Biology

The growth, distribution and abundance of organisms in an ecosystem are controlled by a number of factors and the interactions between these factors. These factors are called ecological factors.

Classification of ecological factors:

Ecological factors are broadly classified into two; namely

1. Biotic factors

2. Abiotic factors

- Biotic factors constitute all living organisms ie plants and animals( including man)

- While abiotic factors include climatic and physiographic factors (edaphic and topographic factors).

- In any ecosystem, these three factors ie Biotic, climatic and phisiographic factors continually interact with each other as shown below:

     

                                         Climatic 

 

               Biotic                                            Physiographic

                                                            (Edaphic & Topographic)

1. BIOTIC FACTORS:

These factors include

- Primary Producers/plants

- Primary Consumers/ Animals (including man)

- Decomposes

- Relationship between plants, animals, and decomposes.

- Activities of organisms in a habitat.

2. ABIOTIC FACTORS:

This is made up of  (a) climatic and (b) physiographic factors.

(a) CLIMATIC FACTORS;

These are made up of

(i) physical factors

(ii) chemical factors

(I) Physical factors: These include

- Rainfall

- Temperature

- Light intensity

- Humidity

- Wind

- Pressure

(II) Climatic factors: They include

- Oxygen, Nitorgen, Water, Carbon dioxide and mineral salts

(b) PHYSIOGRAPHIC FACTORS:

These factors are made up of

(i) Edaphic factors

(ii) Topographic factors

(I) Edaphic factors:

These include

- water content of soil

- degree of acidity or alkalinity of soil (pH)

- Organic content of soil

- Available nutrients

- Soil profile and texture

(II) Topographic factors

These include:

- Nature of soil

- Shape of land

- Altitude

- Drainage

- Erosion

ECOLOGICAL FACTORS THAT AFFECT ONLY AQUATIC HABITATS:

These factors include

1. Salinity (salt content):

• This refers to concentration or quantity of salt that is dissolved in water.
• Sea water has high salt content while fresh water has very low salt content.
• Brackish water (found at river mouth and swamp) has salt content that fluctuates as a result of rides and flood.
• So different organisms exist in each of them.
• Thus organisms living in fresh water have adaptations for removing excess water that enter their bodies.
• While organisms that dwell in sea water have body fluids which concentration is nearly those of sea water.
• However, those living in brackish water have body tissue that can tolerate large changes in concentration of salt in their bodies.

2. Turbidity:

• This is caused by the presence of suspended matter.
• Turbidity reduces the visibility of organisms in water and the amount of light entering the water.
• Turbidity increases during rainy season in freshwater ecosystem. Light can peneterate to a greater depth in less turbid water.
• Thus, photosynthetic organisms and their allies live at a greater depth in clear water than in turbid water.
• This is because turbidity is a very important factor that affects distribution of organisms in aquatic ecosystem.

3. Density:

This factor help the ability of organisms to float in water.  

Water is denser than air; thus organisms that can float and move easily in water possess stream-lined shape which enable them to do so.

4. Depth of water:

Streams or ponds are usually shallow and so sunlight can easily peneterate down to the bottom, unlike deep sea water. Hence green plants can grow throughout the depth of the fresh water; together with animals that feed on them.

5. Water currents:

• It increases turbidity of water and air circulation. It also improves nutrient and temperature in aquatic ecosystem.
• Thus warm waters are carried to colder regions
• Distribution of organisms are affected by water currents.
• Therefore, organisms that live in fast moving waters usually have structures for attaching themselves to rocks, or substratum.

6. Tidal movements and waves:

These factors have the same effect as those of water currents.

7. Dissolved gases:

• All aquatic organisms need dissolved oxygen to carry out cellular respiration.
• Concentration of oxygen is decreased by depth of water body, salinity, presence of organic matter and high temperatures; which conversely affect distribution of aquatic organisms.
• Organisms that live in deep waters and bottom dwellers have special adaptive mechanisms that enable them to adapt well in waters with low oxygen concentration.

ECOLOGICAL FACTORS AFFECTING ONLY TERRESTRIAL HABITATS

These factors include: land surface (topography factor), soil (edaphic factor), and relative humidity.

1. Topographic factor (land surface) : These are related to the features of the earth surface. Eg altitudes, drainage, erosion, shape of land, and those physical features that are perculiar to the habitat. For example, the land surface may be at sea level or above sea level. It may be flat or sloping.

• Thus, the land surface is often responsible for the marked differences/variations in the vegetation of a place.
• High elevations are more exposed to extreme climatic conditions such as wind, temperature, humidity and rainfall.
• The degree of the slope also affects the movement of water and soil; so that erosion is greater on hill tops and least in the valleys.
• So, at hill tops, growth is reduced and only small plants and a few animals are present.
• While in the valleys with gentle slopes, there is slow flow of water, reduced erosion and more water is available for plants.
• Thus more plants and animals are present on gentle slopes such as valleys.

2. Soil (Edaphic factor): This refers to the influence of soils on plants' and animals' distribution.

• Apart from climatic factors, soil factors such as organic content, pH of soil soil profile, soil type or soil particles also play an important role in determining the vegetation of a region.
• They account for the variation in the type of plants that are found in regions with similar climate.
• The different types of plants occur in sandy and clay soils, as well as on highly eroded soils
• In addition, where the soil cover is very thin, deep rooted plants such as trees can not be able to grow there.

3. Relative Humidity: This refers to a measure of the amount of moisture in the atmosphere.

• It varies with other climatic factors such as temperature, rainfall and wind.
• Humidity is usually high in hot-wet regions.
• It affects the rate at which water evaporates from the body surfaces, soil, etc.
• When humidity is low, more water is evaporated from the body surfaces of organisms, water bodies, soil surfaces, etc.
• But when there is high humidity, less water is evaporated from body surfaces into the atmosphere.
• Thus, in deserts where humidity is low, the leaves of plants like cacti and acacia sp have their leaves reduced to spines to prevent excessive loss of water(or for conservation of water in their bodies).
• Animals here also have mechanisms for prevention of water loss.

FACTORS THAT AFFECT BOTH AQUATIC AND TERRESTRIAL HABITATS

Factors common to all habitats are Rainfall, temperature, light intensity, hydrogen ion concentration, wind and pressure. It has been noted that temperature and rainfall determine mjor biomes of the world.

1. Rainfall:

• Rainfall is the most important climatic factor for most living organisms in the tropics.
• Amount of annual rainfall greatly affects the distribution and type of vegetation in any habitat.
• An annual rainfall of 160mm for instance produces forest-type vegetation.
• Moderate rains support grassland (savanna) and extremely dry areas support deserts with very few number of plants and animals
• Rainfall also influences the aquatic environment through its influence in decrease in salinity, water current increases, turbidity increases and transparency decreases; and all these influences have great effect on the distribution of plants and animals in aquatic habitat.
• Rainfall is measured by means of rainguage

2. Temperature

• Temperature is caused by the heating effect of the sun on the earth surface.
• It varies with latitude and also with altitude.
• It is very important for distribution of organisms; because every organism has its optimum temperature at which it can function well to maintain life.
• Thus, below or above this optimum temperature, the organism fails to grow, reproduce, function well and may go into dormancy such as hibernation and aestivaton.
• The organism may however function well by help of adaptove mechanksms
• Temperature also affect processes such as photosynthesis, and respiration.
• Temperature is measured by means of a simple thermometer or maximum and minimum thermometer.

3. Light

• Light is a very important factor for the process of photosynthesis, without which this process cannot occur in green plplants
• And since animals depend on plant for food, light is also important to them
• Light is important for proper functioning of the ecosystem; no ecosystem can function without it.
• It also influences the reproductive and life cycles of both plants and animals.
• The source of sunlight to all ecosystem is sunlight (which is solar energy)
• Light is measured by using a photometer or light meter.

4. Wind:

• Wind is brought about by the movement of air currents.
• Such air movement is responsible for the following activities/processes:

 (a) rainfall patterns of earth

 (b) it affects rate of transpiration and evaporation from moist surfaces generally

 (c) strong winds cause damage to plants eg a whole tree or even a whole farmland can be lost due to strong winds.

 (d) wind is important in the dispersal of certain fruits, and seeds, spores of certain fungi, bacteria, virus, etc

 (e) wind is important in the creation of water current and waves, which are very important ecological factors in aquatic habitats.

Wind direction is measured by Wind Vane while wind speed is measured by Anometer

Subject Teachers

• Mr Okafor Eugenia

Telegram/Phone No. 08028718078

email: This email address is being protected from spambots. You need JavaScript enabled to view it.

2. Corper Henry Emmanuel

Telegram/Phone No. 07039744305

POPULATION STUDIES BY SAMPLING METHOD

 

DEFINITION OF POPULATION:.

Population can be defined as sum total of organisms/ individuals of the same species living in the same habitat at the same time.

POPULATION SIZE

In order to understand how the population is interacting with its environment, it is necessary to find out the size of the population.

- The size of a population gives an indication of the extent of its fitness or success in the environment where it is found.

- Population size is also important in relation to the resources available to it.

- If the population is too large for its resources, then the resources cannot sustain that population and its size may decline; and the area may be affected too.

- If for example, there is population explosion of grazing animals in a grassland; the effect are as follows: (a)There will be overgrazing (b) leading to shortage of food; as a result of competition for food by the animals.

- resulting in reduction in their population

- erosion may occur

- leading to poor soil/destruction of soil structure.

- hence, poor plant growth will occur.

 

POPULATION SIZE can be expressed by its DENSITY ie the number of individuals of the same species per unit area. It can also be expressed in terms of FREQUENCY ie number of times out of a number of searches one encounters the organism.

 

METHODS FOR STUDYING POPULATION SIZE

Two methods can be used to study population of small plants. These two methods are;

1. Quadrat sampling method

2. Transect Sampling method

If animals are to be studied, the methods that can be used to study population size of animals are

1. Capture re-Capture (for animals that live in the forest/Bush)

2. Census method (for human beings).

1. Determination of Population size by Quadrat sampling method:

Meaning of Quadrat: Quadrat is a square or rectangular material. It may be wooden, plastic, or metal frame which may be temporarily or permanently made. It can be used to estimate population size of small plants such as Cida acuta, Asphilia, Emilia, Tridax, etc

Procedure for use of Quadrat sampling method:

- choose and locate sample plot

- first identify the plant species in the plot

- Note the dimension or the area of the plot under consideration.

- Toss or throw the quadrat randomly at intervals for 10 times and above.

- After each toss or throw, the number of species within the area of the quadrat is recorded.

- The density of plant species is calculated; by dividing the average number of times the species occur within the quadrat by the area of the quadrat.

Therefore, the population density calculation can be worked out as follows:

Frequency of organisms = x

Number of tosses/throws = y/10 and above

Average number of species per quadrat = x(specific figure) / y/10 and above

Z/specific figure

Area of quadrat = 1 m²

Population density = Z/specific figure/Area of quadrat

Example

Frequency of an organism ie total number of times an organism occurs in all the quadrat tossed/thrown in the habitat = 50

Number of throws = 10

Average number of organisms per quadrat throw/toss = 50/20 = 5

Area of quadrat = 1m²

Population density of organism = 5/1m² = 5 per M²

Therefore, formula for estimating population density is as follows:

Population density = Average frequency/ Area of quadrat

Note: Size of plants determines size of quadrat to be used.

 

2. Transect Sampling method:

-Transcet sampling method involve use of tape. The tape is marked at intervals; then stretched from one point to another.

- The plants within the various intervals are recorded.

- This is repeated a number of times to ensure accurate estimate of the number and types of plants in the area.

3. Capture-Recapture method:

This is ideal sampling method for estimation of animal population since quadrat cannot be used because animals may be large or fast moving.

 

DEFINITION OF TERMS

1. Population density: it is the number of a particular organism in relation to a unit or quadrat area. The formula used to estimate population density is

                  Population density = average frequency/ Area of quadrat

2. Population frequency: it is how much space an organism occupies in a given area when expressed in percentage.

3. Population growth rate or form: this is the net result of natality and mortality in the habitat

 - Natality: rate at which new individuals are reproduced in a community

 - Mortality: rate at which individuals in a community die.

4. Quadrat: it is square/rectangular wire, wooden, plastic or metal frame which can be temporarily or permanently made (fig 1).

 

 

 

 Fig 1.   A Quadrat

 

5. Distribution: this refers to the way in which individuals of a particular population are arranged in a given habitat. Generally, individuals may be clumped, evenly spaced or randomly spaced.

6. Dominance:

- Dominance is a term used for the most commonly or frequently occurring organism in a community.

- The more common and more abundant organisms in a community is referred to as dominant species.

- Dominant species always exert a great influence on the habitat and other populations.

- for instance, in a savanna biome, grasses are the most dominant plants, while big, tall trees are dominant in rain forest biome.

- Dominant species in a community also affect the soil structure and its chemical composition and in turn, the type of organisms that live in the forest floor.

- The dominant species are usually the more successful and the better adapted of the populations inhabiting the ecosystem.

 

DENSITY FACTORS THAT AFFECT POPULATION SIZE:

- Population of organisms in a habitat is ever changing (dynamic) ie, it is ever increasing or decreasing.

- certain factors may lead to increase or decrease in population size.

Density factors which lead to increase in population are;

a. High rate of natality

b. Low rate of mortality

c. Dispersal (immigration)

d. Abundance of food

e. Adequate medical facilities

f. Good health

g. Conducive climate conditions

 

   DENSITY FACTORS THAT MAY DECREASE/ REDUCE POPULATION SIZE

- High rate of mortality

- low rate of natality

- emigration

- Epidemic, e.g Coronavirus

- shortage of food/ competition

- war

- sudden changes in Environmental conditions e.g flood, heavy rainstorms, strong wind, volcanic eruption, earthquake, fire outbreak, drought, etc.

 

EXPLANATION OF DENSITY FACTORS THAT MAY LEAD TO INCREASE IN POPULATION SIZE

(a) High rate of natality: New organisms are produced through reproductive activities such as birth, laying of eggs, germination of seeds, etc. When number of new organisms produced is higher than number that dies, population increases. Ability of organisms to produce numerous seeds or to lay numerous eggs and also show necessary adaptation, tend to increase population. eg as seen in cockroach, etc

(b) Dispersal (Immigration): This is movement of organisms from one place to another. Many animals can move from one place to another.

- when animals move into other habitats, the population there increases.

- The method of dispersal in animals include the use of locomotory organs.

(c) Abundance of food:

- Animals tend to migrate to where plenty of food is available.

- Human  beings move away from dry lands to fertile lands.

- For example, cattle from Niger and Chad are brought into Nigeria where people believe plenty of food is available.

 EXPLANATION OF DENSITY FACTORS THAT MAY REDUCE POPULATION SIZE

(a) High rate of mortality:

- The rate at which individuals in a community die may cause reduction in population.

- When the rate of mortality is higher than the rate of natality, there is decrease in population.

- Death may be due to disease, illness, accident, sudden death, etc

(b) Emigration:

- Several Individuals may leave a community and go to other areas.

- This may be due to breeding habits as seen in birds and fish.

- It may also be due to scarcity of food such as during drought or natural disasters like flood, famine, war or pest infestation.

(c) Shortage of food/ Competition:

- If there is shortage of food, the individuals that live in the habitat will compete for the little available food.

- The little amount of food will not be enough for the individuals.

- Thus, many individuals struggle/ compete for the little available food; leading to decline/decrease in population.

(d) Sudden changes in Environmental conditions:

- sudden changes in Environmental conditions such as flood, heavy rainstorm, strong wind, volcanic eruptions, earthquakes, fire outbreaks, drought, etc could lead to total elimination of one or more species of plants and animals.

- This type of sudden changes normally produce large changes in population density/size; this is because a whole population can be wiped out.

 

                 Subject Teachers: Mrs Okafor Eugenia & Corper Henry Emmanuel

                Telegram phone number: 08028718078

 

 

ASSIGNMENT  (10mks)(submit before 15^th May, 20)

 

1.        State two sampling methods used in

estimating population size of cida acuta (small plant).

2.   Which instrument is used in quadrant sampling method?

3.   Outline density factors that may increase population size.

4. Outline density factors that may likely decrease population factors.

 

 

Mrs. Eugenia Okafor

Submit your assignment to the teacher`s

Email. This email address is being protected from spambots. You need JavaScript enabled to view it. 

For further inquiry call her on: 08038706265