Grade 9 Academic Science – Biodiversity
Equilibrium, Change and Biodiversity
Section 3.2 and Section 3.3 – Pages 80-86
Equilibrium
 The state of an ecosystem with relatively constant conditions over a period of time.
 Equilibrium is established when abiotic conditions are stable (e.g., energy flows
continually through the ecosystem, nutrients are cycled are a relatively constant rate,
climatic conditions change on a relatively stable trend or pattern)
Questions
 Is the Earth in a state of equilibrium?
 Is the Earth resilient (i.e., Able to respond positively to change)?
 Do your and my actions disrupt the local state of equilibrium?
 What natural events could change equilibrium?
 A major earthquake and tsunami struck Japan in the summer 2011. The scale of
damage (e.g., human loss of life, economic destruction, almost catastrophic events at a
nuclear reactor). Almost hidden, there was also substantial environmental damage. Do
you think the environment can rebound from this natural disaster? Provide three ideas
with your answer.
Succession
 Gradual and usually predictable changes in the composition of a community and the
abiotic conditions…often following a disturbance.
 A process by which an ecological community progressively transforms itself until a stable
community is formed.
 Primary Succession – Ecological succession of plant life on newly formed exposed
ground or an area devoid of vegetation and lacking sufficient soil (e.g., volcanic eruption,
retreated glacier). In primary succession, the initial (…or pioneer …) species are
organisms such as lichen, algae and fungus. These “simple” organisms begin to
"normalize" the habitat and create growing conditions that support the growth of more
complex vascular plants.
 Secondary Succession – Ecological succession of a partially disturbed ecosystem (e.g.,
after a fire, following a hurricane, disruptive human activities). In secondary succession,
soil is present and some vegetation exists. Thus, there are no pioneer species.
Questions
 A logging company removes trees by clear cutting. Is the resulting succession primary or
secondary? Explain your answer.
 Is grass a pioneer species? Explain your answer.
 Almost 2.5 BYA, single-celled cyanobacteria (i.e., blue-green bacteria with the ability to
make their own energy by oxygenic photosynthesis) appeared on Earth. The
cyanobacteria were able to convert the “reducing atmosphere” into an “oxidizing
atmosphere” which, in turn, dramatically changed the composition of life forms on Earth
by stimulating biodiversity. Do you think this is an example of Primary Succession?
Explain your answer.
 Using the illustration on the next page, explain forest succession. What stage of plant
growth achieves a state of stable equilibrium (…called the Climax Community)? Why
does succession proceed from annual plants to grasses to shrubs….? What causes this
change to occur naturally?
Table 1. Comparing plant, community and ecosystem characteristics between early and late
stages of succession
Early Stages of
Late Stages of
Attribute
Succession
Succession
Plant Biomass
Small
Large
Plant Longevity
Short
Long
Well dispersed
Poorly dispersed
Simple
Complex
Photosynthetic Efficiency of Dominant Plants
at Low Light
Low
High
Rate of Soil Nutrient Resource Consumption
by Plants
Fast
Slow
Plant Recovery Rate from Resource
Limitation
Fast
Slow
Multilayered
Monolayer
Litter and Soil
Living Biomass and
Litter
Seed Dispersal Characteristics of Dominant
Plants
Plant Morphology and Physiology
Plant Leaf Canopy Structure
Site of Nutrient Storage
Questions
 What does Table 1 tell you about forest succession? What does it suggest about
succession as it proceeds from one stage to the next?
Importance of Biodiversity
The estimated number of species worldwide is between 5 million and 50 million. Yet, only 1.5
million have been correctly identified and classified. Moreover, over 50% of the known living
species are insects.
Biodiversity
 Variety of life in a particular ecosystem.
Species Richness
 Number of species in an area
Extinct
 A species that has died out and no longer occurs on Earth
 Extinction is a natural process that can be caused by a catastrophic event such as an
asteroid impacting the Earth’s surface.
 Human activity has increased the rate of extinction. About 80 species of animals and
birds have been driven to extinction in North America after the arrival of Europeans.
Species at Risk
In many cases, EXTINCTION is natural. Species disappear and different species emerge to take
the place of the extinct species. In the last 1 billion years, five major extinctions have occurred.
These events are “major” because many different species disappeared (e.g., extinction of
dinosaurs). Extinctions such as these events are usually caused by big events (e.g. massive
meteorite, flooding) BUT they are very rare.
Unfortunately, extinction is also caused by human activity. Humans kill other organisms. Human
destroy the habitats of other organisms. Humans overuse (misuse or over exploit) resources and
cause catastrophic change.
What is BIODIVERSITY?
 The variety of organisms found in one area. It is measured by counting the number of
different species present in the area. This measurement is called SPECIES RICHNESS.
A diverse – and healthier – ecosystem has HIGH species richness. In other words, we
want biodiversity and species richness.
In Canada, there are five classifications of Species at Risk
Classification
Definition
Number of
Canadian
Species
(2008)
Examples
Extinct
No longer exists
13
Passenger pigeon
Extirpated
No longer exists in a certain
area but may live somewhere
else
23
Atlantic walrus
Endangered
Imminent danger of going
extinct or becoming extirpated
238
Barn owl
Swift fox
Threatened
Likely to become endangered if
present trend and conditions
continue
146
Humpback whale
Wood bison
Special
Concern
May become threatened or
endangered due to a
combination of factors
157
Polar bear
Red-headed woodpecker
Questions
 What do you think could be done to protect Species at Risk? Provide three ideas.
 Write an Opinion Piece either supporting or refuting the following idea.
Biodiversity is only important if it performs a valuable service for
humans. That is, biodiversity must offer some economic,
aesthetic or recreational value to humans (…This is called an
anthropocentric point of view…). Biodiversity has no intrinsic
value, and as such, protecting biodiversity for the sake of
biodiversity holds no merit
Homework
 Page 82, Questions 1-4, 6-9
 Page 86, Questions 1-3