Basic Ecological Concepts – SS1 Biology Lesson Note (Second Term)

Ecology is the study of plants, animals and microorganisms in relation to their environment. It covers how organisms are distributed, how they depend on one another and on the non-living environment for survival, and the factors that affect the environment. This note explains the branches of ecology, common ecological terms and the components of an ecosystem.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define ecology and state what ecological studies involve;
2. distinguish between autecology and synecology;
3. explain the terms environment, biosphere, habitat, ecological niche, population, community, ecosystem and biome;
4. name the three major portions of the ecosphere;
5. list the abiotic and biotic components of an ecosystem and give examples.

What is ecology?

Ecology is the study of plants and animals (as well as microorganisms) in relation to their environment. As a practical science, ecological studies involve:

1. Studying the distribution of living organisms.
2. Finding out how living organisms depend on themselves and their non-living environment for survival.
3. Measuring factors affecting the environment.

What are the branches of ecology?

Depending on whether the organisms are studied alone or in groups, ecology is divided into two branches:

1. Autecology: the study of an individual organism or a single species of organism and its environment, e.g. the study of a student and his school environment.
2. Synecology: the study of the inter-relationships between groups of organisms or different species of organisms living together in an area, e.g. the study of fish, crabs, seaweeds, etc. in a pond.

What are the main ecological terms?

The following concepts are closely associated with ecology.

1. Environment

The environment includes external and internal factors, living or non-living, which affect an organism or a group of organisms. These include the habitat (with its peculiar physical conditions, e.g. light, food, water, air), the animals preying on other animals and the diseases affecting the organisms.

2. Biosphere (ecosphere)

The biosphere is the zone of the earth occupied by living organisms to carry out their biochemical activities. The ecosphere consists of three major portions:

1. Lithosphere: the solid portion (the outermost zone) of the earth, made up of rocks and minerals. It forms 30% of the earth’s surface and is the basis of human settlement.
2. Hydrosphere: the liquid (aquatic) part of the biosphere. It covers about 70% of the earth’s crust. It consists of water in various forms (solid, liquid or gas as water vapour) and includes lakes, pools, springs, oceans, ponds, rivers, etc.
3. Atmosphere: the gaseous portion of the earth. It consists of three main gases: nitrogen (78%), oxygen (21%) and carbon(IV) oxide (0.03%). There are also 0.97% rare gases.

3. Habitat

A habitat is a place where an organism is naturally found. A habitat is always affected by environmental factors. Habitats can be divided into three types:

1. Aquatic habitat: where plants and animals (as well as microorganisms) live in water, e.g. sea, ocean, lagoons, streams, etc.
2. Terrestrial habitat: where organisms live on land, e.g. forests, grassland (savanna), desert, etc.
3. Arboreal habitat: tree trunks and tree tops, where some organisms (usually animals) are naturally found.

4. Ecological niche

An ecological niche refers to the habitat and the entire habit (behavioural, feeding, breeding) of an organism. It is the physical space occupied by an organism and its functional role in the community.

5. Population

A population is the total number of organisms of the same species living together in a habitat, e.g. the population of cockroaches in the Biology laboratory.

6. Community

A community is made up of all the populations of living organisms that exist together in a habitat, e.g. a community of decomposers, insects and birds on a decaying log of wood.

7. Ecological system (ecosystem)

An ecosystem is the basic functional unit in nature. It consists of all living factors and their interaction with the non-living factors of the environment. An ecosystem can be natural or artificial.

8. Biomes

A biome is a large natural terrestrial ecosystem. It is a plant and animal community produced and maintained by the climate.

What are the components of an ecosystem?

The biosphere comprises various ecosystems. There are two main components of an ecosystem: the abiotic and the biotic components.

1. Abiotic components

These are the non-living components. They are the basic elements and compounds of the environment in which an organism lives.

Abiotic components include organic substances (e.g. carbohydrates, lipids and proteins), inorganic substances (e.g. CO₂, H₂O), climatic factors (e.g. light, temperature, rainfall) and edaphic factors (e.g. soil types, texture, topography, etc.).

2. Biotic components

These are the living things in the ecosystem. They include the producers, the consumers and the decomposers.

• Producers: These are autotrophs, because they synthesise their food from simple inorganic substances, e.g. green plants, protophytes and chemosynthetic bacteria.
• Consumers: These are heterotrophs which feed on the producers or on one another. They may be primary, secondary or tertiary consumers, e.g. non-green plants, animal protozoa and some bacteria.
• Decomposers: These are saprophytes. They break down the remains of plants and animals and release usable nutrients into the soil. Plants use these nutrients to make food, e.g. fungi and some bacteria.

Living things influence other living things in many ways, such as in feeding (parasitism), shading from sunlight, pollination, dispersal of seeds and competition. Some of these influences are favourable while others are unfavourable.

Evaluation

1. Define ecology.
2. State the difference between autecology and synecology.
3. Name the three types of habitat and give one example of each.
4. List the three main gases in the atmosphere.
5. Name the three kinds of biotic component of an ecosystem.

Assignment

1. Which of the following is not classified as a terrestrial habitat? A. forest B. guinea savanna C. littoral zone D. desert
2. The activities of an organism which affect the survival of another organism in a habitat can be described as A. biotic factors B. abiotic factors C. climatic factors D. edaphic factors.
3. The number of individuals of the same species interacting in a habitat at a particular time is best described as A. community B. ecosystem C. population D. biome.
4. A biotic community with its physical environment (abiotic factors) defines A. ecosystem B. population C. habitat D. biosphere.
5. The most abundant gas in the atmosphere is A. oxygen B. nitrogen C. carbon dioxide D. a rare gas.
6. Define: (i) biotic community, (ii) habitat, (iii) ecosystem.
7. Write short notes on the three major portions of the ecosphere.