Madda Walabu University
Collage of Agriculture and Natural Resource Management
Natural Resource Management
Handout for General ecology course for 1st year NRM
Course instructor Medhanit B
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CHAPTER ONE
1. INTRODUCTION
1.1 Definition of General Ecology
The word ecology (Greek Oikos= home, habitat, logos= study) was coined over a century ago.
So literally; it is the study of organisms at home or the study of the earth’s “house holds”
including the plants, animals, microorganisms and people that live together as interdependent
components. It appears to have been used as early as 1858, and later by the German biologist
H.Reiter in 1865. However, Ernst Haeckel, another German biologist (zoologist) defined it for
the first time in 1869 “as the body of knowledge concerning the economy of nature-the
investigation of the total relations of the animal, both to its inorganic and organic environment,
including above all its friendly and inimical (unfriendly) relations with those animals and plants
with which it comes directly or indirectly into contact”. This definition still holds good if we
simply replace the words “relations of the animal” by “relations of the organism” to include also
the plants and man.
As a recognized distinct field of biology, the science of ecology dates from about 1900 and only
in the past decade has the word become part of the general vocabulary. Since Haeckel, ecology
has been defined variously by different people placing different degree of emphasis on the
components of nature and their interrelations. British ecologist Charles Elton (1927) in his
pioneering book Animal Ecology defined ecology as “scientific natural history concerned with
sociology and economics of animals.” American ecologist Frederic Clements (1916) considered
it “as the science of community.”
Wood bury (1954) treated it as “science which investigates organisms in relation to their
environment, and a philosophy in which the world of life is interpreted in terms of natural
process.”
More recently, renowned (famous) American ecologist because ecology is concerned not only
with organisms but with energy flows and material cycles on the lands, in the oceans, in the air,
and in fresh waters, Eugene. P. Odum defined ecology as “the study of the structure and function
of nature, it being understood that mankind is part of nature and the science of the totality of man
and environment.” R. Margalef of Spain (1968) treats ecology as “the study of ecosystems.”
Indian ecologist R. Misra (1967) defines ecology as “the study of interactions of from, function
and factors.”
Krebs (1985)- defined ecology as the scientific study of the interactions that determine the
distribution and abundance of organisms.
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1.2. The history of man-environment interaction
Until about 10,000 years ago people lived by hunting, fishing and gathering edible plants, tubers,
and roots. Today less than 1 percent of the earth's inhabitants live by hunting and gathering. The
increase in population, resource use, and pollution are merely symptoms of this fundamental
cultural change from humans as hunter-gatherers to human as shepherd and tillers of the soil to
humans in industrial society.
The human-nature interaction in general is divided in to three major stages:-
1. Hunter-Gatherers
a) Early Hunter-Gatherer groups - controlled by the local environment
b) Hunter-Gatherer groups - affected local and regional environment but did not "control" it.
Early humans survived and multiplied due to three major cultural adaptations all the product
of intelligence:
1. The use of tools for hunting, collecting and preparing food and making protective
clothing.
2. Learning to live in an often-hostile environment through effective social
organization and cooperation with other human beings
3. The use of language to increase the efficiency of cooperation and to pass on
knowledge of previous survival experience.
With the use of advanced weapons and fire hunter-gatherer societies made some significant changes
in their environment. Because of their small numbers, however, their impact was insignificant on
even a regional scale. They were examples of humans in nature.
2. Humans against nature
a. Agricultural societies-This society showed more control (force) over nature with increased
undesirable local and regional environmental effects.
About 10,000 to 12,000 years ago there began one of the most significant changes in human history.
People learned how to herd game instead of hunting it, and they " invented agriculture" to grow
selected wild plants close to home instead of having to go out and gather them over a large area.
Over several thousand years the importance of hunting and gathering declined as more and more
people became shepherds and farmers.
The shepherds burned and cleared forests, replacing them with savannas and grass lands containing
annual plants that provided food for their flocks of grazing animals. Some of these grasslands were
in turn degraded when too many domesticated animals were allowed to graze in one area or when
grazers remained in one place for too long. As a result, grasslands were destroyed and soils were
eroded.
The first type of plant cultivation, called horticulture ("hoe-culture") began when women
found that they could quite easily grow some of their favorite food plants by digging a hole
with a stick (a primitive hoe) and placing roots and tubers in the ground. People also
learned how to plant and grow seed crops such as wheat, barley, rice, peas, lentils, corn, and
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potatoes.
Another method that was developed to grow food plants is called slash-and-burn or shifting
cultivation. In this method a small patch of forest is cleared and the dried vegetation is burned
before planting. The ash left after the burning is inorganic fertilizer for the soil. A variety of crops
are grown on this forest opening until the plant nutrients in the ash are exhausted-typically after 2 to
5 years. The farmer and his family then move on and clear another patch, leaving the recently used
cropland fallow for several years. This allows wild plants to repopulate the original cleared area,
making nutrients available again for growing crops. Shifting cultivation works well in the tropical
forest environment with its ample sunshine and rain provided the human population density remains
low and abandoned areas are not replanted for 10 to 20 years.
True agriculture from agri (generally, of ager field): the science and art of cultivating, harvesting
crops and raising of live stock: Tillage, Husbandry, Farming began with the invention of the plow,
pulled by domestic animals. At this point people no longer depended on their own muscle power as
the prime source of energy for growing food. Later improvements such as irrigation, terracing of
hill sides, developing improved strains of crop plants, and using animal manure and commercial
fertilizers allowed farmers to harvest more than one crop per year and greatly increased the amount
of land under cultivation.
As people learned to cultivate plants efficiently, they had not only a constant food supply but a
regular food surplus. This surplus had three important effects:
1. Without the threat of starvation, populations began to increase;
2. People cleared more and more land and began to control and shape the surface of the
earth to suit their requirements
3. Urbanization began- villages, towns, and eventually cities slowly formed as people
developed specialties other than farming.
Agriculture is the deliberate attempt to alter and control the environment in order to grow
food. As farmers grew in numbers and spread out over much of the earth, they created a
much greater environmental impact than had hunter-gatherers.
1. Diverse forests and grasslands were replaced with large areas, typically planted with
a single food crop such as wheat and maize.
2. Poor management of many of the cleared areas allowed vital topsoil to wash away
and pollute streams, rivers, and lakes with silt.
3. Land-clearing activities destroyed and altered the habitats of plant and animal
species endangering their existence and in some cases causing or hastening their
extinction.
4. Irrigation without proper drainage led to the accumulation of salts in topsoil,
decreasing soil fertility.
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5. Pests that were usually controlled naturally by the diverse array of species in forests
spread much more rapidly in areas planted with one or only a few crops. Pesticides
were used to protect food crops, but this led to a new series of problems that
threatened wild life, polluted the air and soil and in some cases increased the number
and size of pest populations.
The development of agriculture thus brought about a fundamental modification in humanities
relationship with the environment, as more and more people began shifting from hunter-gatherers in
nature to shepherds, farmers and urban dwellers against nature.
b. Industrial societies- much more control over nature with more and more undesirable local,
regional, and global environmental effects. Humans have learned how to find and use more and
more energy in their attempts to change and control the environment. Early societies had to rely on
the power of their own muscles to survive. Agricultural societies eventually learned to use draft
animals and later wind and water power to help them exert more control over the land and
their food supplies. During the eighteenth century, however, industrial societies made a
gigantic(massive) leap in using energy by discovering how to unlock the chemical energy stored in
fossil fuels such as coal, oil and natural gas.
The gradual rise of industrial societies, fueled by these new sources of energy, has allowed the
creation of many useful products and has raised the standard of living of many people throughout
the world. At the same time it has intensified many existing environmental problems and created a
series of new ones such as pollution from DDT, Lead, Mercury, PCBs; solid wastes, radioactive
wastes.
Increased mining to provide industries with raw materials has disrupted more and more of the
earth's surface and has threatened plant and animal species.
The benefits of the industrial revolution are great. Increasingly, however, our time, energy, money,
and new forms of technology must be used to correct the ill effects of technological advances. We
are learning that in many cases the more we try to control nature the less control we have.
3. A sustainable Earth Society:
A sustainable earth society-selective control based on ecological understanding and global
cooperation with nature to reduce undesirable environmental effects. There are exciting and
important indications that we may be ready to move into a new phase of cultural evolution- the
transition from an agricultural industrial society based on humans against nature to a sustainable
earth society based on humans learning how to cooperate with nature rather than blindly attempting
to control it.
People have to begin to see themselves as belonging to a global tribe whose cooperative efforts are
necessary for the survival of everyone.
Unlike the frontier society (mentality) which sees the earth as a place of unlimited room and
resources, wherever increasing production, consumption and technology inevitably lead to a better
life forever one i.e. and attempt to dominate nature. A sustainable earth or conserver mentality
(society) sees that the earth is a place of limited room and resources and that ever increasing
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production and consumption can put severe stress on the natural processes that renew and maintain
the air, water, and soil upon which we depend i.e. it calls for cooperating with nature, rather than
blindly attempting to dominate it.
1.3 Level of study in Ecology
Ecology is a wide field that encompasses all life forms in the earth thus their are different types
of ecology. These include:
Organism Ecology: This studies how different living organisms respond to stimuli caused by
physical environment. The organisms adapt to the environment by either embracing or shying
away from its effect. A change in the physical environment will show a change in behavior or
physical attributes e.g. an animal physically will escape an unfriendly environment and a plant
will grow away or halt germination in an unfriendly territory.
Population: All Organisms grow and die. How they will populate will be influenced by factors
such as size of the colony, birth and death rate, population growth rate as well as ‘survival for the
fittest. Thus the most dominant species will always reign supreme on the weaker species.
Community: All organisms dwell in a common ecology having both flora and fauna. In this
ecology, either a food web or food chain there exists a strata detailing the type of species and the
role it plays in the ecosystem. Whether a Parasite, a predator or a food source, each plays a key
role to create harmony in the ecology. Competition, mutualisms are key to establishing and
maintaining a community.
Ecosystem: Living and non living things interact with the atmosphere, energy sources,
temperature, water in a capacity to recycle, regenerate, consumption or production. This ensures
the energy flow cycle is kept in harmony.
1.4. The Application and relevancy of Ecology
The earth is one large entity, and events taking place in the earth’s environment, in the biosphere,
exert a mutual influence upon one another. Climate, soil, vegetation, and animal life should not,
therefore, be considered simply as isolated branches of nature. It is impossible to separate the
phenomena associated with life from environmental factors, and the task of the ecologist is to
understand these interconnections.
Man has been interested in ecology in a practical sort of way since early in his history. In
primitive society every individual to survive, needed to have definite knowledge of his
environment, i.e., of the forces of nature and of the plants and animals around him. Civilization,
in fact, began when man learned to use fire and other tools to modify his environment. It is even
more necessary than ever for mankind as a whole to have an intelligent knowledge of his
environment, if our complex civilization is to survive, since the basic laws of nature have not
been repealed; only their complexion and quantitative relations have changed, as the world’s
human population has increased and as man’s power to alter the environment has expanded.
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The modern subject of ecology includes all phenomena that result from the interaction of
organisms with their environment and with other organisms. Among these phenomena are the
dispersal of species, the speciation mechanism itself, population regulation, life in communities,
modification of the habitat, nutrient cycling, energy flow and efficiency of energy use, and the
maintenance of the earth as a life support system.
Existence in the world is made up of living and non living things. The two groups have to coexist
in order to share the resources that are available within the environmental ecosystem. To
understand about this mutual co relationship we need to study and understand ecology.
Ecology is defined as the scientific study of interactions of organisms (both biotic and abiotic)
with one another within the physical and chemical environment. Ecology involves use of
scientific methodology via lab experiments to understands how the different organisms grow,
populate, how they interact with other organisms either as parasites, predators, how the
organisms die out as well as how they evolve or adapt to changing climatic and environmental
situations.
Importance of Studying Ecology
The study of ecology is all about connections. By carefully using the principles of ecology, we
can learn to predict, extinguish, counteract and prevent potentially adverse effect we might have
on the globe around us.
It is paramount to study Ecology because:
Environmental Conservation: By studying ecology, emphasis is put on how each
species needs the other for peaceful coexistence. Lack of understanding ecology has led
to degradation of land and environment which is home to other species thus leading to
extinction and endangerment of species because of lack of knowledge e.g.
dinosaurs ,mammoth, white shark ,black rhinos , sperm whales etc.
Resource allocation: All the plants and animals need to share limited natural resources
such as air ,minerals, space and environment .Lack of ecological knowledge how has led
to deprivation and looting of these natural resources leading to scarcity as well as
exploitation and competition.
Energy Conservation: All species require energy whether light, radiation, nutrition etc.
Poor understanding of ecology is seeing the destruction of the energy resources e.g. Non
renewable sources like oil, coal, natural gas and also pollution and destruction of the
Ozone layer.
Eco Friendliness: Ecology helps to appreciate harmonious living among the species; this
will ensure natural order of things is followed.
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Application of Ecology
Ecology is very important subject it has applications in major areas such as Water shed
Management, Soil conservation. Agriculture, Wild life Management, Aqua Culture, Land
Utilization, Pollution…
Water is stored in Dams or Reservoirs for the purpose of electricity production at the time of
construction of Dams there should be a ecologist to see ecological aspects, The major aspects are
soil erosion and wind because these two aspects can fill the Dams (silting up)
• Now a day’s many factors are disturbing the soil. Many cultivated lands are being
disturbed by construction of buildings or any other residential areas. With the help of
ecology we can study the topography, climate conditions, soil erosion these are important
aspects of ecology for soil conservation.
• For agriculture of crops following aspects are important Soil, mineral composition,
Temperature, biotic factors of the area all these factors are studied by an ecologist so
without information of all aspects it will be very difficult to grow a plants and it can
result in economic loss.
• For the establishment of wild life, vegetation of area have major role for different species
of animals. There will be different types of food web and food chains both these are
equally important. So for habitat of different species in wild life ecology studies are
important.
• The rearing and breeding of fish in water is called aqua culture. The ratio of predators in
aqua culture is important so for fish culturing there should be dense population of fish
then other types of animals. Other ecological studies such as temperature and soil
conditions are important in fish culturing. Heavy soil are more important for fish
culturing.
• Any physical, chemical or biochemical undesirable changes in environment, soil, water
or for the environment is called pollution. In order to Control pollution, we have to
studies causes of pollution, identification of wastes type to characterize into degradable,
non degradable and recyclable and this can be processed by the help of ecological
knowledge.
During Plantation forest establishment. For selection of area according to ecological adaptability
and profitability of selected plant species
