Indicating shear stress with FST-hemispheres - effects of stream-bottom topography and water depth

1. In order to quantify the effects of substratum roughness on shear stress and Fliesswasserstammtisch-(FST)-hemisphere movement, hemispheres were calibrated against shear stress in a laboratory flume with fully developed turbulent flow. In five different runs, substratum roughness, water depth and location of hemispheres in relation to the surrounding particles, were varied. 2. FST-hemisphere results were strongly influenced by bottom topography. In the case of hydraulically rough flow a linear relationship exists between shear stress (χ_c) and hemisphere density (ρ_h), whereas in the case of quasi-smooth flow a power law was obtained for the χ_c/ρ_h, relationship. Shear stress for a given hemisphere and relative roughness h/k > 4 (h= water depth; k= height of the roughness elements) deviated up to one order of magnitude between roughnesses. In water depths, where h/k 4, the χ_c/ρ_h relationships are dependent on the ratio h/k, due to water surface effects on hemisphere movement. In the case of k = d₉₀=r_h (d₉₀= characteristic diameter of the largest particles of the bottom substratum; r_h= radius of the hemispheres), the location of the hemispheres in respect to the roughness elements is of secondary importance. 3. In the case of hydraulically rough flow and wake interference between the roughness elements, the turbulent flow field close to the substratum is three-layered, each layer being characterized by its own velocity distribution laws (Dittrich & Hammann de Salazar, 1993). Depending on the height of the roughness elements, FST-hemispheres will be subjected mainly to flow forces of the near-bed layer (in rough substrata) or to flow forces distant from the near-bed zone (in fine substrata). The dominant flow forces acting on bottom particles, organisms, or FST-hemispheres are shear force and lift force. 4. The Local Shear Stress Model (Lamouroux et al., 1992) leads to a correct prediction of hemisphere distribution in a stream with a cobble size substratum, but to an overestimation of hemisphere numbers in a sandy-bottom stream. The substratum-dependent shear stress values therefore need to be entered into the model and a measure of substratum roughness included. 5. Macroinvertebrate abundance correlates well with the movement of FST-hemispheres. Samples from points with very high or very low roughness did not contribute to scatter in the data, indicating that the sum of the near-bed flow forces is relevant to macroinvertebrate distribution, not shear stress alone. We conclude, that FST-hemispheres are well suited to characterize near-bottom hydraulics and therefore the microhabitat of the benthos.     

Pleistocene glaciation events shape genetic structure across the range of the American lobster, Homarus americanus

A north/south discontinuity along the northeastern coast of North America in the genetic structure of the American lobster ( Homarus americanus ) was detected using a suite of 13 microsatellite loci assessed using spatial analyses. Population genetic data laid over existing data on physiographic changes and sea-surface temperatures were used to reconstruct the Pleistocene distribution of this species. A postglacial northern-edge colonization model best explains the relative genetic homogeneity of the northern region compared to the southern region centred in the Gulf of Maine. Population genetic analyses identified significant structure (range of standardized theta 0–0.02) but no significant evidence for isolation by distance. The novel application of spatial genetic analyses to a marine species allowed us to interpret these results by providing a greater insight into the evolutionary factors responsible for shaping the genetic structure of this species throughout is natural range.     

Cospeciation of termite gut flagellates and their bacterial endosymbionts: Trichonympha species and 'Candidatus Endomicrobium trichonymphae'

Symbiotic flagellates play a major role in the digestion of lignocellulose in the hindgut of lower termites. Many termite gut flagellates harbour a distinct lineage of bacterial endosymbionts, so-called Endomicrobia, which belong to the candidate phylum Termite Group 1. Using an rRNA-based approach, we investigated the phylogeny of Trichonympha , the predominant flagellates in a wide range of termite species, and of their Endomicrobia symbionts. We found that Trichonympha species constitute three well-supported clusters in the Parabasalia tree. Endomicrobia were detected only in the apical lineage (Cluster I), which comprises flagellates present in the termite families Termopsidae and Rhinotermitidae, but apparently absent in the basal lineages (Clusters II and III) consisting of flagellates from other termite families and from the wood-feeding cockroach, Cryptocercus punctulatus . The endosymbionts of Cluster I form a monophyletic group distinct from many other lineages of Endomicrobia and seem to have cospeciated with their flagellate host. The distribution pattern of the symbiotic pairs among different termite species indicates that cospeciation of flagellates and endosymbionts is not simply the result of a spatial separation of the flagellate lineages in different termite species, but that Endomicrobia are inherited among Trichonympha species by vertical transmission. We suggest extending the previously proposed candidatus name ' Endomicrobium trichonymphae ' to all Endomicrobia symbionts of Trichonympha species, and estimate that the acquisition by an ancestor of Trichonympha Cluster I must have occurred about 40–70 million years ago, long after the flagellates entered the termites.     

Hunting Patterns,Ban on Baiting,and Harvest Demographics of Brown Bears in Sweden

Abstract We analyzed harvest data to describe hunting patterns and harvest demography of brown bears (Ursus arctos) killed in 3 geographic regions in Sweden during 1981–2004. In addition, we investigated the effects of a ban on baiting, instituted in 2001, and 2 major changes in the quota system: a switch to sex-specific quotas in 1992 and a return to total quotas in 1999. Brown bears (n=887) were harvested specifically by bear hunters and incidentally by moose (Alces alces) hunters. Both hunter categories harvested bears 1) using dogs (37%), 2) by still hunting (30%), 3) with the use of bait (18%), and 4) by stalking (16%). The proportion of bears killed with different harvest methods varied among regions and between bear- and moose-oriented hunters. We found differences between male (52%) and female bears (48%) with respect to the variables that explained age. Moose-oriented hunters using still hunting harvested the youngest male bears. Bears harvested during the first management period (1981–1991) were older and had greater odds of being male than during the subsequent period. It appears that hunters harvesting bears in Sweden are less selective than their North American counterparts, possibly due to differences in the hunting system. When comparing the 4 years immediately prior to the ban on baiting with the 4 years following the ban, we found no differences in average age of harvested bears, sex ratio, or proportion of bears killed with stalking, still hunting, and hunting with dogs, suggesting that the ban on baiting in Sweden had no immediate effect on patterns of brown bear harvest demography and remaining hunting methods. As the demographic and evolutionary side effects of selective harvesting receive growing attention, wildlife managers should be aware that differences in harvest systems between jurisdictions may cause qualitative and quantitative differences in harvest biases. (JOURNAL OF WILDLIFE MANAGEMENT 72(1):79–88; 2008)     

How flower biology and breeding system affect the reproductive success of the narrow endemic Polygala vayredae Costa (Polygalaceae)

Polygala vayredae is a narrow endemic species from the oriental pre-Pyrenees. Despite its conservation status and rarity, no information is available on its reproductive biology. As the flower is the structure directly involved in pollinator attraction, its morphological and functional traits have major effects on the reproductive success of the plant. In this work, the flower biology and breeding system of P. vayredae were studied to evaluate how they affect the reproductive outcome in natural populations. Flower morphology, flower rewards, and male and female functioning throughout the lifespan of the flower were assessed. Pollination experiments, involving pollinator exclusion and pollen from different sources, were conducted, and the pollen ovule index was determined. Female fitness and the occurrence of pollen limitation were assessed in three natural populations over 2 years by observing the presence of pollen on the stigma, pollen tube development, and fruit production. Polygala vayredae flowers are elaborate and long-lived with nectar rewards. The floral traits are well adapted to xenogamy and entomophily, which are in accordance with the observed breeding system and auto-incompatibility system. No mechanism of reproductive assurance was observed and P. vayredae strictly depends on pollinators to set fruit. Low fruit production was observed in the studied populations, which was largely the result of scarce, unreliable, and/or inefficient pollinators and poor pollen quality. In addition, available resources may be a limiting factor. The reproductive strategy of P. vayredae prevents inbreeding depression by a self-incompatibility system, which in years of scarce pollinators is overcome by the plant habit.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 67–81.     

Phloem flow and sugar transport in Ricinus communis L. is inhibited under anoxic conditions of shoot or roots

Anoxic conditions should hamper the transport of sugar in the phloem, as this is an active process. The canopy is a carbohydrate source and the roots are carbohydrate sinks. By fumigating the shoot with N₂ or flooding the rhizosphere, anoxic conditions in the source or sink, respectively, were induced. Volume flow, velocity, conducting area and stationary water of the phloem were assessed by non‐invasive magnetic resonance imaging (MRI) flowmetry. Carbohydrates and δ¹³C in leaves, roots and phloem saps were determined. Following flooding, volume flow and conducting area of the phloem declined and sugar concentrations in leaves and in phloem saps slightly increased. Oligosaccharides appeared in phloem saps and after 3 d, carbon transport was reduced to 77%. Additionally, the xylem flow declined and showed finally no daily rhythm. Anoxia of the shoot resulted within minutes in a reduction of volume flow, conductive area and sucrose in the phloem sap decreased. Sugar transport dropped to below 40% by the end of the N₂ treatment. However, volume flow and phloem sap sugar tended to recover during the N₂ treatment. Both anoxia treatments hampered sugar transport. The flow velocity remained about constant, although phloem sap sugar concentration changed during treatments. Apparently, stored starch was remobilized under anoxia.     

Land cover change 2002–2005 in Borneo and the role of fire derived from MODIS imagery

Borneo has experienced heavy deforestation and forest degradation during the past two decades. In this study the Moderate Resolution Imaging Spectroradiometer was used to monitor land cover change in Borneo between 2002 and 2005 in order to assess the current extent of the forest cover, the deforestation rate and the role of fire. Using Landsat and ground observation for validation it was possible to discriminate 11 land cover classes. In 2002 57% of the land surface of Borneo was covered with forest of which 74% was dipterocarp and more than 23% peat swamp forest. The average deforestation rate between 2002 and 2005 was 1.7% yr^{− 1}. The carbon-rich ecosystem of peat swamp forests showed a deforestation rate of 2.2%. Almost 98% of all deforestation occurred within a range of 5 km to the forest edge. Fire is highly correlated with land cover changes. Most fires were detected in degraded forests. Ninety-eight per cent of all forest fires were detected in the 5 km buffer zone, underlining that fire is the major driver for forest degradation and deforestation.     

Ant-mimicry in some Brazilian salticid and clubionid spiders (Araneae: Salticidae,Glubionidae)*

This paper describes the morphological and behavioural adaptations responsible for ant-like appearance in eight species (genera Zuniga, Synemosyna, Sphecotypus, and Myrmecium) of salticid and clubionid spiders studied in Amazonian and SE Brazil. All ant-mimicking spiders have body and legs thin, and the shiny integument typical of their models. Light horizontal hair bands and constrictions of the cephalothorax and abdomen simulate, respectively, the head-thorax joint and segmented gaster of ants. The petiole and postpetiole of the ants are usually mimicked by a lengthened pedicel, together with a narrowing of the posterior cephalothorax and/or anterior abdomen. The prominent pedipalps of the spiders often simulate ant mandibles, but they may also be strikingly similar to an ant's head. All ant-mimicking spiders walked in a zig-zag ant-like pattern, and frequently raised and moved about the first pair of legs as ‘antennae’. The mimics were found in the same microhabitats (foliage or ground) as their models, and displayed strong avoidance reactions toward the latter both in the field and in captivity. The inoffensive characteristics of the mimics and the noxious traits of their models (strong mandibles, potent sting, hard integument, venomous secretions) strongly suggest that the spiders are Batesian ant-mimics. The detailed structural and behavioural adaptations enhancing ant-mimicry provide strong circumstantial evidence that the selective agents involved must have good visual acuity, and are probably small insectivorous vertebrates (e.g. birds, lizards and toads) or arthropods (e.g. wasps and spiders) which avoid ants.     

Neurophysiological Aspects of Song Pattern Recognition and Sound Localization in Grasshoppers

SYNOPSIS. In their intraspecific communication females of thegrasshopper Chorthippus biguttulus are able to detect minutegaps in songs. Males of this species can lateralize sound withless than 1 dB difference between the two ears. Behavioral experimentssuggested that separate pathways exist for song recognitionand sound localization. As for the neurophysiological basis,auditory receptors respond tonically and necessarily carry allinformation explaining behavioral performances in their spikingresponses. However, for pattern recognition as well as for codingof directional information, it seems necessary for the animalto evaluate a whole set of parallel receptor fibres to achievethe precision observed in behavior. The information of receptorsconverges onto thoracic neurons which drive neurons ascendingto the brain. Some of these ascending neurons exhibit dramaticresponse differences either for various temporal patterns orfor sound from different directions and therefore may representpathways specialized for song recognition or for sound localization.     

Tree diversity promotes predator but not omnivore ants in a subtropical Chinese forest

1. Epigeic ants are functionally important arthropods in tropical and subtropical forests, particularly by acting as predators. High predation pressure has been hypothesised to be a mechanism facilitating high diversity across trophic levels. 2. In this study, standardised pitfall traps were used in a highly diverse subtropical forest to test if and how ant species richness is related to tree species richness and a comprehensive set of other environmental variables such as successional age, soil properties or elevation. 3. A total of 13 441 ant individuals belonging to 3839 species occurrences and 71 species were collected, of which 26 species were exclusive predators and 45 species were omnivores. 4. Occurrence and species richness of total and omnivore ants were positively related to soil pH. Predator ant occurrence was unrelated to all environmental variables tested. 5. The species richness of predator ants increased with tree species richness but decreased with leaf functional diversity and shrub cover. Elevation negatively influenced only total ant species richness. 6. The evenness of predators increased with tree species richness, while the evenness of all ants decreased with shrub cover. Omnivore ant evenness decreased with tree evenness, but increased with successional age. 7. The results highlight the value of diverse forests in maintaining species richness and community evenness of a functionally important predator group. Moreover, the results stress the importance of analysing trophic groups separately when investigating biodiversity effects.