Ecology
Ecology is the investigation of the
interactions between living things and their environment.
Ecologists
must use mathematical models and computer simulations because these
approaches allow them to study the interactions of variables and
simulate large-scale experiments.
The environment, that region of the earth where
life can secure a foothold, is called the
biosphere.
The tenacity of living things and their ability to
colonize even the harshest of environments has surprised the
scientific community.
The physical characteristics of the biosphere
The physical characteristics (abiotic
factors) of the biosphere necessary for
life include:
- Presence of water in its liquid state. (see
previous lecture
about water) About 70% of the earth is
covered with water. The largest biome is marine, the salty
environment of the oceans where life first arose and
diversified.
- A gaseous atmosphere.
Living things do not need to be in physical contact with the
atmosphere proper. Nevertheless the atmosphere is essential for
the existence of life because it filters out harmful radiation and
helps maintain a moderate climate. Gases in the atmosphere also
supply the necessary ingredients for many of life's metabolic
processes. (Oxygen for respiration, Carbon dioxide and water vapor
for photosynthesis, and nitrogen for amino acids and
nucleotides.)
Today's atmosphere contains 79%
nitrogen, 20% oxygen. The remaining 1% contains argon, carbon
dioxide, and a variety of other gases. The early atmosphere of the
earth had little or no oxygen.
- A spinning earth on a tilted axis. The earth's
tilt of 23° gives us the 4
seasons. While the southern hemisphere
is experiencing the direct summer rays of sunlight, the northern
climes receive only a glancing stream of light and shorter days.
180 degrees of rotation later (183 days), when the earth is on the
other side of the sun, each hemisphere experiences the opposite
season.
- Light
from the sun provides most of the energy for
life. (Some energy comes from
radioactive decay deep inside the earth.) Although only 1% of
sunlight reaching the surface of the earth is captured in
photosynthesis it accounts for well over 99% of energy using by
living things.
Light is also essential to the
hydrologic cycle, the continuous movement of water from the liquid
state in bodies of fresh and salt water to the clouds and vapors
found in the atmosphere.
Links to Other Lectures
Want
to go on a Web Quest in search of Biomes?
Modified July 10, 2005
