Go with the Flow Would Probably Have Arrived at a Similar Itamar Procaccia Conclusion As to Them
Total Page：16
File Type：pdf, Size：1020Kb
news and views ification of existing terms. Finally, Bjørnstad out of whack: the three-species system et al. apply a statistical method to their raw exhibits transient cycles of longer periods, data, and confirm the findings based on the and eventually becomes extinct. If the time-series method and the population imprints of one or both enemies on these model. cycles could be found, we would be a step We do not yet know how useful Bjørnstad closer to knowing whether Bjørnstad et al.’s et al.’s methods will be in identifying the techniques can be applied to biodiversity important variables in other systems, and conservation research, where one might 100 YEARS AGO including natural ones. Theory predicts6 want to know how a species that is harmless A simple workable, absolutely trustworthy how the dynamics of a population will be in one context can lead to the collapse of part system is still urgently wanted for the affected by the strength of coupling between of a community in another. These tech- detection of criminals, and if the authoress two species. But it is not yet clear whether niques could also be used to show how the of this book has succeeded she certainly coupling to more and more variables inex- use of two natural enemies as biological pest deserves the thanks of all the Governments orably increases the number of lags. controls yields outcomes that are qualita- of Europe… It so happened that about However, on the empirical front, thou- tively different to the outcomes of using seven years ago the reviewer came to the sands of sets of population data exist7. either enemy alone9. I conclusion that the external ear ought to Although it would take a herculean effort to Michael E. Hochberg is at the Institut des Sciences yield some clue to the relationship of man analyse them all, breakthroughs may be in de l’Evolution, Université de Montpellier II, 34095 and ape, and of one race of man to the offing. The same group previously Montpellier, France. another… To test the “criminal-mark” showed8 that by increasing the depth of P. e-mail: [email protected] theory of Lombroso and many others, he interpunctella’s artificial diet, the wasps’ Arthur E. Weis is in the Department of Ecology and examined the ears of more than 800 attack rate could be diminished, resulting in Evolutionary Biology, University of California, confirmed criminals, and of more than two a weaker effect on the moth’s population Irvine, California 92697, USA. thousand inmates of asylums for the insane, dynamics. Combining this system with the e-mail: [email protected] situated in parts of the country where he new analysis techniques will provide an 1. Bjørnstad, O. N., Sait, S. M., Stenseth, N. C., Thompson, D. J. & had already examined the ears of the sane. opportunity to test whether varying a habitat Begon, M. Nature 409, 1001–1006 (2001). Altogether the ears of more than 40,000 2. Woiwood, I. P. & Hanski, I. J. Anim. Ecol. 61, 619–629 people of different races and of different parameter affects the strength of coupling (1992). of the system. The prediction here is that 3. Strong, D. R. Trends Ecol. Evol. 1, 39–42 (1986). moralities, besides those of about 300 apes coupling between moth and wasp popu- 4. Turchin, P. et al. Nature 405, 562–565 (2000). and anthropoids, were examined, but the lation dynamics should decrease as diet 5. Begon, M., Sait, S. M. & Thompson, D. J. Nature 381, 311–315 total results of this elaborate investigation (1996). depth increases. 6. Tanner, J. T. Ecology 56, 855–867 (1975). were almost entirely of a negative nature… There are also broader implications. The 7. NERC Centre for Population Biology, Imperial College. The If the reviewer’s methods and observations group previously found5 that when both Global Population Dynamics Database (1999). are correct, the confirmed criminal’s ear is virus and wasp confront the moth together, http://cpbnts1.bio.ic.ac.uk/gpdd/ the ear of the average inhabitant of Great 8. Begon, M., Sait, S. M. & Thompson, D. J. Proc. R. Soc. Lond. B the simple generation cycles found in the 260, 131–137 (1995). Britain. Nor did the ears of the insane differ, one- and two-species systems are thrown 9. Murdoch, W. W. & Briggs, C. J. Ecology 77, 2001–2003 (1996). on an average, from those of the people from which they were drawn, and if the authoress had carried her observations Turbulence over a number of men of genius or of high ability, instead of drawing elaborate deductions from single observations, she Go with the flow would probably have arrived at a similar Itamar Procaccia conclusion as to them. From Nature 21 February 1901. Traditional devices for measuring turbulence have been unable to keep up with the latest developments in theory. But detectors derived from high- 50 YEARS AGO energy physics may narrow the gap between experiment and theory. Miss Dorothea M. A. Bate, who died after a brief illness on January 13 at the age of urbulence is the chaotic and unpredict- bringing experimental turbulence research seventy-two, was for more than fifty years able motion of fluids flowing at high back on par with theory. one of the outstanding personalities at the Trates. It plays a major role in many In their experiment, Bodenschatz and co- British Museum (Natural History). When only processes from the environmental, for exam- workers1 modified a detector from Cornell’s seventeen, and with neither qualification nor ple cloud formation, to the technological, electron–positron collider. They used ‘silicon encouragement, she started work in the Bird such as in industrial chemical reactors. strip’ detectors to optically image tracer Room as a voluntary worker; but her Clearly, a deeper understanding of this particles (tiny transparent beads) in turbu- interests lay chiefly in palaeontology in phenomenon would be beneficial, and in lent water flow. Compared with previously relation to the Recent fauna, rather than in recent years much progress has been made in available techniques, this method offers un- the Recent fauna itself… During 1901–1902 the fundamental theory underlying turbu- precedented time resolution of up to 70,000 Miss Bate explored the caves of Cyprus and lence. But the ability to measure turbulence frames per second. As a result, the researchers made some notable discoveries, such as the experimentally has not advanced at the same were able to measure the acceleration of the remains of pigmy elephants, and soon rate, making it difficult to verify the theoreti- particles in turbulent water, discovering that extended her interest to cave deposits in cal developments. it can reach 1,500 times the acceleration of Crete, the Balearic—where she discovered On page 1017 of this issue, Eberhard gravity. The high time-resolution of the the unique ‘antelope’ Myotragus—Malta and Bodenschatz and collaborators1 report an measurements indicates that the acceleration Sardinia, working meticulously and important technical improvement to the is highly intermittent, reflecting the complex earnestly and always alone. way in which turbulence is measured. This structure of turbulent flow. From Nature 24 February 1951. advance may make a decisive contribution to At present, the standard probe for turbu- NATURE | VOL 409 | 22 FEBRUARY 2001 | www.nature.com © 2001 Macmillan Magazines Ltd 993 news and views lence research is the hot-wire anemometer. Figure 1 The lagrangian evolution of a group of This consists of a thin wire that is heated by three tracer particles. At any moment in time the the passage of an electrical current and is trio defines a triangle that is fully determined by kept at a constant temperature by means of a scale R, the Euler angles of its orientation in a feedback loop. The wire is placed at right space, and two internal angles. Theory focuses angles to the average flow of a turbulent fluid. on ‘statistically preserved structures’ which are The fluid cools the wire and, because the determined by the distribution on internal cooling effect depends on the fluid’s velocity angles and the scale. These structures dominate — the faster the fluid flows, the more the wire the statistical theory. is cooled — the velocity can be measured as a function of time. As would be expected for turbulent fluids, an erratic time series is obtained. θ Hot-wire technology has progressed in recent years: for example, superconducting ϕ elements have been used to measure the velocities of cryogenic helium turbulence2. But this technology gives only limited infor- mation on the structure of turbulence. Hot- chaotic flow of the fluid demonstrates the the fluid. For theoretical calculations, the wire anemometry is fundamentally limited: presence of high amounts of energy. But mean velocity of the fluid is subtracted from it can provide data only for a fixed point — instability results in energy loss, which cas- the turbulent flow by a ‘galilean’ transform- in other words, for the point at which the cades nonlinearly down to smaller scales. ation. Theorists focus on the lagrangian wire is positioned. But theorists dream about This cascade continues down to the smallest trajectories in the moving frame of the fluid, measuring scale-dependent information scale where molecular friction comes in and and are interested in measuring the physical from points that move with the flow — the energy is dissipated by viscosity. The most phenomena in this lagrangian picture. The so-called ‘lagrangian’ trajectories (Fig. 1). interesting regime to study covers the inter- technique devised by Bodenschatz and co- Turbulent flow is irregular and dis- mediate scales, where the presence of a con- workers brings us closer to this dream.