[PDF Notes] Ecology: Lecture Notes of Ecology and Ecosystem

Ecology is the study of the relationships among organisms and the relationship between them and their surroundings.

These surroundings are called the environment of the organism.

Concepts in Ecology:

The term “ecology” was coined by combining two Greek words, oikos (house or dwelling place), and Logos (the study of), to denote the relationship between organisms and their environment. Ecology is a multidisciplinary enterprise, which cannot be made to fit into one channel of scientific inquiry: it ranges from reductionism in the study of individual species populations, through less reductionist approaches in the study of communities, to the holistic in the studies of the totality of communities on earth.

It is like an enormous puzzle in which each organism has requirements for life which interlock with those of the many other individuals in the area. Although some of these individuals belong to the same species, most of them are very different organisms with very different ways of living or interacting.

The study of these ecological relationships from the point of view of a single species (as illustrated in the figure) is called autecology. If all the species living together are studied as a community, then this study is called synecology.

The basic concepts of ecology include the following:

i. All living organisms and the environment they live in are mutually reactive, affecting each other in various ways.

ii. Environment plays a major role in the critical stages of the life cycle of the species.

iii. The species reacts to the environmental changes and adjusts itself structurally and physiologically.

iv. The environment also changes according to certain species- specific activities like growth, dispersal, reproduction, death, decay, etc.

v. All plants and animals are related to each other by their coaction and reaction on the environment.

vi. Under similar climatic conditions, there may simultaneously develop more than one community, some reaching the climax stage, and others under different stages of succession.

Ecosystem Ecology:

A group of individual organisms of the same species in a given area is called a population. While, a group of populations of different species in a given area is called a community. And, an ecosystem or an ecological system is the whole biotic community in a given area and its abiotic environment. It therefore includes the physical and chemical nature of the sediments, water and gases as well as all the organisms.

An ecosystem can be any size, from an area as small as a pinhead to the whole biosphere. The term was first used in the 1930s to describe the interdependence of organisms among themselves and with the living (biotic) and non-living (abiotic) environment. At ecosystem level, the units of study are comparatively very large and there are no practical units, if the nature is conceived as a single, giant ecosystem.

The overall view of this type of approach is that living organisms and their non-living environment are inseparably interrelated and interact with each other. Keeping this view in mind, A.G. Tansley in 1935 proposed the term “ecosystem”. Eco implies the environment, and ‘system’ ‘implies an interacting, interdependent complex.

Ecosystem Ecology emphasises the movements of energy and nutrients (chemical elements) among the biotic and abiotic components of ecosystems.

Concepts of an Ecosystem:

Following are the basic concepts of an ecosystem:

i. When both biotic and abiotic components are considered, the basic structural and functional units of nature are ecosystems.

ii. There exist varying degrees of positive, negative and even neutral interactions among organisms at both inter- and intra-specific levels.

iii. Energy is the driving force of an ecosystem which is unidirec­tional or non-cyclic.

iv. The chemical components of the ecosystem move in a defined path called biogeochemical cycles.

v. Successful growth of the organism is governed by limiting factors. The minimal and maximum levels of tolerance for all species vary seasonally, geographically and according to the population.

vi. Under natural conditions, different kinds of population undergo succession.

Kinds of Ecosystem:

These are categorised as under:

1. Natural Ecosystems:

These operate under natural conditions without any major interference by man. These are further divided into

i. Terrestrial:

Forest, grassland, desert, etc.

ii. Aquatic:

These may be further classified as (a) freshwater and (b) marine

2. Artificial Ecosystems:

These are maintained artificially by humans where, by addition of energy and planned manipulations, natural balance is disturbed regularly. For example, croplands like wheat, rice fields, etc., where humans try to control the biotic community as well as the physio- chemical environments, are artificial ecosystems.

Structure of An Ecosystem:

An ecosystem has two major components:

1. Abiotic (non-living) component:

It includes inorganic substances, inorganic chemicals and climate of the given region.

2. Biotic (living) component:

It can be further classified as:

(i) Autotrophic component

(ii) Heterotrophic component—Further divided as:

(a) Macroconsumers: herbivores, carnivores, omnivores

(b) Microconsumers: bacteria, actinomycetes and fungi

Functional Aspects of an Ecosystem:

The functional aspects of an ecosystem include the following:

i. The rate of biological energy flow, i.e., the production and respiration rates of the community

ii. The rate of materials or nutrient cycles

iii. Biological or ecological regulation including both regulation of organisms by environment and regulation of environment by the organism.