Ecosystem

Ecosystem
HO Pui-sing
Contents
What is an ecosystem
Three major principles of ecosystem
Components of an ecosystem
Abiotic components
Biotic components
Movement of energy and nutrients
Food chain
Food webs
Trophic levels, biomass and biome
Linkages and interactions in an ecosystem
Carbon cycle and oxygen cycle
Model of nutrient cycle
Environmental Limitation in ecosystem development.
What is an ecosystem
An ecosystem is a grouping of
organisms that interact with each other
and their environment in such a way as
to preserve the grouping.
There is a great variety of ecosystems
in existence, all of them are
characterized by general structural and
functional attributes.
Three major principles of ecosystem
Nutrient cycling:
Movement of chemical elements from the
environment into living organisms and from them
back into the environment through organisms live,
grow, die and decompose.
Energy flow:
Energy is required to transform inorganic nutrients
into organic tissues of an organism.
Energy is the driving force to the work of ecosystem.
Structure
It refers to the particular pattern of inter-
relationships that exists between organisms in an
ecosystem.
Nutrient cycling
Energy flow
Structure
Ecosystem:
Nutrient cycling, energy flow and structure
Components of an ecosystem
Abiotic components
They form the environment and
determine the type / structure of
ecosystem.
Sunlight (temperature)
Nutrients
Rainfall, minerals, carbon, nitrogen,..
Type of ecosystems:
Tropical rainforest, Desert, Tundra,
Grassland,..
Distribution of vegetation / ecosystem
Biotic components
Producers (Autotrophs):
All green plants. They use solar energy,
chlorophyll, inorganic nutrients and water to
produce their own food. (Photosynthesis)
Consumers:
They consume the organic compounds in plant
and animal tissues by eating.
Herbivores (plant feeders) Primary consumers
Carnivores (meat eaters) Secondary consumers
Omnivores (general feeders)
Biotic components
Decomposers
They are tiny organisms includes bacteria and
fungi, which turn organic compounds in dead
plants and animals into inorganic materials.
They cause the continual recirculation of
chemicals within ecosystem (nutrient cycle)
Biotic components and food chain
Movement of energy and
nutrients
Food chain
Food webs
Trophic level, biomass and biome
Food Chain
The particular pathway of nutrient and
energy movement depends on which
organism feeds on anther.
Decomposers
Food Webs
Trophic Levels
A trophic level means a feeding level.
First level all producers
Second level all herbivores
Third level first level carnivores
Fourth level second level carnivores
So on..
Trophic levels
Energy and Nutrients passed through the
ecosystem by food chains and webs from
lower trophic level to the higher trophic level.
However, only 5% to 20% energy and
nutrients are transferred into higher trophic
level successfully.
For this reason, first trophic level has the
largest number of organisms, and second
trophic level is less than first one; the third
level is less than second level, and so on.
Trophic levels
Biomass
Biomass means the total combined
weight of any specified group of
organisms.
The biomass of the first trophic level is
the total weight of all the producers in a
given area.
Biomass decreases at higher trophic
levels.
Biomass
Biomass and productivity
Trophic Level
(Food Pyramid)
Biome
This is a total different concept apart
from Biomass.
Biome are defined as
the worlds major communities, classified
according to the predominant vegetation
and characterized by adaptations of
organism to that particular environment.
Linkages and Interactions in an
ecosystem
Carbon and Oxygen cycle
Nitrogen cycle
A model of nutrient cycle
Carbon Cycle and Oxygen Cycle
Nitrogen Cycle
Nitrogen cycle
Nitrogen cycle can be affected by man in five
major ways:
Fertilizer production (mainly nitrates and ammonium
salts) to grow more food by increasing yields, and
replenishing lost nitrogen from the soil.
Burning of fossil fuels in cars, power plants, and heating
which puts nitrogen dioxide into the atmosphere.
Increasing animals wastes (nitrates) from more people
and from livestock and poultry grown in ranches.
Increased sewage flows from industry and urbanization.
Increased erosion of and runoff nearby streams, lakes
and rivers from cultivation, irrigation, agricultural wastes,
mining, urbanization and poor land use.
Model of Nutrient Cycle
Nutrients (chemicals, minerals or elements)
are circulated around the ecosystem and
recycled continually.
Gersmehl identified three storage
compartments.
Litter: the surface layer of vegetation which
may eventually become humus.
Biomass: the total mass of living organisms,
per unit area.
Soil: the nutrients store in soil (weathered
material) and semi-weathered material.
Model of Nutrient Cycle
3 Difference Nutrient Cycles
Environmental Limitation in
ecosystem development
Principles of limiting factors
Law of the maximum
Law of the minimum
Principle of holocoenotic environment
Limiting factors of an environment
Light
Temperature
Water
Wind
Topography
Soil
Biotic factors
Law of Maximum and Minimum
Principle of holocoenotic environment
A German ecologist Karl Friederich (1927) suggested
that 'community-environmental relationship are
holocoenotic'. This means that there are no 'walls' or
barriers between the factors of an environment and
the organism or biotic community.
If one factor is changed, almost all will change
eventually.
Example: Temperature Air can hold more water
Evaporation rates
Relative Humidity
Dryness of soil Transpiration
Free water in soil Plants absorb soil water

Limiting factors of an environment
Light
Temperature
Water
Wind
Topography
Soil
Biotic Factors
Light
Light is an very important environment
factor:
Source of energy for ecosystem
Control factor for reproduction and migration.
Light
Quality of light:
Red and blue light: green plants (photosynthesis)
Green light: plants in woods or deep water
Ultraviolet light: retards plant growth
Duration of light
Affect the behaviour of plants and animals (flowering,
migration, mating.)
Intensity of light:
Controlling factor for rate of photosynthesis
Net productivity is the function of photosynthesis and
respiration.
Temperature
Very important factor affecting
Directly effects on organisms
Indirectly effects in modifying other environmental
factors such as relative humidity and water availability.
Each species has its own minimum, maximum
and optimum temperatures for life. (vary with
age and water balances in the body)
Aquatic life has narrower tolerance ranges for
temperature than those which live on land.
Tropical plants: > 15oC,
Temperate cereals: >-2oC,
Coniferous forests: withstand many degrees below
freezing.
Water
Water restrict ecosystem development
because ,most organisms need large amounts
of water to survive.
Water requirement for plants will vary both
with environmental conditions and among
different species.
Actual rate of transpiration is the function of
relative humidity
Air movement
Size of leaves
Size of stomata
Water
Plants classification by water requirement.
Xerophytes: plants can survive in extremely arid areas.
Halophytes: plants can survive in saline conditions
Hydrophytes: plants live in water or in moist soil.
Wind
Wind can act as an environmental factor
Directly by causing mechanical damage to plants
Indirectly affecting relative humidity and
evaporation rates.
High wind speed increases the rate of
transpiration.
Mountain summits, coasts and open plains
vegetation may be dwarfed as a result of
wind action.
Topography
Topography can influence ecosystem
development in three major ways.
Direct effects of altitude on temperature
normal lapse rate (-6.5oC/km)
The combination of changes in temperature
and relative humidity
an altitudinal zonation of ecosystems.
Slope orientation and angle
South-facing slopes (in the northern hemisphere)
are warmer and drier than north-facing slopes.
Angle of slope will be a critical factor in soil
formation and drainage.
Topography
Topography
Soil
Attributes of soils, such as texture, pH,
soil climate and organic content operate
in a closely inter-related fashion to exert
control on
rates of decomposition
nutrient cycling,
plant distribution
productivity.
Biotic Factors
Biotic factors are the interactions that occur
between living things.
Some species are beneficial or even essential for
the existence of others, whereas some may be
harmful.
The dominant plants will grow tallest and modify the
light conditions for the rest of the community.
Plants struggle for light will influence root development
and the competition for water and nutrients in the soil.
Many plants rely on animals for pollination and seed
dispersal.
Many animals are directly dependent on plants for food.
Biotic Factors
Man is by far the most important biotic factor.
Man modifies of ecosystems by fire, hunting
and agriculture,...
Industrialization and the intensification of
agriculture, man has obliterated large areas
of natural systems and caused pollution of
both terrestrial and aquatic habitats.

Ecosystem

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Ecosystem

Free water in soil Plants absorb soil water

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