The ecosystem


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General Objectives:
At the end of this module, you are expected to know the different principles and concepts of ecology and ecosystem.

Specific Objectives:
At the end of the lessons you should be able to:

  1. differentiate ecology from human ecology;

  2. explain the meaning of a system;

  3. define the ecosystem;

  4. enumerate the components of the ecosystem;

  5. compare and contrast the ecosystem structure from the ecosystem function.


  1. Read and understand the module very carefully.

  2. Perform all the activities required in this module.

  3. Answer all the questions in all the activities.


  1. Ecology: Scope and Meaning

  2. The System Approach

  3. The Ecosystem Concept and Components

  4. E


    cosystem Structure and Function

Ecology is the study of the relationships between the living organisms and their environment.

No living organism exists in isolation. Organisms interact with one another and with the chemical and physical components of the nonliving environment (Sutton and Harmon, 1973).

Human ecology is the study of ecosystems as they affect human beings and vice versa. Human ecology draws together knowledge and experience from many branches of learning and considers chemical, economic, political, social and ethical questions as well as strictly biological ones (Sutton & Harmon, 1973).

As people’s interactions with the environment become more drastic, more people have become concerned with human ecology.
The term “ecology” was first coined by the German biologist Ernst Haeckel from “oikos” meaning a “house” or “living place” and “logos” to mean the “study” or “science of” (Odum, 1971 and Green et. al. 1984). Literally, ecology means the study of the earth’s house.
The study of ecology is of two types. These are autecology and synecology. Autecology deals with the relationships between an organism or population and the environment whereas synecology focuses on the relationships between communities and their environment. For example, the study of the ecology of one species of mango (Mangifera indica) tree is autecology while studying the whole mango community and its relationships with the environment is synecology.
Ecology is related with other branches of biology. This shows that living organisms can be studied at different levels of organization, each level representing a type of biological system. In Figure 1, notice that each level of organization involves a biotic component interacting with an abiotic component through the exchange of matter and energy.

Biotic components Genetics Cytology Histology Anatomy ------------------- Ecological ---------------

Cell Biology Concern
Molecular Biochemistry and Physiology


interacting genes  cells  tissues  organs  organisms  populations  communities

with       


Abiotic components matter  energy


    

Biological genetic cell tissue organ organismic population ecosystem

Systems systems systems systems systems systems systems

Figure 1. Levels of organization spectrum and relationship of ecology to other

branches of biology (Odum, 1971 and Green 1984)

Please look at the diagram. Don’t you notice that ecology is concerned only with the right side of the organizational spectrum.

Before we proceed, let us define the following important terms which you will always read in the modules that follow. Please try to understand the definitions and their illustrations. Perhaps you can give better and more examples. Here they are:

  • Population is a group of organisms belonging to one kind of species living in a specific area or habitat. (Sutton and Harmon, 1973). A typical example is the population of tilapia living in a pond.

  • Community is a group of organisms belonging to different species that exist and interact in a specific area. (Sutton and Harmon, 1973). For example, the CLSU community includes all the people, plants, animals and microorganisms thriving in CLSU.

  • Ecosystem is a community of organisms and their nonliving environment interacting as a whole unit (Sutton and Harmon, 1973). It is simply the interaction of the living organisms and its non-living organisms. We consider the CLSU community and its interaction with the soil, atmosphere, water, sunlight, climate and temperature as an example of an ecosystem.

However, when we consider all living organisms on or around the earth, we are referring to BIOSPHERE.

Now, are you ready to do Activity 1? This is just to check what you have picked up from your reading.

Activity 1.

Kindly answer the following questions without necessarily copying the reading text.

  1. What is ecology? _____________________________________


  1. What is human ecology? _______________________________


  1. Differentiate the two types of ecology.


  1. What are the levels of organization that ecologist are mostly interested to study?


  1. Please fill up the chart below as the first column requires:




a. organisms


b. Relationship

with non-living


(present or absent)

c. Give an



A system is a collection of components, parts, and events which are linked together to form a working unit or unified whole. As such, any change in one part of the system produces changes in all the other parts. In short a system implies an organization of things that are linked together (Tivy and O’Hare, 1981) in which the parts or events are related and dependent with one another.

We will consider two basic types of systems.

  1. Open systems are those that depend upon the outside environment to provide inputs and accept outputs (Sutton and Harmon, 1973). The amount of output produced is directly related to the amount of input received. Figure 2 shows the general model of an open system.

Input(s) Output(s)

---------- System ------------
Figure 2. General model of open system (Sutton & Harmon, 1973)

This figure illustrate that in order to function, an open system must constantly require inputs such as materials and process and change them in the system to and give off waste or by-products (outputs). For example, the most important input is energy in a concentrated form (coal, oil, electricity); and the most important output is energy in a dispersed form (heat) (Tivy & O’Hare, 1981).

  1. Cybernetic Systems use some feedback mechanisms to regulate themselves. The basic idea behind feedback is that some of the output of the system is used to control some future input to the system. Cybernetic systems usually have an ideal state or set point at which the system maintains itself (Sutton and Harmon, 1973). Figure 3 shows the diagram of a simple cybernetic negative feedback system. In either case, the feedback that causes the readjustment to the set point is called negative feedback. It is negative because it halts or reverses the tendency or movement away from the set point.

egative Excess




Deficiency Negative


Figure 3. A simple cybernetic negative feedback system

An individual organism, be it a plant, animal or human being can be thought of as a system. For instance, a warm blooded animal, such as a rabbit or a human being, can be compared to a self-regulating, homeostatically controlled system. It is capable within limits of maintaining its body at a constant temperature, eventhough that of the surrounding environment may vary considerably. Figure 4 shows that when the atmospheric temperature increases, the body loses heat by increased sweating; when it falls, heat is generated by shivering, and conserved by the contraction of blood vessel and decreased sweating. This ability of a system to regulate itself is called homeostasis (Tivy and O’Hare, 1981)


Higher body

Rise in temperature

Temperature Increased

Positive metabolic rate

Homeostatic Threshold Feedback

--------------- ---------------- ---------

Less heat lost by

evaporation Higher body

More body heat temperature generated
Negative Feedback


Decreased sweating Increased sweating

shivering Reduction in

Increased in activity

Metabolic rate 39.5C – Optional


Lower body Greater loss of

temperature heat e.g. evaporation

radiation and _______

heat production
---------------- --------- ----------------------------

Lower body Positive

temperature Feedback Homeostatic Threshold


metabolic rate



Figure 4. A regulatory (homeostatic) control showing the

negative and positive feedback in rabbit

Activity 2

Ooops!!! Don’t forget to answer this activity before proceeding to the next topic

  1. Define an open system. ________________________________


  1. Give an example of an open system and fill-up the diagram below. ________________________________________


------------> ------------->

  1. Define a cybernetic system. __________________________


  1. Give another example of cybernetic system aside from what is given in the reading text.


An ecosystem is the interaction of the community and the non-living environment. An ecosystem is composed of biotic components or living components. It consists of plants (produces), animals (consumers) and the microorganisms (decomposers) and the abiotic or non-living components which include air, water, soil, inorganic substances, organic substances, and climate regime that are present in a given area. A schematic representation of an ecosystem is shown in Figure 5.

Living Water


Solid Atmosphere


Figure 5. A schematic representation of an ecosystem
To give you a better picture of an ecosystem, look at Figure 6 showing an ecosystem with its biotic and abiotic components.
Can you see in Figure 6 that an area consists of many species of plants and animals all interacting with each other? Do you also see that these living organisms are interacting with the abiotic factors such as sunlight, climate, temperature, soil, and atmosphere?
We can think of all of all of these organisms, abiotic factors, and interactions as one single thing – a system – an ecosystem. So if one population of organisms becomes extinct or the temperature increases two fold, these modifications can make the ecosystem unstable as they may be unable to regulate it.

Figure 6: An ecosystem with its biotic and abiotic components

Activity 3.

How well did you understand ecosystem? Will you test yourself by doing this activity? Please do this activity before studying the next lesson.

  1. What is an ecosystem? _________________________________


  1. Give the two components of the ecosystem and give specific examples. By filling up the table below.

__________ Components ___________ Components

  1. a.

  2. b.

  3. c.
  4. d.

  5. e.

  1. Can you draw a diagram of an agro-ecosystem? Remember the components of agriculture and how these can illustrate an agro-ecosystem.


The ecosystem has both structure and function. Ecosystem structure refers to the organizational set-up of the system specifically its species composition (kinds and numbers) and their patterns of distribution in time and space (vertical and horizontal arrangement of species). You can therefore divide the ecosystem structure into two: the physical and the biological structure.

Physical Structure
The physical structure of the ecosystem is described as follows:

  1. Stratification is the separation of organisms in space or time. An ecosystem can be stratified in space either vertically (layers) or horizontally in concentric rings. In a terrestrial ecosystem spatial stratification is largely determined by the plant forms present. In aquatic ecosystems, spatial stratification is usually determined by the depth, light penetration, and temperature of the water (Sutton & Harmon, 1973).

Let us look at the various ways that an ecosystem is structurally subdivided.

  1. Vertical stratification is the distribution of different life of plants – their size, branching and leaves. These are influenced by the vertical gradient of light. Several layers of vegetation, provide habitat for animal life in the forest (Smith, 1990).

The upper stratum of a terrestrial ecosystem, such as the forest, can be divided into various layers according to the various heights of its vegetation (Sutton & Harmon, 1973). A tropical rain forest, for instance, has five main layers (Figure 7).

  1. The tallest trees (overstory) make up the canopy and receive the full sunlight.

  2. The shorter trees (understory) contain some of the younger individuals of the canopy species that do not reach canopy height. The trees that thrive in this layer prefer some shade.

  3. The shrubs receive only about 10 percent of the sunlight after it has filtered down through the overstory and understory.

  4. The young trees, herbs, and ferns need very little sunlight of about 1 to 5 percent to exist.

  5. The mosses (ground layer) receive only 1 percent of sunlight.






Figure 7. Stratification in the tropical rain forest

(Sutton and Harmon, 1973)

  1. Horizontal stratification is the study of vegetation in concentric rings from the outer boundary of the ecosystem toward the center (Sutton and Harmon, 1973).

Horizontal heterogeneity results from an array of environmental and biological influences (Figure 8.) Soil structure, soil fertility, moisture conditions and aspects influence the microdistribution of plants. Patterns of light and shade shape the development of understory vegetation. Run off and small variations in topography and microclimate produce well-defined patterns of plant growth.

Grazing animals have subtle but important effects on the spatial patterning of vegetation, similar to the abiotic disturbances like wind and fire. Likewise the mode of plant reproduction and availability of propagules over time affect vegetation patterns. Plants with wind dispersed and animal dispersed seeds have a wider distribution across the landscape than plants with heavy seeds. Vegetative or clonal reproduction produces distinctive clumps or patches of certain plants. Allelopathic effects and shading lead to the suppression of some plant species and to the development and growth of others (Smith, 1990).


Fire Wind


(Phenology, Structure, Species Diversity)


EFFECTS Grazing preferences

Microclimate Seed Dispersal

Run off VEGETATION Caching

EFFECTS Nutrient Deposition

SOIL Transpling

EFFECTS Allelopathy

Nutrients, Shading,etc.

etc. Reproductive

Texture patterns


Figure 8. General relationship of some of the

major influences that govern vegetational

patchiness in terrestrial environment

(Wiens, 1976 and Smith, 1990)

  1. Edges and Ecotone – These two terms are often used synonymously but they are different. An edge is where two or more different vegetational communities meet. An ecotone is where two or more communities not only meet but also integrate or blend (Smith, 1990). Figure 9 shows examples of edge and ecotones.


Y X X2 Y2 Y

  1. (b)

Edge Ecotone
Figure 9. Edge and Ecotone showing an abrupt, narrow

edge with no development of an ecotone (a)

and an ideal ecotone development in which

plants from both communities invade each

others create a wide ecotone X2Y2 (b).

(Smith, 1990)

  1. Biological Structure

The ecosystem is influenced not only by the physical or abiotic conditions, but also by biological conditions. The biological structures of the ecosystem are as follows:

  1. Dominant species – These are single species or group of species that biologically control an ecosystem or modify the environment of that ecosystem. The dominants may be the most numerous, possess the highest biomass, preempt the most space, make the largest contribution to energy flow or mineral cycling or by some other means control or influence the rest of the ecosystem, (Smith, 1990).

2. Species richness refers to the number of species occupying a specific area (Smith, 1990).

3. Species evenness refers to the relative abundance of individuals among the species (Smith, 1990) or degree of equitability in the distribution of individuals among a group of species.

  1. Species diversity refers to the number of different species and the relative abundance of individual species in a given area. This implies both the richness and evenness of individuals among the species (Smith, 1990).

  1. Species abundance is associated with species diversity. It is the relationship between abundance of individuals within a species and the number of species having similar abundances.

Activity 4.

Let us review some important concepts we have learned from our previous lessons. Answer the question before going to the next lesson.

  1. Enumerate the physical structure of the ecosystem.





  1. Give an example of a vertical stratification in an aquatic ecosystem. Draw a diagram below:

  1. Describe the different biological structures of the ecosystem.




Ecosystem function refers to the processes in the ecosystem associated with energy flow, biological cycling and co-regulation.

Energy flow refers to the initial fixation of energy in the ecosystem by photosynthesis, its transfer through the system along a food and its final dissipation by respiration (Tivy & O’Hare, 1981).

Biological cycling or biogeochemical cycling refers to the continuous circulation of elements from an inorganic (geo) to an organic (bio) form and back again (Tivy & O’Hare, 1981).
Self-regulating mechanisms within the ecosystem result in ecological succession, the process by which one community replaces another in a given site. Self-regulating processes also enable the ecosystem to achieve a final steady state known as the ecological climax (Tivy & O’Hare, 1981).


These concepts will be further explained in the next lesson.

Activity 5.

Go to a nearby pond ecosystem and perform this exercise (Alberto, 1986 & Alberto & Abella, 1998). Make sure you bring the following:

Thermometer String Plastic bags

pH paper marker pen big bottles

meter stick or calibrated pole


  1. Abiotic Factors

  1. Temperature – Measure the following

  1. air temperature – Get three readings and compute for the average.

  2. water temperature (just below the surface of the water) – Get three readings and compute for the average.

  3. bottom temperature (just above the substratum) – Get three readings and get the average. Record all data.

  1. Transparency – Make a rough estimate of the transparency of the medium. This can be expressed in relative terms such as clear, murky, turbid, etc.

  1. Depth – By means of a meter stick or any calibrated pole, measure the depth in the different areas of the pond.

  1. Bottom conditions – Note the type of the substratum. This can be described as rocky, story, sandy, etc.

  1. Chemical Factors

a) pH (Hydrogen ion concentration) - Measure pH by using pH paper. Note whether the pond is acidic or basic.

  1. Biotic Factors

  1. Microscopic Life – Take water samples at different levels of the pond and identify the microscopic organisms present. (You can do this if you have microscope in your school) but if you don’t, just skip this part)

  2. M
    acroscopic organisms – Observe and list all the plants and animals that you can find in the area of study. The activities of the animals should be recorded.


Record all your data in a data notebook. This data notebook should be shown to your professor when you report for class.

Discussion: Answer the following questions:

  1. Are the animals noted confined to the area you are observing, or do they move in a out of the area? What do the animals eat?

  2. What organisms act as the food producers in the pond?

  3. What structural characteristics are common to the majority of microorganisms you have observed?

  4. What are the important functions of microorganisms in the pond ecosystem?

  5. Enumerate the macro organisms you have observed.
  6. How do these organisms depend upon each other for survival?

  7. What physical and biological structures are present in the pond ecosystem?

  8. How are human beings dependent upon the organisms?

  9. Discuss the pond ecosystem you observed in terms of all the concepts in ecosystem you have learned.


Make an activity report and submit this report when you come to class.

You can take the test if

you are ready at the office

of your instructor, then you

can proceed to the next



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