UNDERSTANDING THE BASICS OF ECOLOGY
Introduction
In this section we will look into various terminologies which are specific to Environmental Ecology. These
definitions give a rather articulated stance of the key terms which may be used frequently hereafter. The
student is advised to memorise these terms and their definitions before proceeding further. This would
assist you in developing a basic understanding of the subject to be dealt with.
Species to Community – exhibition of Social traits
To begin with, let us understand what a species is meant by and how does it differ in its biological and
ecological definitions. Biologically, a species can be defined as one of the basic units of biological
classification and a taxonomic rank. It is in fact a group of interbreeding and reproducing organisms. In
1962, Merrel has described Species as a ‘natural biological unit tied together by sharing of a common Gene
pool.’ But when viewed through an ecological lens the distribution, development and preservation of gene
pool also assume immense significance.
Definition
In Ecological terms, “Species can be defined as an interbreeding population, distributed spatially and
temporally, and which preserves its genetic stock for maintenance of uniformity in structure, function,
reproduction, growth and development.”
A species consists of one or more individuals. As explained above they might be distributed over a spatial
and temporal scale. A group of such individual organisms of a defined species in a given space is termed as
a population. A cluster of such populations of different species form a community. Thus community
includes all the populations in an area like plants animals and microorganisms.
Fig.01 Species, Population and Community
Vegetation, Flora and Fauna
In space, many communities comprising of a number of populations of a variety of such species exist. This
can be manifested with an example of Banyan trees and grass growing in a space like forest, together. In
the case of plants, this collection of communities is marked by vegetation with communities as its basic and
discrete units.
Definition
Vegetation can be defined as sum total of all the complex plant populations covering a space with
intermixing communities of various plant species.
Unlike vegetation, flora gives an indication of various species of plants and is irrespective of the numerical
strength of such species in populations and communities. Vegetation hence is always described whereas
flora is always listed. Besides, Flora is said to have physiological mechanisms which indicate different
seasons of a year and are hence called as Biological clocks.
Definition
Flora is defined as the plant species content of a region irrespective of its numerical strength of species,
community or population. In case of animals it is termed as Fauna.
Environment, Factors and Adaptation of Species
The vegetation and the animal communities are always affected by various forces like wind, chemical
substances, geological processes like earthquakes and volcanic eruption and many conditions that are
unpredictable. Such forces and conditions are called factors. All such factors form a complex of factors
with mutual interference of communities affected by them. That complex of factors constitutes an
environment and is referred to as environment complex. An environment provides the required nutrient
pool for the flora and fauna in a particular area.
Environment vs. Habitat
An environment is a complex of all the factors affecting the communities of plants and animals. An
environment sets conditions necessary for a habitat of one or more species. A habitat is only a physical
space where an organism or a population of a species lives in. An environment thus can be defined as a
complex of one or more individual habitats. It is to be noted that in large habitats like African Savanna,
many type of environments can occur within a single habitat. Similarly, a habitat can represent a set of
environmental conditions suitable for its successful growth.
Fig 02: Environment and a habitat
The nutrient pool thus provided by the environment is utilized for sustenance by all the species that exist
therein. They protect themselves from adverse conditions by developing certain characteristics. All such
features of organism aid them in their survival by utilisation of the available conditions and nutrient pool
from within their respective habitats and the process is termed as adaptation.
Ecads, Ecotypes, Ecotones and Biological spectrum
Organisms thus may have to adapt to the changing environmental conditions induced by varying habitats.
These changes may effect alterations in characteristics like size, colour, shape, number of stems etc.
However, these environmentally induced changes are temporary in nature and are reversible. Such
organisms of different characteristics but of same gene pool are called Ecads. But when the genetic
makeup differs the change remains permanent and irreversible. Thus populations of individuals of same
species which differ in their genetic makeup are called Ecotypes.
These adapted species which grow in association which each other as communities cannot be
distinguished precisely, in nature. Instead of a line of distinction a zone of transition occurs normally, which
may represent special ecological interests of the populations that form the community. Such a transition
zone is called an Ecotone. Physiognomic method of plant study terms the adaptation of plants to the
combination of habitats, their intermediary ecotones, and the climate as a life form. Such life forms may
consist of a number of species and they are represented by a percentage distribution. Such a
representation is called a biological spectrum. An example is given below (Fig.03): Biological Spectrum.
Biological Spectrum
15%
18%
16%
27%
7%
11%
4%
1%
1%
Teak
Sal
Butterfly
Langur
Leopard
Deer
Civet
Fungi
Grass
Ecological Succession
Hope you remember that plant species in given vegetation is dynamic in nature and changes its character
over spatial and temporal scale. This is true in the case of lower forms of fauna also, but only to an extent.
Anyhow these special forms tend to attain stability in choosing a habitat and adapting to them. Thus, the
natural process by which different groups or communities colonize the same area in a definite sequence,
over a temporal scale, is termed Ecological Succession.
If the succession starts from a primitive substratum without any previous life form, it is called a primary
succession. If the colonization occurs upon a primarily succeeded life form, it is called secondary
succession. Succession of a community can happen, either due to reaction with its own environment or
due to action of external forces. Replacement of an existing community by its own members as in the
former case is called autogenic succession whereas in the latter it is called allogenic succession.
Climax and Biomes
Thus it became clear that one community follows another in the natural process of succession. However,
with time a climax stage will come when a community cannot be displaced under the prevailing
environmental conditions. Mono-climax theory proposes that one such community will form that terminal
community which remains in equilibrium with the environmental conditions and will be called as Climax
community. This climax community will chiefly be controlled by climate and the geological changes that
occur. Poly Climax theory proposes that there will be multiple climax communities in different spaces
under the same climatic conditions. Biomes are the sum total of all these communities – those in
succession and climax stage.
Biome is a complex of all communities - some in climax stage and others in various stages of succession
which are constantly in interactions with the environment they live in. Biomes exist under more or less
similar climatic conditions.
Ecosystem and Biosphere
As explained, the communities of plants and animals interact with the environment which sets conditions
for their habitat. These interactions of such assemblage ensure a flow of energy which forms distinct
trophic levels and a resultant trophic structure. Biotic diversity, nutrient and chemical cycles will also form a
part of such interactions. A combination of all these factors forms the ecosystem.
ECOSYSTEM = BIOMES + ENVIRONMENT
ECOSYSTEM = BIOTIC COMMUNITY + ABIOTIC ENVIRONMENT
With the definition of ecosystem in hand, let us consider our mother earth as a giant vast ecosystem with
all its living organisms interacting with their physical environment comprising of land, air and water. This
could be deduced as the most efficient, self-sufficient biological system and is called ecosphere or
biosphere.
Standing quality and Ecological Pyramid
Similarly, it should also be understood that in a given time the physical environment consists of various
organic and inorganic constituents, which are in continuous state of flow in a bio-geo chemical cycle. As
noted earlier, such a flow ensures the trophic structure of an ecosystem. The amount of inorganic
substances like Phosphorus, Sulphur, Carbon, Nitrogen, Hydrogen etc. present in the environment at a
given point of time can be referred to as standing state or standing quality. Similarly, standing crop is the
term used for the amount of living matter present in a population at a given time. Standing crops are
expressed In terms of their numbers or weight/unit area. When expressed in terms of weight it is called
Biomass. In a similar way, Ecological pyramids represent the trophic structure and functions in a graphical
way.
Ecological Pyramids graphically represent the trophic structure and function at successive trophic levels of
an ecosystem. Ecological Pyramids can be represented in terms of the number, biomass or energy content
of standing crop.
Food connections and productivity
Food habits of organisms define their sequential arrangement in an ecosystem and the resultant energy
flow which was mentioned earlier. In an ecosystem, a transfer of energy from producer plants to consumer
animals and then to decomposers in a linear pattern with recurring consumption and being eaten is termed
a food chain. A number of food chains can occur simultaneously and such linear chains are connected at
several points leading to the formation of a food web.
Fig.04: Food Chain
The production and consumption of energy lead to accumulation of organic matter in a given period of
time. The rate of such accumulation in unit time is termed as productivity of the ecosystem. The rate at
which plants accumulate organic matter using sunlight through photo synthesis and bacteria through
chemosynthesis is termed as primary productivity. While consumption, the consumers store energy and
the rate of storage is termed as secondary productivity. Gross Primary Productivity is the total rate of
photosynthesis. It includes the organic matter used up in the process of respiration while measuring the
productivity. Gross primary productivity is also called total photo synthesis or total assimilation. Net
primary productivity is the rate of storage of organic matter in unit time in excess of the energy used for
respiration by plants. It is also called apparent photosynthesis or net assimilation. The rate of storage of
organic matter not used by heterotrophs during a given time is termed Net Productivity of a community.
Ecological Niche and Ecological Equivalent
A complex of the physical space occupied by an organism, organism’s functional role in the community, the
trophic position and its locus with respect to gradients of temperature, moisture, pH, soil etc. is defined as
the Ecological Niche. Organisms may occupy same Ecological niche at different geographical locations.
They are called Ecological equivalents.
Pollution and Conservation
Pollution is an undesirable change in the physiochemical or biological attributes of our various resources.
Human interference is the main cause of pollution to air, water and land and it has aggravated into
multitudes after late 20th century. Conservation is the preservation of quality of environment we live in,
with deliberate manipulations so as to create a balance between the nutrients, yield and productivity.
CONCEPTS
Holism, Ecosystem, Succession and Conservation are the four basic concepts of Ecology. Ecology as a study
of biomes and their interactions with the environment involves many hierarchical levels ranging from
individual organism of a species to biosphere (Fig.05). Each of these hierarchical levels possesses unique
characteristics and with the interactions from lower levels each of them becomes a whole build up.
Holism
Holism which focuses on system paradigm of interrelationships was considered as the real base of ecology
by William Ophuls in 1974. Holism has its roots on the Greek term ‘holon’ which means entity. The term
holism was coined by Jan Christian Smuts in his work Holism and Evolution in 1926. He explained how lesser
wholes (hierarchical levels) come together to form the universe through the process of evolution.
Fig.05: Realms of ecology (Hierarchical levels in an ecosystem)
Holism as a concept or philosophy advocates a process by which lesser wholes or lower hierarchical levels
integrate to form the higher levels or integrated wholes. In doing so, integrated wholes acquire additional
characteristics due to the process of integration and thus differ from individual traits of lower wholes. This
results in increasing organisational complexity towards higher levels.
The density of population, spatial distribution of a community, rate of nutrient transfer, productivity of an
ecosystem, nutrient cycle etc. are a result of such interrelations and interactions between lesser wholes.
Holism emphasises on the integration of such parameters which may pep up the integrated whole with
attributes like stratification, diversity etc. A.G. Tansley (1935) believed in the theory of Holism to develop
his idea of ecosystem. However, there were advocates for the concept of biomes simultaneous with the
concept of ecosystem in the likes of Clements and Shelford (1939).
Ecosystem
As said the concept of ecosystem was developed by Tansley in 1935.Tansley paid attention on the
functional aspects along with the structural aspects. He adopted ecosystem as the discrete unit of ecology.
Ecosystem as a distinct unit consisted of populations which occupy specific niches and communities which
interact among themselves and with their abiotic environment. These interactions may be neutral, positive
(+) or negative (-) in nature at inter specific or intra specific levels. For example, competition is an
interaction at the same trophic level whereas prey-predator relations exemplify the interactions between
different trophic levels.
Energy flow and bio geo chemical cycles are other major characteristics of an ecosystem. However these
aid in growth and development of an organism only when is in a balanced state and deficiency and excess
can limit the development and hence are termed limiting factors. Ecosystem thus provides ample scope for
research through all its constituents as it forms the basic unit of the integrative discipline which
encompasses the research on biosphere.
Succession
The biotic as well as the abiotic factors of an ecosystem are dynamic and constantly interact with each
other. Succession is a process by which the said elements of an ecosystem develop various kinds of
organisms with their interactions. The process continues till a final and stable community called climax is
formed which will keep itself adjusted in equilibrium with the environment.
In other words succession can be termed as a phenomenon of replacement of an earlier ecosystem with a
higher biomass rich and trophically diverse ecosystem. Anyhow such a stable diversity will be altered with
disruptive and exploitative actions as caused by anthropological interference. Such disrupted ecosystems
are often termed managed ecosystems which were altered to channelize the productivity to human needs.
Anyhow it should be clear that a naturally stable ecosystem will always be productive than a human
managed one.
Conservation
As insisted above, the anthropological interference has made it mandatory to check the human
exploitation for the betterment of ecosystem services. This has led to the concept of conservation of
ecosystem. Ecological conservation is a necessity of life systems and involves ensuring the continuity of its
dynamics. Besides that, resilience of an ecosystem can only be ensured with naturally operating trophism,
which regulates the populations by itself. However, productivity of an ecosystem only increases with
species diversity, though stability is attained by inter-special competition and the resultant dominance.
Often the said environmental dynamics is altered by human deeds like industrial revolution, over
exploitation of natural resources, burning of coal etc. This will lead to deterioration in the health of an
ecosystem and as it is the basic unit, the cumulative effect overlaps to cloud the entire biosphere with
consequences like pollution, global warming and climate change. Conservation assumes immense
significance in this aspect and recent days have witnessed many conservation activities like setting up of
Protected Areas, Climate change deliberations, Conventions on Biodiversity etc. so as to regain the health
of ecosphere and to impart sustainable development.
Taxonomic groups, Habitat and Levels of Organisation are the three aspects based on which ecological
research was done from time to time. These aspects and the related studies have developed various
disciplines of Ecology. Earlier, the botanists and zoologists tried to delineate ecological studies based on
taxonomic groups of the plants and animals and subsequently developed plant and animal ecology.
However, since it has been proved that all organisms constitute a biome and constantly interact with their
environment, isolated ecological studies for plants and animals lost sense.
Hence, modern researchers concentrate more on such dynamic interactions which the living matter makes
with their physical environment. They advocate that such interactions along with energy and material flow
should be made the pivot of ecological studies. Later habitat ecology was developed as a branch of
ecology with researchers focusing on organisms and their habitats. Further individual organisms and group
of organisms were looked upon as the studies were based on the levels of Organisation. Thus Autecology
and Synecology were developed as new branches of ecology.
Fig.
07:
Divisions of Ecology
Autecology & Synecology
Autecology is also known as ecology of individuals. In Autecology, the relation of individual species with its
environment is studied. Since individual species remains the key unit of an autecological approach, their
geographical distribution, morphology, taxonomic position, life cycle, interactions with the environment
they live in etc. come into the main focus of research. In synecology however the interrelations and
interactions between organisms of different species are taken into consideration. In synecology the basic
unit of study is the group of organisms. Synecology may deal with population, community, biome or
ecosystem based on the levels of organisations.
Population ecology & Community Ecology
In population ecology the interdependence between organisms of a population is dealt with and
charactecteristics like size, growth rate etc are taken into consideration. Another aspect which is in focus in
population ecology is Competition. Since the members of a population will always be in the same trophic
level, a competition will arise between the organisms for survival. Population ecology also deals with the
interaction between populations of different communities. Hence members of different trophic levels and
their interactions also forms a subject of research. Eg: prey predator relationship. In contrast to Population
ecology, in Community Ecology, study is focused on interdependencies between various organisms of
different species. Direct interactions between individuals of different populations are stressed upon in
Community Ecology.
Biome ecology and Ecosystem Ecology
Communities existing in an ecosystem may be in climax stage or in stages of succession in more or less
similar climatic conditions. Interactions between different communities under different stages of
development in an area constitute the basics of Biome ecology. Ecosystem Ecology has been the most
recent development in ecology. Ecosystem ecology studies about ecosystem -an ‘integrated whole’ of
biotic and abiotic components that are dynamic and in constant interference between each other. With
focus on such ecological complexes, ecosystem ecology remains the most complicated synecological
approach till date. It has also been termed as bio-energetic approach and the discipline concentrates more
on energy flow and nutrient cycle.
Levels of Ecological Organisation
The lowest level of ecological organisation is represented by an individual organism of a species. It is the
smallest unit of study in ecology. A group of such organisms occupy the next level and is called population.
Various populations of different communities exist in clusters called communities which form the next
level. A complex group of organisms and abiotic components connected by exchange of nutrients and
energy, like an ocean, is the smallest unit of ecology which can sustain life in isolation from all but
atmospheric surroundings. It is called an ecosystem and occupies the next level to community. Large areas
of vegetation under similar climatic characteristics constitute the biome in which many communities exist
together in various levels of succession. Biomes may consist of more than one ecosystem and hence
occupy the next level of Ecological organisation. Finally Ecosphere/biosphere forms the highest level of the
organisation as the entire earth when considered with its biomes and atmosphere constitute the single
largest and self-sustainable ecosystem.
Systems of Ecology
 Organism: A system always tends to attain equilibrium under constant conditions. Such a property
by which a system regulates is internal environment to achieve equilibrium is called homeostasis.
An organism – the smallest unit of ecosystem is capable of response to stimuli, reproduction,
growth and development and maintenance of such homeostasis as a stable whole. Organisms are
of many types – unicellular or multicellular, terrestrial, aquatic or amphibians, mammals and nonmammals etc.
 Population: A group of interbreeding organisms of same species at a given time with additional
characteristics to individuals is termed a population. Sex ratio, population density, birth rate, age
distribution, mortality etc. are some attributes which are assigned to a population. Population
growth assumes significance and growth rate is depicted with population curves – J curve or the
density independent growth and S curve or the sigmoid curve. Further, the response of a
population to the abundance of resources and predators is represented by Ecological Niche which
also gives the relative position of the population under study in an ecosystem.
 Community: When the populations of different species share a common habitat the cluster of
interacting populations is termed a community, with species diversity as the most important
attribute. Communities with high species diversity, despite being disturbed, return to a stable
condition easily. Depending upon the type of habitat a range of populations which creates
diversity, interact with each other to develop indigenous attributes on integration as a whole. In
the case of vegetation, this may result in stratification which in a way is a strategy to limit
interspecies competition, an attribute of a lower level – the population.
 Habitat: A habitat is an area inhabited by a particular species of an organism for its sustenance. It
may be Terrestrial, Fresh water, Estuarine or Ocean. Habitat fragmentation often remains the sole
reason for vulnerability of a species.
Evolution and speciation
Evolution points to the change in characteristics of a species over time. The species change their attributes
through the process of natural selection and evolution.
 Natural Selection: Charles Darwin first proposed the theory of Natural Selection. It was also
termed the principle off Survival of fittest. The theory proposes that the genetic diversity in a
species tends to converge so that some genes replicate more frequently over generations within a
population of species. Those organisms which are fittest survive and have the favourable genes
which allow them in their survival. Such favourable genes dominate in the future populations and
thus the unfavourable genes become recessive. This will result in exhibition and expression of
favourable genes over timeand hence is called survival of the fittest.
 Evolution & Coevolution: Natural selection result in change of inherited attributes over
generations in a populations and this change over time is termed evolution. Constant interactions
between two different species can result in evolution of both the species due to evolution of one.
This phenomenon is called Coevolution.
 Speciation: Over a sufficiently large temporal scale one species may evolve into a completely
different form due to various reasons like geographical alienation. The transformation of ancestral
population of a species to new species having entirely different characteristics is termed
speciation.
 Extinction: Extinction of a species means complete disappearance of the species from our
ecosphere. Biological completion and environmental change remains the primary reasons for
extinction. Slow evolution of a species with the surrounding changes, catastrophic events like
volcano eruption, tsunami etc. also contribute to the threat of extinction. Anyhow, of late human
activities like deforestation, pollution, poaching etc. has heightened the danger of extinction of
many species.