SAN DIEGO MESA COLLEGE
SCHOOL OF NATURAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
Chapter 36: Ecology: The Earth’ Ecosystems
- Part II -
11.. A
Aqquuaattiicc E
Eccoossyysstteem
mss

aquatic ecosystems comprises the Earth’s oceans, lakes, rivers and streams

oceans cover about 75% of our planets surface and contain about 97% of the Earth’s
water reservoirs

the oceans have an enormous impact on the Earth’s biosphere
A. equatorial evaporation of ocean waters creates Earth’s cloud formations and
rainfalls in the more temperature-moderate regions on our planet
B. the temperature profiles of the Earth’s oceans have a major effect on the global
climate and control the globe-spanning wind-patterns
C. the photosynthesis rate of the marine algal populations, including the diatoms
supply great portions of the biosphere’s oxygen and serve as important socalled “carbon sinks”

examples of typical aquatic ecosystems are:
A
A.. FFrreesshhw
waatteerr eeccoossyysstteem
mss
 includes the lakes, ponds, rivers & streams
 rivers and streams support quite different communities than
lakes or ponds
 they are characterized by low salinity because of scarcely dissolved minerals
and ions
 the larger lakes and rivers also have photic and aphotic zones
B
B.. M
Maarriinnee eeccoossyysstteem
mss
 the latter comprises of many so-called oceanic zones,
such as:
1. Estuaries
 areas where freshwater merges with sea water
 very productive environments with rich flora and fauna
2. Intertidal zones
 a type of wetland characterized by recurrent flooding and
drying out of its areas
3. Pelagic zones
 defines the ocean water itself which supports many
communities of motile animals
 it’s also the space of the photosynthesis active
1
SAN DIEGO MESA COLLEGE
SCHOOL OF NATURAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.
phytoplankton, including the marine algae, cyanobacteria
and the zooplankton, e.g. the Krill
4. Benthic zones
 defines the ocean floors including its unique flora and fauna
 depending on the depth and light penetration, the benthic
community consists of attached algae, fungi, bacteria,
sponges, burrowing worms, sea anemones, clams, crabs
and fish
5. Photic zone
 comprises the benthic and pelagic oceanic zones, which
receive ample light to enable photosynthetic processes and
the development of complex food chains
6. Aphotic zone
 the vast, dark regions (= “abyssal regions”) of the oceans,
which are not reached by the solar light anymore
 it is the most extensive but least explored part of the Earth’s
biosphere
 in the recent years scientists discovered surprisingly diverse
and “alien” life forms in this region, especially so-called
hydrothermal vent communities thriving around submersed
volcanoes (= black smokers”)
2. Terrestrial Ecosystems (= Biomes)

the Earth houses nine major types of terrestrial ecosystems, or also called
biomes, which cover the land surface

the distribution of the biomes largely depends on climate factors, and strictly
follow the global temperature lines and rainfall indices

each biome is characterized by a type of perfectly adapted biological community,
comprising a different assembly of species in different biomes

widely separated biomes may look alike and house independently evolved species
with similar traits; this phenomenon is called convergence

today many biomes are broken up and disturbed by human land development,
industrial and agricultural activities
2
SAN DIEGO MESA COLLEGE
SCHOOL OF NATURAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.

A closer look at the nine major biomes on planet Earth (listed beginning with the
most northern biomes)
1. Polar ice caps and high mountain ice
2. Tundra (arctic and alpine)
 stretches at the northernmost limit of plant growth below areas of permanent
ice and snow = arctic regions
3. Coniferous forests
 areas include Northeastern US, Russian taiga, Scandinavia, and vast parts of
New Zealand
4. Temperate deciduous forest
 grow in latitudes between 35o – 50o
 areas include Eastern North America, Central Europe, Eastern Asia and
Australia
5. Temperate grass land
 found in regions which climate is characterized by relatively cold winter
temperatures and seasonal droughts;


important regions on Earth are:
e.g.
Pampas

Argentina
Prairie

North America
Steppes

Asia, Mongolia
intensively farmed and belong to the most productive agricultural regions on
our planet
6. Chaparral
 characterized by dense, spiny scrubs with touch, evergreen leaves, e.g.
Jojoba bush, Brittle bush, etc.
 Important chaparral regions on Earth are:
e.g.
Mediterranean region (S. Italy, S. Spain)
Coastal areas of Chile
SW Africa
SW Australia
Southern California
7. Desert
 biomes which climate is characterized by low rainfalls (< 30cm/year) and
usually high daytime temperatures; evaporation greatly exceeds precipitation
 important desert regions on Earth are:
e.g.
Kalahari desert

Africa
Gobi desert

Central Asia
Sahara desert

N. Africa
Arabian desert

E. Africa
Sonora, Anza Borrego desert

NW America
3
SAN DIEGO MESA COLLEGE
SCHOOL OF NATURAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.

today, deserts are growing in size due to conversion of other biomes and
anthropogenic deforestation
8. Savanna
 biome dominated by grass and scattered trees
9. Tropical rainforest
 are the most complex of all biomes characterized by an enormously rich
diversity of biological organisms (= biodiversity)
 e.g. up to 300 different species can be found in a single hectar
 experiences the highest rate of species extinction
3. The Biosphere

the biosphere is the total of all ecosystems existing on planet Earth … it is the
global ecosystem!
 it is the thin portion of Earth that harbors all life forms and supports
the life functions

The biosphere is comprised of only a very thin, life-supporting layer which
surrounds the Earth; this layer consists of the following parts and regions
1. Atmosphere
 The air-filled layer which reaches from sea level to an altitude of about 6-7 km
2. Land
 The crystallized, solid magma layer (which reaches down to approx. 1500 m
depth), including the water-bearing rocks, its erosion forms and the very thin
top layer called soil
 the lakes, rivers and streams
 the caves
3. Oceans
 The salt water-containing layer which reaches down to a maximum depth of
about 11 km (Marianna fault)
4. Cryosphere
 The regions of permanent ice and snow, including the polar caps, central
Green land, high mountain glaciers

The biosphere is a closed, self-contained and life-sustaining system, which has
only two major interactions with the surrounding space
1. its primary food producers, i.e. the photosynthesizing organisms, ultimately
depend on the incoming electromagnetic energy, most of all the visible light, from
the sun
2. it transmits heat energy back into space during the night periods
4
SAN DIEGO MESA COLLEGE
SCHOOL OF NATURAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.

one of the hallmark features of the Biosphere is its patchiness or fractalization
into different habitats, e.g. forests, lakes, rivers, meadows, etc.

the life in the biosphere is dependent on and influenced by many physical and
chemical, so-called abiotic factors
 the most important abiotic factors are:
1. Solar energy
 powers nearly all surface terrestrial and shallow
water ecosystems
 is the limiting factor for many aquatic ecosystems
2. Water
 limiting factor for all terrestrial life forms and
crucial parameter in terrestrial ecosystems
3. Temperature
 most biological organisms can only maintain a
productive metabolism at temperatures higher than
0oC and lower than 40oC
 temperatures higher than 50oC destroy the
enzymes, which catalyze the biochemical reactions
within the organisms bodies
4. Wind
 nutrients of many organisms are spread and
delivered by wind
 the successful reproduction of many plants is strictly
dependent on wind pollination
 local wind damage by strong winds, e.g. taifuns or
hurricanes, create openings in forests that enable
succession and increase in patchiness
5. Soil Structure/Composition
 various stages of decomposition of organic matter,
pH, nutrient content, mineralization, all contribute to
soil structure and composition
6. Wildfires, e.g. caused by lightning
 the germination of certain plant species is triggered
by the heat of wild fires
 the survival of certain plant species, e.g. sequoias, is
dependent on recurrent wildfires which eliminate
competing plants
5
SAN DIEGO MESA COLLEGE
SCHOOL OF NATURAL SCIENCES
General Biology Lecture (BIOL107); Instructor: Elmar Schmid, Ph.D.

on the other hand, the inter-dependently and highly dynamically interacting life forms
in the biosphere can influence many important factors of the biosphere, such as
gas composition, water quality, erosion and sedimentation rates, etc.

due to the enormous and steadily increasing impact of a rapidly growing human
population on the biosphere, a thorough study and understanding of the biosphere’s
structure, dynamics and inter-dependencies is of crucial importance to ultimately
avoid future environmental dilemmas caused by human activities

today the diversity of our biosphere is touched and threatened by the many
human activities and modern technology, e.g. urbanization, creation of vast
agricultural mono-cultures, deforestation, mining, oil drilling

evaluating the impact of human activity and technology on our Biosphere
mandates a detailed knowledge and scientific study of its structures and dynamics
6