The social organization and behaviour of the Hoatzin Opisthocomus hoazin in central Venezuela

The social organization and behaviour of the Hoatzin Opisthocomus hoazin , a cooperatively-breeding folivorous bird, was studied in the central plains (llanos) of Venezuela. In this area Hoatzins nested in communal social units of two to eight individuals. Units were usually composed of a breeding pair and up to six helpers at the nest. Helpers, usually offspring retained from the previous years' nesting, aided in all breeding activities of their social unit except egg production. On the study site, Hoatzin units defended extremely small, all-purpose territories along watercourses during the rainy (breeding) season, but migrated up to 2 km to areas with permanent water during the dry season. Nesting extended from early May to October. Nest and egg measurements and growth rates of young are provided. Nesting success was low (27%), primarily due to predation by Cebus olivaceus and several other species. Annual survival of adults and young was high. Young did not breed during their first year; 90% of yearlings remained on their natal territories as helpers. Females appear to be the dispersing sex. The results are discussed in relation to previous work on the Hoatzin. The demography of the study population fits the criteria for several recent theories regarding the evolution of cooperative breeding in birds.     

Behavioral Regulatory Mechanisms in the Social Homeostasis of Termites (Isoptera)

Recent progress in the elucidation of the behavioral mechanismsresponsible for maintaining the steady state in a termite colonyis discussed. It is pointed out that various homeostatic mechanismshave common behavioral mechanisms. The mechanisms involved innest repair and construction, foraging, defense, and generalmass movements within nests are explained. An experiment isdescribed in which differential responses to a discrete simplestimulus (heat) are made by two different castes of Nasulitermescorniger and the homeostatic significance emphasized. The factorsin volved in foraging behavior in Reticulitermes are described.An hypothesis for the significance of the behavioral phenomenonof head-banging in termites is put forward: it is consideredto be connected with the maintenance of accelerated activityin a colony after "General Alarm".     

CHARGE CONTRAST IMAGING OF EXCEPTIONALLY-PRESERVED FOSSILS

Abstract:  Charge contrast images are a variant of secondary electron images acquired by operating a variable pressure scanning electron microscope in low vacuum mode; i.e. a gas is present in the specimen chamber. Spatial variation in the amount of charge that accumulates on the surface of the specimen is expressed as differences in greyscale tone; areas that are charging less are darker in tone. The precise mechanisms by which charge contrast images are generated are not known fully. Various different properties of a mineral may create a charge contrast; electrical conductivity is known to be one potentially important variable. As carbon is highly conductive but typical host lithologies (carbonates, silicates) less so or dielectric, the technique is potentially very suitable for imaging organically preserved fossils such as those from the Solite and Jehol biotas. It can also be applied to Burgess Shale fossils: complex films comprising 'aluminosilicates' with or without carbonaceous remains. Charge contrast images reveal anatomical detail not visible using either optical or other scanning electron microscope-based imaging methods.     

Stable isotope analysis indicates microalgae as the predominant food source of fauna in a coastal forest stream,south‐east Brazil

Abstract: Stable isotope studies of food webs in floodplains, large rivers, mangroves, and seagrasses have shown that, although a large proportion of the biomass may come from higher plants, microalgae provide a disproportionate amount of carbon assimilated by metazoan consumers. Evidence is building that this may also be the case for streams, especially those in the tropics. At the level of individual consumer species we also see that the apparent diet may not be reflected in the carbon assimilated. Tropical streams commonly have omnivore‐detritivore species that potentially show this phenomenon. We tested these concepts in four moderately shaded sites in a stream in well‐preserved Atlantic rainforest at Ilha Grande, Rio de Janeiro. We sampled aquatic insects, shrimps and fish as well as potential terrestrial and aquatic primary food sources. Carbon stocks from terrestrial sources predominated over carbon of algal origin (>99% of total). The primary sources of carbon showed distinctly different isotopic signatures: terrestrial sources had δ¹³C values close to ?30‰, microalgae were ?20‰ and macroalgae were ?25‰. All fauna had δ¹³C values consistent with a carbon source derived from microalgae. Baetid mayflies and atyid shrimps exert a strong grazing pressure on periphyton and organic sediments but appear to assimilate predominantly microalgae. The palaemonid shrimp Macrobrachium olfersi also ingests large amounts of detritus of terrestrial origin, but apparently assimilates animal prey with algal δ¹³C signatures. These results support the growing view that tropical stream food chains are primarily algal based.     

Evaluating the population‐level impact of an invasive species,Ring‐necked Parakeet Psittacula krameri,on native avifauna

The introduction of exotic species to ecosystems can have severe consequences for populations of native organisms, but logistical limitations and shortage of historical data often hinder attempts to quantify the ecological implications of such relationships. The establishment and rapid expansion of Ring‐necked Parakeets Psittacula krameri in England therefore presents a rare opportunity to apply novel analytical methods to existing extensive national bird monitoring data from the UK Breeding Bird Survey for an invasive species. A previous study from Belgium suggests that Ring‐necked Parakeets have the potential to reduce the abundance of Eurasian Nuthatch Sitta europaea through competition for nesting cavities. Our analysis provides no evidence for a significant impact through competition on Nuthatch populations or those of any other cavity‐nesting species within the Parakeet’s current range in the UK. However, we cannot exclude the possibility that competitive exclusion could be occurring at a minority of sites at which availability of nest cavities is limiting. This may yet have significant implications for future conflict if Parakeets continue to increase in numbers and range.     

Initial cultivation of a temperate-region soil immediately accelerates aggregate turnover and CO2 and N2O fluxes

The immediate effects of tillage on protected soil C and N pools and on trace gas emissions from soils at precultivation levels of native C remain largely unknown. We measured the response to cultivation of CO₂ and N₂O emissions and associated environmental factors in a previously uncultivated U.S. Midwest Alfisol with C concentrations that were indistinguishable from those in adjacent late successional forests on the same soil type (3.2%). Within 2 days of initial cultivation in 2002, tillage significantly (P=0.001, n=4) increased CO₂ fluxes from 91 to 196 mg CO₂‐C m^?2 h^?1 and within the first 30 days higher fluxes because of cultivation were responsible for losses of 85 g CO₂‐C m^?2. Additional daily C losses were sustained during a second and third year of cultivation of the same plots at rates of 1.9 and 1.0 g C m^?2 day^?1, respectively. Associated with the CO₂ responses were increased soil temperature, substantially reduced soil aggregate size (mean weight diameter decreased 35% within 60 days), and a reduction in the proportion of intraaggregate, physically protected light fraction organic matter. Nitrous oxide fluxes in cultivated plots increased 7.7‐fold in 2002, 3.1‐fold in 2003, and 6.7‐fold in 2004 and were associated with increased soil NO₃^? concentrations, which approached 15 μg N g^?1. Decreased plant N uptake immediately after tillage, plus increased mineralization rates and fivefold greater nitrifier enzyme activity, likely contributed to increased NO₃^? concentrations. Our results demonstrate that initial cultivation of a soil at precultivation levels of native soil C immediately destabilizes physical and microbial processes related to C and N retention in soils and accelerates trace gas fluxes. Policies designed to promote long‐term C sequestration may thus need to protect soils from even occasional cultivation in order to preserve sequestered C.     

Are Roots a Source of Abscisic Acid for the Shoots of Flooded Pea Plants?

Flooding the soil for 2–5 d decreased stomatal conductancesof pea plants (Pisum sativum L., cv. Sprite) with six or sevenleaves. This coincided with slower transpiration, increasedleaf water potentials and increased concentrations of abscisicacid (ABA) in the leaves. No increase in ABA was found in theterminal 20 mm of roots of flooded plants over the same timeperiod. Small stomatal conductances associated with increases in foliarABA were also found in plants grown in nutrient solution whenaeration was halted, causing the equilibrium partial pressuresof dissolved oxygen to fall below 05 It Pa. No increase in ABAconcentration in young secondary roots of the non-aerated plantswas detected after 24, 48 or 72 h, even when the shoot, thepresumed site of deposition for any ABA from the roots, wasremoved 5–6 h before analysis. Similarly, ABA concentrations in roots were not increased whenthe nutrient solution was de-oxygenated by continuous purgingwith nitrogen gas. The abscisic acid concentration in leaf epidermis,the tissue most likely to be the recipient of any ABA movingin the transpiration stream from oxygen-deficient roots, waslower than in the remaining parts of the leaf when examinedin the mutant Argenteum which possesses easily removable epidermallayers. It is concluded that the leaves of plants subjectedto flooding of the soil or oxygen shortage in the root environmentare not enriched substantially with ABA from the roots. A moreprobable source of this growth regulator is the leaf itself. Key words: Pisum sativum, flooding, roots, hormones, aeration stress, abscisic acid, Argenteum mutant