Physiological differences in the growth of <Emphasis Type="Italic">Sargassum horneri</Emphasis> between the germling and adult stages

The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance (10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m⁻²s⁻¹) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m⁻²s⁻¹), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day⁻¹ (25°C, 20 μmol photons m⁻²s⁻¹) and 13% day⁻¹ (8 h daylength). In contrast, the RGRs of the blade weights were 4% day⁻¹ (15°C, 20 μmol photons m⁻²s⁻¹) and 5% day⁻¹ (12 h daylength). Negative growth rates were found at 20 μmol photons m⁻²s⁻¹ of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m⁻²s⁻¹, and 8 h daylength for construction of Sargassum beds and restoration of barren areas.     

Greater Soil Carbon Sequestration under Nitrogen-fixing Trees Compared with <Emphasis Type="Italic">Eucalyptus</Emphasis> Species

Forests with nitrogen-fixing trees (N–fixers) typically accumulate more carbon (C) in soils than similar forests without N–fixing trees. This difference may develop from fundamentally different processes, with either greater accumulation of recently fixed C or reduced decomposition of older soil C. We compared the soil C pools under N–fixers with Eucalyptus (non–N–fixers) at four tropical sites: two sites on Andisol soils in Hawaii and two sites on Vertisol and Entisol soils in Puerto Rico. Using stable carbon isotope techniques, we tracked the loss of the old soil organic C from the previous C₄ land use (SOC₄) and the gain of new soil organic C from the C₃, N–fixer, and non–N–fixer plantations (SOC₃). Soils beneath N–fixing trees sequestered 0.11 ± 0.07 kg m⁻² y⁻¹ (mean ± one standard error) of total soil organic carbon (SOC_T) compared with no change under Eucalyptus (0.00 ± 0.07 kg m⁻² y⁻¹; P = 0.02). About 55% of the greater SOC_T sequestration under the N–fixers resulted from greater retention of old SOC₄, and 45% resulted from greater accretion of new SOC₃. Soil N accretion under the N–fixers explained 62% of the variability of the greater retention of old SOC₄ under the N–fixers. The greater retention of older soil C under N–fixing trees is a novel finding and may be important for strategies that use reforestation or afforestation to offset C emissions. Received 12 March 2001; accepted 5 October 2001.     

Relationship of winter concealment habitat quality on pool use by juvenile spring Chinook salmon (<Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>) in the Grande Ronde River Basin,Oregon USA

Winter concealment habitat quality was assessed and its use by juvenile spring Chinook salmon (Oncorhynchus tshawytscha) quantified in three hatching areas of the Grande Ronde River Basin, Oregon USA. Fish densities were significantly higher in pools with a higher winter concealment habitat index than pools with a lower index. The mean fork length and mean growth rate of fish did not differ between pools with a higher or lower winter concealment habitat index, even though residual fish were significantly larger than fish that emigrated. Biomass–density was significantly higher in pools with a higher winter concealment habitat index than pools with a lower index in all three hatching areas. Biomass–density was positively associated with the amount of cobble substrate (10–24.9 cm/m²) in all three hatching areas, and inversely associated with embeddedness in two of the hatching areas. Results of this study indicate that enhancing winter concealment habitat could improve habitat quality resulting in increased carrying capacity and winter usage by juvenile spring Chinook salmon. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. A. Cambray     

A review: limnological management and biomanipulation in the London reservoirs

Low algal biomasses and high water transparencies are a feature of the storage reservoirs that supply most of London's treated water. This is a result of knowledgeable limnological management and biomanipulation and despite the eutrophic nature of the River Thames with its high nutrients (7 gN m⁻³; 1 gP m⁻³) and particulate organic carbon (2 gC m⁻³). Built-in possibilities of jetting input water are managed to prevent stratification, to ensure isothermy, to mix chemicals and plankton vertically and horizontally and to manipulate the mixed-depth of the algal populations such that their potential for biomass growth is reduced by light-energy limitation. Spring algal growth is delayed and the spring peak is reduced and curtailed by the grazing impact of considerable biomasses of large-bodied daphnid populations (Daphnia magna, pulicaria & hyalina) whose development is also supported by the continuous input of high riverine algal crops. The existence of a large-bodied daphnid zooplankton in the reservoirs is associated with low levels of fish predation since the late 1960s. Variations in the intensity and nature of this vertebrate predation during the subsequent twenty years (1968–88) are illustrated by the changes that have occurred in the relationship between the phytoplankton and zooplankton biomasses of the April-May-June quarter of the year. This example of the London reservoirs serves to illustrate biomanipulation in deep water bodies by bottom-up as well as top-down effects.     

Role of the polychaete <Emphasis Type="Italic">Neanthes succinea</Emphasis> in phosphorus regeneration from sediments in the Salton Sea,California

The Salton Sea currently suffers from several well-documented water quality problems associated with high nutrient loading. However, the importance of phosphorus regeneration from sediments has not been established. Sediment phosphorus regeneration rates may be affected by benthic macroinvertebrate activity (e.g. bioturbation and excretion). The polychaete Neanthes succinea (Frey and Leuckart) is the dominant benthic macroinvertebrate in the Salton Sea. It is widely distributed during periods of mixing (winter and spring), and inhabits only shallow water areas following development of anoxia in summer. The contribution of N. succinea to sediment phosphorus regeneration was investigated using laboratory incubations of cores under lake temperatures and dissolved oxygen concentrations typical of the Salton Sea. Regeneration rates of soluble reactive phosphorus (SRP) were lowest (−0.23–1.03 mg P m⁻² day⁻¹) under saturated oxygen conditions, and highest (1.23–4.67 mg P m⁻² day⁻¹) under reduced oxygen levels. N. succinea most likely stimulated phosphorus regeneration under reduced oxygen levels via increased burrow ventilation rates. Phosphorus excretion rates by N. succinea were 60–70% more rapid under reduced oxygen levels than under saturated or hypoxic conditions. SRP accounted for 71–80% of the dissolved phosphorus excreted under all conditions. Whole-lake SRP regeneration rates predicted from N. succinea biomass densities are highest in early spring, when the lake is mixing frequently and mid-lake phytoplankton populations are maximal. Thus, any additional phosphorus regenerated from the sediments at that time has potential for contributing to the overall production of the lake. Guest Editor: John M. Melack Saline Water and their Biota     

Restocking a keystone species in a biodiversity hotspot: Recovering the European rabbit on a landscape scale

Rabbit populations in Iberia remain at low densities in several areas in which their endangered predators still coexist, and the recovery of these populations is therefore urgent if the integrity of Iberian Mediterranean ecosystems is to be maintained. The enhancement of wild rabbit populations has been attempted through the use of in situ extensive rabbit captive breeding enclosures (restocking plots), which reduce mortality caused by terrestrial predators and dispersal movements and permit the breeding of young individuals which can then naturally disperse to settle in the surrounding areas. However, their effectiveness, the role of its size, the optimal habitat management that should be promoted around them and the habitat features remains uncertain. Here, we show results from a four year study of an ambitious rabbit restocking plan on a landscape scale. We measured rabbit abundance in a vast area in which thirty-two restocking plots were built to create an initial rabbit population for further dispersion, in addition to an intensive habitat management program. We also compared rabbit abundance between managed and unmanaged UTM cells of 2.5 km × 2.5 km. Our results showed that rabbit abundance was three times higher in managed cells, but four years after restocking, rabbit abundances had only reached the threshold needed to support stable Iberian lynx presence (at least 10 latrines per km^?1) in 9 of the 23 managed cells. Rabbit abundance was strongly affected by habitat treatment and scrub coverage. The increase of shelter was useful in low cover areas but ineligible in places with high scrub cover, where the increase of refuge plus scrub clearing to create pastures improve rabbit abundance more effectively. In the light of our results, restocking plots should be built only in places with suitable habitat, whereas pastures should be created in dense scrublands and refuge in low cover areas.     

Evidence of a sharper decrease in a non-indigenous mussel Mytilus galloprovincialis than in indigenous bivalves from 1978 to 2006 on Japanese rocky shores

In various studies encompassing large spatiotemporal scales, the densities of non-indigenous species and indigenous species in the same habitat increased and decreased, respectively, prior to reaching an equilibrium. We examined whether this is true for a non-indigenous mussel Mytilus galloprovincialis, introduced into Japan before 1934, and the sympatric indigenous bivalves: Septifer virgatus, Septifer bilocularis, Hormomya mutabilis, Saccostrea kegaki, Saccostrea mordax and Barbatia (Savignyarca) virescens. Seven quadrat surveys during 1978–2006 on 19 rocky shores (26.6–41.4°N) showed unexpected results. Density of M. galloprovincialis decreased on 89% of the shores where this mussel had previously been found. In contrast, densities of the indigenous bivalves decreased on lower percentages (17–71%) of shores where the bivalves had been found. Shore-to-shore mean density of M. galloprovincialis decreased from the 1970s (27.0–88.7 m⁻²) to the 2000s (0.0–1.1 m⁻²), more sharply than any of the indigenous bivalves (from 4.6–9.1 m⁻² to 0.7–1.5 m⁻² for S. bilocularis, which showed the most marked reduction). The conspicuous decrease for M. galloprovincialis suggests that some factors on the studied shores have become disadvantageous especially for this non-indigenous mussel from the earlier to the later surveys.     

Relationships between the biomass production of invasive <Emphasis Type="Italic">Ludwigia</Emphasis> species and physical properties of habitats in France

Ludwigia grandiflora ssp. hexapetala and L. peploides ssp. montevidensis have invaded many types of fresh water ecosystem in France leading to serious problems of management of these macrophytes. The prediction of extracted plant biomass quantities for every control method could considerably help in plant removal and selecting management choices. The paper presents results of the research program “Biological Invasions” granted by the French Environmental Agency concerning the Ludwigia species (2003–2006): “Characterization of the relations between biotopes, plant populations and human activities: Implications for management”. The objective of this work is: (1) to compare environmental variables in the western part of France where colonised water bodies are widespread, (2) to link these parameters with the evaluation of standing crops and (3) to propose implications for management planning and control methods. Measured dry biomass of Ludwigia spp. varied from 200 g DM m⁻² in shallow lakes to 4,500 g DM m⁻² in a meander of a eutrophicated river. Results depend on the scale of the analysis: within sites, between-sites, at different seasons or years. In sunny conditions, optimal for these plants and in nutrient rich areas, biomass is high. In general, exposure to wind, waves and currents reduces the standing crop. For plant production as well as removal work, the status of plant development and water level, are key factors.     

Life history and secondary production of Glossosoma nigrior Banks (Trichoptera: Glossosomatidae) in two Alabama streams with different geology

We studied life history and secondary production of a caddisfly scraper, Glossosoma nigrior, in two Alabama streams. Collier Creek, located within the Appalachian Plateau physiographic province, is underlain by sandstone bedrock, while Hendrick Mill Branch is located in the Valley and Ridge physiographic province with limestone bedrock. G. nigrior populations in both streams exhibited trivoltine life histories, which were attributed to the higher water temperature regimes than those found in more northern streams. Mean larval density (556 m⁻²) and biomass (B) (49.2 mg AFDM m⁻²) were much higher in Hendrick Mill Branch than Collier Creek (78 m⁻² and 6.7 mg AFDM m⁻²). G. nigrior in Hendrick Mill Branch maintained continuous larval growth and higher larval density than Collier Creek throughout the year mainly due to a greater availability of optimal habitat, a more stable hydrology, and warmer winter water temperature. These factors also resulted in the much higher annual secondary production (P) in Hendrick Mill Branch (965 mg AFDM m⁻²; P/B = 18.3) than Collier Creek (115 mg AFDM m⁻²; P/B = 17.9). Gut content analysis revealed that algae (>50%) and detritus (>40%) were the major diet items for G. nigrior, and the majority of secondary production (>80%) was contributed by the consumption of algae. Glossosoma populations play an important role in trophic linkage in these streams with their high production and grazing activities. Handling editor: D. Dudgeon     

Effects of light and temperature on the attachment and development of <Emphasis Type="BoldItalic">Gloiopeltis tenax</Emphasis> and <Emphasis Type="BoldItalic">Gloiopeltis furcata</Emphasis> tetraspores

Two 60-day experiments were conducted to study the influence of photon flux density (PFD) and temperature on the attachment and development of Gloiopeltis tenax and Gloiopeltis furcata tetraspores. In the first experiment, tetraspores of the two Gloiopeltis species were incubated at five temperature ranges (8°C, 12°C, 16°C, 20°C, 24°C) under a constant PFD of 80 μmol photons m⁻² s⁻¹ with a photoperiod of 12:12. In a second experiment, tetraspores were incubated under five PFD gradients (30, 55, 80, 105, 130 μmol photons m⁻² s⁻¹) at a constant temperature of 16°C with a photoperiod of 12:12. Maximum density of attached tetraspores was observed at 16°C for both species. Maximum per cent of spore germinating into disc was recorded at 12–16°C for G. tenax and 8–12°C for G. furcata. Maximum per cent of discs producing erect axes for G. tenax and G. furcata were recorded at 24°C and 20°C, respectively. Light had no significant effect on tetraspore attachment and developing into disc, but it affected the growth, sprouting and survival of its discs. Under 30–55 μmol photons m⁻² s⁻¹, the discs of the two species of Gloiopeltis did not form thallus until the end of the experiment. Optimum PFD range for G. tenax discs was 80–105 μmol photons m⁻² s⁻¹, whilst it was 80–130 μmol photons m⁻² s⁻¹ for G. furcata. Results presented in this study are expected to assist the progress of artificial seeding of Gloiopeltis.     

Earthworm secondary production and N flux in agroecosystems: a comparison of two approaches

Production was estimated for Aporrectodea spp. and Lumbricus spp. populations in corn agroecosystems with a 5-year history of manure or inorganic fertilizer applications during 1994–1995 and 1995–1996. Earthworm biomass and production were greater in manure than inorganic fertilizer plots, although biomass and production declined by about 50% between 1994–1995 and 1995–1996 due to unfavorable climatic conditions. Production was highest during the spring and autumn when soil temperatures were between 4 and 22°C. Production was higher in Lumbricus spp. than Aporrectodea spp. populations due to greater Lumbricus spp. biomass. Aporrectodea spp. production was 3.47–16.14 g ash-free dry weight (AFDW) m^–2 year^–1, while Lumbricus spp. production was 6.09–18.11 g AFDW m^–2 year^–1, depending on the fertilizer treatment and the method used to estimate production. However, production estimates from the instantaneous growth rate method were within 27% of the values calculated using the size-frequency method. Nitrogen flux through earthworms was used to estimate efficiency quotients. Net production efficiency (P/A) ranged from 0.64 to 0.76, assimilation efficiency (A/C) ranged from 0.1 to 0.3, and gross production efficiency (P/C) ranged from 0.06 to 0.22. Annual N flux through earthworm populations was higher in manure than inorganic fertilizer plots, and ranged from 2.95 to 5.47 g N m^–2 year^–1 in 1994–1995 and 1.76 to 2.92 g N m^–2 year^–1 in 1995–1996. The N flux through earthworms represented an amount equivalent to 16–30% of crop N uptake during 1994–1995 and 11–18% of crop N uptake during 1995–1996. We concluded that the effects of earthworms on N cycling in corn agroecosystems were substantial, and that N flux through earthworms was influenced significantly by fertilizer amendments. Received: 20 September 1999 / Accepted: 24 March 2000     

Secondary production and diet of an invasive snail in freshwater wetlands: implications for resource utilization and competition

Invasive species can monopolize resources and thus dominate ecosystem production. In this study we estimated secondary production and diet of four populations of Pomacea canaliculata, a freshwater invasive snail, in wetlands (abandoned paddy, oxbow pond, drainage channel, and river meander) in monsoonal Hong Kong (lat. 22°N). Apple snail secondary production (ash-free dry mass [AFDM]) ranged from 165.9 to 233.3 g m⁻² year⁻¹, and varied between seasons. Production was lower during the cool dry northeast monsoon, when water temperatures might have limited growth, but fast growth and recruitment of multiple cohorts were possible throughout much (7–10 months) of the year and especially during the warm, wet southwest monsoon. The diet, as revealed by stomach-content analysis, consisted mainly of detritus and macrophytes, and was broadly consistent among habitats despite considerable variation in the composition and cover of aquatic plants. Apple snail annual production was >10 times greater than production estimates for other benthic macroinvertebrates in Hong Kong (range 0.004–15 g AFDM m⁻² year⁻¹, n = 29). Furthermore, annual production estimates for three apple snail populations (i.e. >230 g AFDM m⁻² year⁻¹) were greater than published estimates for any other freshwater snails (range 0.002–194 g AFDM m⁻² year⁻¹, n = 33), regardless of climatic regime or habitat type. High production by P. canaliculata in Hong Kong was attributable to the topical climate (annual mean ~24°C), permitting rapid growth and repeated reproduction, together with dietary flexibility including an ability to consume a range of macrophytes. If invasive P. canaliculata can monopolize food resources, its high productivity indicates potential for competition with other macroinvertebrate primary consumers. Manipulative experiments will be needed to quantify these impacts on biodiversity and ecosystem function in wetlands, combined with management strategies to prevent further range extension by P. canaliculata.     

A direct comparison of the performance of the seaweed biofilters, <Emphasis Type="Italic">Asparagopsis armata</Emphasis> and <Emphasis Type="Italic">Ulva rigida</Emphasis>

The tetrasporophyte of Asparagopsis armata has been previously established as a novel seaweed biofilter for integrated land-based mariculture. The species growth and biofiltration rates were much higher than the values described in the literature for Ulva spp., the most common seaweed biofilter. However, a validation of the advantage of one species over the other requires a study of the performances of these two species in the same system at the same time. In this work, we compared the biofiltration performance and biomass yield of A. armata and Ulva rigida cultivated in the effluents of a fish farm in southern Portugal. Comparisons were performed at different water renewal rates and in two seasons of the year. The maximum total ammonia nitrogen (TAN) removal rates were similar for both species in December (2.7 and 2.8 g TAN m^–2 day^–1 for U. rigida and A. armata, respectively) and higher for A. armata (6.5 g TAN m^–2 day^–1) than for U. rigida (5.1 g TAN m^–2 day^–1) in May. Higher differences were observed when estimating the nitrogen biofiltration through the organic nitrogen yield (N yield) of the biomass produced, particularly in May. This estimate is directly related with the biomass yield and the N content in the tissue which were always higher for A. armata than for U. rigida. In December, the maximum biomass yields were 71 g dry weight (DW) m^–2 day^–1 for A. armata and 44 g DW m^–2 day^–1 for U. rigida, while in May, the yield of A. armata was 125 g DW m^–2 day^–1 and of U. rigida was 73 g DW m^–2 day^–1. This study confirmed that A. armata is indeed a more efficient biofilter than U. rigida. To the best of our knowledge, the production rates reported here are the highest ever reported for macroalgae cultivated in tanks.     

Is habitat management an effective tool for wild rabbit (<Emphasis Type="Italic">Oryctolagus cuniculus</Emphasis>) population reinforcement?

Wild rabbit scarcity in Spain is a serious problem due to its economic and ecological value; thus, management techniques to reinforce their populations are being implemented. Translocations are traditionally applied but high short-term mortality by predation makes them unsuccessful and increases their biological cost. An alternative to translocation would be to strengthen local reduced populations through habitat management (building artificial warrens and increasing food availability). Here, we test this method to determine its efficiency as an exportable protocol to recover wild rabbit populations. We compare two areas with and without artificial warrens and increased food availability and assess relative rabbit abundance by means of pellet counts. Results show that, during the 2 years following habitat management, rabbit numbers increased in the experimental plot in contrast to the not managed one, suggesting its effectiveness to reinforce low-density rabbit populations.     

Intracellular Mg<Superscript><Emphasis Type="Bold">2+</Emphasis></Superscript> Influences Both Open and Closed Times of a Native Ca<Superscript><Emphasis Type="Bold">2+</Emphasis></Superscript>-activated BK Channel in Cultured Human Renal Proximal Tubule Cells

Effects of intracellular Mg²⁺ on a native Ca²⁺-and voltage-sensitive large-conductance K⁺ channel in cultured human renal proximal tubule cells were examined with the patch-clamp technique in the inside-out mode. At an intracellular concentration of Ca²⁺ ([Ca²⁺]_i) of 10⁻⁵–10⁻⁴ M, addition of 1–10 mM Mg²⁺ increased the open probability (P_o) of the channel, which shifted the P_o –membrane potential (V_m) relationship to the negative voltage direction without causing an appreciable change in the gating charge (Boltzmann constant). However, the Mg²⁺-induced increase in P_o was suppressed at a relatively low [Ca²⁺]_i (10^−5.5–10⁻⁶ M). Dwell-time histograms have revealed that addition of Mg²⁺ mainly increased P_o by extending open times at 10⁻⁵ M Ca²⁺ and extending both open and closed times simultaneously at 10^−5.5 M Ca²⁺. Since our data showed that raising the [Ca²⁺]_i from 10⁻⁵ to 10⁻⁴ M increased P_o mainly by shortening the closed time, extension of the closed time at 10^−5.5 M Ca²⁺ would result from the Mg²⁺-inhibited Ca²⁺-dependent activation. At a constant V_m, adding Mg²⁺ enhanced the sigmoidicity of the P_o–[Ca²⁺]_i relationship with an increase in the Hill coefficient. These results suggest that the major action of Mg²⁺ on this channel is to elevate P_o by lengthening the open time, while extension of the closed time at a relatively low [Ca²⁺]_i results from a lowering of the sensitivity to Ca²⁺ of the channel by Mg²⁺, which causes the increase in the Hill coefficient. M. Kubokawa and Y. Sohma contributed equally to this work.     

Evaluation of ammonium and phosphate release from intertidal and subtidal sediments of a shallow coastal lagoon (Ria Formosa – Portugal): a modelling approach

During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater ammonium profiles evidenced a peak in the top-most muddy sediment (380 μM) suggesting higher mineralization rate when oxygen is more available, while maximum phosphate concentration (113 μM) occurred in the sub-oxic layer probably due to phosphorus desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were always lower than in intertidal muddy sediments, ranging annually from 20 μM to 100 μM for ammonium and from 0.05 μM to 16 μM for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, in both muddy (104 nmol cm⁻² d⁻¹––NH₄⁺; 8 nmol cm⁻² d⁻¹––HPO₄⁻²) and sandy sediments (26 nmol cm⁻² d⁻¹––NH₄⁺; 1 nmol cm⁻² d⁻¹––HPO₄⁻²), while during lower temperature periods these fluxes were 3–4 times lower. Based on simulated nutrient effluxes, the estimated annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal areas (22 ton year⁻¹––NH₄⁺; 2 ton year⁻¹––HPO₄⁻²), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH₄⁺ in porewater and consequent diffusive fluxes, what will probably affect the system productivity due to a N/P ratio unbalance.     

Population Density Estimates of the Critically Endangered Yellow-tailed Woolly Monkeys (<Emphasis Type="Italic">Oreonax flavicauda</Emphasis>) at La Esperanza,Northeastern Peru

The critically endangered yellow tailed woolly monkeys (Oreonax flavicauda, Humboldt 1812) are endemic to the cloud forests of northeastern Peru. We surveyed populations of Oreonax flavicauda in the Centro Poblado La Esperanza, Amazonas department between May 2008 and March 2009. We conducted census work in an area comprising disturbed primary cloud forest interspersed with pasture lying between 3 protected areas, all of which are known to contain populations of Oreonax flavicauda. We used standardized line transect methodology to census an area of ca. 700 ha. We also recorded group size and composition. We compared the results of transect width estimation, Krebs’ method, and an ad libitum total group count. We calculated individual densities of 8.27/km² and 9.26/km2, and group densities of 0.93/km² and 1.04/km2 using Krebs’ method and transect width estimation, respectively. Average group size was 8.9, with 1–3 adult males, 1–6 adult females, and 0–6 juveniles and infants. The results from our transect surveys coincided well with our estimated total group count. Our results are similar to those from previous studies, although differences in methodologies and site-specific environmental factors make comparison difficult, and suggest that Oreonax flavicauda is able to survive in disturbed habitat when hunting pressure is low.     

Population structure,growth and production of the yellow clam <Emphasis Type="Italic">Mesodesma mactroides</Emphasis> (Bivalvia: Mesodesmatidae) from a high-energy,temperate beach in northern Argentina

The yellow clam Mesodesma mactroides (Bivalvia: Mesodesmatidae) was once the most abundant intertidal species on the Atlantic coast of northern Argentina and an important commercial resource in South America. This study of a population inhabiting the intertidal zone of the sheltered-dissipative sandy beach Santa Teresita documents the species’ population biology, including demographic structure, growth and production during December 2004 and December 2006, and adumbrates the critical state of M. mactroides at present. A total of 3,015 M. mactroides were collected and measured, whereas individuals were found with an anterior–posterior shell length between 2 and 64 mm. A von Bertalanffy growth function with an asymptotic length (L _∞) of 85 mm and a growth constant (K) of 0.47 year⁻¹ was established from length–frequency distributions. The longevity of the species is estimated at approximately 6 years, and instantaneous mortality rate was about three times higher than 40 years ago. Besides, this study confirmed that the overall growth performance index (OGP) is habitat-specific and can be used to group M. mactroides and M. donacium from different areas into temperate and upwelling species. Furthermore, OGP is inversely correlated with the latitudinal distribution of Mesodesma populations. The intertidal biomass ranged between 0.06 and 0.07 g AFDM m⁻² year⁻¹. Individual production was observed to be highest at 47 mm length (0.35 g AFDM m⁻² year⁻¹), and annual production ranged between 0.12 and 0.19 g AFDM m⁻² year⁻¹, resulting in productivity values (P/B) between 1.84 and 2.93. The comparison of the results of the present study with those of growth studies conducted on M. mactroides 40 years ago revealed the following considerable differences in the population structure of M. mactroides, indicating the conservation status of this intertidal bivalve as endangered: (1) present growth rates are faster, but that the maximum length attained has decreased, (2) the numbers of individuals per square metre were many times higher in the past than in the present, (3) bivalves from the present work never reached the ‘commercial size’ of 60 mm and (4) 40 years ago, the population of M. mactroides was composed of up to three cohorts, whereas in this study, there was only one single cohort visible.     

Relationships Between Na+/Glucose Cotransporter (SGLT1) Currents and Fluxes

The relationships between currents generated by the rabbit Na⁺/glucose cotransporter (SGLT1) and the fluxes of Na⁺ and sugar were investigated using Xenopus laevis oocytes expressing SGLT1. In individual voltage-clamped oocytes we measured: (i) the current evoked by 10 mmαMG and the ²²Na⁺ uptake at 10 mm Na⁺; (ii) the currents evoked by 50 to 500 μm [¹⁴C]αMG and the [¹⁴C]αMG uptakes at 100 mm Na⁺; and (iii) phlorizin-sensitive leak currents in the absence of sugar and ²²Na⁺ uptakes at 10 mm Na⁺. We demonstrate that the SGLT1 leak currents are Na⁺ currents, and that the sugar-evoked currents are directly proportional to both αMG and Na⁺ uptakes. The Na⁺/αMG coupling coefficients were estimated to be 1.6 at −70 mV and 1.9 at −110 mV. This suggests that the rabbit SGLT1 Na⁺/αMG stoichiometry for sugar uptake is 2 under fully saturating, zero-trans conditions. Coupling coefficients of less than 2 are expected under nonsaturating conditions due to uncoupled Na⁺ fluxes (slippage). The similarity between the Na⁺ Hill coefficients and the coupling coefficients suggests strong cooperativity between the two Na⁺ binding sites. Received: 6 October 1997/Revised: 5 December 1997     

Dominance of an invasive earthworm in native and non-native grassland ecosystems

More attention is currently being focused on earthworm invasions; however, in many ecosystems the relative abundance of native and invasive earthworm species is unknown. We characterized earthworm populations of two grassland types within the Palouse region: native prairie remnants and Conservation Reserve Program (CRP) set asides planted with exotic grasses. The earthworm community in both grassland types was completely dominated by the exotic-invasive Aporrectodea trapezoides. Only one individual of a native species, Driloleirus americanus (the giant Palouse earthworm), was found in a prairie remnant. No differences were found between prairie remnants and CRP sites for mean earthworm density (24–106 individuals m⁻²) or fresh weight (12–45 g m⁻²). Our results suggest that the combined effects of land-use change, habitat fragmentation and competitive interactions have resulted in the decimation of native earthworm populations and dominance of invasive earthworms in native and non-native grasslands of the Palouse region.