6 ecosystem structure and processes
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Biology 1Carmela Española
Room 107, IB Main Building
M 10-12AM
TTh 10-12AM & 3-5PM
Ecosystems
Structure and Processes
“
”
Though the organism may claim our
primary interest…We cannot separate them
from their special environment, with which
they form one physical system. It is the
[eco]systems so formed which, from the
point of view of the ecologist, are the basic
units of nature on the face of the earth. Arthur Tansley, 1935
The Ecosystem
But first…
What is ecology?
What is the environment?
What’s the difference?
Ecology
oikos + logos
“study of the home”
study of relationships between
organisms and the environment
Environment
includes all the external conditions and factors,
biotic and abiotic, that affect the life of an organism.
consists of resources and conditions
Resources
Anything an organism uses or consumes in the environment
– Perpetual
• Inexhaustible in a human time scale e.g. sun
– Nonrenewable
• Available in a fixed amount; may be reused/recycled e.g. minerals
– Renewable
• May be depleted but may ultimately be replaced by natural processes e.g. biofuels
Resources
Sustained yield
– Use of resources without depletion
When use of resources goes beyond sustained yield, you have
ENVIRONMENTAL DEGRADATION
Conditions
• Environmental factors to which organisms respond
– e.g. temperature, salinity, humidity
• Influences availability of resources
• An organism’s survival depends on its tolerance to conditions
Ecosystem Structure: Ecological
Levels of Organization
emergent properties
integrative levels
Emergent Properties
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
In life’s hierarchy of organization,
new properties emerge at each level
The upper tier is a global perspective of life
• Biosphere—all the environments on Earth that support life
• Ecosystem—all the organisms living in a particular area; pathways
followed by energy and matter as these move among living and non
living elements
• Community—the array of organisms living in a particular ecosystem
• Population—all the individuals of a species within a specific area;
presence/absence of species, abundance or rarity, trends and
fluctuations in numbers
In life’s hierarchy of organization,
new properties emerge at each level
The middle tier is characterized by the organism,
an individual living thing, which is composed of
• Organ systems—have specific functions; are composed of
organs
• Organs—provide specific functions for the organism
• Tissues—made of groups of similar cells
In life’s hierarchy of organization,
new properties emerge at each level
Life emerges at the level of the cell, the lower tier,
which is composed of
• Molecules—clusters of atoms
• Organelles—membrane-bound structures with specific
functions
• Cells—living entities distinguished from their environment by a
membrane
Ecosystem Function
1. Energy Flow In Ecosystems
2. Feeding Relationships in Food Chains/Webs
3. Biogeochemical Cycles
4. Biodiversity
5. Change: Growth and Development
6. Cybernetics
Solar energy runs the engines
of the earth. It heats its
atmosphere and its lands,
generates its winds, drives the
water cycle, warms its oceans,
grows its plants, feeds its
animals, and even (over the
long haul) produces its fossil
fuels. This energy can be
converted into heat and cold,
driving force and electricity.
Energy
Flow
Pathway of Energy
• Light → producers (photosynthesis) → consumers → decomposers
• Energy diminishes as it passes through the ecosystem
• Energy is lost as heat
• Energy input must be continuous
Trophic Level
a position in a food web and is determined by the number of
transfers of energy from primary producers to that level
Energy loss limits
the number of
trophic levels in
ecosystems
Biogeochemical Cycles
• Gaseous type - the reservoir is the atmosphere (examples: N2, CO2, O2)
• Sedimentary type - the reservoir is the earth’s crust (example: phosphorous)
• Linkage type - the reservoir includes major pathways in air, water and crust
(example: sulfur)
Hydrologic Cycle
Nitrogen Cycle
Phosphorus Cycle
Sulfur Cycle
Change: Growth and Development
Organism
Population
Ecosystem
Population
• A group of interbreeding individuals occupying a particular place at a
particular time
• Is subject to change
– In quantity by growth
– In quality by evolution
Population change. Population growth results from the net
effect of all factors adding to the number of individuals in
that population and those decreasing the number of
individuals in that population. These factors in turn are the
result of species characteristics and environmental
conditions.
Births Deaths
Population change = + +
Immigration Emigration
Populations either increase, decline, or remain stable.
Carrying Capacity
Maximum number of individuals of one or more species that can
be supported by a particular ecosystem on a long-term basis
Biotic Potential and Environmental Resistance. Seldom
does the growth rate of a population equal its biotic
potential – its growth rate under ideal, nonlimiting
conditions. Environmental factors such as food
supply, habitat, and disease limit growth.
Biotic Potential
the maximum reproductive capacity of
a population under optimal conditions
Environmental Resistance
any factor in the environment that prevents a
population from expressing its biotic potential
Community: Succession
change in plant, animal, and microbial communities in an area
following disturbance or creation of new substrate
Terms
Pioneer community
Primary succession
Secondary succession
Climax community
Ecological succession is orderly, directional and predictable.
Steps
1. colonization
2. site modification
– environment limitations are biotically controlled
3. species replacement
– community structure changes with time
→ culminates in a quasi-steady state
– maximum biomass is maintained by a unit of energy flow
“
”Everything changes.
Panta Rei
Heraclitus
Cybernetics
natural ecosystems are self-regulating
Resilience
describes speed with which a community
returns to its former state after it has been
perturbed and displaced from that state.
Resistance
describes the ability community to avoid
displacement in the first place.
Key Concepts and Principles
1. The components of the ecosystem (biotic and abiotic) are continually
interacting and exchanging materials and energy.
Key Concepts and Principles
2. The biotic components of an ecosystem include the producers, consumers
and decomposers; the abiotic components refer to the climate, soil and
topographic factors.
Key Concepts and Principles
3. Ecosystem functions cover the major life sustaining processes that include
food webs, energy flow, nutrient cycling, biodiversity, change and
cybernetics.
Key Concepts and Principles
4. In a food chain, there exists a feeding relationship in which energy-rich
molecules stored by producers are taken in by a series of consumers.
5. There is a one-way flow of energy in an ecosystem. Entering the living
world mostly as light through the trophic chain, energy leaves mostly as
heat.
Key Concepts and Principles
6. Materials flow in an ecosystem in a cyclic pattern. Materials utilized by the
biotic components of the ecosystem return to the physical world mainly
through the processes of respiration and decomposition.
7. Biodiversity is important, because every living species has a role to play.
Key Concepts and Principles
8. Everything changes. Organisms, populations and communities change as
expressed in growth and development.
Key Concepts and Principles
9. A balanced ecosystem is achieved when the natural processes involved are
maintained in a dynamic steady state.
Concept of Interdependence
Complex interactions exist between the living
and non-living components of the
ecosystem.
Concept of Interdependence
The structure
and function
of ecological
systems are
interrelated
with socio-
economic
systems.
Applied Ecology
• Concerned with applications of ecological principles to major environmental
and resource management problems
• Forest, range, wildlife and fishery management
• Conservation biology, restoration ecology, landscape ecology
Sources
• Bio 12 slides
• Bio 160 slides
• Dr. Daniel Lagunzad
• Dr. Catherine Lagunzad
• Dr. Ma. Dolores Tongco
• http://gerrymarten.com/humanecology/chapter01.html#p1
• Pearson Education, Inc.
Anthropogenic Impact and
Sustainable Natural ResourcesNext meeting
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