Transcript E6 COMMUNITIES ARE CONTINUALLY UNDERGOING CHANGE …

Chapter 22
E6 COMMUNITIES ARE CONTINUALLY
UNDERGOING CHANGE
E6.1 ILLUSTRATE HOW COMMUNITY CHANGE MAY
INVOLVE SUCCESSION OVER TIME WHICH LEADS TO
CHANGES IN THE MIXTURE OF SPECIES
Resources and energy available influence
productivity of a community
 Type of conditions also has influence on the
community and habitats
 Organisms occupy specific habitats because their
needs are met and have adaptations that enable
them to survive there
 Succession is the gradual process by which the
species composition of a community changesbrought about by modification of the habitat
caused by the organisms living there

AS A RESULT OF LIVING IN AN ENVIRONMENT,
ORGANISMS MAY CHANGE THEIR HABITAT IN A
VARIETY OF WAYS:
They may provide food or shelter for others.
Trees trap the sun’s energy and provide food
and shelter for various bird species
 They may change the soil structure by causing
the breakdown of rock or increasing the organic
matter in the soil
 They may decompose dead material and make
nutrients available for others to use.

SUCCESSION

If an area is devoid of all life and colonisation
begins from scratch- succession can be studied
 New
sand dunes
 Lava flow as in the Hawaiian Islands
Hardy species that have special adaptations to
enable them to survive harsh environments move in
first- lichens
these break down rock/bacteria break down the
lichen and new soil is formed
This is the first stage of succession-soil formation
LICHEN AND SUCCESSION COMMUNITIES

Lichen
PRIMARY /SECONDARY SUCCESSION
Primary succession is where there is nothing and
life forms after creation of new soil as stated mosses survive these new conditions- from the
lichen forming soil- then as more decomposition
occurs, new grasslands, then plants and shrubs,
then birds move in and insects
 seeds are dispersed, more species grow, havens
and habitats develop for more and more species
as do the food resources

SECONDARY SUCCESSION
Changes occur in an environment that has been
exposed to a disaster like fire, logging etc
 There is some basis to support life remaining and
maybe some life itself….so a community and
environment are rebuilt on the foundations
remaining…small animals move in and then larger
and so , new plants grow from seed dispersal by
the new organisms coming in.
 http://www.youtube.com/watch?v=jFBCBmK9E3U
&feature=c4-overview&list=UUEikU3T6u6JA0XiHLbNbOw
 Succession and biodiversity-bozoneman

ECOLOGISTS VIEW SUCCESSION AS THE RESULT
OF COMPETITION BETWEEN ORGANISMS
In new or disturbed habitats those species with
higher reproductive effort tend to have the
advantage
 As an ecosystem develops those organisms with
low reproductive effort and longer lifespans
proliferate and take over
 Sometimes established ecosystems still undergo
succession if damaged in some way like fire, flood
or extreme weather conditions
 Secondary succession is quicker than primary as a
greater mix of organisms is available

CHARACTERISTICS OF SUCCESSION
COMMUNITIES
As ecosystem matures there is more Biomass, but
productivity decreases
 There are usually more species in mature
ecosystems
 As the ecosystems matures the number of
heterotrophic species tends to increase more than
the number of autotrophic species
 Mature ecosystems are more efficient at recycling
nutrients
 Mature ecosystems have organisms that tend to
be more specialised

E6.2 EXPLAIN WHY BIODIVERSITY IS ESSENTIAL
FOR THE PERPETUATION OF COMMUNITIES

Biodiversity can be considered at three levels:
 Genetic
diversity
 Species diversity
 Ecosystem diversity
 Biodiversity
refers to the variety of life forms that
are found in the biosphere, the different sets of
genes they contain and the variety of ecosystems
found in different habitats.
AUSTRALIA
Geographically isolated
 Highly endemic fauna and flora- found no
where else in the world
 High level of species richness
 Arid climate/ poor soils- unique adaptations
have arisen with various species

 Thick
leaves/waxy cuticles
 Urine concentration in hopping mice etc
 READ PAGES 202-203
ECOSYSTEM RELATIONSHIPS:
Species diversity must be maintained for the
growth and productivity of communities
 Communities-several trophic levels
 Producers trap suns energy-herbivores feed on
them-and so on- each organisms having its
place in the food chain or web
 Organisms then interact with each other in
various ways-predator/prey relationships

MUTUALISM/PREDATOR/PREY RELATIONSHIPS
ETC
In an ecosystem some organisms offer benefits
to one another
 No organisms are in isolation they work
together/interact for survival
 Bacteria and fungi recycle
 Nitrogen fixing bacteria and some plants have a
crucial relationship in terms of survival

CO-EVOLUTION
Australian plants and animals living in the same
area often have unique interactions resulting on
co-evolution
 This means the evolution of two species occurs in
tandem- they depend on each other
 Many insects evolved side by side with plants to
develop pollination techniques??? (mm)
 Some orchids are shaped like the wasps that
pollinate them
 Some fungi form symbiotic relationships with
plants and when destroyed the plants are
adversely affected

ECOSYSTEMS ARE NOT STATIC





Constantly changing
Populations and communities shaped by forces of
evolution
Disturbed areas- faster reproducing species have the
advantage, colonise first causing changes to the
ecosystem and allow other organisms to colonise
Biodiversity and genetic variability within a species as
stated is essential for species survival
When organisms are selcted to survive for their
differences which may be better adapted to a particular
habitat- NATURAL SELECTION