Adaptive Mechanisms in the Ecology of Vision

pp 583-628

The behavior of animals around twilight with emphasis on coral reef communities

  • W. McFarlandAffiliated withFriday Harbor Marine Laboratory, University of Washington
  • , C. WahlAffiliated withDepartment of Anatomy, Veterinary College, Cornell University
  • , T. SuchanekAffiliated withDivision of Environmental Studies, University of California
  • , F. McAlaryAffiliated withFriday Harbor Marine Laboratory, University of Washington

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Light, which represents a limited range of the electromagnetic spectrum, is characterized by three primary qualities — spectral frequency, intensity and polarization. Natural ambient light that organisms respond to emanates primarily from astronomical light sources and to a lesser extent from bioluminescence. For both sources, be it due to the earth’s daily rotation and the moon’s monthly procession about earth, or the flashing of fireflies on land or fishes in the deep sea, light is presented to animals with a distinct temporal component. From midday through night-time light intensities on earth’s surface can vary 8 to 9 orders of magnitude, with the most rapid changes of 5 to 6 decades of intensity occurring during twilight (Figure 1) Animals exhibiting visual behaviors over this dynamic range are few, and those that do usually possess duplex visual mechanisms, one sensitive to the ‘bright’ light of day (photopic), and the other sensitive to the ‘dim’ light of night (scotopic).