Risk Sensitivity and the Paradox of Colonial Web-Building in Spiders

Group foraging is rare in spiders, occurring only where preyavailability is high. If colonial web-building increases individualprey capture rates as shown, why does group foraging not occurmore often where prey are scarce? Risk sensitivity may explainthis paradox, as variance in prey capture is reduced in groups;risk-averse spiders should join groups only when prey exceeda threshold level. Field studies show that group foraging variesas predicted between species, between populations of a singlespecies, and between sites within a population. However, recentmodels suggest the necessity of examining variance within individualsover time rather than between individuals within populations.Additionally, mechanisms responsible for variance reductionin colonial webs may be less effective than previously assumed.New field data suggest that while prey variance over time maybe somewhat less for individual spiders in groups than for solitaries,the relationship between colonial web-building and variancein prey capture is far more complex than originally thought.The influence of risk sensitivity on reproductive success andthe evolution of colonial web-building is discussed.     

New Data on Axial Locomotion in Fishes: How Speed Affects Diversity of Kinematics and Motor Patterns

Despite considerable recent progress in understanding the functionof the axial muscles and skeleton in fishes, generalizing fromthese results has been hindered by the great phylogenetic diversityof taxa, the lack of quantitative morphometric data on axialmusculoskeletal structure, and limited analysis of the fullrange of locomotor behaviors exhibited within any one taxon.This paper reviews novel results from our studies of two taxawithin a single monophyletic clade, the sunfish family Centrarchidae.Integrated analyses of lateral displacement, lateral bending,and axial muscle activity reveal widespread effects of swimmingspeed both within a particular mode of swimming and among differentbehavioral modes. The longitudinal position along the body ofthe fish also commonly affects kinematics, muscle activity andthe timing of electromyograms (EMGs) relative to kinematics.EMGs and kinematic events propagate from head to tail for bothsteady and kick and glide swimming. In contrast, during theescape response, the onset of EMGs forms a standing wave pattern,whereas kinematic events are propagated. Several novel featuresof the axial motor pattern are summarized for the kick and glidemode of unsteady swimming. For example, the onset of white fiberEMGs lags significantly behind that of the red fibers at thesame longitudinal position, and red fibers are inactivated athigher unsteady swimming speeds. Muscle activity propagatesposteriorly via the sequential activation of myomeres, but thereare statistically significant differences in the timing of EMGsfrom the contractile tissue opposite a single vertebra. Duringrelatively slow kick and glide swimming, the extreme dorsaland ventral portions of myomeres are not active. Estimates ofthe longitudinal extent of the fish with simultaneous muscleactivity indicate that EMGs from an individual myomere usuallyhave temporal overlap with more than 20 neighboring myomereson the same side of the fish. Consequently, the functional unitsfor axial locomotion of fishes do not correspond simply to theanatomical units of individual myomeres. Rather the in vivomotor pattern is a primary determinant of the functional unitsinvolved in swimming.     

An Effect of 2-n-butyramido-5-bromothiazole on Leaf Area of Spring Wheat in Pot Experiments

2-n-butyramido-5-bromothiazole (BABT) sprayed on to spring wheatplants at the second or third leaf stage, or applied as a seeddressing, enlarged the length and breadth of the upper leavesbut caused a 2–4 day delay in ear emergence. Tilleringwas reduced by foliar sprays. Some cytokinin activity was discoveredin BABT and related amidothiazole compounds, so that increasedleaf area is possibly due to a direct stimulatory effect. Alternativelythe slight check to vegetative growth which is caused by BABTtreatments could favour the expansion of leaves in the primordialstage.     

Species concepts and the determination of historic gene flow patterns in the Eulemur fulvus (Brown Lemur) complex

Eulmur fulvus , a complex comprising six subspecies, is a classic example of species status conferred through evolutionary taxonomy. We used the phylogcnctic species concept as an alternative method to the biological species concept for determining historic patterns of gene flow between the various E. julvus subspecies and for conferring species status. In this paper, we used population aggregation analysis to determine the proper species partitions and cladistic analysis to reconstruct the evolutionary relationships of the different populations in the Eulemur fulvus complex. We sequenced three mtDNA gene regions (d-loop, 12S, and cyt-b) and one nuclear region, casein kinase, for a total of 1247 bases. Through population aggregation analysis, we determined that the E. fulvus complex should be split into three units; one unit supported by six diagnostic sites comprising E.f. albocollans , one unit supported by three diagnostic sites comprising E.f. collaris , and one unit supported by two diagnostic sites comprising the four other subspecies. Although all six subspecies in the E. julvus complex share a common ancestor, we found in our cladistic analysis that E. J. collaris and E. j. albocollans share a common ancestor that more recently split off from the common ancestor of the four other E. fulvus subspecies.     

Addressing the influence of instrument surface heat exchange on the measurements of CO2 flux from open-path gas analyzers

There is a growing concern in the flux community that using the eddy covariance method with open‐path CO₂ analyzers often leads to measurements of an apparent ecosystem CO₂ uptake during off‐season periods, especially in cold climates. Such uptake has not been observed when measurements were made with closed‐path analyzers, chambers, or profile methods, suggesting it is an artifact due in some way to the use of open‐path analyzers. In this study, a series of laboratory tests and field experiments were conducted to determine the magnitude of the instrument surface heat exchange in the open path and its relationship with the measured CO₂ flux. Results showed that (1) the surface of an open‐path instrument became substantially warmer than ambient due to electronics and radiation load during daytime, while at night, radiative cooling moderated temperature increases in the path; (2) high‐frequency temperature measurements inside the path were correlated with vertical wind speed producing sensible heat flux inside the instrument path exceeding the ambient heat flux by up to 14%; (3) enclosing the open‐path instrument eliminated the sensible heat flux in the path, and caused measured CO₂ flux to match a closed‐path reference; (4) using sensible heat flux measured directly inside the open path in the WPL term instead of the ambient sensible heat flux also led to a match in CO₂ flux between open‐path instrument and closed‐path reference; and (5) correcting previously collected open‐path CO₂ flux data was possible by estimating the instrument heating effect with a semi‐empirical model using standard weather variables. Results showed that all proposed techniques led to a significant reduction in apparent CO₂ uptake during off‐season periods and to a reduction of the underestimation of CO₂ release in other periods. Close agreement between the open‐path measurements and closed‐path references was achieved in all cases.