THE INUNDATION ZONE OF THE NIGER AS AN ENVIRONMENT FOR PALAEARCTIC MIGRANTS

Of at least 350 species so far recorded within the boundaries of the Niger Inundation Zone, no less than 108 (31%) are wholly or partially of Palaearctic origin. Five main habitats are recognized in the region: wetland, hygrophilous grassland, transition zone, non-flooded areas and aerial. The habitats, the Palaearctic migrants and their possible Ethiopian competitors are described and discussed. The annual Niger flood regime enables Palaearctic waterbirds to find suitable habitats somewhere within the region during all seasons, but most widely during the autumn and winter months of the flood recession. Non-aquatic species inhabiting flood plain grassland are scarce during the Palaearctic autumn, when the growth of vegetation reaches its maximum, becoming commoner and more diverse during the winter months. Wetland warblers of the genera Acrocephalus and Locustella have not been recorded on autumn passage. It is suggested that in some years at least, these and other trans-Saharan migrants from the West Palaearctic overfly the Sahelian latitudes of mid-West Africa. Species inhabiting the transition zone (which increases in area during years of below average rains and floods) are most in evidence at the end of the winter period and during the spring hot dry season, prior to northward trans-Saharan migration. Habitats and species encountered in the non-flooded areas are similar to those recorded in the Sahel zone elsewhere in West Africa. Aerial habitat is utilized by Common Swifts arriving en masse in early August, at the maximum development of the south-westerly monsoon airstream. Several aquatic species and the first few trans-Saharan migrants also occur during the summer rainy season. Some species (e. g. Whiskered Tern, Lesser Kestrel, Turtle Dove, Short-toed Lark and Sand Martin) are most numerous during the late winter and spring hot seasons, when conditions provided by the Inundation Zone may be more suitable for pre-migration feeding than in other parts of the Sahel zone. As yet there is virtually no information available to determine any effects that drought seasons or flood variation may have on the migrant populations.     

Pectoral fins of rhizodontids and the evolution of pectoral appendages in the tetrapod stem-group

The Rhizodontida are an extinct order of large, predatory, lobe-finned fishes, found world-wide in Devonian and Carboniferous freshwater deposits. They are thought to be basal members of the tetrapod lineage. In this paper the pectoral fin skeleton of Rhizodus hibberti , a derived member of the group, is described in detail for the first time. It shows that muscular processes of the humerus (the deltoid and supinator processes) may have appeared later in tetrapod evolution than previously thought. The rhizodontids share an unusual fin-ray morphology, with highly elongated basal hemisegments, overlapping extensively with the endoskeleton. This morphology raises the possibility that segmentation and endoskeletal overlap share some common upstream genetic control during lepidotrichial development. The relative size of the lepidotrichia and the complexity of the endoskeleton does not fit with a 'clockface' model of limb developmental evolution.     

THE CARBONIFEROUS FISH GENERA STREPSODUS AND ARCHICHTHYS (SARCOPTERYGII: RHIZODONTIDA): CLARIFYING 150 YEARS OF CONFUSION

Abstract:  The Carboniferous genus Strepsodus contains several described species, but has been mired in taxonomic confusion for nearly 150 years. The little-known genus Archichthys (with two described species) is usually treated as a junior synonym of Strepsodus . These problems have been caused by, among other things, the poor quality of most specimens, and a heavy reliance on tooth and scale morphology when erecting new species. Both genera are known from Upper and Lower Carboniferous river and lake deposits in the UK, particularly coal shales, cementstones and freshwater limestones. However, Strepsodus has also been discovered at a number of North American localities (e.g. Greer in Iowa, USA, and Horton Bluff in Nova Scotia, Canada) and more recently in Australia (Ducabrook, Queensland). Rhizodontid remains from two Upper Devonian sites (one in Colombia, one in Turkey) have been attributed to Strepsodus , due to a misunderstanding of the defining characteristics (autapomorphies) of the genus. This paper reviews what is known of Strepsodus and Archichthys , and advocates that each be treated as a monospecific genus until reliable morphological evidence of further speciation is found. A neotype specimen for Strepsodus sauroides is proposed, and a check-list of published rhizodontid species is appended.     

Environmental controls on water use efficiency during severe drought in an Ozark Forest in Missouri,USA

To accurately predict ecosystem responses induced by climate warming at local‐to‐global scales, models are in need of more precise knowledge of response during periods of environmental stress such as drought. In this paper, we studied environmental control of canopy‐level water use efficiency (WUE) during drought at an eddy flux site in an oak‐hickory forest in central Missouri, USA. Two consecutive severe droughts in the summers of 2006 and 2007 afforded coverage of a broad range of environmental conditions. We stratified data to obtain subranges that minimized cross‐correlations among putative WUE‐controlling factors. Our results showed that WUE was subject to control by atmospheric saturation deficit (ASD), soil water potential (SWP) and the ratio of diffuse to total photosynthetically active radiation (I_f/I_t). Generally, WUE was found to scale with 1/(ASD)^0.5, consistent with predictions from stomatal optimization theory. In contrast, SWP and I_f/I_t were related to WUE in a linear fashion. ASD was better correlated with WUE than either of the other two factors. It was also observed that the relationship between WUE and any single controlling factor was subject to influence of the other two. One such example was an opposite response of WUE to SWP between low and high ASD values, suggesting a breakdown of stomatal optimality under severe environmental stresses and a shift from optimal stomatal regulation to nonstomatal regulation at leaf scale. We have demonstrated that different data handling (stratified vs. nonstratified) or selection (hourly vs. daily) could lead to different conclusions on the relationship between WUE and its controls. For this reason, we recommend modelers to be cautious when applying WUE‐response formulas at environmental conditions or at time scales different from those at which they are derived.     

Temperature-controlled open-top chambers for global change research

To enable experiments on the interactive effects of elevated atmospheric CO₂ and increased air temperature on physiological processes in trees to be carried out, we altered the standard design of open-top chambers by replacing blowers with evaporative coolers and in-line heaters, with a feedback control system to maintain ambient or elevated air temperatures within the chambers. Ambient and elevated (+ 4 °C) temperature regimes were attained consistently and reliably throughout the growing season, with high reproducibility between chambers. From May through December the average of nearly 300,000 temperature measurements was 18.5 °C in ambient air, 18.9 ± 0.6 °C in six ambient chambers, and 22.4 ± 0.9 °C in six elevated temperature chambers. The difference in soil temperature between ambient and elevated chambers was 1.2 °C. Absolute humidity (vapour pressure) in the chambers was higher than that of ambient air, but it was generally similar between temperature treatments. Vapour pressure deficit therefore was higher in elevated temperature chambers than in ambient chambers, and this difference is considered an inseparable part of the temperature treatment. The addition of a temperature control system to open-top chambers removes what has been an important flaw in this important tool for global change research.     

A method for experimental heating of intact soil profiles for application to climate change experiments

A new system for simulating future belowground temperature increases was conceived, simulated, constructed and tested in a temperate deciduous forest in Oak Ridge, TN, USA. The new system uses low‐wattage, 3 m deep heaters installed around the circumference of a defined soil volume. The heaters add the necessary energy to achieve a set soil temperature differential within the treatment area and add exterior energy inputs equal to those, which might be lost from lateral heat conduction. The method, which was designed to work in conjunction with aboveground heated chambers, requires only two control sensor positions one for aboveground air temperatures at 1 m and another for belowground temperatures at 0.8 m. The method is capable of achieving temperature differentials of at least +4.0±0.5 °C for soils to a measured depth of ?2 m. These +4 °C differential soil temperatures were sustained in situ throughout 2009, and both diurnal and seasonal cycles at all soil depths were retained using this simple heating approach. Measured mean energy inputs required to sustain the target heating level of +4 °C over the 7.1 m² target area were substantial for aboveground heating (21.1 kW h day^?1 m^?2), but 16 times lower for belowground heaters (1.3 kW h day^?1 m^?2). Observations of soil CO₂ efflux from the surface of the target soil volumes showed CO₂ losses throughout 2009 that were elevated above the temperature response curve that have been reported in previous near‐surface soil warming studies. Stimulation of biological activity within previously undisturbed deep‐soil carbon stocks is the hypothesized source. Long‐term research programs may be able to apply this new heating method that captures expected future warming and temperature dynamics throughout the soil profile to address uncertainties in process‐level responses of microbial, plant and animal communities in whole, intact ecosystems.     

Phosphonoacetic Acid: Effect on and Disposition by Tetrahymena1

The antiviral agent phosphonoacetic acid inhibits growth of Tetrahymena thermophila at concentrations comparable to those inhibiting growth of other eukaryotic cells, with 50% inhibition at 0.5 mM phosphonoacetic acid. The compound is cytotoxk to Tetrahymena at concentrations greater than 2.0 mM. When a culture of Tetrahymena the growth of which was totally inhibited by 2.0 mM phosphonoacetic acid was diluted with fresh medium, growth resumed in an exponential, rather than synchronous, fashion. [2–¹⁴C]phosphonoacetic acid is not metabolized by Tetrahymena.     

Priority effects on the life‐history traits of two carrion blow fly (Diptera,Calliphoridae) species

1. Third instars of the invasive blow fly Chrysomya rufifacies are facultative predators on larvae of the native blow fly Cochliomyia macellaria. 2. The effects of priority arrival time on the survivorship and fitness of C. rufifacies and C. macellaria were investigated in laboratory experiments. 3. Cochliomyia macellaria colonising a resource within 1–2 days after C. rufifacies resulted in a 20–70% reduction in survivorship, pupal weight and fecundity compared with those colonising a resource more than 2 days before or after C. rufifacies. Inversely, C. rufifacies exhibited a 50% increase in survivorship and fecundity when closely (～2 days) associated temporally on the resource with C. macellaria and was negatively affected by disparate arrival. 4. These results demonstrate that arrival sequence significantly affects the fitness of both C. rufifacies and C. macellaria. Early colonisation may allow C. macellaria to persist in a community, while there are fitness benefits for C. rufifacies colonising after C. macellaria. 5. The 60% reduction in C. macellaria survivorship when in close temporal association with C. rufifacies may act as an agent of selection for C. macellaria to colonise a resource early and develop quickly to avoid predation on resources colonised by C. rufifacies. 6. Selection for such traits may explain how C. macellaria is able to persist despite intraguild predation by this invasive species. In contrast, the 50% increase in survivorship and fecundity exhibited by C. rufifacies when arriving after C. macellaria may select for C. rufifacies to delay colonisation.