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Unit 01: Life Science - Sustainability of Ecosystems
What are the Factors Affecting the Sustainability of an Ecosystem?:
Introduction to Ecology
Ecology:
Ecology is the scientific study of the interactions of organisms and their environment.
As a scientific study, ecology involves observations and experiments to test
hypothetical explanations of ecological phenomena. Ecology has a long history as an
observational or descriptive science, but is relatively young as an experimental science.
Ecology is a multidisciplinary field of study involving all areas of biology as well as the
physical sciences. Interactions of organisms and their environment refers to the way
the organism affects the environment as well as how the environment affects the
organism.
An Ecosystem is a community of organisms
and the physical environment in which it lives.
When an ecologist studies the organisms living
in a forest and includes a study of the physical
factors that affect the organisms in the forest,
then the ecologist is studying an ecosystem.
Each of the following concepts describes the
organisms within their environment and their
interactions with other organisms in their
environment. You may recognize some of these
concepts from your earlier studies in science.
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Abiotic Factors
Biotic Factors
Symbiotic Relationships
Trophic Structure
Herbivore, Carnivore, Omnivore and Saprobes
Abiotic Factors
Abiotic factors are the nonliving factors which affect life in any ecosystem. Some
abiotic factors are described below:
 Space - All organisms require enough space or territory to insure adequate
resources to food, water, shelter, and mates.
 Temperature - Environmental temperature affects biological processes and the
ability of most organisms to regulate their temperature. Few organisms have
active metabolisms at temperatures below 0oC or above 45oC because
enzymes function best within a short range of temperature and become
denatured if the temperature is too high. Most organisms are ectotherms and
can maintain their body temperature only within a few degrees of ambient
temperature. Even endotherms function best in a temperature range for which
they are adapted.
 Oxygen - Most living organisms require oxygen for cellular respiration, which is
a process that releases energy from food. Terrestrial organisms obtain oxygen
from the atmosphere as they breath (usually with lungs). Aquatic organisms
generally have gills and extract oxygen which is dissolved in the water.
 Sunlight - Sunlight is the ultimate
source of energy for all
photosynthetic organisms which in
turn provide the resources for other
living things (in most ecosystems).
Light also affects the development
and behaviour of many organisms
which are sensitive to photoperiod.
 Water - Water (humidity) is
necessary for all life. The ability to
find water, to maintain water
balance, and to conserve water help
determine the habitat range for each species.
 Inorganic and Organic Soil Nutrients - Inorganic soil nutrients include
minerals such as phosphates, nitrates, potassium, magnesium and a host of
other minerals derived from rocks. Organic nutrients include organic
compounds in humus which promote the growth of bacteria, fungi, and a host
of other organisms beneficial to the soil. The physical structure, water holding
potential, pH, and nutrient level of soil limit the distribution of plants and in
turn the animals that inhabit a terrestrial region. The composition of the
substrate in a stream affects the chemistry of the water above and in turn
affects plant and animal life living there. the type of substrate also influences
what animals can attach to or burrow in (especially in the intertidal zone).
Biotic Factors
Biotic factors refer to the living environment and include all other organisms that
interact with the individual both of the same species and all other species. Biotic factors
also includes decomposing animals and plants (detritus), disease, predator/prey
interactions, competition, and symbiotic relationships (symbiosis).
 Detritus refers to decomposing plant and animal materials including their dead
bodies as well as their wastes. Bacteria and fungi living in the ecosystem help
to break down the materials within the detritus and recycle these materials
back to the plants.
 Disease is the result if infection by fungi, bacteria, virus, and other pathogens.
Disease is an important biotic factor because disease tends to reduce the
number of organisms within the community.
 Predator/prey interaction is another important
biotic factor which helps to limit the size of
populations within an ecosystem. A predator is an
animal that kills and eats another animal for food.
The prey is the hunted animal. An example is the
lion and the zebra. When a lion kills a zebra for
food, the lion helps to prevent the overpopulation
of the zebra. If the number of zebra declines too
much the lion will starve. There is a balance between the number of predator
and prey in any ecosystem.
 Competition is a struggle for survival that occurs between two organisms either
of the same or different species. Birds often compete for nesting space. Lions
and hyenas compete for food. Competition tends to limit the size of the
population keeping it in balance with the available resources.
Symbiotic Relationships
Symbiotic relationships are biotic relationships in which two different organisms live
in close association with each other to the benefit of at least one. There are five types
of symbiotic relationships including: mutualism, commensalism, parasitism,
parisitoidism. and predation.
 Mutualism is the type of symbiosis resulting in mutual benefit to both of the
organisms in the relationship. An example of this would be the relationship
between the algae and fungus of lichens. The fungi penetrate the roots of the
plants and make soil nitrogen available to the plant, receiving carbohydrates in
return. This allows them to live in an environment in which neither could
survive alone. An example is a polyp found in the deep water off the coast of
Newfoundland; it attaches itself to the shell of a certain species of the hermit
crab, and by budding, covers the entire shell with a colony that dissolves the
original shell. Because the colony grows at the same rate as the crab, it
furnishes continuous protection, and the crab does not shed its shell at periodic
intervals as it normally would. The polyp in turn benefits by moving about with
the crab, thus obtaining a greater food supply then it would obtain if attached
to a stationary object.
 Commensalism is a relationship in which one organism benefits from the
relationship but the other organism seems to neither be harmed nor benefited.
One example to illustrate commensalism is the beaver and the fish. A beaver
builds a dam to regulate water level which helps the beaver survive winter. Fish
often inhabit the beaver pond. The fish benefit from the beaver, but the beaver
is neither harmed nor gains benefit from the
fish. Another example of commensalism is
the relationship between trees and nesting
birds. The tree provides a nesting space for
the bird but the bird may neither harm nor
benefit the tree. On the other hand, if the
bird eats insects that normally cause harm
to the tree or if the bird produces wastes
that are absorbed by the tree, one might
argue that the tree and the bird both
benefit. In this case the example would be
considered mutualism. It is often difficult to determine the complete nature of
any relationship and as a result it is often difficult to distinguish between
mutualism and commensalism.
 Parasitism is a symbiotic relationship in which one organism benefits and the
other is harmed. The organism that benefits is called the parasite, the organism
that is harmed is called the host. Some parasites only cause slight damage to
their host, while others kill them. Therefore one organism is injured in
satisfying the needs of the other. An example would be the tapeworm. they live
in the digestive tracts of various organisms, while there they are provided with
nutrient and an environment in which to grow and reproduce. However, the
host is harmed by the presence of the tapeworm.
 Parisitoidism is similar to parasitism. One organism benefits but the other is
eventually killed - a sort of slow death. An example of parisitoidism is when a
female wasp stings a spider causing paralysis but not death. The wasp then
lays a single egg on the spider. When the egg hatches into a larva, it slowly
eats the body of the spider eventually killing it - but slowly.
 Predation is where the interaction is beneficial to one species and detrimental
to the other. This is not always considered a symbiotic relationship, although it
is quite similar to parasitism, except for the degree of harm to the host or prey.
With predation, the prey is killed. An example of predation is when a lion kills a
zebra and eats it as its source of
food.
Trophic Structure:
Trophic structure refers to the feeding
relationships within the ecosystem. These
feeding relationships are generally divided
into five trophic levels based on their source
of nutrition and include primary producers,
primary consumers, secondary
consumers, tertiary consumers, and
decomposers (also known as
detritivores). The various organisms that
comprise each of the trophic levels
determines the flow of energy and the
cycling of materials within the ecosystem.
Feeding relationships are generally viewed as
a food web consisting of all the possible
food chains that exist within the ecosystem.
Since the primary producers are the only
photosynthetic organisms, they determine
the amount of energy (trapped from the sun)
that can be passed up through the food web.
The detritivores enable the recycling of materials and are therefore the organisms that
are the foundation for biogeochemical cycling.
Producers or autotrophs are organisms, such as green plants, that produce their own
food. They make organic compounds (food such as sugar) from inorganic compounds
(carbon dioxide and water) by photosynthesis. The ultimate source of energy for life on
Earth is the sun. Solar energy is trapped during the process of photosynthesis and
converted into a chemical form that we normally call food. Food contains both materials
(the elements carbon, hydrogen, nitrogen, and the other essential elements) as well as
stored energy. The materials within the food are recycled. They pass from the
producers to the consumers and finally are recycled back to the producers by the action
of the decomposers. Energy, unlike the materials, is not recycled. As the food is passed
through the food web, most of the energy is lost. In general terms, about 10% of the
energy stored in one trophic level (such as producers) is actually transferred to the next
trophic level (for example the herbivores). This is known as the pyramid of energy.
Eventually there is so little energy remaining in the top trophic level that no higher
trophic level can be supported. This is why there are so few if any fourth order
consumers in an ecosystem.
Consumers or heterotrophs are organisms that obtain nutrients from other
organisms. They cannot synthesize their own food so they must obtain it ready made.
They eat other living things. There are two different ways to classify carnivores. The
first group are known as predators. Predators hunt and kill other animals for food.
Animals like lions, wolves, snakes, and sharks are all classified as predators. Another
group of animals that are considered carnivores are scavengers. Scavengers are
animals that feed on the dead bodies of other organisms. Animals such as vultures,
hyenas, and griffins and all classified as scavengers. Scavengers eat the food that has
been killed and left behind by predators. Scavengers are a very important group
because they dispose of the carcass's of animals that have been left to decompose.
Decomposers are organisms of decay. These are also called saprobes. They are
generally fungi or bacteria that break down the complex compounds in the remains of
dead animals and plants, producing simple substances that can be used again by the
producers. Decomposers are therefore very important because they recycle materials
within the ecosystem. The decomposers are the final consumers in any ecosystem.
Herbivores, Carnivores, Omnivores, and Saprobes:
There are several groups of heterotrophs. Heterotrophs are all
organisms that obtain their food from the environment. All animals
and certain types of micro-organisms are heterotrophs. These
organisms must take in, or ingest, food containing already made
organic nutrients from other plants or animals. It all depends on what
they eat and how they obtain it. Heterotrophs include herbivores,
carnivores, omnivores and saprobes.
 Herbivores are animals that feed only on plants. Rabbits,
cattle, horses, sheep and deer are all herbivores.
 Carnivores are animals that feed on other animals. Some
carnivores may be predators (such as lions, hawks, and
wolves who attack and kill their prey and feed on their
bodies) and some may be scavengers (they feed on dead
animals that they find).
 Omnivores are animals that feed on both plants and animals. Examples of
omnivores are humans and bears.
 Saprobes are organisms that get nutrients by breaking down the remains of
dead plants and animals, or their wastes. Examples of saprobes are bacteria
and fungi. Saprobes are also known as decomposers are an essential
component of any ecosystem. Their main role is to recycle nutrients in dead
organisms and their wastes. Without the decomposers to recycle nutrients,
there could be no life since plants would run out of nutrients.