Oct 27 2009

Oct 27 2009 - Movements & Migrations 27 October 2009 -...

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27 October 2009 - Hastings Readings 1) Levinton: Chapter 6, pp. 137-141; Chapter 8, pp 212-219 2) Wilcockson & Zhang. Circatidal clocks. Current Biology 18: R753- 755. 3) versus social facilitation models for green turtle migration. Science 248:724-726. 4) Shaffer, S. et al., 2006. Migratory shearwaters integrate oceanic resources across the Pacific Ocean in an endless summer. Proc. National Acad. Sci. 103(34):12799-12802. 5) Gross, Coleman and McDowall. 1988. Aquatic productivity and the evolution of diadromous fish migration. Science 239:1291-1293. Dispersal = one way movement, often by a “dispersal stage” such as a larva Migration = directed movement between areas; often two- way movement Basis of Migration is often related to food, reproduction or both Small scale movements maintain optimal feeding position Common in intertidal organisms - tidal clock Figure 1. Spring and neap tides. (A) The gravitational pull of the moon and sun, together with the rotation of the earth and moon and sun, pull water masses into bulges on each side of the earth nearest and furthest from the moon. This movement of the earth’s water masses (shaded blue around the earth) produces the tides which, on most coasts occur twice per solar day. Each tidal cycle takes 12.4 hours to complete. When the earth, moon and sun are aligned, at new and full moons, their combined gravitational forces create greater tidal range: these are known as spring tides. When the moon is at right angles relative to the sun and earth, at the first and third quarters of the moon, gravitational pull is at its weakest and the tidal range is small, the so-called neap tides. (B) The relative amplitude of spring and neap tides. During the course of the lunar month the alternation between spring and neap tides occurs twice at ~15 day intervals. Because of the inclination of the earth relative to the moon, the tidal range is unequal between successive high tides. The expanded view (blue panels) shows the spring tidal amplitude is maximal at night time (dark blue panels) high water. These cartoons demonstrate a rather simple scenario. In reality of course the situation is more complex and there may be considerable local differences in tidal regimes. Biology 18: R753-755.
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Figure 2. Tidal clocks. The intertidal isopod Eurydice pulchra shows rhythmic swimming activity that coincides with high tide. When removed from the wild into the laboratory the swimming activity persists for several days and matches the time of expected high water on the beach from where the animals were collected. The actograph (top right) shows the activity recorded from a single animal held in constant dark after being taken from a beach in North Wales. The histogram (bottom right) illustrates the mean behaviour of ten individuals taken from the same beach over five complete tidal cycles. Black arrows indicate the
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Oct 27 2009 - Movements & Migrations 27 October 2009 -...

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