Optimal foraging in bumblebees: Why is nectar left behind in flowers?

Summary Queen bumblebees (Bombus appositus) leave nectar behind in Delphinium nelsoni flowers with high-standing crops of nectar. Bumblebees deplete flowers in areas with lower-standing crops. Residual volumes predicted by an optimal feeding hypothesis agree with field measurements.     

Effects of secondarily-treated sewage effluent on the early life-history stages of two species of brown macroalgae: Hormosira banksii and Durvillaea potatorum

Sewage effluent has a deleterious effect on the early life-history stages of Hormosira banksii (Turner) Decaisne and Durvillaea potatorum (Labillardière) Areschoug. High concentrations of sewage effluent (28 and 40% in seawater) inhibit zygote germination by 55 to 95%, retard embryo growth (80 to 100%) and cause severe embryo mortality, with less than 60 and 5% surviving after 14 d, respectively. It is probable that such adverse effects would significantly reduce levels of recruitment of these species in sewage-affected localities, and that sewage effluent has played an important role in the decline of these species from several rock platforms in south-east Victoria, Australia. Zygote germination, embryo growth and embryo mortality were inhibited 40% more strongly in sewage effluent than diluted seawater, showing that the effect of sewage effluent is not simply one of seawater dilution. However, this effect was only observed at high concentrations (28 and 40%). The absence of any difference between the low concentrations of sewage effluent (4 and 12% in seawater) and diluted seawater suggests that the dilution of waste water is important in mitigating its more harmful effects. The sensitivity of H. banksii and D. potatorum embryos to the composition of the medium in which they grow and the ease with which they can be manipulated in culture suggest that they may be utilised as biological indicators of water quality.     

Effects of a Proposed Ex Situ Conservation Program on In Situ Conservation of the Babirusa, an Endangered Suid

Abstract: Detailed data are rarely available to show how interventions such as captive breeding programs can create an uncontrolled demand for live specimens of endangered species. We present a case study of the effect of a planned, internationally recognized captive breeding program on trade in the endangered babirusa wild pig from July to December 1998. Although the program had not yet begun, international interest in the captive breeding of babirusas gave hunters and dealers the false impression that there was a potentially lucrative and officially sanctioned national and international demand for any live babirusas they might catch. Swift action by the Indonesian authorities halted this trade, but the study provides a warning about the damage that can be caused to the conservation of a species if management programs are instituted without a full understanding of the practicalities of its conservation, particularly interactions between the species and local people.     

Neurophysiological and behavioral development in birds: Song learning as a model system

The avian song system is a particularly good model for studying the behavioral and physiological aspects of animal development. One seemingly trivial but very important reason for this is that the sound spectrograph enables sounds to be described, measured and analyzed objectively and in detail. Secondly, birdsong is one of the few behaviors which is performed by a separate chain of brain regions and is therefore relatively easy to investigate neurophysiologically. Work on song also provides a clear illustration of the subtle way in which birds are influenced by their internal and external environments during development.     

Chemical aspects of mass spawning in corals. II. (-)-Epi-thunbergol,the sperm attractant in the eggs of the soft coral Lobophytum crassum (Cnidaria: Octocorallia)

Sea turtles migrate between feeding and nesting areas that are often geographically separated by hundreds or thousands of kilometers. Observations of their aggregations at sea and at nesting beaches have led to the hypothesis that sea turtles migrate in socially structured groups. While this migratory strategy is common to many marine vertebrates, socially facilitated behavior is not well documented in testudines. In 1990 and 1991, we attached satellite transmitters to olive ridleys (Lepidochelys olivacea Eschscholtz) found ovipositing together during a mass nesting at Nancite Beach, Costa Rica, to determine whether they migrate independently or in groups after they leave the nesting beach. Results showed that the turtles were not spatially associated during the internesting period, were capable of re-establishing themselves as a group during a subsequent nesting emergence, and were not spatially associated during their postnesting migrations to oceanic feeding areas. We suggested that what appear to be socially structured groups of L. olivacea are in fact individual turtles simultaneously using the same habitat.     

An application of Bayesian variable selection to spatial concurrent linear models

Spatial concurrent linear models, in which the model coefficients are spatial processes varying at a local level, are flexible and useful tools for analyzing spatial data. One approach places stationary Gaussian process priors on the spatial processes, but in applications the data may display strong nonstationary patterns. In this article, we propose a Bayesian variable selection approach based on wavelet tools to address this problem. The proposed approach does not involve any stationarity assumptions on the priors, and instead we impose a mixture prior directly on each wavelet coefficient. We introduce an option to control the priors such that high resolution coefficients are more likely to be zero. Computationally efficient MCMC procedures are provided to address posterior sampling, and uncertainty in the estimation is assessed through posterior means and standard deviations. Examples based on simulated data demonstrate the estimation accuracy and advantages of the proposed method. We also illustrate the performance of the proposed method for real data obtained through remote sensing.     

Response of marine phytoplankton to nitrogen deficiency: Decreased nitrate uptake vs enhanced ammonium uptake

The uptake of nitrate and ammonium was measured separately in uni-algal, nitrogen-deficient cultures of four species of marine phytoplankton. Nitrogen-deficient phytoplankton took up ammonium at initial rates which greatly exceeded those measured for nitrogen-sufficient phytoplankton. However, nitrate uptake by nitrogendeficient cultures was generally much slower than either nitrate or ammonium uptake by nitrogen-sufficient cultures or ammonium uptake by nitrogen-deficient cultures. Considerable species differences were observed in the degree to which nitrogen deficiency increased ammonium uptake or decreased nitrate uptake. Loss of ability to take up nitrate, but enhanced ability to take up ammonium, as a result of nitrogen deficiency may be an adaptation to the different mechanisms by which nitrate and ammonium are supplied to the euphotic zone. In areas with an intermittent supply of nitrogen, changes in the ability of some species to take up nitrogen as a result of nitrogen starvation will influence species composition and complicate interpretations of measurements of nitrogen uptake.Contribution no. 1249 from the Department of Oceanography, University of Washington, and contribution no. 82006 from the Bigelow Laboratory for Ocean Sciences