May 2011
Environmental Science Ch # 6
ECOSYSTEMS and COMMUNITIES
Purpose :
6 – 1 Successions
Terrestrial Primary
Climax Communities
Aquatic Primary
Observing Aquatic Successions
Secondary Successions
Modern Concept of Succession and Climax.
6 – 2. Biomes determined by Climate
6 – 3. Major Types of Climax Communities
Desert
Grassland
Savanna
Tropical Dry Forest
Tropical Rain Forest
Mediterranean Shrub lands (Chaparral)
Temperate Deciduous Forest
Coniferous Forests (Boreal)
Tundra.
Temperate Rain Forest
6 – 4. Major Aquatic Ecosystems
Characteristics
Marine Ecosystems
Pelagic
Benthic – Abyssal
Coral Reef
Mangrove
Estuaries
Human Impact on Marine Ecosystems
Fresh Water Ecosystems
Characteristics
Lakes- Eutrophic /BOD/ Oligotrophic
Streams
Swamps
Marshes
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ECOSYSTEMS AND COMMUNITIEs
PURPOSE.
1. To recognize differences between primary and secondary
successions.
2. Describe the process of successions in both land and water
ecosystems.
3. Associate typical plants and animals with the various biomes
4. Recognize the physical environmental factors that determine
the kind of climax communities that will develop.
5. Differentiate the forest biomes that develop based on
temperature and precipitation.
6. Describe the kinds of ecosystems and their determining
factors.
6.1 Successions
Ecosystems are dynamic (constantly changing) units. (Successions)
Communities go thru a series of changes in structure,
recognizable and predictable. The pace and direction of change
depend on climate, seeds, disturbance frequency and organisms
introduced from outside the area.
The predictable community changes in structure over time is
called a succession. The end result is a CLIMAX community,
determined by climate and soil.
Two successions are recognized:
1. Primary starts with newly exposed surface (bare rock).Eg.
glaciated areas, newly covered volcanic places, surface
exposed by drop in sea level.
2. Secondary starts with destruction of an existing ecosystem,
leaving behind some soil, seeds and roots.
Terrestrial Primary Succession
It depends on the type of substrate (rock, sand or clay), spores,
seeds or reproductive structures, and climate. Biodiversity is
influenced by the type of plants.
Pioneer stage results from colonization by a pioneer
community such as: Lichen a mutualistic relationship between
Algae (or bacteria) and Fungus.
Intermediate stage
Soil development follows, which supports worms, bacteria, etc.
Primary Succession is the replacement of the Pioneer Community.
Later stages contribute to the organic matter dominated by
Replacement, e.g. annuals by perennial grasses, herbs, woody
shrubs, animals, and trees. Each replacement is a successional
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stage (SERAL STAGE).
A “total” succession from Pioneer to climax community is a SERE .
The successional community is not the same as a climax community.
Climax Communities
Can reproduce them selves and are in energy balance. They have a
larger number of types of organisms and a trend towards
increasing complexity and energy efficiency.
Climax Community tends to have many specialized ecological
niches, whereas, successional tend to have more generalized
niches.
Climax communities maintain their mix for a long time, while
successional is temporary.
Climax tends to recycle nutrients and maintain a constant
biomass.
Secondary succession starts with the destruction of an existing
community.
In Terrestrial Climax Communities, the biomes produced, depend on
two abiotic factors:
TEMP. (Constant or changing)
PPT. How much and when
Soil and Wind (dries out soil rapidly)
Periodic fires.
Aquatic Primary Succession
Most aquatic successions are temporary, eventually to be
replaced by terrestrial ecosystems. (Receive soil particles and
organic matter continuously from land).
Early stages : Aquatic vegetation (floating plants trap
sediments, eventually forming a wet meadow.
Later stages : Shallow lakes fill gradually. Accumulation of
organic matter along with sediments. Eventually the wet soil
dries; grass starts to grow (a bog stage)
Observing Aquatic Successions.
In the deeper portion of the lake, there are submerged plants,
algal mats and emergent vegetation. Next grasses that can
tolerate wet soil adjacent to the shore.
Secondary Succession
Occurs when an existing community is destroyed but much of the
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soil and some organisms remain. The succession advances more
rapidly. It is likely that the new climax community will resemble
the earlier one.
Modern Concept of Succession and Climax.
The type of climax community which develops, depends on many
factors other than climate, seeds and human activities.
6.2 Biomes are Determined by Climate.
Biomes are terrestrial climax communities with wide geographic
distribution
Precipitation and Temperature are abiotic factors that have major
impact on the developing climax community. Several other factors,
namely: periodic fires, wind, soil type and currently living
organisms.
The Effect of Elevation on Climate and Vegetation. As elevation
increases, temperature decreases
Climax communities are:
1. Able to maintain a mix in species
2. In energy balance
3. Many kinds of organisms with different kinds of interaction
6.3 Major Types of Climax Communities (Biomes) of the World.
1. DESERT:
Ppt.:Brief periods of infrequent rains less than 10”/y. Runoff in
gullies. Very high evaporation rates. Windy, with high evaporation
rates.
Temp.: Variations are high, vary greatly in a 24 hr. period.
Biodiversity: Many small organisms have the ability to survive with
little water. There are many species but few individuals. Plants
have small leaves and are spiney, transpire very little water.
Plants grow and blossom when moisture is available. Insects
lizards, snakes, small mammals, grazers, carnivores and birds all
avoid extreme heat.
Human Impact. There is nomadic herding. Modern technology is
changing that way of existence.
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2. TEMPERATE GRASSLAND:
Ppt.: Receives between 10 to 30” ppt/year.
Temp.: Windy summers are HOT. Winters are cold to mild.
Biodiversity: widely distributed; Grasses and other plants roots
are intertwined, which binds the soil. Few trees are located along
river valleys.
There are herds of grazing animals, insects, and birds. Herbivorous
mammals - mice and squirrels, foxes, coyotes and some reptiles are
common.
Human Impact: Steppes /prairies are converted to agriculture or
grazing lands.
3. SAVANNA: in tropical parts of Africa, S. America and
Australia
Ppt.: Tropical climate (heavy rains) with seasonal droughts. 20 to
60”/year.
Biodiversity: Grassland with occasional clumps of trees. Trees use
bacteria for Nitrogen fixation.
Grazers are kangaroos antelope, elephants, lions and llamas
inhabit. Mound building termites are common.
Human Impact : Ecotourism . There is now conflict of interest.
4. TROPICAL DRY FOREST:
Ppt.: 20 to 80”/year is seasonal in Central America, India.
Biodiversity : Many trees drop their leaves during the dry season.
Human Impact : Harvesting the forest and converting to agriculture
and Habitats.
5. TROPICAL RAIN FOREST:
Ppt.: abundant (> 80”/y).
Temp: normally warm.
Biodiversity: Many species of trees (teak, Balsa) grow rapidly.
Have an extensive root system close to the surface. Get their
nutrients from decaying matter. Vines climb to the Canopy.
Significant # of organisms depends on sound to communicate due to
lack of light. Has a high diversity of species, greater than any
other biome. Insects, birds, climbing mammals, lizards and frogs
are common residents.
Nutrients are recycled. Rain washes away nutrients, left with poor
quality soils.
Human Impact : Logging, Agriculture and Mining.
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6. MEDITERRANEAN SHRUB LANDS (Chaparral)
Temp.: Wet cool winters and hot dry summers. Located near the
oceans.
Ppt.: Rainfall is 15 to 40”/year.
Biodiversity: Vegetation is dominated by shrubby, woody plants.
Fire is common. Insects, reptiles, birds and mammals are the
primary inhabitants.
Human Impact : Agriculture conversion due to irrigation practices.
7. TEMPERATE DECIDUOUS FOREST
Temp: Mild winters.
Ppt.: Rains all year 50”/year Evenly distributed. Located in NE US,
SE Canada, S. Africa, parts of Europe and Asia.
Biodiversity: There are few dominant trees, lose leaves in winter
(maple, aspen, oak, birch, and wild spring flowers).
Foxes, rabbits, squirrels, deer, badgers and Migratory birds (few
residents, grouse, woodpeckers , turkeys) and large variety of
insects inhabit.
Human Impact : Trees cleared for farming and occasional logging.
8. CONIFEROUS FOREST (Boreal Forest)
Temp: short cool summers and long cold winters. Begins where the
Tundra ends. The area is dotted with lakes. Taiga (swamps) Soil
freezes during winter.
Biodiversity: Trees are Evergreens, spruce, fir, etc. no snow
damage. Animals (Deer, Caribou, Moose and wolves) are migratory.
Few reptiles and amphibians.
Ppt.: 10 to 40”/year. Humid climate. Typically dotted with lakes.
Human Impact : Less severe than in other biomes. Logging and
herding reindeer
9. TUNDRA: Includes alpine.
Ppt.: 10”/y. Frozen soil - Permafrost. Damage is very slow to heal.
Temp.: Cold, windy climate, less than 10” ppt/year.
Biodiversity: No trees (growth is short), reptiles nor amphibians.
Migratory ducks, few permanent residents. (Arctic hares, lemmings,
caribou, Reindeer, Musk Ox). Ptarmigan and snow owl are resident
birds. There are clouds of insects.
Human Impact : Few people live in this region.
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10. TEMPERATE RAIN FOREST
Climate : More than 50”/year ppt. (up to 120”) Cool climate slows
evaporation, leaves a damp atmosphere.
Biodiversity : Evergreens up to 800 years old (Spruce, Fir, Western
Hemlock) with mosses and ferns. Trees die and fall to the ground.
They rot. Called “Nurse trees”
Dwellers include Woodpeckers, chickadees, elk, deer, bear and
Salmoon fish.
Human Impact : Home of the endangered species Spotted Owl. Logging.
Relationship between high latitudes and elevation is evident in the
distribution of the various biomes including Alpine Tundra.
6. 4 MAJOR AQUATIC ECOSYSTEMS
Owe their characteristics to:
1. Temp.
2. Amt. and kind of ppt. and indirectly on
a) Ability of sunlight to penetrate
b) Bottom substrate
c) Water temp.
d) Dissolved salt
e) Soil type.
Marine Ecosystems
Influenced by amt. of dissolved salts and other nutrients.
There are two types of marine ecosystems:
1. Pelagic ecosystems – swimmers, not attached to the bottom.
Phytoplankton (algae) is the major food source in the euphotic
zone. (Photosynthesis)
The Zooplanktons live at lower depths, feed on the phytoplanktons
at shallow depths at night in the delta regions and areas of high
current activity. They are subsequently eaten by larger fish.
2. Benthic ecosystems - bottom dwellers, indirectly controlled by
the nature of the substrate (sand, mud or rock) and temperature.
a) Abyssal ecosystems accommodate scavengers, who depend on
drifting dead material
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b) Coral reefs require warm, clean, marine water, exist in a
mutualistic relationship with Algae. It is one of the most
productive of systems.
c) Mangrove swamps - near shore in areas of Tropical mud
flats. Trees have an extensive root system through which they
absorb CO2, and excrete salt thru leaves. (Not much wave action in
area). Located in the Caribbean, South Florida, SE Asia.
4. Estuaries - shallow, brackish water in partially enclosed
areas. A sediment and nutrient trap and fish hatchery. The
salt content changes with the tide. A pollutant trap?
Eventually becomes a salt marsh.
Human Impact on Marine Ecosystems
Overfishing has destroyed some traditional fishing grounds. A
resulting consequence is farm fishing, which have caused additional
nutrients to the water pollution and spread of diseases to wild
fish.
Fresh water Ecosystems
Differentiated from marine waters by
Salt content (Taste)
Temp. Variations
Oxygen content
Downhill flow and organisms.
Two categories, one relatively stationary:
1. Lakes - Littoral zones have abundant rooted vegetation –
submerged plants, emergent plants protrude above the water
(water lilies), algae and associated animals, fish and insects.
Euphotic zone in large lakes, where light penetrates.
Limnetic zones have NO rooted submerged plants
Productivity depends on
Temp
Sunlight penetration (water depth)
Nutrient content
Oligotrophic lakes are deep, cold, without nutrients, have a low
productivity.
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Eutrophic lakes are shallow, warm with abd. nutrients. Have a high
BOD (Biochemical Oxygen Demand)
Organisms need molecular Oxygen (from the air or photosynthesis).
Wave action or tumbling increases the oxygen content in the water.
In contrast, human impact or plant die off causes a decrease in O2
and fish kills.
2. Streams and Rivers - are not very productive, because most
nutrients come from the banks. Most algae grow on the rock bottom.
The collection of algae, fungus, etc is called the Periphyton.
Transition between aquatic and terrestrial ecosystems.
3. Swamps - are permanently flooded areas, a transition between
terrestrial and fresh water ecosystems.
4. Marshes - are dominated by grasses.
CASE STUDIES
(1) Inupiat Eskimos consider themselves part of Nature.
They have hunted the Bowhead whale for generations, use all of it
and do not lose many catches.
Today, they use modern equipment to hunt, have access to other
foods. Are limited to 3/year (30 met. tons/whale)
Should whaling be stopped because the Bowhead is an endangered
species?
(2) Salmon Fishing in Scotland: salmon is a pelagic, difficult
to harvest commercially.
Today, a net is spread across the bay and the fish is prevented
from going out to sea. Fed by the fisherman and later harvested.
Floating farms. Feed with steroids?
(3) Farming in a Tropical Forest: slash and burn cause rapid
erosion. Abandoned after a few years. Soil leached to produce a
laterite, but the use of temperate farming methods is a failure.
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