Flock density, social foraging, and scanning: an experiment with starlings

Social foraging differs from individual foraging because italters both resource availability and the forager's behavior.We examined responses of starlings to the presence of conspecificsby manipulating foraging-group density experimentally, whileensuring that each subject's foraging opportunities were unchanged.To do this, we used individuals foraging simultaneously in fourbottomless enclosures placed at various separations in naturalforaging grounds. We measured foraging and scanning intensityand qualitative aspects of scanning of focal individuals. Additionally,we examined the temporal distribution of scanning between individuals.The focal individual analysis showed that (1) food-searchingactivity increased, while time spent scanning, time off theground and scanning bout length decreased with flock density;(2) food finding per unit of searching effort increased withdensity; (3) head orientation during scanning was sensitiveto companions' proximity: heads pointed away from the companionsat close distance, toward them at intermediate distance, andwas random farther away. The analysis of the (temporal overlappingin scanning) temporal distribution of scanning for the groupshowed that scanning was significantly synchronized when companionswere adjacent to each other but was not significantly differentfrom random at further separations. We conclude that behavioralresponses of individuals to the presence of others generateimportant changes in foraging performance even in the absenceof physical interference and, more generally, that assessingthe mechanisms that control the behavior of group members atdifferent flock densities offers a way to understand the functionaland ecological significance of foraging aggregations.     

Polyamine and methyl jasmonate-influenced enhancement of betalaine production in hairy root cultures of Beta vulgaris grown in a bubble column reactor and studies on efflux of pigments

Hairy root cultures of red beet (Beta vulgaris) were grown in 3 l bubble column reactor for studying growth and pigment production under the influence of polyamines (PA) and elicitor treatment. Earlier studies with shake flask cultures had shown that combined feeding of spermidine (spd) and putrescine (put) (each 0.75 mM) significantly enhanced betalaine productivity in hairy root cultures of red beet. The present study has been focused on betalaine production in 3 l bubble column bioreactor where the growth pattern and betalaine synthesis under the influence of similar levels of polyamines were followed. A combination of spermidine and putrescine fed to the roots each at levels of 0.75 mM efficiently increased growth and pigment production resulting in 1.23-fold higher biomass (39.2 g FW l⁻¹) and 1.27-fold higher betalaine content (32.9 mg g⁻¹ DW) than control. Treatments with various levels of elicitor-methyl jasmonate (MJ), though progressively retarded biomass, at 40 μM level resulted in a significant increase in betalaine content resulting in 36.13 mg g⁻¹ DW which was 1.4-fold higher than the control. Further higher concentrations of methyl jasmonate treatments supported high as well as rapid accumulation of betalaines, the overall betalaine productivity was hampered mainly because of the inhibitory action on biomass. Pigment release studies with cetyl trimethyl ammonium bromide (CTAB) resulted in optimization of concentration for better efflux of betalaines without showing any inhibitory effect on hairy root viability. These studies on product enhancement and on-line extraction of pigment are useful for developing a bioreactor system for betalaine production using B. vulgaris hairy root cultures. In particular the use of elicitors and efflux studies provide an insight for integrating unit operations and developing a process for continuous operation and higher production of phytochemicals.     

Pathogenic Variability and Genetic Diversity of Phaeoisariopsis griseola Isolates from Two Counties in the State of Goias, Brazil

Angular leaf spot disease of common bean (Phaseolus vulgaris), caused by Phaeoisariopsis griseola, is one of the most important disease of this crop in Brazil. Control strategies for the disease include cultural practices, chemical control and genetic resistance. This pathogen is known to vary greatly in pathogenicity. For durable use of genetic resistance to control this disease, it is necessary to manage resistant cultivars by taking into account the population structure of P. griseola. Isolates of the pathogen from Goias, Brazil exhibited an important virulence polymorphism when inoculated on 12 differential cultivars. A total of 13 pathotypes was identified within a series of 96 isolates collected in Inhumas and Damolandia counties. Only pathotypes 63‐15, 63‐23, 63‐31 and 63‐63 were identified in both counties. Since all the isolates were capable of inducing disease in both Andean and Mesoamerican differential cultivars, they were considered to be of Mesoamerican origin. Random amplified polymorphic DNA (RAPD) analysis performed on the same 96 isolates revealed a great genetic diversity clustering the series into five groups at an Euclidean distance of 62.5%. Although the results did not show any clustering according to the isolate origin, it was possible to observe a tendency of the isolates to cluster in different groups according to their origin. No pathotype‐specific band was observed in the present study.     

Inter- and intraspecific differences in climatically mediated phenological change in coexisting Triturus species

Climate and weather affect phenological events in a wide range of taxa, and future changes might disrupt ecological interactions. Amphibians are particularly sensitive to climate, but few studies have addressed climatically mediated change in the phenology of closely related species or sexes. Here, we test the hypothesis that changes in spring temperatures result in phenological change among Triturus, and we examine inter‐ and intraspecific differences in response. Coexisting populations of Triturus helveticus and Triturus vulgaris at Llysdinam pond in mid‐Wales (53°12′59″N 3°27′3″W) were monitored using pitfall traps along a drift fence during 1981–1987, and again in 1997–2005. Spring temperature over the same period explained up to 74% of between‐year variability in median arrival date, with a significant advance of 2–5 days with every degree centigrade increase. Changes were greater for males than females of both species, and greater for T. helveticus than T. vulgaris within sexes, resulting in an increasing temporal separation between arrivals of male T. helveticus and all other groups. These data illustrate for the first time how climatic change might have differential effects on sympatric species and on the two sexes.     

Effect of elevated CO2 on the demography of a leaf-sucking mite feeding on bean

The effect of elevated CO₂ on the demography of the arachnid species Tetranychus urticae feeding on Phaseolus vulgaris plants was analysed. This class of herbivores (Arachnida) and its feeding guild (cell content feeders) are under-represented in studies of the combined effects of herbivory and CO₂. The growth of bean was strongly stimulated by elevated CO₂. The number of leaves on lateral stems and of flowers increased but pod weight decreased. Leaf nitrogen content was 25% lower at elevated CO₂ due to an increase in non-structural sugar concentration. Leaf water content was lower at elevated CO₂ while leaf-specific mass and epidermis thickness were higher. Females of the mite raised at ambient or elevated CO₂, but all fed with leaves grown at ambient CO₂, had similar progenies. When females were raised on plants grown at elevated CO₂, the numbers of their progeny were reduced by 34% and 49% in the first and second generation respectively. Later stages of development were more reduced in elevated CO₂, suggesting that both fecundity and rate of development were affected. This study suggests that the abundance of T. urticae, and consequently the damage to the many crops it infests, might decrease in a future elevated-CO₂ environment. Received: 8 May 1999 / Accepted: 4 November 1999     

Long distance seed dispersal by wind: measuring and modelling the tail of the curve

The size and shape of the tail of the seed dispersal curve is important in determining the spatial dynamics of plants, but is difficult to quantify. We devised an experimental protocol to measure long-distance dispersal which involved measuring dispersal by wind from isolated individuals at a range of distances from the source, but maintaining a large and constant sampling intensity at each distance. Seeds were trapped up to 80 m from the plants, the furthest a dispersal curve for an individual plant has been measured for a non-tree species. Standard empirical negative exponential and inverse power models were fitted using likelihood methods. The latter always had a better fit than the former, but in most cases neither described the data well, and strongly under-estimated the tail of the dispersal curve. An alternative model formulation with two kernel components had a much better fit in most cases and described the tail data more accurately. Mechanistic models provide an alternative to direct measurement of dispersal. However, while a previous mechanistic model accurately predicted the modal dispersal distance, it always under-predicted the measured tail. Long-distance dispersal may be caused by rare extremes in horizontal wind speed or turbulence. Therefore, under-estimation of the tail by standard empirical models and mechanistic models may indicate a lack of flexibility to take account of such extremes. Future studies should examine carefully whether the widely used exponential and power models are, in fact, valid, and investigate alternative models. Received: 7 March 1999 / Accepted: 2 April 2000