lecture note 22 for BGYB50

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Biological Sciences
Herbert Kronzucker

LECTURE 22: - Predation can be seen as an extreme form of competition, and the distinction between competition and predation is often blurry - Predation drives the flow of energy in ecosystems, and as such has far-reaching effects in ecology and evolution -The interactions between predators and their prey are among the most fascinating in all of biology, with a bewildering array of adaptations in both: the interaction is so intimate and intense that the evolutionary refinement of predators and their prey is often tightly linked in coevolution (the complementary evolution of closely associated species: an evolutionary advance in the predator triggers an adaptive response in the prey; the prey tends to be a step ahead: this is seen as a consequence of the Life Dinner Principle, recognizing that only dinner is at stake for the predator, but life is at stake for the prey!) - Predator adaptations for prey detection and recognition are manifold and include the utilization and refinement of: - sight (e.g. eagles with two fovea centralis focal points in the eyeball; night vision in viper snakes includes the perception by special head sensors of infrared radiation emitted as body heat by potential prey; sharks can see electrically, using the organ known as the Ampullae of Lorenzini), - sound (e.g. echolocation in bats: emission of high-frequency ultrasonic soundwaves to locate insect prey as small as 0.1 mm; directional changes within less than 1 degree of arc and frequency differences between ears of as little as 0.0001 kHz can be distinguished by some bats; the middle ear has a special muscle which temporarily disengages the sound transmission bones some 6 ms prior to sound emission; this avoids self-destruction of the auditory system), - smell (e.g. the vomeronasal organ of snakes allows them to detect individual molecules sampled by the tongue, which is then placed into olfactorily sensitive pits in the roof of the mouth; many dogs can detect odors in concentrations of a few parts per billion drug sniffing, detection of minute www.notesolution.comquantities of volatile chemicals, as are emitted prior to the onset of epileptic seizures in humans; ticks smell butyric acid in the sweat of homeotherms), - touch (e.g. web-building spiders detect vibrations through their legs; to determine the location of an insect caught in the web, the spider sequentially plucks the individual strands of the web, and vibration dampening gives away the location of the prey), - locomotion, i.e. the ability to outrun, outfly, outswim, outcrawl - Crypsis, in combination with chemical or mechanical means of warfare, is used effectively by many predators as well as by prey. Some examples discussed in class include: - stonefish: the most venomous fish on earth; looks like an encrusted rock as it waits for small fish or shrimp to swim by (prey are sucked into its mouth in less than 0.015 s!); spines on its back can release jets of poison from bulging, and rechargeable, venom glands: result: excrutiating pain and paralysis - box jellyfish (The Box of Death): Chironex fleckeri, kills more people than sharks, crocodiles and stonefish combined; due to its perfect translucency it is virtually invisible in open water; up to 60 tentacles, reaching 5 m in length and armed with 5 billion stinging
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