Chapter 4
Characteristics of Ecosystems
4.1 Interactions within ecosystems
Define the following terms:
Ecology:
The study of interactions between organisms and
their living and non-living environment.
Abiotic factor:
A non-living factor that influences an organism
Biotic factor:
A living factor that influences an organism
Ecotones are the transition areas between
ecosystems where organisms from both
ecosystems interact with each other.
Would you expect the biodiversity to be higher or lower in an ecotone?
Roles in Ecosystems:
Ecological niche describes an organisms
place in the food web, its habitat, breeding
area and time of day that it is most active
(diurnal = active during the day; nocturnal =
active at night)
Although they occupy a
very similar niche,
competition between
hawks and owls is
reduced because of the
time of day they feed.
In general, the higher
the number of niches
in an ecosystem, the
higher the
biodiversity.
Exotic species are species that have been
introduced to an ecosystem.
Can you think of any potential issues that
may arise as a result of a new species
entering an ecosystem?
4.2 Terrestrial and Aquatic Ecosystems
Define biome.
A large geographical region with a specific
climate, and the plants and animals that are
adapted to that climate.
Terrestrial Ecosystems are found anywhere on
Earth that is not covered by water.
Most of Alberta’s terrestrial ecosystems are
found within two major biomes. Which two do you
think are found in Alberta?
Taiga and grassland
The Taiga:
Also called the boreal forest, the taiga can be
found throughout northern Alberta and along the
Rocky Mountains.
What type of trees dominate the taiga?
Conifers
What characteristics of conifers makes them well
adapted to the taiga biome?
The parts of the trees that reach up into the
forest make up the canopy.
How does the canopy differ between a deciduous
forest and a coniferous forest?
How do these differences determine what plants
(and animals) will be found in the understory?
Muskeg Ecosystems:
Climate refers to the average conditions of
temperature and precipitation of a region.
What happens to the climate as we move further
North in Alberta, and into the Northwest
Territories?
In the most Northern regions, it is sufficiently
cold enough that there is a layer of permafrost
beneath the soil that never melts.
Rain and melted snow cannot drain in this part of
the taiga, and the water soaks the decomposing
plants and peat moss.
This forms muskeg, ground that is swampy or
boggy in the summer.
Would you expect the organisms to be the same as
those found in the conifer ecosystems?
Decomposition is very slow in the muskeg
ecosystem.
How do you think this effects the quality of the
soil in this ecosystem? Why?
Would you expect the biodiversity to be high or
low in the muskeg ecosystem?
What types of plants and animals do you think you
would find in this ecosystem?
Ecosystems of the Grassland Biome:
The black earth of the grasslands is said to be the
most fertile in the world.
Short lived grasses with deep roots provide a
large biomass for decomposition.
Warm temperatures cause rapid decay.
What kind of limiting factors determine the
biodiversity of the grassland ecosystem?
How does the fact that there is only one layer in
which to support life make the grasslands
different from the forests?
Deciduous Forests:
At the edge of the grasslands, before it turns into
taiga, are ecosystems dominated by trees.
What types of trees do we find in the forests
surrounding River Glen School?
Deciduous forests require lower amounts of water
than conifers, and are found in areas where the
rainfall is intermediate between the taiga and true
grasslands.
Aquatic ecosystems:
Water covers more than two-thirds of our
planet. Ninety-seven percent of that water
is salt water.
Most freshwater on Earth exists as snow
and ice.
There are still vast amounts of freshwater
on Earth’s surface, housing millions of
organisms in many different ecosystems.
Lake Ecosystems:
The littoral zone is the most productive part of a lake, the
area where algae and plants take advantage of sunlight.
The limnetic zone is the area of the open lake where there
is enough light for photosynthesis. The most common
organisms in this zone are plankton.
The profundal zone is found where there is not enough
light for photosynthesis to occur.
The only nutrients found in the profundal zone is
the rain of detritus that falls from the limnetic
zone.
This detritus is broken down by bacteria or
consumed by other bottom-dwelling invertebrates
and fish, called detritus feeders.
What consequences can the decay of falling
organic matter have on the ecosystem?
The word plankton is used to describe both
autotrophic and heterotrophic microorganisms.
Heterotrophic plankton, or zooplankton
(invertebrate animals) feed on the autotrophic
phytoplankton (tiny plants and algae). Both kinds
of plankton are food for consumers in the higher
trophic levels.
Factors Affecting Aquatic Ecosystems:
Aquatic ecosystems are limited by three
main abiotic factors.
Chemical Environment:
 This includes the type of water, whether
freshwater or saltwater.
 Organisms that live in freshwater ecosystems
can seldom survive in saltwater ecosystems, and
visa versa.
 Another component of the chemical
environment is the amount of dissolved oxygen.
 The amount of dissolved O2 depends on
temperature, pressure, and the amount of salt
and other substances dissolved in the water.
 Finally, the chemical environment includes any
other dissolved substances such as, nitrogen
phosphorus, and organic pollutants.
Temperature and Sunlight:
 There may be seasonal temperature and sunlight
differences over the course of a year.
 The depth of the water will affect these
factors.
Name the three main zones found in an aquatic
ecosystem.
Littoral, limnetic and profundal
Do all aquatic ecosystems have all three?
Can organisms exist beyond the level of light
penetration?
List two ways these organisms obtain nutrients.
Water Pressure:
 Plants and animals living in aquatic ecosystems
have adapted to conditions dramatically
different from those on land.
 Water is about 800 times more dense than air,
making it more difficult to move through.
 At a depth of 10m, the pressure is roughly
double what it is at the surface, and the
pressure increases by 100kPa for every 10m of
depth.
 Very few organisms are adapted to survive both
near the surface, and at the depths of the
ocean.
Seasonal Variations in Canadian Lakes
Seasonal Variations
A. Winter
The formation of ice over lakes in the winter acts as a shield over the water.
This can block sunlight, therefore reducing __________. It also cuts down
on the amount of ___________ available to respiring organisms within the
water below. Temperatures at the bottom of the lake are about _________,
while temperatures just below the ice are about ___________. Water is
most dense at _________.
B. Spring
As warmer temperatures of spring melts surface ice, the water is exposed
to the air once again. This is important in returning oxygen to the water.
The process of spring overturn occurs. This is brought about by:
1.
2.
C. Summer
In the summer the lake forms 3 layers that do not exchange materials
easily. This is because water at different temperatures forms layers. There
are 3 major layers in a lake in the summer.
1.
2.
3.
Two of the above layers have problems in maintaining the oxygen content.
How does the graph help explain the problem that
may occur in the epilimnion? Why might the
hypolimnion have difficulty maintaining dissolved
oxygen content?
D. Autumn
In the fall the lake is turned over again. Air temperatures cool causing a
change in the density of the water. This causes ________ to be delivered
throughout the lake. How are arctic lakes distinct from most lakes around
the world?
4.4 Limits on Populations and Communities in
Ecosystems
Biotic potential is the maximum number of
offspring that a species could produce if
resources were unlimited.
What kind of growth could occur if resources
were unlimited, and predation wasn’t a factor?
What factors do you think effect biotic
potential?
Birth potential
The maximum number of offspring per birth
What are some examples of high birth potential?
Low birth potential?
Capacity for survival
The number of offspring that reach reproductive
age
Example: Sea Turtles
Breeding frequency
The number of times that a species reproduces
each year
Length of reproductive life
The age of sexual maturity and the number of
years the individual can reproduce
Limiting Factors:
 Factors in the environment can prevent
populations from attaining their biotic
potential.
Abiotic
Biotic
Factors that cause a population to
increase
Factors that cause a population to
decrease
 Favourable light
 Favourable Temperature
 Favourable chemical
environment
 Too much or too little light
 Too cold or too warm
 Unfavourable chemical
environment
 Sufficient food
 Low number or low
effectiveness of predators
 Few or weak diseases and
parasites
 Ability to compete for resources
 Insufficient food
 High number or high
effectiveness of predators
 Many or strong diseases and
parasites
 Inability to compete successfully
for resources
Carrying Capacity: the maximum number of
individuals of a species that can be supported at
the time by an ecosystem.
Can a population exceed its carrying capacity?
What factors will determine carrying capacity?
Availability of resources such as food and water
Limits of Tolerance:
 The survival and reproduction of an organism
depends on the presence of nutrients and the
ability of the organism to withstand the abiotic
factors in the environment.
 Law of minimum states that the nutrient in the
least supply is the one that limits growth.
 Law of tolerance states that an organism can
survive within a certain range of abiotic factor;
above and below the range it cannot survive.
 The greater the range of tolerance, the
greater the organism’s ability to survive.
Density-Independent and Density-Dependent
Factors of ecosystems:
 Density refers to the number of organisms
found in a specific area at a given time. A
population is said to be dense when there is a
large number of organisms in a small area.
 Density-Independent factors affect members
of a population regardless of population density.
 Density-Dependent factors affect a population
because of the density of the population.
At your table, come up with a list of densityindependent and density-dependent factors that
may affect an ecosystem.
Density-Independent Factors
Flood
Fire
Spraying with pesticides
Change in climate or
temperature
 Destruction of habitat
 Drought




Density-Dependent Factors
 Food shortage
 Competition for mates,
breeding areas (habitat)
 Disease caused by a
microorganism or a parasite
 Introduction of an exotic
species
 Increased predation
 Competition for water and other
resources
Chapter 4.5: Changes in Ecosystems
Changes in Terrestrial Ecosystems:
Forests are important resources as they:
 Affect climate by recycling water and CO2
 Control water runoff
 Hold ground water
 Prevent soil erosion
 Act as shelters for wildlife
 Provide nesting sites and food for many
different animals
Forestry Practices:
Deforestation is a controversial way in which we
change ecosystems. There are three main
categories of deforestation.
1. Slash-and-Burn the complete clearing of a
forest by felling and burning the trees. Most
commonly used in tropical areas to clear
forest for agriculture
2. Clear-cutting involves the removal of all trees
in an area for use in timber or pulp. In Canada,
tree planting dominant trees often follows clearcutting.
3. Selective cutting (logging) involves harvesting
certain trees from an area, leaving the others to
regenerate.
Can you think of some positive and negative effects of
these forestry practices?
The Effects of Fire:
 Fire is an important and often helpful cause of
change in ecosystems.
 Fire creates and maintains a mosaic of
different vegetation types, such as grassland,
wetland, shrub area, and aspen parkland.
 Many forest fires are caused by lightning
 Prescribed Burns are fires set intentionally in
defined areas.
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Changes in Lake Ecosystems
 Aquatic ecosystems are sustained by the
dynamic equilibrium among biotic and abiotic
factors.
 There are two kinds of lake.
Oligotrophic
lakes
 Typically deep and cold
 Low nutrient levels
 Limited size of producer
population
 Because there are a limited
number of a few kinds of
organisms, the water is usually
very clear
Eutrophic Lakes




Generally shallow and warmer
High nutrient levels
Many autotrophs
Because many photosynthetic
organisms find these conditions
favorable, the water is often
murky
Oligotrophic lakes gradually become eutrophic over
time. Eutrophic lakes become increasingly shallow,
eventually filling in and becoming dry land. This
transformation may take hundreds or even
thousands of years. How can humans effect this
process?
The Process of Eutrophication
Water Pollution:
Any physical or chemical change in surface water or
groundwater that can harm living things. Biological,
chemical and physical forms of water pollution can
be grouped into five categories.
 Organic solid waste includes sewage and waste from
food processing. What do you think happens as this
matter is decomposed by bacteria?
 Disease-causing organisms come from sewage and animal
wastes. These may trigger an outbreak of waterborne
disease such as typhoid.
 Inorganic solids and dissolved minerals include waste
from mining, fertilizers and salts from road runoff in
winter.
 Thermal energy comes from electricity generating
plants and other industries. What happens to the
solubility of oxygen as the water gets warmer?
 Organic compounds include oil from roads, pesticides
and detergents (organophosphates). How might these
factors effect the aquatic environment?
Indicators of Water Quality:
Water quality is classified according to its
intended use.
 Bacteria: the presence of coliform bacteria
indicates that animal wastes are polluting the
water, and may indicate that more dangerous
bacteria is present.
 Dissolved oxygen: This can be performed using
colour change solutions and by examining the
types of living things found in the water. Trout
indicate high oxygen levels while carp and
catfish indicate low levels.
Biological Oxygen Demand: The BOD measures
the amount of dissolved oxygen needed by
decomposers (bacteria) to break down the organic
matter in a sample of water. As the number of
organisms in an ecosystem increases, so does the
BOD.
A cold, less productive lake with fewer organisms
might have a BOD near 2mg of oxygen per litre,
while a more productive lake might have a BOD as
high as 20 mg/L.
There is an inverse relationship between BOD and
dissolved oxygen levels.