A latitudinal gradient in climate effects on seabird demography: results from interspecific analyses

For an understanding of the effect of climate change on animal population dynamics, it is crucial to be able to identify which climatologic parameters affect which demographic rate, and what the underlying mechanistic links are. An important reason for why the interactions between demography and climate still are poorly understood is that the effects of climate vary both geographically and taxonomically. Here, we analyse interspecifically how different climate variables affect the breeding success of North Atlantic seabird species along latitudinal and longitudinal gradients. By approaching the problem comparatively, we are able to generalize across populations and species. We find a strong interactive effect of climate and latitude on breeding success. Of the climatic variables considered, local sea surface temperatures during the breeding season tend to be more relevant than the North Atlantic Oscillation (NAO). However, the effect of NAO on breeding success shows a clear geographic pattern, changing in sign from positive in the south to negative in the north. If this interaction is taken account of, the model explains more variation than any model with sea surface temperature. This superiority of the NAO index is due to its ability to capture effects of more than one season in a single parameter. Mechanistically, however, several lines of evidence suggest that sea surface temperature is the biologically most relevant explanatory variable.     

Anthropology As Empirical Science

Many anthropologists argue that human affairs are subjective and therefore outside the realm of empirical science. While this position is based on important observations about the process of understanding human affairs, the arguments employed do not imply that the application of empirical science to the explanation of human affairs is either impossible or inappropriate, as some critics maintain.     

Comparative Studies on the Properties of Two Ferredoxins from Pisum sativum L.

Two ferredoxins in approximately equal amounts were isolatedfrom 3 week old Pisum sativum L. seedlings. Both ferredoxinshad identical absorption spectra with maxima at 276, 327, 424,and 468 nm in the oxidized state, and each possessed a single2Fe-2S active centre. The isoelectric points of the two ferredoxinswere both at pH 3·3, and mixtures could not be separatedby isoelectric focusing on polyacrylamide gels. The midpointredox potentials of the ferredoxins were close to –415mV, but they differed slightly in their biological activity.Ferredoxin I was slightly the more active of the two in catalysingNADP⁺ photoreduction by Pisum or Hordeum chloroplasts whereasferredoxin II was more active in catalysing the oxidative cleavageof pyruvate by extracts of Clostridium pasteurianum. Thoughthe molecular weights of the ferredoxins determined by ultracentrifugationwere the same within experimental error, the amino acid compositionsshowed marked differences. The N-terminal 40 amino acid residuesof ferredoxins I and II were determined by means of an automaticsequencer. There were 15 differences, suggesting that gene duplicationhad occurred early in evolutionary time. Ferredoxin I appearsto be more closely related to the other angiosperm ferredoxinssince it differed in only 6 positions compared with the correspondingsequence for Medicago sativa (alfalfa) ferredoxin. The ratioof the two ferredoxins in Pisum sativum was shown to be dependenton the age of the seedlings and environmental growth conditions.     

Prolonged copulation, sperm reserves and sperm competition in the Aquatic Warbler Acrocephalus paludicola

The Aquatic Warbler Acrocephalus paludicola has a quasi-promiscuous mating system with high levels of multiple paternity and, thus, intense sperm competition. The duration of copulation in the Aquatic Warbler is unusually long. In hand-reared, captive birds the duration of mounting was 23.7 ± 11.8 min (mean ± s.d.). On average, six cloacal contacts (inseminations) occurred during each copulation. Between inseminations the male remained in contact with the female, either on top of or directly behind her. Protracted copulation may be a form of contact mate guarding, a behaviour not previously recorded in birds. Copulation was most frequent during the evening and early morning. Male Aquatic Warblers also exhibit extreme morphological adaptations of their reproductive system compared with other Acrocephalus species and other birds: their testes, cloacal protuberance and seminal glomera (which contain 198 × 10⁶ spermatozoa) are all relatively large. Frequent insemination during protracted copulation and contact mate guarding may be alternatives to paternity guarding found in other birds.     

The use of periphytic diatoms as a means of assessing impacts of point source inorganic nutrient pollution in south-eastern Australia

1. Periphytic diatoms are used as indicators of water quality because their ecological tolerances or preferences to environmental variables are thought to be predictable. However, much of the present autecological information for periphytic diatoms has been derived from studies conducted in the northern hemisphere. In this present study we used periphytic diatoms to determine the impacts of inorganic nutrient pollution in a tidal river system in the temperate latitudes of south‐east Australia. In so doing, we assess the suitability of the use of the ‘northern hemisphere’ ecological tolerance/preference data for periphytic diatoms. 2. Artificial substrates were used to collect periphytic diatoms at 35 sites, which were positioned along the riverbanks and the middle of the river at various distances upstream and downstream of the sewage outfall. The sampling design took into account tidal excursions and the observed sewage plume dynamics. Periphytic diatoms were collected during the austral winter month of August and the austral spring months of September and October. We deployed the artificial substrates for 4 weeks to allow the periphytic diatoms to recruit and colonise, before identifying and enumerating the assemblages. 3. Data analysis included two approaches: multivariate visualisations of combinations of environmental and biological data to investigate shifts in species structure of the periphytic diatom assemblage and multimetric indices based on ecological tolerance/preference data. 4. We found that the spatial patterns inferred from multivariate and multimetric analyses were consistent. Temporal variation in the composition of the periphytic diatom assemblage was greater than the spatial variation along horizontal sections of the river (in any one deployment) due mainly to shifts between winter and spring species. 5. Outfall effects were most apparent in winter, possibly because subsequent deployments were swamped by growth of spring periphytic diatoms. The outfall effects included a shift towards pollutant tolerant species and a reduction in the variability of the periphytic diatom assemblage across the river. 6. We conclude that the use of periphytic diatoms and associated ecological tolerance/preference data as a means of assessing impacts of point source inorganic nutrient pollution is effective. An understanding of river and sewage flow patterns is essential to the design of appropriate monitoring programmes and to the interpretation of results, especially as periphytic diatoms are sensitive to many environmental variables.     

Associations between anuran tadpoles and salinity in a landscape mosaic of wetlands impacted by secondary salinisation

1. The secondary salinisation of wetlands is a global problem that poses a great threat to most freshwater biodiversity, including amphibians. We examined tadpole diversity in relation to wetland conductivity (our proxy for salinity) in wetlands in south‐eastern Australia to better understand (i) how salinity and amphibian diversity interact and (ii) the threat posed by secondary salinisation. 2. Six tadpole species were trapped in 56 wetlands that reflected a typical salinity gradient for the study region. We developed Bayesian models to examine the relationships between conductivity and both the probability of species occupancy and expected number of species with the imperfect detection probability of species accounted for in the models. 3. The probability of occupancy for all species and expected species number was negatively associated with wetland conductivity. Our results predict that conductivity should not limit tadpole presence below about 3000 μS cm⁻¹ at 25 °C (approximately 6% seawater) in the region, but will largely exclude amphibian larvae beyond about 6000 μS cm⁻¹ at 25 °C (approximately 12% seawater). 4. We also detected subtle among‐species differences in salinity tolerance. The results reported here show that tadpoles in the study region are likely to be negatively affected by projected future increases in salinisation.     

Relationship Between Photosynthate Supply and Endosperm Development in Maize

Maize (Zea mays L., cultivar Pioneer 3925) plants were givenshaded, thinned and control light treatments during 10 d or20 d periods surrounding pollination. Glucose, sucrose, starch,and dry matter (DM) contents were measured at intervals in compositesamples of pericarp/nucellus (PN), and in endosperms taken fromdeveloping kernels. Total kernel DM per ear at maturity washigher in the thinned treatment than control and shaded treatmentsdue to higher kernel set in apical regions of ears. In PNs at11 d after pollination (DAP), DM and sucrose contents were slightlygreater in thinned than control and shaded plants. Glucose contentswere substantially greater than controls in PNs of thinned plantsand were less than controls in shaded plants. In endospermsfrom apical kernels at 8 to 12 DAP (during cell division), DM,glucose and sucrose contents were substantially less in shadedthan control and thinned plants. Sucrose contents were greaterin endosperms of thinned than control plants. Sugar contentsin endosperms from basal kernels were nearly the same in thethree light treatments. At 12 DAP, apical and basal endospermsin shaded plants had fewer nuclei than those of the other lighttreatments. The light treatments appeared to effect apical kernelgrowth by influencing the extent of cell division. Zea mays L, maize, light treatment, endosperm, cell division, glucose, sucrose, starch     

The frequency distribution of bird body weights: aquatic and terrestrial species

The frequency distribution of the log-transformed body-weights of the world's bird species is right-skewed. The reasons for this skew are unknown. Aquatic bird species are on average heavier and have a less skewed distribution of weights than would be expected if they were a random sample from the overall weight distribution. Conversely, terrestrial species on average weigh less, and their weight distribution is more skewed. This is partly a phylogenetic effect; species of aquatic and terrestrial birds belong to different families. These differences suggest factors which may be important determinants of the overall weight distribution of birds.