nota biodiversiti

Ecosystems – what are they ?

(Refer to Essentials of Ecology,

G. Tyler Miller)

Ecosystems

Levels of organization

Individual/Organism

Population

Community

Ecosystem

Biosphere

an Ecosystem consists of all of the organisms

living in a community (or communities) together

with the abiotic factors with which they interact

Rocky Shore community – an example

• the mix of barnacles, algal mats,

herbivorous snails on rocks etc.

• the physical environment (dessication,

temp, wave action) leads to a vertical

zonation pattern

• predation and competition influence

distribution eg. snails grazing algal spores,

predatory snails eating herbivores

• disturbance opens spaces, allows

establishment of new species

• different communities result in different

locations

Rocky Shore

community

Structure of a community is usually the result

of many interactions

results from:

– many competitive interactions

– complex mutualisms

– predators increasing and decreasing

– variety of disturbances through time

– environmental fluctuations and more!

Biomes – ecosystems & communities on a global scale

(Miller Ch 4 Fig 4.8)

• vegetation structure in different parts of the

world is similar in similar environments - even

though species are different

• biomes are communities with similar structure

Biosphere (ecosphere) - the biosphere (i.e. all

ecosystems on earth) is an additional level of

organization

• Existence of life depends upon

– an energy source (the sun)

– oxygen, carbon, nitrogen and other elements, all

of which are part of worldwide geological and

chemical cycles

• All ecosystems on Earth are linked via global

biogeochemical cycles.

• an ecosystem is all of the organisms living in a

community (or communities) together with their abiotic

factors

Ecosystem function

through

Energy flow

Cycling of materials

• A systems approach attempts to understand

– the way energy is passed through the system

– how nutrients are cycled

• Individual organisms or species can be

considered in terms of the function they perform

What does biodiversity actually do ?

biological diversity allows the different ecosystem

functions to be carried out

the primary ecosystem functions are to

• Capture

• Store

• Transfer

Energy

Carbon dioxide

Nutrients

Water

ECOSYSTEMS

ecosystems are a network of

interactions, beginning with

the PRIMARY PRODUCERS

(the PLANTS) and

connecting to herbivores,

carnivores, parasites,

decomposers

...energy, nutrients & water

are cycled through the

network by these different

groups

Miller Ch 4

Fig 4.6

Flow of

energy

and

materials

through an

ecosystem

Systems approach to ecosystem function

Essential characteristics of ecosystems

1. Energy flow

Energy flows in a unidirectional way (it does not

cycle!) fig 4.13 Miller Ch 4

This requires a continuous input of energy into an

ecosystem

Energy source autotrophs heterotrophs


1. Energy flow

• Autotrophs

(e.g. plants, algae)

organisms capable of

synthesizing all their

required organic

molecules from simple

organic substances and

an energy source


1. Energy flow

• Heterotrophs

(e.g. animals)

organisms that cannot

synthesize complex

organic compounds and

must feed on organic

material formed by other

organisms to obtain

energy and necessary

molecular building blocks

for metabolism and

growth


2. Cycling of materials

• Materials (e.g. carbon, nitrogen, phosphorus)

are cycled from the abiotic environment,

through living organisms, and back to the

abiotic environment

• This results from metabolic activities of plants

and animals, and organisms such as bacteria

and fungi that break down organic matter

Energy in ecosystems

• All organisms require energy

– maintenance, growth, reproduction, (and movement)

• The energy driving the biosphere (and all

ecosystems) is solar radiation, captured via

photosynthesis by autotrophs

• about 1% of visible light converted to chemical energy

• about 120 billion tonnes of new organic material

produced each year

• about 99% of all organic matter in the biosphere is

autotrophs (i.e. mostly plants)

Sunlight - the source of energy for the biosphere

Miller Ch 4 Fig 4.14

Photosynthesis

Photosynthesis

6 CO2 + 12 H2O C6H12O6 + 6 O2 + 6H2O

Respiration

Energy (from photosynthesis) is released and used

by the organism when the complex molecules are

subsequently broken down during metabolism

(+ solar energy)

Productivity in ecosystems

(Refer to David T. Krohne ;Pg 358-366)

Primary productivity - the rate at which solar

radiation is converted into chemical energy

by autotrophs (plants) (amount of material or

energy per unit time,

e.g. g/m2/yr)

Secondary productivity - the rate at which

heterotrophs (animals) convert the chemical

energy of their food into new tissue


• However, not all of the energy is converted into

new living tissues

– respiration (metabolism) accounts for a large part

• Gross primary productivity - energy fixed in

photosynthesis per unit time

• Nett primary productivity - energy fixed in

photosynthesis minus energy used in respiration (that is, it

is the amount available for harvest at next level)


A measure of nett

primary productivity is

the change in biomass

per unit time (but be aware of what may

have been lost)

Biomass - the weight

of living tissue per unit

area (e.g. kg/ha)

What limits primary productivity?

(The factors that limit rate of photosynthesis limit

production)

• light

• water

• temperature

• nutrients (N, P, trace elements)

• all are essential - the resource in shortest supply

will be the one limiting biomass production

Which are the most productive

ecosystems on Earth?

Which are the most productive ecosystems?

Ecosystem Nett primary World primary

production production

(g/m2/yr) (billion t/yr)

Tropical rain forest 2200 37.4

Woodland/shrubland 700 6.0

Temperate grassland 600 5.4

Desert and scrub 90 1.6

Swamp and marsh 2000 4.0

Open ocean 125 41.5

Upwelling ocean zones 500 0.2

Algal beds and reefs 2500 1.6

Productivity through time

• Primary productivity will vary seasonally

depending on environmental conditions

- ‘growing season’ in agriculture

- tropical vs temperate forests

• Productivity may change with the age of an

ecosystem (regenerating vs older)

Young ecosystems - often a greater proportion of young

actively growing tissue

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