ECOLOGY

Ecology is the scientific study of the interaction between organisms and components of

their environment.

Synecology is the ecological study of the different species.

Autecology is the ecological study of a single species.

Ecological levels, from the smallest to the largest:

 Habitat: a place where an organism lives.

 Population: a group of organisms of the same species living together in the

same habitat.

 Community: a group of populations living in a prescribed area or habitat. This

is a naturally occurring group of organisms of different species,

inhabiting a common environment and interacting with each

other, especially through food relationships and which is

independent of other groups.

 Ecosystem: is any unit of the environment, composed of living and non-living

components whose interactions result in a stable system.

 Biome: is a collection of similar communities in a certain large area of the earth,

where climate and topography are fairly uniform.

 Biosphere: is that part of the earth and its atmosphere which is inhabited by

living things.

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ECOLOGICAL FACTORS

Ecological factors are divided into two: physical or abiotic (non-living) and biotic

(living factors).

1. Physical (or abiotic) factors:

a) Climatic factors:

i) Precipitation: this refers to the amount, reliability, distribution and

seasonality of rainfall and all these are important aspects of climate.

ii) Humidity: often expressed as Relative Humidity (RH). It is a measure

of moisture content of the atmosphere, expressed as a percentage of

the quantity of water present in a given volume of air in relation to

maximum quantity of water the air can hold at the same temperature.

Note that RH is influenced by temperature.

iii) Light: both quality (effect of the different wavelengths, e.g. UV, blue,

etc) and quantity.

iv) Temperature: temperature is important for enzyme activity in living

cells. It also affects the rate of transpiration and evaporation.

v) Air/Water currents: Water currents would include both vertical and

horizontal currents. Horizontal currents are for example in the transfer

of algal cells, where if the previous day’s currents blew towards the

shore, the following morning, the water along the shore is all green.

When strong winds blow away from the shore, the water clears

because the algal cells have been transferred away from the shores by

the horizontal currents.

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b) Edaphic (or soil) factors: these are the physic/chemical factors which affect

soil and hence, plant and animal life.

i) Soil organisms: for example, soil micro-organisms, like bacteria, algae

and fungi, which affect the soil turn-over and hence, aeration.These

organisms affect seed germination by breaking seed dormancy. They

also contribute to N-cycling as N2 fixers (for example, some blue-

green algae, the Cyanobacteria).

ii) Soil moisture: affects supply of water and minerals; also seed

germination as a necessary factor. But too much of it may render the

soil water logged

iii) Soil texture: this refers to the size of the particles and their fractional

proportions. This affects soil aeration, water content and thus, soil

productivity.

iv) Soil structure: this is the arrangement of the soil particles, which has an

effect on drainage, percolation, erosion and aeration.

v) Soil temperature: this affects soil formation, respiration of organisms

and N2 fixation. It also influences seed germination and root growth.

vi) Soil pH: this affects the activity of the soil microorganisms, solubility of

solutes, e.g. PO4, Mg, Ca and Fe. It also influences distribution of

vegetation.

vii) Soil aeration: this is the amount of air in the soil which depends on soil

texture, water content, and amount of humus present in the soil.

c) Topographical factors: which are factors which are controlled by altitude,

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 slope and other geographical aspects of the place.

Abiotic factors of aquatic ecosystems, e.g. Lakes:

 Salinity

 Wave action

 Water currents, both vertical and horizontal

 Light: quality and quantity and its penetration

 Nutrients, e.g. N, P, Si, etc.. and their ratios, e.g. the N:P ratio.

 O2, CO2 concentration and pH.

Fires as an ecological factor:

Fires have both positive and destructive effects.

Positive effects of fires:

 Breaks seed dormancy in some species, e.g. Acacia.

 Destroys pests and parasites, e.g. ticks of cattle.

 Etc.

Negative effects of fires:

 Removes vegetation cover, leading to soil erosion.

 Destroys some organisms important in the habitat.

 Destroys humus and the soil.

 After a fire, some seeds of unwanted plant species may invade the area

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2. Biotic ( or living or biological) factors:

These are factors resulting from the effects of the living organisms on one another within

a habitat where they live. Such interactions may result in associations like: predation,

commensalism, symbiosis, herbivory, competition (intraspecific or intespecific) , etc.

Humans as important biotic factors:

Through his activities in trying to make a living, man has affected the lives of other

organisms through such activities like:

 habitat destruction for: settlement, road construction, agriculture, etc..

 pollution of many natural ecosystems: rivers, lakes and land, through his use of

radioactive materials in warfare, oil leaks, nuclear reactor disasters.

 Destruction of the ozone layer (how)

 Over-exploitation of natural resources (e.g forests, etc.), leading to the

greenhouse effect (global warming).

The greenhouse effect (Global warming):

CO2 concentration

Photosynthesis Respiration Combustion Volcanic eruptions

Note:

 Carbon dioxide is the least gas in the atmosphere (0.04%)

 It is used for photosynthesis by plants (forests and other vegetation)

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  It is availed to the atmosphere through activities like respiration, combustion

and volcanic eruptions.

 Carbon dioxide uptake and release are not in balance: its release into the

atmosphere tends to be higher than its uptake (which is only through

photosynthesis). Thus its concentration to continuously increase. Carbon dioxide

is transparent to incoming, visible solar radiation, like glass (in green houses). It

absorbs infrared heat re-radiated from the earth’s surface and therefore CO2

forms a heat blanket by shielding heat from earth back into the outer space

and therefore this increase in heat results in increasing temperatures on the globe

(earth’s surface). This phenomenon is referred to as ”the Green House effect or

 Global warming”. Thus, Man’s activities increase CO2 concentration when he

cuts down forests and other vegetation which results in reduction of CO2 uptake

by photosynthesis. Also his burning of fossil fuels increases CO2 concentration.

POLLUTION

Pollution is the act of introducing harmful substances/impurities to the environment as a

result of human activities and/or other natural processes. Pollution can be by biological,

chemical or physical agents. Pollution remains a major cause of ill health in rural, peri-

urban and urban areas. Increase in human population and urbanization has caused more

production of domestic and industrial wastes and such wastes have become a major

pollutant of the environment.

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Human activities such as industrialization, have resulted in the production of chemicals

which include heavy metals and products from the petroleum industry. Human waste,

agricultural chemicals, e.g. herbicides, insecticides, etc. have worsened the situation.

Such pollutants finally reach and pollute the food chain, surface waters (lakes, rivers,

wells, etc.) or ground water and can finally be ingested by humans.

Types of pollution:

 Air pollution: this is the discharge of foreign gases, dust, fumes, electro-

magnetic particles, noise, pollen from industrial, agricultural and domestic

processes, vehicles, military explosives and smoke; all the above into the

atmosphere.

 Water pollution: this is as a result of discharge of effluent from: factories,

industries, agricultural fields, sewage treatment plants, wastes from homesteads,

spilling over filled latrines into water bodies. Also the introduction of heavy

metals, e.g. CU, etc., pesticides, herbicides, insecticides into water bodies.

 Ground pollution: this results from disposal of solid waste, e.g. polythene bags,

etc., liquid wastes and gaseous wastes. Other ground pollutants include:

radioactive wastes, medical wastes, wastes from research laboratories, industrial

wastes, agro-chemicals and raw sewage.

Pollution of food staff and water bodies can cause diseases like cancer, chest infections,

suppression of body immunity and destruction of plant and animal life. Pollution can also

cause degradation of land and other natural resources. It can also bring about offensive

smells irritation and discomfort. Land pollution can also promote the spread of parasitic

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worm infection whose eggs flourish in the soil. It can also facilitate the survival and

growth of disease-causing organisms.

Preventive measures of pollution:

1. Avoid discharging pollutants in the environment.

2. Urban areas should be well planned and designed and these plans and designs

should be adhered to.

3. Test all imported and locally manufactured chemicals.

4. Treat all categories of wastes before disposal.

5. All laws and regulations governing pollution should be strictly enforced.

6. All industrial workers should strictly use protective gear.

POPULATION DYNAMICS

Every population has its own unique properties:

a) Density: is the number of individuals per unit area.

b) Mortality (or Death) Rate: is the number of individuals dying in a given time.

It is usually expressed as /1000 individuals of the population / annum.

c) Birth (or Natality) Rate: is the number of individuals born in the population in

a given time. It is also expressed as a percentage (%) or /1000 people /year.

d) Age distribution or structure: is the proportional distribution of individuals of

various ages in a population and this gives a future trend of that population

growth. For example, if a population has most of its individuals as youths, that

population is likely to grow or increase very fast.

This is shown in the following diagrams: (p. 9 notes)

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 e) Dispersion: is the structural distribution of individuals within a given area.

f) Biotic Potential: is the maximum rate at which members of a population

(species) can reproduce within the available resources and living conditions

g) Growth Form: is the variation in apopulation size with time. Growth may

exponential, giving a J-shaped curve or it may be sigmoid.

Nos Nos

Time Time

J- Curve Sigmoid Curve

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 ENERGY FLOW IN AN ECOSYSTEM (Simplified)

Energy Flow from

the Sun

Energy fixed in
Photosynthesis
(Primary Producer)

Heat Loss in Primary Consumers Energy Loss to

Respiration Detritus

Secondary Consumers

Tertiary Consumers

Decomposers

Food relationships in an Ecosystem:

1. Food chain: this is a linear nutritional relationship in which one organism eats

another and is also eaten. It can also be a transfer of food energy from it source in

green plants through a series of organisms with repeated eating and being eaten.

a) Grazing Food chain:

E.g. Grass Grasshopper Snake Owl

0 0 ndry
1 Producer 1 Consumer 2 Consumer 3tiary Consumer
10 Trophic level 2nd Trophic level 3rd Trophic level 4th Trophic level

Trophic levels refers to a feeding level within a nutritional relationship.

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 b) Detritus Food chain:

E.g. Organic matter Microorganisms Detritus Feeders Predator

c) Food Web:

Mountain Lion

Mice Foxes

Predatory Birds

Insects Fish Deer Birds Rabbits

Green Plants

In this case, each organism is a member of a number of different food chains.

Terms relating to energy production and transfer:

1. Primary Production: is the amount of energy which primary producers fix in

form of organic matter , expressed in terms of:

Unit Mass / Unit Area/ Unit Time

E.g. Kg / Km2 / Year or Kg Km-2 Yr-1

a) Gross Primary Production (GPP): is the total amount of energy fixed by

10 Producers in photosynthesis / unit area / unit time.

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 c) b) Net Primary Production (NPP): is Net Assimilation of energy by plant

tissues. This excludes that portion used by the plant in its own respiration and

represents the energy available to the 10 Consumers.

Thus: GPP – Respiration = NPP

2. Biomass: is the mass of organisms per unit area of ground (or water). It is

expressed (usually) as Dry mass / Unit area E.g. Tonnes / Hactare

or as Energy / Unit area E.g. Joules / m-2.

3. Standing Crop: is the Dry weight (energy content) of organisms in an area at a

particular time.

4. Secondary Production: is the rate of production ….?

5. Trophic Efficiency: is the amount of energy that a trophic level can convert into

organic tissue. It is usually 10% of what it receives from the previous trophic

level.

ECOLOGICAL PYRAMIDS

Ecological pyramids are histograms used to show how various ecological factors

diminish with the trophic level.

1. Pyramid of Numbers: is a histogram showing the proportions of number of

organisms aat various trophic levels in a food chain. It shows a progressive

decrease in numbers, from the producers to the final consumers.

2. Pyramid of Biomass: is a histogram showing the proportion of biomass of

organisms at various trophic levels in the food chain.

3. Pyramid of Energy: is a histogram showing the proportion of energy

available in organisms at various trophic levels in the food chain.

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FACTORS AFFECTING A POPULATION

1. Density-dependent Factors: are factors of the environment whose effect

depends much on the population size. Examples of such factors include:

 Food shortage

 Competition

 Diseases, e.g. epidemics

 Pollution due to accumulation of waste

 Psychological effects of overcrowding on the reproductive rate (lower

production of people are overcrowded) ???????

2. Density-independent Factors: are factors factors of the environment whose

effect does not on the size of the population. Examples of such factors

include:

 Rainfall

 Light

 Nutrients in the soil

 Drought

 Fires

 Floods

 Natural catastrophes like landslides, accidents, etc..

ECONOMIC IMPORTANCE OF ALGAE

1. Positive importance of algae:

 Algae are primary producers

 Algae are used as food for fish and higher animals

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 Algae are used as food by humans, e.g. sea food eaten by the coastal

people

 Diatomite earth: a type of rock resulting from deposits of the heavy diatom

cells which form a white, porous and chemically inert rock used for

filtration processes (in breweries and sugar refineries), also as a

constituent of tooth paste and explosives.

 Alginic acids extracted from the cell walls of brown algae readily reacts

with anions (e.g. Mg, Na, etc) to form highly viscous gels used as food

thickeners in ice creams and diary products; as a constituent of cosmetics

and shaving creams and also in the making of artificial teeth.

 Agar powder, extracted from the cell walls of red algae, is used as a

culture medium for bacteria, fungi and algae; as food thickeners like

alginates; also as a component of cosmetics, ointments and lotions and as

an anti-drying agent in bread; and as a component of cheese, puddings,

creams and jellies; etc..

 Algae also act as biological indicators of the extent of pollution of aquatic

ecosystems, e.g. as shown by presence of blooms of ‘blue-green’ algal

species.

 Algae are much used in research (e.g. Space research and paleo-ecology of

aquatic ecosystems, using diatom cells, together with pollen grains)

 Algae as fertilizers (dead algae add organic matter to the environment) and

some ‘blue-green algal’ forms capture N2 and incorporate it in the

ecosystem.

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 Negative importance of algae

 Some ‘blue-green algal’ forms produce toxins: hepatotoxins, neurotoxins

and dermatotoxins which affect humans and may be lethal.

 Algal blooms cover water surfaces, reducing light penetration which leads

to competition for light and some cells die and sediment to the bottom and

their decomposition leads to reduction in O2 which could result in ‘fish

kills’, bad odour, colour and taste.

 Algal forms that are slippery, like Spirogyra spp covering ground/rock

surfaces causes accidents to cattle and humans.

 Algal cells also coat water containers, like jerrycans.

ECONOMIC IMPORTANCE OF BRYOPHYTES AND FERNS

Bryophytes include liverworts and mosses and their economic importance include the

following:

 Bryophtes act as primary producers

 Bryophytes provide seed-beds for higher plants.

 Ecologically, many bryophytes are pioneer plants on bare rock.

 Liverworts produce volatile oils, which have a potential as anticancer and

anti-microbial chemicals.

 Ferns are also primary producers; food for animals and provide manure

when they rot.

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ECONOMIC IMPORTANCE OF GYMNOSPERMS

Examples of Gymnosperms include the conifers and the common examples of conifers

include Pinus, Cuppressus, Casuarina (X-Mas tree), etc. Their importance include the

following:

 Gymnosperms are important as forest trees, e.g. the Coniferous forests, in

the Government forests, e.g. where Pines dominate and these forests

reduce soil erosion and are also important in rain formation.

 Some species of Gymnosperms, e.g. the Cycadales are used as human

food as a source of starch.

 Some Gymnosperm species produce Essential oils, used as perfumes for

scenting soaps. Canada balsam is a type of thick oil used as mounting

medium in microscopy when making permanent slides (it does not

crystallize nor granulate on drying). Canada balsam is also used to fix

lenses in spectacle frames. Cedar oil from Juniperus virginiana is used as

immersion oil.

 Gymnosperms as drugs: the alkaloid drug Ephedrine is extracted from

the green branches of Ephedra sinica and E. equisetina. This drug is an

important constituent of cough mixtures; it dilates bronchial tubules and

also contracts mucous membranes and it is, thus used in nasal drops and

inhalents Extracts from Ginkgo biloba are used to treat cerebral

inefficiency (poor memory), an is sold as ‘Ginkgo’ by Food Supplement

Companies, e.g. Swissgarde, House of Health, Tianshi, etc.. Extracts from

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 leaves of Taxus baccata and are used to treat asthma, bronchitis, epilepsy,

indigestion and hiccough.

ECONOMIC IMPORTANCE OF ANGIOSPERMS

Angiosperms as medicinal plants: Medicinal plants and plant-derived medicines are

widely used in traditional cultures all over the world and have become very popular in

modern society. They are being used side by side with synthetic chemicals (Western

medicine). Natural products and their derivatives make more than 50% of all drugs in

clinical use in the world. Examples of plant-derived medicines include:

 Quinines

 Morphine

 Codein

 Colchicines

 Atropine reserpine

 Digoxin ( for improving heart-bit – it digitalizes the heart

Plant extracts may be flavours, spices, dyes, perfumes, stimulants, bio-pesticides (e.g.

fungicides, anti-virals, insecticides, herbicides, etc).

Pharmacognosy is the study that deals with the identification of medicinal plants and

drugs therefrom and the study requires botanical, anatomical and phytochemical

knowledge. In traditional cultures, plant products are used in combination with

psychological treatment in an integrated approach to primary health care. The

psychological part of the treatment takes the form of magical, ritual and spiritual

approach.

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Examples of medicinal plants commonly used:

 Acacia Senegal (Gum Arabica): A small, thorny shrub in arid regions, up to 6m

high. The part of the plant used is the exudate from the stem. It is used to protect

the skin and mucosa and also to treat bacterial and fungal infections of the skin

and mouth. The product may be applied directly on the skin or included in the

formulations and tablets. Gum Arabic is a complex polysaccharide, containing

galactose, etc..

 Allium cepa (Onions): Parts used include bulb and leaves, used as antibiotics to

lower cholesterol, to treat appetite loss, digestive disorders, insect stings, etc..

When mixed with honey, it treats colds and cough. It can also treat dysentery,

scars, asthma and diabetes and can also lower pressure.

Preparaation:

- 50 g of fresh onion or 20 g of dried product

- Raw bulb may be applied directly

- Or extract may be mixed with honey or add sugar.

N.B. The pungent smell of onions is due to S-containing compounds.

 Allium sativum (Garlic): Parts used are bulbs, garlic powder, or garlic oil. Garlic

lowers lipid and is also antibacterial, antiviral and also cures common colds. It is

best used when fresh. Garlic powder can also be carefully prepared. Tinctures and

syrups can also be prepared.

 Aloe spp (e.g. A. vera, A. ferox, etc..) Whole leaf may be crushed and extract

obtained. It is used to heal wounds, also for skin care, tonic drinks, etc.. E.g. 50 –

100g of gel x 3, daily.

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  Ananas comosus (Pineapple): Pineapple juice is used as digestive tonic, cures

inflammations. Juice contains enzymes, collectively known as Bromelains; also

Vit C and Caffein.

 Artemesia spp This is a herbaceous plant whose extracts have antimicrobial

properties, cures coughs, malaria, colds, sore throat, influenza, asthma, headache,

indigestion, constipation, intestinal worms, etc.. Fresh or dried leaves are used;

leaves may be boiled in water and used as steam bath and fumes inhaled or fresh

leaves may be inserted in the nostrils to treat a blocked nose.

ANIMALS AND HUMAN DISEASES

People’s health is always under threat from organisms that carry disease-causing agents.

The biggest impact on health and longevity of people has resulted from a better

understanding of the causes of diseases. Examples of the animal groups that are

associated with human diseases:

Invertebrates:

Phylum Platyhelminthes: (Flat worms)

- Class Trematodes – the flukes, e.g. the liver flukes in domestic animals,

like cattle

- Class Cestoda – the tape worms, e.g. Taenia spp (T. saginata, T. solium)

Phylum Nematoda: (Round worms)

- The Nematodes

- The Round worms, e.g. Ascaris

Phylum Mollusca: (Snails and slugs) Snails are important vectors of parasites that

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 cause human diseases. Example is the snail Biomphalaria, an

intermediate host of Bilharzia (Schistosomiasis).

Phylum Arthropoda: With various classes of organisms that transmit parasites that

cause human diseases.

- Class Insecta: This includes different types of insects: cochroaches,

houseflies, mosquitoes, tse-tse flies, beetles, butterflies and moths, and the

stinging wasps and bees.

Below is a table, showing various vectors and the diseases associated with each vector:

VECTOR DISEASE

Anopheles Mosquito Malaria

Housefly Dysentery, Cholera, Trachoma

Tse tse fly Sleeping sickness

Flea Plague

Cockroach Typhoid

Lice Typhus

Dog Rabies

Birds Bird flue

Etc…. ….

The damage to crops by locusts and grasshoppers can also cause problems to humans.

Termites are another nuisance to humans, although they are eaten and have high protein

content.

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ECONOMIC IMPORTANCE OF FUNGI

Positive importance:

1. As research tools: fungi are used in the study of the laws of genetics, e.g. Genus

Neurospora: biochemistry and cytology

2. Preparation of organic acids: an example is Cytric acid and gluconic acid which

are commercially produced from Aspergillus niger. Fumaric and Lacti acids are

produced from Rhizopus stolonifera.

3. Fungi in various industries: e.g. bread-making (yeasts), wine-making (yeasts),

beer-making (Saccharomyces spp., cheese-making (Penicillium spp.), etc..

4. Production of antibiotics: e.g. penicillin obtained from Penicillium spp.,

griseofulvin (a fungicide against skin fungal infection) extracted Penicillium

grisiofulvum.

5. Enzymes and vitamins: Vitamin B complex and Riboflavin are extracted from some

Saccharomyces spp; ergosterol (containing vitamin D) is extracted from a number of

moulds and yeasts.

6. Hormones: E.g. the plant hormone: Giberellin (which accelerates plant growth) is

extracted from some species of Gibberella.

7. Fungi as insecticides: Many fungi attach a number of insects which attack

plants/crops and thus relieve man of these dangerous insects.

8. Fungi as food: edible mushrooms, e.g. Agaricus spp. This has the types that are

cultivated and such fungi have a high protein and vitamin content. Some species of

Saccharomyces are used in the production of yeast cake.

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Negative importance of Fungi:

1. Human diseases:

. Aspergillosis is a human disease with symptoms like those of TB and is caused

by Aspergillus niger and A. flavus.

. Infections of lungs, brain and gastric tissues are caused by some species of

Rhizopus and Mucor.

. Skin infections, e.g. skin infections of the penis is caused by Trichophyton spp.

. Ringworm infections: common in children and locally referred to as Bisente or

Mashiringi.

. Candidiasis: attacking skin, oral cavity and vulva. It causes a lot of itching and

the fungus responsible is Candida albicans.

Note that fungal infections are difficult to cure because there are a few non-

toxic antifungal compounds known . There is also the

problem of ‘wrong treatment’ (e.g. treatment before lab tests are done): where

for example a patient infected with a fungus does self-treatment with an

antibiotic instead of a fungicide.

2. Spoilage of food and stored grains:

For example, Aspergillus, Rhizopus, Mucor, and Penicillium are commom food-

spoiling fungi. Species of Ascomycetes and Deuteromycetes (Imperfect Fungi)

usually attach food grains stored in places with high humidity.

3. Crop diseases:

The notorious coffee/banana wilt, e.g. Hemileia vastatrix causing coffee wilt.

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 Phytophthora annamoni attacks Eucalyptus. Fusarium spp. attack bananas,

causing banana wilt. Fusarium lycopersicum attacks tomatoes.

4. Mushrooms very poisonous to humans:

Some species of fungi (mushrooms) are very poisonous and sometimes cause

death to humans.

5. Wood fungus:

Wood-rotting fungus attack wood, breaking down the wood components and thus

reducing its mechanical strength. This causes monetary losses.

6. Fungi causing problems in aircrafts and fuel tanks:

Certain fungi grow in fuel tanks containing kerosene-based fuel. These fungi form

hyphae which can block pipes, leading to fatal accidents to the aircraft.

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