Monday, July 2, 2007

Intro' Ecology - Light

Introductory remarks on Ecology and Light
By G. Mathew Srirangam

origin of word: oikos = the family household logy = the study of
interesting parallel to economy = management of the household many principles in common – resources allocation, cost benefit ratios
definitions: Haeckel (German zoologist) 1870: “By ecology we mean the body of knowledge concerning the economy of Nature - the investigation of the total relations of the animal to its inorganic and organic environment.”
Burdon-Sanderson (1890s): Elevated Ecology to one of the three natural divisions of Biology: Physiology - Morphology – Ecology
Andrewartha (1961): “The scientific study of the distribution and abundance of organisms.”
Odum (1963): “The structure and function of Nature.”
Definition we will use (Krebs 1972):
“Ecology is the scientific study of the processes regulating the distribution andabundance of organisms and the interactions among them, and the study of how theseorganisms in turn mediate the transport and transformation of energy and matter in the biosphere (i.e., the study of the design of ecosystem structure and function).”
The goal of ecology is to understand the principles of operation of natural systems and to predict their responses to change.
Solar radiation is the primary determinant of global climate. The amount of energy reaching the outer atmosphere from the sun is known as the solar constant: 2.0 cal/cm2/minute. Most, but not all, of solar radiation is visible light.
Of this light:
21% is reflected by clouds
5% reflected by dust, aerosols, and soot.
6% reflected by earth
32% total reflected (due to albedo)
18% of radiation is absorbed by dust, water vapor, clouds, carbon dioxide, and soot.
Total radiation removed by atmosphere: 50%. However, different wavelengths are removed differently. Nearly all ultraviolet light is removed.
albedo: Reflection of solar radiation by the earth. Snow and ice have high albedos, forests have low albedos.
Solar radiation is lower at poles than at equator because of the curvature of the earth.


Introduction. Light from the sun supports photosynthesis, permits vision, and heats the earth.
Solar constant = 1.94 cal/cm2 striking upper atmosphere perpendicular to sun at mean distance from sun Fate of 100 units striking atmosphere
Reflected Absorbed
Atmosphere 25 25
Earth 5 *45

*29% = thermals & evaporation, 16% = long wave IR)
88% of IR light is reflected back to earth (12% passes through IR windows)
Low intensity. Low intensity of light reduces photosynthesis. Some animals are adapted to darkness.
Winter: angle of sun greater, more air absorption, shorter day length
In shade: ferns, mosses survive in low light
Under water
Absorption in water is logarithmic for a given wave length
Affected by water color, suspended materials, plankton
Photosynthesis down to 5-50 m in fresh water, 100 m in ocean
Compensation intensity is about 1% of surface intensity for terrestrial and aquatic plants
At night
Carnivores and ungulates have a reflector behind their retina that sends light back through it.
Insects, owls, see in low light
Pit viper snakes, boas detect infra red

High intensity. Plants must adapt to high amounts of light that can destroy their enzymes. When sun directly overhead, and toward equator
Photosynthesis decreases
Photo-oxidation of enzymes, increased respiration
Photosynthesis maximal at 10-20% of full sunlight for leaf perpendicular to sun
5% efficient at high light, 20% at low light
Move to low intensity areas (phytoflagellates)
Turn angle of leaves from sun
Sun vs. shade leaves

Wave length. Visible light is only a small portion of the electromagnetic spectrum that ranges from short wave length gamma radiation to long wave length radio waves.
Electromagnetic spectrum
Gamma: danger in space travel, bombs, radioisotopes, reactors
X-ray: danger from x-ray machines
Ultra violet: kills surface cells (germicidal lamps)
Visible: photosynthesis, vision
Infra red: heat, laser = burns
Microwave: radar, microwave ovens cellular phones TV
Radio: no known effects
Long wave (submarines)
Ecological considerations
Photosynthesis: chlorophyll mainly uses blue and red
Color vision in some arthropods, fishes, birds, mammals
Insects see UV to orange
Absorption by water
IR, UV, red, orange absorbed first
Yellow = intermediate
Blue, green, violet = penetrate deepest (red algae use these wavelengths)

Duration. Animals use variation in day length or phase of the moon coordinate their periodicity.
Daily variation: diurnal, crepuscular, nocturnal
Monthly: moon light used to coordinate reproductive periods
Seasonal: day length varies with seasons, used in timing of migration, reproductive cycles, etc.

1 comment:

gowtham said...

sir I have a doubt regarding effect of light on pigmentatioin of animals........... i.e,

we know that generally africans have dark pigmentation, at the same time animals like bat,which live in dark regions(caves) also have dark pigmentation..

my question is .........
In caves there will be no light, but the bats have dark pigmentation, where as in the africa there will be more light when compared to that of light in the caves and people are having dark pigmentation. Why there is no major difference in the pigmentation among the above two cases even though there is a difference in light intensity/penetration?