Searching efficiency and the functional response of a pause-travel forager

1. The feeding rates of many predators and parasitoids exhibit type II functional responses, with a decelerating rate of increase to reach an asymptotic value as the density of their prey or hosts increases. Holling's disc equation describes such relationships and predicts that the asymptotic feeding rate at high prey densities is set by handling time, while the rate at which feeding rate increases with increased prey density is determined by searching efficiency. Searching efficiency and handling time are also parameters in other models which describe the functional response. Models which incorporate functional responses in order to make predictions of the effects of food shortage thus rely upon a clear understanding and accurate quantification of searching efficiency and handling time. 2. Blackbird Turdus merula exhibit a type II functional response and use pause-travel foraging, a foraging technique in which animals search for prey while stationary and then move to capture prey. Pause-travel foraging allows accurate direct measurement of feeding rate and both searching efficiency and handling time. We use Blackbirds as a model species to: (i) compare observed measures of both searching efficiency and handling time with those estimated by statistically fitting the disc equation to the observed functional response; and (ii) investigate alternative measures of searching efficiency derived by the established method where search area is assumed to be circular and a new method that we propose where it is not. 3. We find that the disc equation can adequately explain the functional response of blackbirds feeding on artificial prey. However, this depends critically upon how searching efficiency is measured. Two variations on the previous method of measuring search area (a component of searching efficiency) overestimated searching efficiency, and hence predicted feeding rates higher than those observed. Two variations of our alternative approach produced lower estimates of searching efficiency, closer to that estimated by fitting the disc equation, and hence more accurately predicted feeding rate. Our study shows the limitations of the previous method of measuring searching efficiency, and describes a new method for measuring searching efficiency more accurately.

'Thou glorious kingdome, thou chiefe of empires': Persia in seventeenth-century travel literature

Bringing together a range of little-considered materials, this article assesses the portrayal of Persia in seventeenth-century travel literature and drama. In particular it argues that such texts use their awareness of Islamic sectarian division to portray Persia as a good potential trading partner in preference to the Ottoman Empire. A close reading of John Day, William Rowley and George Wilkins’ The Travailes of the Three English Brothers (1607) demonstrates how the play develops a fantasy model of how relations between Persia and England might function. The potential unity between England and Persia, imagined in terms of both religion and trade, demonstrates how Persia figured as a model ‘other England’ in early modern literature.

‘These changes and accessions of knowledge’: translation, scientific travel writing and modernity - Alexander von Humboldt's Personal Narrative

A second English translation of Alexander von Humboldt's account of travel to South America, the Relation historique (1814–25), was published between 1852 and 1853. Appearing some 30 years after the first seven-volume translation (1814–29) by Helen Maria Williams, this second rendering of the Personal Narrative by Thomasina Ross was an abridged version that aimed to make Humboldt's travelogue more relevant to the mid-century reader. This translation has largely been overlooked by Humboldt scholars, despite it being a far more affordable, accessible and popular edition. I discuss here how Ross's revisions can be understood within a larger process of rereading and revision that responded to critics’ assessments of the first translation. Emphasising the status of the Personal Narrative as a text in flux, I assess how Ross modernised it to meet the demands of a new readership, recasting the image that Humboldt had constructed of himself as a travelling scientist, scientific writer and member of the international scientific community.

'Thou glorious kingdome, thou chiefe of empires': Persia in seventeenth-century travel literature

This article discusses a series of texts by or about travellers to Safavid Persia in the early seventeenth century, and in particular the literature surrounding the Sherley brothers. It looks at the ways in which, in order to encourage support for the voyages they described, English travel writers emphasised the potential for closer Anglo-Persian relations. In doing so, such narratives took advantage of a developing awareness of sectarian division within Islam in order to differentiate Persia from the Ottoman Empire. The article then examines how The Travailes of the Three English Brothers (1607) by Day, Rowley and Wilkins, built on the possibilities suggested by the travel writings, and specifically their recognition of Islamic sectarian division, to develop an idealised model of how relations between Persia and England might function. More broadly, these texts demonstrate travellers’ interest in looking for potential correlation between Christian and Muslim identities during this period.

Effect of hypobaric hypoxia, simulating conditions during long-haul air travel, on coagulation, fibrinolysis, platelet function, and endothelial activation

CONTEXT: The link between long-haul air travel and venous thromboembolism is the subject of continuing debate. It remains unclear whether the reduced cabin pressure and oxygen tension in the airplane cabin create an increased risk compared with seated immobility at ground level. OBJECTIVE: To determine whether hypobaric hypoxia, which may be encountered during air travel, activates hemostasis. DESIGN, SETTING, AND PARTICIPANTS: A single-blind, crossover study, performed in a hypobaric chamber, to assess the effect of an 8-hour seated exposure to hypobaric hypoxia on hemostasis in 73 healthy volunteers, which was conducted in the United Kingdom from September 2003 to November 2005. Participants were screened for factor V Leiden G1691A and prothrombin G20210A mutation and were excluded if they tested positive. Blood was drawn before and after exposure to assess activation of hemostasis. INTERVENTIONS: Individuals were exposed alternately (> or =1 week apart) to hypobaric hypoxia, similar to the conditions of reduced cabin pressure during commercial air travel (equivalent to atmospheric pressure at an altitude of 2438 m), and normobaric normoxia (control condition; equivalent to atmospheric conditions at ground level, circa 70 m above sea level). MAIN OUTCOME MEASURES: Comparative changes in markers of coagulation activation, fibrinolysis, platelet activation, and endothelial cell activation. RESULTS: Changes were observed in some hemostatic markers during the normobaric exposure, attributed to prolonged sitting and circadian variation. However, there were no significant differences between the changes in the hypobaric and the normobaric exposures. For example, the median difference in change between the hypobaric and normobaric exposure was 0 ng/mL for thrombin-antithrombin complex (95% CI, -0.30 to 0.30 ng/mL); -0.02 [corrected] nmol/L for prothrombin fragment 1 + 2 (95% CI, -0.03 to 0.01 nmol/L); 1.38 ng/mL for D-dimer (95% CI, -3.63 to 9.72 ng/mL); and -2.00% for endogenous thrombin potential (95% CI, -4.00% to 1.00%). CONCLUSION: Our findings do not support the hypothesis that hypobaric hypoxia, of the degree that might be encountered during long-haul air travel, is associated with prothrombotic alterations in the hemostatic system in healthy individuals at low risk of venous thromboembolism.