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Ecosystems
Abdulhafez Selim, MD, PhD
Ecosystem
Organisms
+
Physical
environment
=
Ecosystem
Earth
The organisms living in a particular area, together with the physical environment
with which they interact, constitute an ecosystem.
At a global scale, Earth is a single ecosystem.
Climate on Earth, Solar Radiation
Biological processes on Earth are driven primarily by solar radiation.
Climate on Earth; Solar Radiation
Climates on Earth; Global Air
Circulation
At equator, warm
raising air produces a
belt of
low pressure and
winds.
More energy received at
equator than at poles
 Rising air expands and cools, releasing moisture.
 Descending air warms and dries and takes up moisture,
Creating rain shadows.
 Global air circulation is driven by solar radiation and the spinning of
Earth on its axis
Climates on Earth; Global Air
Circulation
Air circulation around the
globe would be simple (and
the weather boring) if the
Earth did not rotate and the
rotation was not tilted
relative to the Sun.
Please click to enlarge!
Climates on Earth; Global Air
Circulation
Climate on Earth, Ocean currents
Poleward-moving currents are warm, and equatorward-moving currents are cold.
Surface ocean currents are driven by global winds and play an important role in
redistributing heat around the globe.
Climate on Earth, Ocean currents
Description: Map showing the seven major ocean currents
Energy Follow
Photosynthesis
Photosynthesis is a process in which
green plants use energy from the sun to
transform water, carbon dioxide, and
minerals into oxygen and organic
compounds. It is one example of how
people and plants are dependent
on each other in sustaining life
Energy flow
Before 1977, scientists believed that all forms of life ultimately depended on
the Sun for energy.
A few deep-sea and cave ecosystems are powered by chemosynthesis rather
than photosynthesis.
Chemosynthesis is the biological conversion of 1-carbon molecules
(usually carbon dioxide or methane) and nutrients into organic matter using
the oxidation of inorganic molecules (e.g. hydrogen gas, hydrogen sulfide) or
methane as a source of energy, rather than sunlight, as in photosynthesis.
Crops need many things for good growth and maximum
productivity- light, carbon dioxide, nutrients, water and a
sufficiently long period without frost. What is often forgotten is
that another requirement for growth and development of crops
is needed - heat. Each crop is very specific as to its heat
requirements. the most rapid growth and development takes place at
2 l' C (70' F). The growth rate decreases with the increase in
temperature and finally stops at 30 C (86' F).
The amount of energy flowing through an ecosystem depends
on primary production and on the efficiency of transfer of energy
from one trophic level to another
Nutrient Cycle
Material Cycle
Food Web
Who eats whom in a ecosystem can be diagrammed as a food web.
Food web
Cycles of Materials in Ecosystem, oceans
primary production.
Primary production in oceans is highest
adjacent to continents,
where nutrient-rich waters rise to the
surface
Cycles of Materials in
Ecosystem, Layers of
Atmosphere
Layers of the Atmosphere
The atmosphere is divided into five main
layers plus the ionosphere.
It extends over 430 miles (700 km) into the sky.
Layers of Atmosphere
The two lowest layers of Earth's atmosphere differ
from each other in their circulation patterns,
the amount of moisture they contain,
and the amount of ultraviolet radiation they receive.
Cycles of Material in Ecosystem,
Temperate-Zone Lake
Temperate-zone lakes turn over
twice each year as water cools and warms.
Biogeochemical Cycles
 The elements organisms need in large quantities
cycle through organisms to the environment and
back again.
Biogeochemical
Cycles
Water cycle
Carbon dioxide cycle
Nitrogen cycle
Phosphorus cycle
Water Cycle
The cycle of water-the hydrological cycle-is driven by evaporation of water;
most of it from ocean surfaces.
Carbon Cycle
Atmospheric carbon dioxide is the immediate source of carbon for
earthly organisms, but only a small part of Earth's carbon is in the atmosphere.
Carbon Cycle
Nitrogen Cycle
Although nitrogen makes up 78 percent of Earth's atmosphere, nitrogen can be
converted into biologically useful forms only by a few species of bacteria and
cyanobacteria.
The most striking example of a local effect of altered bio-geochemical cycles is
lake eutrophication.
Human Alterations of Biogeochemical Cycles, lake
eutrophication.
• Normal lakes that have minimal levels of nutrients are
said to be enriched, or oligotrophic. An oligotrophic lake
has clear water and supports small populations of
aquatic organisms. Eutrophication is the enrichment of
water by nutrients; a lake that is enriched is said to be
eutrophic. The water in a eutrophic lake is cloudy and
usually resembles pea soup because of the presence of
of vast numbers of algae and cyanobacteria that are
supported by the nutrients.
• Eutrophication can be markedly accelerated by human
activities, and it results from the enrichment of water by
inorganic plant and algal nutrients- most commonly in
sewage and fertilizer runoff.
A great lake - Lots of
birds! Hypertrophic
A great lake - Gin-clear water!
Oligotrophic
Acid rain is a term for precipitation that is polluted by acids, which have a pH below 7.0