Download Grade 10 (SNC 2D)

Grade 10 (SNC 2D)
Biology: Sustainability of Ecosystems
Monday Nov 10/2008- Day 2
Chapter 3 Change and Sustainability
3.2 Change and Succession
Overhead #1
Succession
The act or process of following in order or sequence
Ecological Succession


Orderly changes in the composition or structure of an ecological community.
A process where one ecosystem is gradually replaced by another over time.

Succession may be initiated by formation of new, unoccupied habitat (e.g., a lava
flow or a severe landslide)
or

Succession may be initiated by some form of disturbance (e.g. fire, severe windthrow,
logging) of an existing community.
Overhead #2
Primary Succession
The sequence of changes that begins with a bare landscape and ends with a climax
community is known as primary succession. (p.82, fig. 3.9)
Pioneer Organisms
An organism that populates a region after a natural disaster (or any other event) has
caused most life in that area to disappear.
In other words, organisms that can live in inhospitable places, without soil or shelter, are
called pioneer organisms
Common pioneer organisms include lichens, and algae.
Pioneer organisms modify their environment and establish conditions under which more
advanced organisms can live because they slowly start to transform the environment and
create conditions that are suitable for other organisms.
In some circumstances, other organisms can be considered "pioneer organisms". Birds are
usually the first to inhabit newly created islands, and seeds, such as the coconut, may also
be the first arrivals on barren soil.
Climax Community
If left undisturbed, an ecosystem will eventually develop into a climax community.
A climax community is a community of organisms that has a maximum level of
productivity.
When a biological community of plants and animals reaches a steady state, i.e maximum
level of productivity, through the process of ecological succession, we call it a climax
community.
The type of climax community in an ecosystem depends on a combination of climate and
soil.
On the board:
Type of climate and soil
Type of climax community
Dry Areas
Deserts
Areas with more precipitation but not
enough support for tree growth
Grasslands
Wetter areas of Earth
Forests
Handout #1
Primary Succession on a Glacial Moraine
(http://bcs.whfreeman.com/thelifewire/content/chp55/55020.html)
A change in community composition following a disturbance is called ecological
succession.
Ecologists divide successions into two major types: primary succession and secondary
succession.
Primary succession begins on sites that lack living organism.
Secondary succession begins on sites where some organisms have survived the most
recent disturbance.
The patterns and causes of ecological succession are varied, but the species that colonize
a site soon after the disturbance often alter environmental conditions so that they become
favorable for other species.
A good example of a primary succession is the change in the plant community that
followed the retreat of a glacier in Glacier Bay, Alaska, over the last two hundred years.
No human observer was present to measure changes over the 200-year period, but
ecologists have looked at the succession by measuring plant communities on moraines
(gravel deposits formed where the glacier front was stationary for a number of years) of
different ages.
As a glacier retreats it leaves behind gravel deposits called a moraine. The youngest
moraines are populated with bacteria, fungi, and photosynthetic organisms. Slightly older
moraines that have already gone through the earlier stages of succession have lichens,
mosses, and a few species of shallow-rooted herbs.
Because nitrogen is virtually absent from recently exposed moraines, only a few plants
can grow. In the case of Glacier Bay two plants that will grow are a herbaceous plant
(Dryas) and alder trees (Alnus), both of which have a nitrogen-fixing bacteria in nodules
on their roots.
Nitrogen fixation by alder trees and Dryas improves the soil. As soil condition improves,
alder stands are invaded by spruce.
Spruces the outcompete and displace the alders and Dryas. If the local climate does not
change dramatically, a stable forest community dominate by spruces is likely to persist
for many centuries.
Overhead #3
Secondary Succession
One of the two types of ecological succession of plant life.
As opposed to primary succession, secondary succession is a process started by an event
(e.g. forest fire, harvesting, hurricane) that reduces an already established ecosystem (e.g.
a forest or a wheat field) to a smaller population of species.
Secondary succession occurs on preexisting soil where as primary succession usually
occurs in a place lacking soil.
Simply put, secondary succession is the succession that occurs after the initial succession
has been disrupted and some plants and animals still exist.
Succession and Energy Flow
Irreversible Change
Although succession can change disturbed ecosystems back to more complex biological
communities, frequent and severe disturbances can produce irreversible changes.
The risk is especially great if species of organisms are exterminated or if soil is lost or
poisoned over a wide area.
Phytoremediation
The use of plants, which can accumulate toxic compounds in their tissues, to clean soil of
contaminans.
Some plants, such as mustard, radish, and sunflower, accumulate toxic metals in their
tissues. These plants can be planted, grown, and then harvested to remove the toxic
metals from the soil.
Consists in depolluting contaminated soils, water or air with plants able to contain,
degrade or eliminate metals, pesticides, solvents, explosives, crude oil and its derivatives,
and various other contaminants, from the mediums that contain them.