6 Ecosystem Structure and Processes

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



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



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.


2. The biotic components of an ecosystem include the producers, consumers

and decomposers; the abiotic components refer to the climate, soil and

topographic factors.


3. Ecosystem functions cover the major life sustaining processes that include

food webs, energy flow, nutrient cycling, biodiversity, change and

cybernetics.


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.


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.


8. Everything changes. Organisms, populations and communities change as

expressed in growth and development.


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

6 Ecosystem Structure and Processes

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