (Hymenoptera, Cynipoidea, Figitidae), with a phylogenetic analysis of related genera

Abstract.  A new Holarctic genus, Quasimodoana gen.n. is described for the Palearctic eucoiline wasp Eucoila decipiens Förster, 1869, as Quasimodoana decipiens comb.n. A lectotype is designated for this species. A new North American species is described here as Quasimodoana gibba sp.n. As the new genus has similarities with several eucoiline genera, belonging to two related but distinct lineages, a phylogenetic analysis was carried out, based on 83 morphological characters. The two lineages included in the analysis are referred to here under the tribal names of Eucoilini and Trichoplastini stat.nov. We discuss reasons for adopting available tribal names (rather than 'informal genus groups'), and Trichoplastini is removed from synonymy with Eucoilini. The phylogenetic analysis places Quasimodoana unambiguously within Eucoilini, as a sistergroup to the Trybliographa complex. However, there is only weak support for the monophyly of Eucoilini and for the hypothesized sistergroup relationship between Eucoilini and Trichoplastini.     

Spawning site selection by feral cane toads (Bufo marinus) at an invasion front in tropical Australia

Abstract Spawning sites are a critical and often scarce resource for aquatic‐breeding amphibians, including invasive species such as the cane toad (Bufo marinus). If toads select spawning sites based on habitat characteristics, we can potentially manipulate those characteristics to either enhance or reduce their suitability as breeding sites. We surveyed 25 spawning sites used by cane toads, and 25 adjacent unused sites, in an area of tropical Australia recently invaded by these feral anurans. Water chemistry (pH, conductivity, salinity, turbidity) was virtually identical between the two sets of waterbodies, but habitat characteristics were very different. Toads selectively oviposited in shallow pools with gradual rather than steep slopes, and with open (unvegetated) gradually sloping muddy banks. They avoided flowing water, and pools with steep surrounds. In these respects, cane toads broadly resemble previously studied toad species in other parts of the world, as well as conspecifics within their natural range in South America.