Download Ecology Introduction 1. Ecology

Ecology
Introduction
Ecology is the study of the natural environment and organisms, how they interact and how
they change their environment. There is a dynamic relationship between every organism in
any environment, as well as between the organisms and the physical environment.
For conservation to be successful in Namibia, it is essential that every inhabitant is familiar
with the basic principles of ecology.
The aim of this unit on ecology is not to teach you about conservation. The emphasis in this
unit will be to trace the energy pathway from the sun through living things and identify the
roles of various organisms (producers, consumers, decomposers, predators, prey) in a food
chain and a food web.
Upon completion of this unit you will be able to:
 explain the essentials of ecology, some ecological components, principles and
terminology;
 explain how all factors, living and non-living, are dependent on each other and are in
constant interaction with one another
 explain what an ecosystem is, and how we can study one
 explain the application of ecological concepts into everyday living
 summarise the concept of energy flow through a food web
1. Ecology
1.1 Origin of the word…”ecology”
The word ecology has a Greek origin
 OIKOS = household
 LOGOS = study of…
Study of the “house/environment” in which we live. The study of the interactions that take
place among organisms and their environment
1.2 What is an environment?
 Everything that affects an animal and plant makes up its environment - where it lives,
the weather and all the living things it comes into contact with. Every living thing,
including people, has an effect upon the environment.
1.3 Animal and Plant Adaptations
 All living things have to be suited to their environment if they are to survive. Fish have
streamlined bodies, fins and specially shaped tails to help them move quickly and easily
through the water. Ground squirrels have bushy tails to shade them from the hot Namibia
sun. Squirrels have sharp, strong claws for gripping tree trunks and branches and strong
teeth for eating nuts.
1.4 What is a habitat?
The place in which an organism lives provides the kinds of food and shelter, the
temperature, and the amount of moisture the organism needs to survive.
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Alternatively, you can also say that a habitat is any place where organisms live together
naturally. It is like a neighbourhood in nature.
1.5 What does an organism need in a habitat?
In a habitat an organism need shelter, water, food and plants need sunlight (Fig 45).
Figure 45:
Shelter
Water
Food
Difference between environment and habitat
Environment – condition in which an organism lives e.g. temperature, light, humidity etc. these be
affected by other organisms.
Habitat – specific environment in which organisms’ lives.
1.6 What about our habitat?
Just like other animals and plants, we need our own habitat. What are our needs? Food,
shelter and water (fig 46)

Figure 46:
Food
Shelter
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Water
What is the difference between environment and habitat?
Environment includes all living & non-living things that exist on this
earth. The living things (biotic factors) include all the plants, animals
including man, & micro-organisms. The non-living factors (abiotic
factors) include the air, light, water, temperature, soil, humidity,
rainfall etc.
A habitat is a specific natural environment. The area or environment
where an organism or ecological community normally lives or occurs: a
marine habitat.
1.7 Biosphere
The part of Earth that supports life is the top portion of Earth's crust, all the waters that
cover Earth's surface, and the atmosphere that surrounds Earth.
The biosphere, like the human body, is made up of systems that interact and are
dependent on each other.
1.8 Ecosystem
The biosphere’s systems are called Ecosystems.
All ecosystems must have a constant source of energy (usually the sun) and cycles or systems
to reuse raw materials. Examples are the water, nitrogen and carbon cycles. An ecosystem
is made up of all the biotic or living and the abiotic or non-living components in a given
area. The study of ecosystems mainly consists of the study of certain processes that link
the living or biotic components to the non-living or abiotic components
1.9 What is a Population?
All the members of a species living in one place at one time.
Example – All the terrapin in Avis Dam or all the barbel (catfish) in Avis dam or all the
sweethorn trees growing around Avis Dam.
Figure 47: Terrapin (left). Pelicans (right)
Source: B. Curtis
1.10 What is a community?
All the species in a given area (or) all populations (different species) that live in a
particular area.
Example – all the living things in Goreangab dam or Avis dam.
In Goreangab dam we find – terrapin – barbels – frogs – pelicans etc.
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Figure 48: The community of animals along the Chobe River consists of a population of
waterbuck and a population of baboons (as well as other animals and plants).
Source: B. Curtis
Density and dispersion patterns are important population variables
Two important aspects of population structure are population density and dispersion
pattern. Population density is the number of individuals of a species per unit area or
volume-the number of oak trees per square kilometre (km 2) in a forest, for instance, or the
number of earthworms per cubic meter (m3) in forest soil. Because it is impractical or
impossible to count all individuals in a population in most cases, ecologists use a variety of
sampling techniques to estimate population densities. For example, they might base an
estimate of the density of alligators in the Florida Everglades on a count of individuals in a
few sample ploys of 1 km2 each. The larger the number and size of sample plots, the more
accurate the estimates. In some cases, population densities are estimated not by counts of
organisms but by indirect indicators, such as number of bird nests or rodent burrows.
Within a population’s geographic range, local densities may vary greatly. The dispersion
pattern of a population refers to the way individuals are spaced within their area. A
clumped dispersion pattern, in which individuals are grouped in patches, is the most
common in nature. Clumping often results from an unequal distribution of resources in the
environment. For instance, plants or fungi may be clumped in areas where soil conditions
and other factors favour germination and growth. Clumping of animals is often associated
with uneven food distribution or with mating or other social behaviour. For example, fish
are often clumped in schools, which may reduce predation risks and increase feeding
efficiency.
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A uniform dispersion pattern (an even one) often results from interactions between the
individuals of a population. For instance, some plants secrete chemicals that inhibit the
germination and growth of nearby plants that could compete for resources. Animals may
exhibit uniform dispersion as a result of territorial behaviour shows uniform dispersion in
king penguins.
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In a random dispersion pattern, individuals in a population are spaced in an unpredictable
way, actually without pattern. Plants, such as dandelions, that grow from windblown
seeds might be randomly dispersed. However, varying habitat conditions and social
interactions make random dispersion rare.
Estimates of population density and dispersion patterns enable researchers to monitor changes
in a population and to compare and contrast the growth and stability of populations in
different areas.
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1.11 Abiotic factors
The nonliving things in an environment are called abiotic factors.
Examples of abiotic factors are sunlight, temperature, water, rainfall, climate and soil (fig
49).
Figure 49: clouds are examples of abiotic factors.
1.11 The abiotic components
1.11.1 Topography
Topography is important since it includes such factors as the height above sea level and the
slope and degree of exposure by sunlight.
North-facing slopes receive more sunshine and the soil temperature is higher. The water
content of the soil is lower, while that of the south-facing slopes is higher. The soil is
cooler and there are also more plants on the south-facing slopes.
1.11.2 Edaphic or soil factors
Soil is obtained through the weathering of rocks by physical, chemical and biotic processes.
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Soil is classified on the basis of soil particle size:
Eg; sand, clay and loam.
Humus makes soil more fertile, assists in binding sandy soil and increases the water-holding
capacity of the soil.
The depth of soil is very important. The upper layer is formed continuously over many
years –about 30mm over 500 years!
The type and the composition of the soil influences the biotic components, but the biotic
components also influence the soil. Example: the enrichment of the soil and the formation
of humus during the decomposition process of biotic components.
1.11.3 Climatic factors
1 Light
Plants and animals are adapted to light in many ways, including the following: (i) Light is
essential for plants because it is needed for photosynthesis. (ii) Animals such as the
earthworms, bats, and lions are active at night.
2
Temperature
Temperature influences the biological functioning of organisms and therefore their
distribution around the world.
Some animals are cold-blooded, for example fish, amphibians and reptiles. Their
temperature varies according to the environment’s temperature. When it is cold their body
metabolism activity decreases (hibernate).
Other animals are warm-blooded, for example mammals and birds. They maintain a
constant body temperature which is not affected by external temperature changes. Some
warm-blooded animals hibernate during the cold season (bats). Others migrate to warmer
areas and return in the spring (swallow, storks).
Temperature influences plant life activity
E.g. fruit trees and plants such as grapes lose their leaves in winter and thereby limit their
metabolism.
Hibernate – to pass the winter in a dormant condition with metabolism greatly slowed down.
1.11.4 Water and the water cycle
a) Water is probably the most important ecological factor. It is responsible for all physical
processes which occur in plant and animals.
b) Once water has been used, it does not disappear. Instead, it is recycled.
c) The water cycle plays a very important role in plant and animal life:
The water cycle is the continuous movement of water in a cycle
between the soil and the atmosphere.
d) Referring to figure 50, the following occurs during the water cycle:
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Figure 50: The water cycle
i) Precipitation: frost, mist, hail, snow, and rain: this is the water moving from the
atmosphere to the soil, providing moisture, absorbing the heat and cooling the soil.
ii) The water that has fallen is absorbed by the upper layers of soil.
Infiltration: the water moves through the topsoil into the subsoil and into the water table
where it is stored, and becomes available for plant roots.
Some of the water also flows away into the dams and the sea.
iii) Evaporation: the water reaches the atmosphere again from the large water surfaces
that make up 70% of the earth’s surface, and also by means of evaporation from the soil.
iv) Transpiration: plants lose water by means of transpiration and this reaches the
atmosphere.
1.11.5 Fires
Fire is a natural part of the sawannah ecosystems in many parts of the world e.g. Namibia.
It can be good for plants. In some plants the germination of seed is stimulated by fire.
However, too much fire or fire at the wrong time of the year is extremely bad to the
environment.
Uncontrolled and unplanned fires cause a lot of damage ecologically and economically and
must be prevented.
1.11.6 Atmospheric gases
All living organisms are dependent on the air around them. The most important gases for
animals and plants are: oxygen, carbon dioxide, nitrogen and water vapours. In the
atmosphere there is about 21% oxygen, 0.03% C02 and 79% Nitrogen.
Oxygen is obtained from photosynthesising plants.
Carbon dioxide in the atmosphere comes from the carbon dioxide in the soil and in the water.
It is also released during the decomposition of organic material and as a by-product of
respiration (breathed out by humans and animals)
Nitrogen is important for the synthesis of substances such as proteins. It is produced by
Nitrogen-fixing bacteria in the soil and is also made available to plants in the form of
nitrates during thunderstorms.
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All the elements essential for life move in cycles. Without this cycling of nutrients and
elements, the natural resources would soon be exhausted. Two such cycles, namely the
oxygen and the carbon dioxide cycles will be discussed.
1. The oxygen cycle
Atmospheric oxygen is important for the cellular respiration in living organisms.
During respiration, oxygen combines with hydrogen, and water is formed in the cells.
This water can be excreted by the organisms. It is also used by green plants for
photosynthesis.
A by-product of photosynthesis is oxygen-and this oxygen is made available for respiration
once again.
Atmospheric oxygen in the form of O is part of the ozone layer which helps to prevent highenergy radiation from the sun reaching the earth.
2. The carbon dioxide (carbon) cycle
Carbon dioxide is built up from carbon and oxygen.
Carbon is essential for all living organisms.
Carbon dioxide is constantly being produced:
1) By the respiration processes of animals on land and in the sea;
ii) Through the burning (combustion) of oil, petrol, coal, by motorcars, factories, aeroplanes
and households;
iii) Through fires (veld fires, household fires);
iv) Bacterial respiration during decomposition: at the death of a plant or an animal. These
plant and animal remains will during the course of millions of years again form products
such as oil and coal.
Removal of carbon dioxide occurs through the photosynthetic processes of plants. During
photosynthesis, the carbon dioxide from the atmosphere is used to make carbon products such
as glucose.
1.12 Biotic factors
Biotic factors are all the living things or their materials that directly or indirectly affect an
organism in its environment. Factors such as parasitism, disease, and predation (one
animal eating another) would also be classified as biotic factors.
1.13 The biotic components
All the living factors in an ecosystem are known as the biotic components.
The biotic components of an ecosystem can be divided into two large groups
1 the autotrophic component (self feeding – make their own food)
2
the heterotrophic component (various feeding)
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1.13.1 The autotrophic components
Organisms that can use the energy in sunlight to convert water and carbon dioxide into
Glucose (food - photosynthesis)
Autotrophs are also called Producers because they produce all of the food that
heterotrophs use
Without autotrophs, there would be no life on this planet
E.g. Plants and Algae
Figure 51:
Autotrophs that get their energy from inorganic substances, such as salt are called
Chemotrophs. They live deep down in the ocean where there is no sunlight.
E.g. Bacteria and Deep Sea Worms
1.13.2 The Heterotrophic components
Organisms that do not make their own food
 Another term for heterotroph is consumer because they consume other organisms in
order to live. Heterotrophs live from the organic substances produced by the autotrophs –
the photosynthesizing green plants
E.g. Rabbits, antelope, mushrooms
Figure 52: Impala
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Source: B. Curtis
Heterotrophs may be divided into the following groups:
1 The primary consumers
These are also known as the herbivores. They are plant-eaters and live on the producers or
the green plants
Examples: garden snails, caterpillars, locusts, mice, giraffe, cows, elephants, hippos,
rhinos, antelope.
Figure 53: Giraffe
Source: B. Curtis
The secondary consumers
Carnivores – eat ONLY meat. They include the predators. They prey on the herbivores and
other (smaller) carnivores.
E.g. lions, lizards, spiders, leopard, cheetah,sharks
Figure 54: Cheetah (left). Leopard (right)
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Source: B. Curtis
Predator
A predator eats other animals. For example:
 The cat is a predator, because it eats other animals. The bear is a predator, because it
eats other animals.
Figure 55: Cats (left) and bears (right) eat fish
 People are predators too!
Figure 56:
Prey
Any animal which is hunted and killed by another animal for food is prey.
Figure 57:
Predator
Prey
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3. The omnivores
Omnivores – eat BOTH plants and animals. Omnivores are therefore also heterotrophs and
may be primary or secondary consumers.
Eg; human beings, pigs, crabs, baboons
Figure 58: Human being (left)
Source: humanitarianreform.org
4. Scavengers/Detritivores – feed on the tissue of dead organisms (both plants and animals)
or they eat the remains of dead organisms left by the consumers
Eg. – Vultures, hyaenas, crows and shrimp
Figure 59: Black-backed jackals (left) Vultures (right)
Source: B. Curtis
1.13.3. The decomposers
The last links in the chain are the decomposers. They are also known as the microconsumers. They are also heterotrophs which feed on decaying or dead matter. (They
break down all dead organic matter).
 If you defecate (poop), they eat that.
 If you lose a leaf, they eat it.
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Whenever something that was alive dies, the decomposers get it. Decomposers break down
nutrients in the dead material and return it to the soil.
The producers can then use the nutrients and elements once they are in the soil. The
decomposers complete the system, returning essential molecules to the producers.
Decomposers are very important since they break down complex organic substances into
simpler substances which are released into the environment and absorbed by the
producers.
E.g. – Bacteria, insect larvae and Mushrooms
1.14 Trophic levels
Energy moves from one organism to another when food containing the energy. Each step in
this transfer of energy is known as a trophic level. The main trophic levels are producers,
consumers, and decomposers. There is a constant flow of energy between these trophic
levels and a contanst loss from one level to the next.
The primary consumers obtain their energy from the producers; the secondary consumers
eat the primary consumers and/or other secondary consumers and in this way obtain their
energy.
The cycle ends when the producers and consumers are decomposed by the decomposers to
form abiotic components again. Decomposers – bacteria and fungi that break down dead
organisms and recycle the material back into the environment.
There is therefore a constant flow of energy from the sun through different organisms and
back to the soil and atmosphere.
1.15 Food chains
The energy flow from one trophic level to the other is known as a food chain. A food chain
is simple and direct. It involves one organism at each trophic level.
This transfer or flow of energy from its source (the sun) and then through green plants and a
series of other organisms – each of which is food for the next – is known as a food chain.
Figure 60:
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1.16 Food web
Most organisms eat more than JUST one kind of organism. When more organisms are
involved it is known as a FOOD WEB. Food webs are more complex and involve lots of
organisms. Isolated single food chains as shown in figure 58 never occur in nature. Usually a
number of food chains are interwoven to form a large and complex food web. Food webs
show what eats what in order to gain the energy it needs to live. Food webs use arrows to
show what eats what. Nearly all food webs start with a green plant. Green plants are called
producers because they produce their own food. Animals are consumers. Some consume
plants to get the energy they need to live (primary consumer). Others consume other
animals (secondary consumers – they eat the primary consumers). Animals that are eaten
by other animals are called prey . Some prey animals are herbivores. Some omnivores and
carnivores are also prey to other animals. Animals that eat other animals are called
predators. Some animals are predators and prey. This means they eat some animals but are
eaten by others. The top predator that is prey to no other animal is called an apex
predator. Eg; lion. However if a lion dies it is eaten by scavengers (Eg; vultures and jackal)
and decomposed by bacteria.
Figure 61: Food web
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1.17 Ecological pyramid
 An ecological pyramid shows the relationship between producers and consumers at
different trophic levels in an ecosystem. It shows the relative amounts of energy or matter
contained at each trophic level. The Pyramid shows which level has the most energy and
the highest number of organisms. The producers form the base of the pyramid (fig 60) and
the consecutively smaller trophic levels are placed higher up the pyramid until the apex is
reached. With these pyramids it can be seen that the producers are the most numerous,
the secondary consumers still fewer, and so on. There are three types of pyramid that can
be used to display ecological systems:

Pyramids of NUMBER

Pyramids of BIOMASS

Pyramids of ENERGY
Figure 62:
 Which level has the most energy?
 Which level has the most organisms?
 Which level has the least organisms?
 Which level has the least energy?
1 Pyramid of Numbers
The food chains and webs show the flow of material and energy in ecosystems, but they do
not give you any idea of how many organisms there are in the ecosystem.
A pyramid of numbers (fig. 61) shows the numbers of organisms present in each level of a
food chain.
Suppose the numbers found in a particular habitat are as follows:
 2000 plants
 25 mice
 1 owl
The pyramid of numbers would be as shown below.
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Figure 63: Pyramid of Numbers
In some cases, however, a numbers pyramid can seem inverted.
An inversion seems to exit when an organism that occurs in the greater number does not
fall at the bottom of the pyramid.
Sometimes you do not get a pyramid because one organism in the chain is unusually large,
e.g. one large tree providing food for thousands of caterpillars and hundreds of secondary
consumers, such as spiders and birds (fig 64).
Figure 64: numbers pyramid can seem inverted
2
Pyramids of Biomass
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 Biomass is a word used to describe the mass of living material in an area. If you could
collect all of the plants and animals in an area and weigh them, this would be the biomass
of that area. A pyramid of biomass is a diagram showing the total weight (mass) of
organisms at each level of a food chain. Biomass always gives a pyramid since producers
must have the most biomass and consumers must have less. Measured in Kg, grams.
Pyramids of biomass are always pyramid-shaped.
Figure 65: Pyramids of Biomass
3
Pyramid of Energy
 Shows the energy available at each trophic level. The size of the blocks represents the
proportion of productivity. Measured in Joules or Calories. Most of the energy available to
the community is in the 1st trophic level. Only 10-20% of the energy is available to the next
trophic level (≈ 90% lost).
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Figure 66: Pyramid of Energy
This is the most important pyramid since energy is what is really being transferred from
one level to the next. Just as numbers of plants or animals can be misleading (fig 66) so
can biomass e.g. 1kg of grass contains less energy than 1 kg meat.
1.18 Breaking the chain
Organisms living in a ecosystem depend on each other. If one part of a food chain dies out
or is greatly reduced, the consumers have to find alternative food, move away, or starve.
This then affects the consumers further along the chain/web.
1.19 Endangered or extinct?
The number of people in the world is growing at an alarming rate. But this is not true for
all animals and plants. In some cases, there are only a few of one type of animal and plant
left in the wild. These organsiums are endangered. If they die out completely, they
become extinct.
1.20 Why does this happen?
There are lots of reasons why organsims become endangered or extinct.
The most common are:
 Loss of habitat (woodlands cut down, rivers drying up, bush encroachment).
 Chemicals or pollution poison the animals.
 Overexploitation – too much use e.g. hunting (for sport, their fur, tusks or meat) or
collecting (for firewood etc.)
1.21 Caring for the environment
It is in our own best interests to look after the world we live in. If a habitat is lost or
damaged, it has an effect on everything else, even if we do not see or understand it
straight away. Remember - once something becomes extinct, it’s gone forever!
We can mismanage the environment and cause it to become unproductive e.g. too many
herbivores on a farm will kill the grass and lead to erosion.
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1.22 The mutual interactions in an ecosystem
As you must have seen during walks through the bush and the veld, a number of interesting
interactions occur in nature, ensuring the survival of a particular species:
 shrubs provide twigs for spiders to spin their webs
 insects use leaves on which to lay their eggs
 plants depend on animals for the dispersal of seed
 large trees offer shade to plants and to animals
There is an endless list of these interactions occurring in nature. Let us study these
interactions, as well as the different forms of interactions, in some more detail:
1.23 Competition
Organisms within a community often have to share water, food and living space. When
there is enough of everything for everybody, then sharing is easy. However, if one factor is
limited (scarce), the organisms will compete with one another.
Example:
(i) competition between animals for a limited supply of food, water or shelter
(ii) Competition between plants to obtain enough sunlight or space to grow, example seeds
which have been sown too close together.
 Intraspecific competition is competition between two or more individuals of the same
species, because their needs are similar. E.g. lions fighting at a kill
 Interspecific competition is competition between organisms of different species (ex.
between kudu and giraffe)
1.25 Symbiosis
A close and permanent association between organisms of different species.
1 Commensalism – a relationship in which one organism benefits and the other is not
affected
 Example: cow seeking shade beneath a tree
 Bird nest in the tree
 Bromiliad Roots on Tree Trunk Without Harming Tree
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2
Mutualism – a relationship in which both organisms benefit from each other
 Example: Birds eating pest off a rhino’s back
 Bees visit a flower to obtain nectar; the flowers need the bee for pollination.
 Anemones Protect and Feed Clownfish

3
Parasitism – A relationship in which one organism benefits and the other is harmed
 Example: Ticks on a dog
 Tapeworm (Taenia solium) lives in the intestine of man
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There are two types of parasites:
a) The ectoparasite living outside the body of the host: - ticks (parasite) on cattle
(host).
-
lice on fowls;
-
-fleas on dogs and cats
-
Aphids on plants
b) The endoparasites living inside the body of the host; in the digestive system, in
the blood vessels, the tissues, the air passages:
4
-
bilharzias (schistosoma) lives in the bladder or the intestine of man
-
the plant parasite: dodder, living on Lucerne, sunflowers and mealies.
Predation- Predators are secondary consumers and eat other living animals
Predators have a number of victims (parasites normally have only one). They either eat
their entire prey or leave the rest to scavengers
Example: lions, hawks, snakes, parying mantis, spiders.
Disturbances
Disturbances are events such as storms, fire, floods, droughts, overgrazing, or
human activity that damage biological communities, remove organisms from
them, and alter the availability of resources. The types of disturbances and
their frequency and severity vary from community to community. By
gathering data from specific communities over many years, ecologists are
beginning to appreciate and understand the impact of disturbances.
We think disturbances in negative terms, but not always. Small-scale
disturbances often have positive effects. For example, when a large tree falls
in a windstorm, it disturbs the immediate surroundings, but it also creates
new habitats. For instance, more light may now reach the forest floor, giving
small seedlings the opportunity to grow; or the depression left by its roots
may fill with water and be used as egg-laying sites by frogs, salamanders,
and numerous insects. Small-scale disturbances may enhance environmental
patchiness, which can contribute to species diversity in a community.
Communities change drastically following a severe disturbance that strips away
vegetation and even soil. The disturbed area may be colonized by a variety of
species, which are gradually replaced by a succession of other species, in a
process called ecological succession.
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Ecological Succession
•
•
A change in the community in which new populations of organisms
gradually replace existing ones
– 1. Primary Succession – occurs in an area where there is no
existing communities and for some reason (s) a new community of
organisms move into the area
A change in the community in which new populations of organisms
gradually replace existing ones
– 2. Secondary Succession – occurs in an area where an existing
community is partially damaged
– 3. Climax Community – a community that is stable and has a
great diversity of organisms
An example of succession
1. There are certain grasses, example the Aristida, which are
known as pioneer grasses. As the grass grows and dies,
humus and soil is formed. Insects and decay microbes are
also part of this community.
2. This pioneer community changes the abiotic surrounding
and creates favourable conditions for other organisms:
secondary succession can now take place. Shrubs and
bushes grow, mice, jackals and birds arrive.
3. Next, small trees, then taller trees grow. The variety and
number of plant species increases.
4. Eventually a forest with a mature, self-supporting climax
community is formed.
5. Climax communities may be formed in the veld, a dam, or in
the ocean.
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