What is ecology?

The word ‘ecology’s first proposed by a zoologist named Reiter in 1885, is derived from Greek words, Oikos meaning the dwelling place or home and logos meaning the discourse or study. Although, it was a German Biologist, named Ernst Haeckel who popularized this term and defined Ecology as the total relationship of an organism with both its organic and inorganic environment.

The things of the world are classified into two major groups i.e. biotic component and abiotic component. The biotic component includes all types of living organisms, both plants and animals and the abiotic component includes the non-living materials (soil, water, air etc) and the forces of nature (light, gravity and molecular energy).

What is environment?

The word “environment” literally means surroundings and as such it refers to the aggregate of all those things and set of conditions, which directly or indirectly influence not only the life of organisms but also the communities at a particular place.  In fact, th word environment is derived from a French word, environ meaning envelope or surroundings.

The life-supporting environment of planet earth is called Biosphere. The biosphere is composed of three chief media-air, soil and water and on this basis biosphere has been divided into three-divisions: Atmosphere, Lithosphere and Hydrosphere respectively. Thus environment is a complex of factors acting, reaching and interacting with the organism complex. The totality of interactions that organisms have with each other as well as with their environment constitutes a system of nature called as Ecosystem.

Some basic terms in Ecology

Life can be organized into several different levels of function and complexity. These functional levels are: species, populations, communities, and ecosystems. It is significant to note that the terms, populations, communities and ecosystems have precise meanings in ecology such as:

Species

Species are the different kinds of organisms found on the Earth. A more exact definition of species is a group of interbreeding organisms that do not ordinarily breed with members of other groups. If a species interbreeds freely with other species, it would no longer be a distinctive kind of organism. This definition works well with animals. However, in some plant species fertile crossings can take place among morphologically and physiologically different kinds of vegetation. In this situation, the definition of species given here is not appropriate.

Populations

A population comprises all the individuals of a given species in a specific area or region at a certain time. Its significance is more than that of a number of individuals because not all individuals are identical. Populations contain genetic variation within themselves and between other populations. Even fundamental genetic characteristics such as hair color or size may differ slightly from individual to individual. More importantly, not all members of the population are equal in their ability to survive and reproduce.

Communities

Community refers to all the populations in a specific area or region at a certain time. Its structure involves many types of interactions among species. Some of these involve the acquisition and use of food, space, or other environmental resources. Others involve nutrient cycling through all members of the community and mutual regulation of population sizes. In all of these cases, the structured interactions of populations lead to situations in which individuals are thrown into life or death struggles.

In general, ecologists believe that a community that has a high diversity is more complex and stable than a community that has a low diversity. This theory is founded on the observation that the food webs of communities of high diversity are more interconnected. Greater interconnectivity causes these systems to be more resilient to disturbance. If a species is removed, those species that relied on it for food have the option to switch to many other species that occupy a similar role in that ecosystem. In a low diversity ecosystem, possible substitutes for food may be non-existent or limited in abundance.

Ecosystems

Ecosystems are dynamic entities composed of the biological community and the abiotic environment. An ecosystem's abiotic and biotic composition and structure is determined by the state of a number of interrelated environmental factors. Changes in any of these factors (for example: nutrient availability, temperature, light intensity, grazing intensity, and species population density) will result in dynamic changes to the nature of these systems.

Biome:

It is a recognizable community unit formed as a result of interaction of regional climates with regional substrata.  In short, a biome is characterized by climate and precipitation and then the kind of life inhabiting. The members of a biome are the plants and animals inhabiting it. Thus, a biome is a large region characterized by certain forms of life. Most biomes are determined by their characteristic weather pattern or climate. Every biome is home to a number of ecosystems.

Similarly, Tundra biome is the northern most region adjoining the ice bound poles. It is devoid of trees except stunted shrubs in the southern part of tundra biome, ground flora includes lichen, mosses. The typical animals are reindeer, arctic fox, polar bear, snowy owl, lemming arctic hare. Reptiles/amphibians are almost absent.

Biosphere:

The different ecosystems of the world constitute what we call as biosphere or ecosphere. This includes all living organisms and the physical environments with which they interact.

Thus, the oceans, land surface and lower parts of the atmosphere all form part of the biosphere.

Sub-divisions of ecology or different approaches to ecological studies:

Ecology may be divided into two subdivisions broadly; autecology and synecology.

What is Autecology? The word “autecology” is derived from a Greek word “autos’ meaning self i.e. the study of single species or individual organism in relation to the environment or the habitat in which it grows at all stages of its life span.

What is Synecology? The word “synecology” is derived from the Greek prefix Syn meaning together, so as to study the groups of organism in relation to their habitat and environment in which they grow.

On this basis, the different approaches to ecological studies are:

1. Habitat Ecology: Concerned with the nature of habitat.
2. Ecosystem ecology: - involves the analysis of ecosystem from structural and functional point of view.
3. Population ecology-concerned with the study of inter relationship of different groups of organisms.
4. Paleoecology-concerned with the organisms and geological environments of the past.
5. Production ecology-involves the study of gross and net production of different ecosystems.
6. Gene ecology-concerned with the genetic constitution of species or population with respect to its environment.
7. Conservation ecology: -includes the proper management of natural resources.
8. Radiation ecology: involves the study of radioactive substances, radiation and the environment.
9. Human ecology: concerned with man in relation to his environment
10. Integrated ecology: concerned with the energy conservation and flow in the organisms within an ecosystem.

Degradation of environment & ecology- a major concern:

Humans depend on environment for survival as it gives us oxygen to breathe, food to eat and water to drink. We also get fibre, medicines, fuel etc. from the environment.

The rapid growth of human population and rapid industrialization has lead to the environmental degradation in two ways:

(i) depletion of natural resources

(ii) pollution of the environment (air, water and soil).

Natural resources have been depleted through deforestation, excessive use of fossil fuels; mining etc.  Whereas, air/water has been polluted by toxic gases emitting from motor vehicles, toxic wastes discharged into water bodies.

Figure showing: Ecological interactions in totality

ORIGIN OF LIFE

Scientists believe that somewhere around 10 to 13 billion years ago the universe was a huge rotating red hot gaseous cloud of matter called as Ylem.

The said cosmos was made up particles of matter and anti matter and according to the famous Big Bang theory of Abbe Lemaitre proposed in the year 1931, a huge explosion; unimaginable in physical terms could have occurred as a result of collision between matter and antimatter that caused the formation of an abundant amount of hydrogen and hence, the galaxies were formed including our very own milky way galaxy of which earth is a part.

The huge cloud of gases that fragmented from the big bang over a period of millions of years lost heat and condensed to form the planets and stars that is our solar system as a whole.

Chemical evolution theory of life:

This theory was proposed by the duo of A.I. Oparin of Russia and Haldane, an England born Indian Scientist, independently in the year 1923 and 1928 respectively.

Today, their theory of evolution of life is famous after their names, Oparin- Haldane theory of evolution of life. Although, it is better remembered as the Chemical evolution theory of life.

Oparin even went on to publish his theory in his book entitled evolution of life in the year 1936.

Two important assumptions of the theory:

1)  That the origin of life on the primeval earth was not the result of a sudden, chance and spontaneous chemical reaction event instead, it was a slow and steady process of chemical reactions that occurred over a period of millions of years as the conditions of the Earth progressively changed that favored the formation of a varied assemblage of products ,starting with the formation of the simplest of the inorganic compounds followed by the synthesis of  the simplest of the organic molecules and then, the formation of the highly complex organic molecules in the form of Carbohydrates & nucleic acids.

The formation of these substances eventually led to the formation of the basic life substance called as PROTOPLASM and hence, a cell. These reactions occurred in the primitive ocean under favorable conditions.

2) That it was only the primitive earth that actually caused the formation and hence, the accumulation of either the complex organic molecules or for that matter, the formation of the basic substance of life, protoplasm just because of the presence of unique atmospheric conditions on the primitive earth. Today, since such primitive atmospheric conditions are not present on the earth nor they can possibly be created, therefore origin of any new life cannot be possible on the present Earth.

Various steps involved in the origin of first life:

Step 1: All those elements of the matter as are present on present earth were very much present on the primitive earth, but only in their atomic form. Even the constituent gases of the atmosphere were also in their atomic form.

The temperature of the primitive earth was unimaginably very high somewhere, between 5000 to 6000 degree centigrade.

It is believed that the rotating hot cloud of gases of which primitive Earth was made, lost its heat gradually over a period of time & the rotation and gravitation of the cloud, caused its atoms to segregate into three distinct layers according to their respective weight and hence, the core, lithosphere as well as the atmosphere of the primitive Earth were formed.

Step 2: This step marked the formation of the molecules from the combination of various free atoms and hence, the formation of the very first simple in-organic compounds. 

It is believed that on the primitive earth, the hydrogen was not only the most abundant of the free atoms, but was also very reactive. Therefore, it combined at the outset with all the available free oxygen atoms and formed the water molecules. It also combined with free nitrogen atoms of the primitive atmosphere to form Ammonia.  Since, hydrogen had combined with all the free oxygen atoms thereby making the primitive atmosphere reducing in nature leaving no free oxygen.

Step 3: This step marked the formation/ synthesis of first ever organic compounds. As the primitive earth was still very hot, the eruption of the volcanoes was almost the order of the day that used to emit hot metallic lava along with the gases like CO2, CO, N2 & H2. The nitrogen and the carbon of the atmosphere readily combined with the metallic atoms of the lava thereby, forming substances like carbides and nitrides.

The water being in the vaporized form due to extremely high temperature, reacted with the metallic carbides to form the very first organic compounds such as Methane. The water vapors might have also reacted with the metallic nitrides to form more of Ammonia.

Step 4:  The temperature of the earth decreased substantially to around less than 100 degrees that led to the condensation of water vapors which fell down on the earth as torrential rains that eventually formed the water bodies of the earth. It is believed that the torrential rains submerged the entire lithosphere of the primitive earth to form the primitive oceans. As the primitive ocean had a vast assemblage of the substances like NH3, CH4 & HCN etc dissolved in it that freely moved, collided and reacted with water to form a huge assemblage of materials in the primitive ocean.

Corroboration of Oparin –Haldane theory:  Stanley Miller in 1953, simulated  through his experiment called as spark-discharge apparatus” that consisted of a flask that was fed with a gaseous mixture of Methane, Ammonia and hydrogen approx in the ratio of 2: 1: 2. This flask was connected to another smaller flask that contained boiling water through a glass tube for supplying the water vapors. The source of electric discharge was created by inserting two Tungsten rods into the larger flask after being connected to an electric source simulating the effect of thunder lightening. Interstingly, after over a week, a mixture of simple amino acids like glycine and alanine along with some simple organic acids were found synthesized.

Conclusion:

Now it has been proved more than once that the origin of life occurred in water that appeared in the form of a primitive ocean and literally acted like as what JBS. Haldane described “Hot soup solution” of innumerable organic molecules mixed in it. Owing to the prevailing environmental conditions that were conducive enough to cause the polymerization of such organic molecules to form the more complex macromolecules and eventually, the synthesis of the basic life substance, the protoplasm.

According to Oparin, the first living molecules that eventually appeared in the primitive ocean were proteinaceous in nature what he called them as Coacervates. The coacervates were larger and denser colloidal particles but for the lack of a lipid membrane and nucleic acid in them, they did not replicate. They soon acquired a cell membrane and nucleic acids and emerged as a complete cell.

Sequence in which life originated:

Anaerobic chemoheterotrophs survived on the diverse organic compounds of the primitive ocean which they consumed for energy.

Anaerobic chemoautotrophs derived their energy by consuming the carbon dioxide and hydrogen sulphide to form sugar and hence, they very much resembled the modern day’s sulphur bacteria.

Anaerobic photosynthetic autotrophs are modern day’s cyanobacteria (BGA)

Aerobic photosynthetic autotrophs are modern day’s green plants.

At the outset, we must understand that the much talked about term-flora and fauna does not merely include all those big plants and animals around us, but necessarily sum total of all that life which is even microscopic in nature. We may call this microscopic life as micro flora or micro fauna which encompasses all those unicellular prokaryotes (bacteria, BGA) and unicellular eukaryotes (Protistans) which actually made this planet habitable for the first time during the course of evolution. Therefore, in the context of ecological studies, the significance of this micro flora and fauna probably hold even much more importance than that of the macro flora and fauna obviously for being the main agents of detritus food chain below the ground or so called as the decomposers of every ecosystem. In fact, the ecological significance of flora and fauna can be made out from some of the following view points:

Firstly: How do organisms adapt to different habitats; what physiological and morphological adaptations they undergo for this purpose so as to form the distinct ecosystems and biomes on the planet earth. This way they have adapted to almost every part of this biosphere and hence, have occurred the distribution of biodiversity although, unevenly but scattered everywhere on this planet.

Secondly: How do organisms of the same kind, (of the same species) come to live together in a particular habitat to form distinct populations; how do organisms in a population interact with each other, most importantly, compete with each other for the same resources of food and habitat and thus always limit the size of population. This way, the ecological significance of flora and fauna becomes relevant for understanding the unique mechanism that the nature creates for maintaining a perfect balance insofar as the population sizes of different organisms in the nature are concerned. The nature thus does not allow a population to exceed beyond what ecologically termed as the nature’s “carrying capacity”. Mankind could learn a lesson or two from this functional aspect of the nature as how to contain the size of ever burgeoning human population because, directly or indirectly, it is ultimately going to impact this ecological balance only. 

Thirdly: How do organisms interact with other organisms either of their own species or different thus, forming distinct populations and communities which makes us to understand the dynamics of the Mother Nature in maintaining its carrying capacity and hence, a perfect balance.

Fourthly: How do an ecosystem function as a perfectly balanced functional unit of nature through which traverses not only a unidirectional flow of energy from the universal celestial source called as the Sun and how does it flow through the successive trophic levels thereby, forming a variety of food chains and webs and eventually, ecological pyramids.

Fifthly: How do certain organisms both flora and fauna come to occupy such a unique position in an ecosystem that they have come to be christened as “keystone species” which not only act as the main drivers of an ecosystem, but whose absence can amount to collapse of an ecosystem as a whole. This necessarily calls for their utmost protection and conservation.

Sixthly: How do certain organisms particularly, the flora, act as the “pioneer species” and thus, facilitate in the much significant ecological succession through successive seral stages culminating in the emergence of so called climax communities with the advent of dominant species. These pioneer species initiate primary succession and can convert even a barren land or rock into a habitable habitat and

Finally: How does this flora and fauna maintain the much needed, ecologically significant biogeochemical cycles also referred to as “nutrient cycling” and thus, maintain not only a perfect balance in this nature, but also ensures that nothing goes out as waste from this Mother nature.

In the pages that follow, we shall be evaluating the significance of flora and fauna in the context of above aspects mainly.       

Ramdeo Mishra- “The father of Indian Ecology”

Ramdeo Mishra is revered as the Father of Ecology in India. Born on 26 August 1908, Ramdeo Mishra obtained his PhD in Ecology (1937) under Prof. W.H. Pearsall, FRS, from Leeds University in UK. He established teaching and research in ecology at the Department of Botany of the Banaras Hindu University (BHU), Varanasi. His research laid the foundations for understanding of tropical communities and their succession, environmental responses of plant populations and productivity and nutrient cycling in tropical forest and grassland ecosystems. Mishra formulated the first postgraduate course in ecology in India. Over 50 scholars obtained PhD degree under his supervision and moved on to other universities and research institutes to initiate ecology teaching and research across the country. He was honoured with the Fellowships of the Indian National Science Academy and World Academy of Arts and Science, and the prestigious Sanjay Gandhi Award in Environment and Ecology. Due to his efforts, the Government of India established the National Committee for Environmental Planning and Coordination (1972) which, in later years, paved the way for the establishment of the Ministry of Environment and Forests (1984).

Undoubtedly, our living world is fascinatingly diverse and amazingly complex. As noted at the outset, we can try to understand its complexity by investigating processes at various levels of biological organization-macromolecules, cells, tissues, organs, individual organisms, population, communities and ecosystems and biomes. At any level of biological organization we can ask two types of questions – for example, when we hear the bulbul singing early morning in the garden, we may ask – ‘How does the bird sing? Or, why does the bird sing?

The ‘how-type’ questions seek the mechanism behind the process while the why-type questions seek the significance of the process. For the first question in our example, the answer might be in terms of the operation of the voice box and the vibrating bone in the bird, whereas for the second question the answer may lie in the bird’s need to communicate with its mate during breeding season. When we observe nature around us with a scientific frame of mind, we will certainly come up with many interesting questions of both types, say for example,

why are night-blooming flowers generally white? The simple answer is to attract the night pollinators.  How does the bee know which flower has nectar? Why does cactus have so many thorns? How does the chick recognize her own mother? And so on as the examples are legion in the natural world around us…  

Now as we have had already understood that Ecology in its simplest manifestations is a subject which studies the interactions among organisms so called as biotic interactions and between the organisms and its physical (abiotic) environment.

In short, Ecology is basically concerned with four or five levels of biological organization – organisms, populations, communities, ecosystems and biomes.

To start with, we shall first explore ecology at organismic and population levels and try to understand how does a single organism interact with its surrounding environment although, it is inconceivable that in ecological studies, a single organism can ever live as a single individual without having any other organism by its side to interact with so as to form populations or communities.

But then to study ecology at an individual, organismic level i.e. ecology at the very basic level, it is certainly the interactions that it makes with its surrounding environment which forms the focus of ecological studies as we are excluding any other organism from our purview for the time being although, in nature, this is an inconceivable situation where a single organism can ever exist.

Ecology at the basic level – An Organism

Ecology at the organismic level is essentially physiological ecology which tries to understand how different organisms are adapted to their environments in terms of not only survival but also reproduction. Here thus comes to the fore, the very basic factor of ecological significance of flora and fauna from the fact that by way of such ecological adaptations, the organisms not only make almost whole of the biosphere habitable and hence, cause the distribution of biodiversity to different regions (biomes) of the globe, but also drives the ecosystems of such particular biomes.

As we already know that how the rotation of our planet earth around the Sun and the tilt of its axis becomes responsible for annual variations in the intensity and duration of temperature across the globe and hence, in the resultant appearance of distinct seasons. These variations together with annual variation in precipitation (remember precipitation includes both rain and snow) eventually, account for the formation of major biomes, such as desert, rain forest and tundra as shown in the (Fig.) below:

Figure showing:  Biome distribution with respect to annual temperature and precipitation.

It must be noted that regional and local variations within each biome lead to the formation of a wide variety of habitats. While the fact remains that on the planet Earth, life exists not just in a few favorable habitats but even in extreme and harsh habitats – scorching Rajasthan desert, perpetually rain-soaked Meghalaya forests, deep ocean trenches, torrential streams, permafrost polar regions, high mountain tops, boiling thermal springs, and stinking compost pits, to name only a few. Surprisingly enough, even our own intestine is itself a unique habitat for hundreds of species of microbes, notably, E.coli.

Now the pertinent question is: What are the key elements that lead to so much variations in the physical and chemical conditions of different habitats?

 The most important ones obviously are: temperature, water, light and soil. We must remember that the physico-chemical (abiotic) components alone do not characterize the habitat of an organism completely; the habitat includes biotic components as well that include – pathogens, parasites, predators and competitors – of the organism with which they interact constantly. These factors thus become responsible for the formation of distinct ecological niches within the habitat found in a particular biome as such.

Another relevant question that also comes to the fore in the context that how has an organism become so fit to survive in a particular habitat it lives in?

 We can argue that over a period of time, the organism had through natural selection, evolved such adaptations in the form of physiological or morphological modifications so as to optimize its survival and reproduction in its very habitat. In order to understand such of the modifications and adaptations, it is important to go into little details of such environmental or abiotic factors to which an organism has learnt to acclimatize itself with which even holds equally true to human beings as well…

Major Abiotic Factors

Determinants of distinct ecologically important habitats & Niches:

Temperature

Temperature is the most ecologically relevant environmental factor. Every one of us may be aware that the average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from plains to the mountain tops. It ranges from subzero levels in polar areas and high altitudes to >50⁰C in tropical deserts in summer. There are, however, unique habitats such as thermal springs and deep-sea hydrothermal vents where average temperatures exceed 100⁰C. It is general knowledge that mango trees do not and cannot grow in temperate countries like Canada and Germany, snow leopards are not found in Kerala forests and tuna fish are rarely caught beyond tropical latitudes in the ocean. We can thus, readily appreciate the significance of temperature to living organisms when we realize that it affects the kinetics of enzymes and through it the basal metabolism, so called as BMR and other physiological functions of the organism. A few organisms can tolerate and thrive in a wide range of temperatures (they are called eurythermal), but, a vast majority, say upto 99% of them are restricted to a narrow range of temperatures (such organism are called stenothermal). The levels of thermal tolerance of different species determine to a large extent their geographical distribution. In this regard, Birds & Mammals including insects and human beings with all flowering plants (Angiosperms), can be cited as the examples of so called eurythermal animals and plants whereas, rest of all animals with xerophytes or cryophytes, can be quoted as stenothermal animals and plants.

In recent years, there has been a growing concern about the gradually increasing average global temperatures. If this trend continues, we can certainly reason out that the distributional range of some species would be severely affected. This is why the contemporary phenomenon of global warming today, has become a war cry of global warning in the context of global biodiversity.

Water

Next to temperature, water is the most important factor influencing the life of organisms. In fact, life on earth originated in water and is unsustainable without water. Its availability is so limited in deserts that only special adaptations make it possible to live there. The productivity and distribution of plants is also heavily dependent on water. Every layman can think that organisms living in oceans, lakes and rivers should not face any difficulty surviving there, while the fact remains that the quality (chemical composition, pH etc.) of water becomes equally important a factor for their survival. The salt concentration (measures as salinity in parts per thousand), is less than 5 per cent in inland waters, 30-35 per cent the sea and > 100 per cent in some hyper saline lagoons. Akin to the adaptability of organisms (flora & fauna) to temperature ranges, similar is the case of some organisms which are tolerant of a wide range of salinities and thus are referred to as (euryhaline), while others are restricted to a narrow range of such salinities in terms of their survival and hence, are called as (stenohaline). Many freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems, they would face owing to the lack of such adaptive physiological mechanisms (absence of enzymes etc.) which otherwise are present in such organisms which are adapted to living under such hostile conditions.

Light

Since plants produce food through photosynthesis, a process which is only possible when sunlight is available as a source of energy, we can quickly understand the importance of light for living organisms, particularly autotrophs. Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesize optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees. Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering, a phenomenon referred to as photoperiodism in plants. For many animals too, light is important in that they use the diurnal (wake and sleep) and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities. The availability of light on land is closely linked with that of temperature since the sun is the source for both. Deep (> 500m) in the oceans, the environment is perpetually dark and its inhabitants are not aware of the existence of a celestial source of energy called Sun. What then is their source of energy? Obviously, such organisms meet their requirement of energy by feeding on the organic matter synthesized by other organisms in the ocean. At the same time, the spectral quality of solar radiation is also important for life. The UV components of the spectrum is harmful to many organisms while not all the colour components of the visible spectrum are available for marine plants living at different depths of the ocean. Among the red, green and brown algae that inhabit the sea, we can reasonably argue that it is the red algae that thrive in the deepest waters of the ocean as they have learnt to photosynthesize optimally well by absorbing the low wavelength solar radiations of the visible spectrum.

Soil

The nature and properties of soil in different places vary; it is dependent on the climate, the weathering process, whether soil is transported or sedimentary and how soil development occurred. Various characteristics of the soil such as soil composition, grain size and aggregation determine the percolation and water holding capacity of the soils. These characteristics along with parameters such as pH, mineral composition and topography determine to a large extent the vegetation in any area. This is in turn dictates the type of animals that can be supported. Similarly, in the aquatic environment, the sediment-characteristic often determine the type of benthic animals that can thrive there.

Responses to Abiotic Factors

How do organisms (Flora & Fauna) adapt to different environmental conditions?   

Having realized that the abiotic conditions of many habitats may vary drastically in time, we now ask-how do the organisms living in such habitats cope or manage with stressful conditions? But before attempting to answer this question, we should perhaps ask first why a highly variable external environment should brother organisms after all. One would except that during the course of millions of years of their existence, many species would have evolved a relatively constant internal (within the body) environment that permits all biochemical reactions and physiological functions to proceed with maximal efficiency and thus, enhance the overall fitness of the species. This constancy, for example, could be in terms of optimal temperature and osmotic concentration of body fluids. Ideally, then, the organisms should try to maintain the constancy of its internal environment (a process called homeostasis) despite varying external environmental conditions that tend to upset its homeostasis. Let us take an analogy to clarify this important concept. Suppose a person is able to perform his/her best when the temperature is 25⁰C and wishes to maintain it so, even when it is scorchingly hot or freezingly cold outside. It could be achieved at home, in the car while traveling and at workplace by using an air conditioner in summer and heater in winter. Then his/her performance would be always maximal regardless of the weather around him/her. Here the person’s homeostasis is accomplished, not through physiological, but artificial means. How do other living organisms cope with the situation? Let us look at various possibilities (Fig.)

(i)   Regulate: Some organisms are able to maintain homeostasis by physiological (sometimes behavioral also) means which ensures constant body temperature, constant osmotic concentration, etc. All birds and mammals, and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation). Evolutionary biologists believe that the ‘success’ of mammals is largely due to their ability to maintain a constant body temperature and thrive whether they live in Antarctica or in the Sahara desert.

      The mechanisms used by most mammals to regulate their body temperature are similar to the ones that we humans use. We maintain a constant body temperature of – 37⁰C. In summer, when outside temperature is more than our body temperature, we sweat profusely. The resulting evaporative cooling, similar to what happens with a desert cooler in operation, brings down the body temperature. In winter when the temperature is much lower than 37⁰C, we start to shiver, a kind of exercise which produces heat and raises the body temperatures. Plants, on the other hand, do not have such mechanisms to maintain internal temperatures.

(ii) Conform: An overwhelming majority (99 per cent) of animals and nearly all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. In aquatic animals, the osmotic concentration of the body fluids changes with that of the ambient water osmotic concentration. These animals and plants are simply conformers. Considering the benefits of a constant internal environment to the organisms, we must ask why these conformers had not evolved to become regulators. Recall the human analogy we used above; much as they like, how many people can really afford an air conditioner? Many simple ‘sweat it out’ and resign themselves to suboptimal performance in hot summer months. Thermoregulation is energetically expensive for many organisms. This is particularly true for small animals like shrews and humming birds. Heat loss or heat gain is a function of surface area. Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then they have to expend much energy to generate body heat through metabolism. This is the main reasons why very small animals are rarely found in Polar Regions. During the course of evolution, the costs and benefits of maintaining a constant internal environment are taken into consideration. Some species have evolved the ability to regulate, but only over a limited range of environmental conditions, beyond which they simply conform.

      If the stressful external conditions are localized or remain only for a short duration, the organisms have two other alternatives.

(iii) Migrate: The organisms can move away temporarily from the stressful habitat to a more hospitable area and return when stressful period is over. In human analogy, this strategy is like a person moving from Delhi to Shimla for the duration of summer. Many animals, particularly birds, during winter undertake long-distance migrations to more hospital areas. Every inter the famous Keolado National Park (Bhartpur) in Rajasthan host thousands of migratory birds coming from Siberia and other extremely cold northern regions.

(iv) Suspend: In bacteria, fungi and lower plants, various kinds of thick-walled spores are formed which help them to survive unfavourable conditions – these germinate on availability of suitable environment. In higher plants, seeds and some other vegetative reproductive structures serve as means to tide over periods of stress besides helping in dispersal – they germinate to form new plants under favourable moisture and temperature conditions. They do so by reducing their metabolic activity and going into a date of ‘dormancy’.

      In animals, the organisms, if unable to migrate, might avoid the stress by escaping in time. The familiar case of bears going into hibernation during winter is an example of escape in time. Some snails and fish go into aestivation to avoid summer-related problems-heat and desiccation. Under unfavorable conditions many zooplankton species in lakes and ponds are known to enter diapauses, a stage of suspended development.   

Morphological and Physiological adaptations in organisms

Ecological significance

While considering the various alternatives available to organisms for coping with extremes in their environment, we have seen that some are able to respond through certain physiological adjustments while others do so behaviorally (migrating temporarily to a less stressful habitat). These responses are also actually, their adaptations. So, we can say that adaptation is any attribute of the organism (morphological, physiological, behavioural) that enables the organism to survive and reproduce in its habitat. Many adaptations have evolved over a long evolutionary time and are genetically fixed. In the absence of an external source of water, the kangaroo rat in North American deserts is capable of meeting all its water requirements through its internal fat oxidation (in which water is a byproduct). It also has the ability to concentrate its urine so that minimal urine so that minimal volume of water is used to remove excretory products.

Many deserts plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits to minimize water loss through transpiration. They also have a special photosynthetic pathway (CAM) that enables their stomata to remain closed during day time. Some desert plants like Opuntia, have no leaves – they are reduced to spines and the photosynthetic functions is taken over by the flattened stems.

Mammals from colder climates generally have shorter ears and limbs to minimize heat loss. (This is called the Allen’s Rule). In the polar seas aquatic mammals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat.

Physiological adaptations

Some organisms possess adaptations that are physiological which allow them to respond quickly to a stressful situation. Say for example, we as humans, whenever we go to higher altitudes say, to mountains, every one of us would experience what is called altitude sickness. Its symptoms include nausea, fatigue and heart palpitations due to the reason that our body does not get enough oxygen as higher the altitude, the ambient air gets thinner and hence, lesser in oxygen content. But, gradually then, we get to acclimatize to the surrounding environment and stop experiencing what is called as altitude sickness.

In most animals, the metabolic reactions and hence all the physiological functions proceed optimally in a narrow temperatures range (in humans, it is – 37⁰C). But there are microbes (archaebacteria) that flourish in hot springs and deep sea hydrothermal vents where temperatures far exceed 100⁰C. How is this possible? The reason is that they have special body adaptations to survive under such boiling temperatures say, in the form of a special material; their cell walls are made of.

Many fish thrive in Antarctic waters where the temperature is always below zero for the similar reasons of having special physiological and morphological adaptations say, fatty blubber in seals that acts as an insulator to prevent the loss of heat from their body.  

Similarly, a large variety of marine invertebrates and fish live at great depths in the ocean where the pressure could be > 100 times the normal atmospheric pressure that we experience on the surface of the earth. How do they live under such crushing pressures and do they have any special enzymes? Obviously, the organisms living in such extreme environments show a fascinating array of biochemical adaptations in their body.

Some organisms on the other hand, show some behavioral responses to cope with variations in their environment. Desert lizards lack the physiological ability that mammals have to deal with the high temperatures of their habitat, but manage to keep their body temperature fairly constant by behavioral means. They bask in the sun and absorb heat when their body temperature start decreasing and move back to shade as soon as the ambient temperature starts increasing. Some species are even capable of burrowing into the soil to hide and escape from the above-ground heat.

STRATEGIC ADAPTATIONS IN PLANTS

It is not only the animals, but the plants too have acquired the unique adaptations for survival under different environmental conditions and thus, become responsible for constituting a unique vegetation or flora of a particular biome say for example, some plants have evolved to tolerate wide range of light regimes, while others have evolved to survive under extremely dry conditions, high temperature, water-saturated conditions or under saline environments and so on. Few of such adaptations may be discussed as below:

Plant Adaptations to light regimes

Not only individual plants but also plant communities show adaptations to different intensities of light. Plants that have adapted to bright sunlight are called sun plants or heliophytes while those growing in partial shade or low intensity light are called shade plants or sciophytes. In forests, plants show stratification or layering as they are arranged in different strata due to their shade tolerance. Heliophytes (sun plants) have higher temperature optima for photosynthesis and also have high rates of respiration. On the contrary, sciophytes (shade plants) possess low photosynthetic, respiratory and metabolic activities. Ferns and several herbaceous plants are shade tolerant - plants. They grow on the ground under the dense canopy of trees.

Plants Adaptations to Water Scarcity and Heat:

Many species of plants are adapted to dry habitats and high temperature conditions e.g. plants of hot deserts. They are termed as Xerophytes. The xerophytes have special adaptations to withstand prolonged period of drought. These are of four types - ephemerals (drought escapers), annuals (drought evaders), succulents (drought resistants) and non-succulent perennials (drought endurers).

(i)   Ephemerals (drought escapers): The xerophytes which evade dry conditions by remaining in the form of seeds but live for a brief period and complete their life cycle during the rains. Common examples are Euphorbia andArgimone etc.

(ii) Annuals (drought evaders): These are the xerophytes which continue to live for a few months even after rains in hot dry conditions. They have modifications to reduce transpiration. Common example is Echinops.

(iii) Succulents (drought resistants): These xerophytes have fleshy organs to store large amounts of water. Succulence results from the proliferation of parenchyma cells, enlargement of vacuoles in cells as well as due to reduction of intercellular spaces. Plants like Opuntia, Euphorbia, and Asparagus etc are noted for having fleshy stems which are green and photosynthetic. In order to minimize the loss of water, such xerophytes have not only gone through a wonderful morphological adaptation of reducing their leaves to leaf spines. At the same time, such xerophytes or Succulents do possess a very thick cuticle, sunken stomata which open during night only for the purposes of conserving maximum water

(iv) Non-succulent perennials: These are true xerophytes. These perennial plants have many morphological modifications to withstand dry conditions. These have extensive root system that spreads along the soil surface to absorb maximum amount of water. They also possess waxy coatings on leaves, sunken stomata, reduced leaf blades etc. to reduce transpiration. Examples include Acacia, Zizypus jujube and Calotropis etc.

      Noted further that there are many tropical plants e.g. grasses which grow in hot and dry climates. These therefore come to possess a very unique and efficient photosynthetic pathway called as C4 pathway of photosynthesis. As a result of this, such plants are not only able to survive in conditions of water scarcity, but are also capable of achieving very high rates of photosynthesis in the midst of this water scarcity and that too under abnormally high temperatures.

       Many xerophytes even accumulate an amino acid proline in the cells of leaves to maintain osmotic and water potential. On the other hand, Chaperonins (heat shock proteins) are also present in some xerophytes which provide them physiological adaptations against high temperatures. Heat shock proteins help other proteins to maintain their structure and avoid denaturisation at high temperatures.

Plant Adaptations to Aquatic Environments:

Plants which grow in water or water rich sub-stratum are called hydrophytes. By adapting themselves to such aquatic habitats, these hydrophytes come to possess some of the following adaptive features such as:

1. Mucilage: Submerged parts of hydrophytes are covered with mucilage for protection.
2. Absent or poorly developed Roots: These may be absent (e.g. Wolffia) or poorly developed (e.g. Hydrilla). If present, they may serve the function of anchorage (e.g. Ranunculus). Instead of root caps, root pockets are present (e.g. Eichhomia, Pistia).
3. Stems: Stems are generally weak, slender and have long internodes (e.g. Hydrilla).
4. Leaves: In surface floating hydrophytes, leaves are generally large, broad and thick (e.g. Victoria). In submerged hydrophytes, leaves are either ribbon-shaped (e.g. Vallisneria) or finely dissected (e.g. Ceratophylium). Heterophylly (occurrence of more than one type of leaves) is common in partially submerged hydrophytes (e.g. Ranunculus).
5. Inflated organs: Special air-storing organs occur in floating plants e.g. petioles or leaves for storing air. Moreover, presence of aerenchyrna (large air spaces) helps to transport oxygen produced during photosynthesis to other parts including roots. These organs also impart buoyancy to the plants.

Plant Adaptations to Saline Environments

The plants which grow in saline environments are called halophytes. Saline environments have high concentrations of salts (e.g. NaCI, MgC12, MgSO4 etc.) in soil or water. Halophytes are found in tidal marshes and coastal dunes, mangroves and saline soils. They have the ability not only to tolerate high concentrations of salts in their rooting habitat but are able also to obtain water from the same. Halophytes inhabiting hot and dry conditions possess characteristics of xerophytes like succulence in leaves, stems or both for storing water in large sized cells. It helps in diluting ion concentration of salts.

Connecting concept: How do mangroves survive under extremely salty habitats?

Mangroove plants are found wonderfully adapted to marshy conditions of tropical deltas and along ocean edges

Plant Adaptations to Oligotrophic Soils

Oligotrophic soils refer to those soils which have very low quantity of nutrients or nutrient content. Such type of soils generally develops in old and geologically stable regions e.g. tropical rain forest regions. Nutrient retention capacity of such soils is poor due to intense weathering and high rates of leaching. Therefore, the plants that survive under such soil conditions are known to possess mycorrhizae (mutualistic association of plant roots with fungi). Mycorrhizae help in absorption of water, minerals (especially retrieval of critical elements like phosphorus from organic compounds) and protection from pathogenic organisms. This natural association has formed the basis of modern day’s agricultural practice called as mycorrhizal biotechnology under which plants have not only been enabled to grow in nutrient deficient soils, but have also been vested with an ability to resist drought and soil borne pathogenic conditions- (Question asked in CSP/GS-2013).

STRATEGIC ADAPTATIONS IN ANIMALS

Other than the most familiar adaptations so called as behavioral adaptations exhibited by the animals say in the form of migration, suspension, hibernation or aestivation as noted above, some of the animals do exhibit a unique kind of adaptation of blending with their surrounding environment so as to avoid themselves from being eaten by their predators, a phenomenon referred to as camouflage. While some animals do exhibit a kind of behavioral or morphological adaptation to attract their mate say for example, bright plumage in birds.

Camouflage (cryptic appearance)

It is the ability of the animals to blend with the surroundings or background. In this way, animals remain unnoticed for protection or aggression.

Examples

Mimicry

It is generally considered a defensive mechanism adopted by palatable organisms to protect themselves from predators. It also includes deceiving or alluring of the prey at the hands of

Stick insect (A) leaf insect (B).

predators. It can be defined as the superficial but close resemblance of one organism to another or to the natural objects among which it lives that secures its concealment, protection or some other advantage. In order to deceive the predator or prey, the subject conceals itself in its surroundings (background).

In such situations, the subject is known as mimic or mimetic and the object it copies is called the model. Mimetic animals, in addition to colour, also imitate their models in shape, size, action, attitude etc. Mimicry is of four types:

1. Batesian mimicry: The phenomenon of resemblance of palatable prey species (mimetic) to unpalatable ones (model) in order to deceive the predator is known as Batesian mimicry.

(ii)  Mullerian mimicry: In nature, a set of two or more unpalatable related species attempt to resemble each other thus compounding their dispelling effect in the mind of their common predators. This phenomenon is called Mullerian mimicry

(iii)       Aggressive Mimicry:  Sometimes, predators take advantage of mimicry phenomenon. Here, predators really become the proverbial wolf in sheep's clothing. This is often called aggressive mimicry.

Viceroy butterfly (left) which mimics the monarch butterfly (right).

(iv)       Feigning Death or Conscious Mimicry: Certain organisms, sensing danger from predators, pose as if they are dead objects. Tenebrinoid beetles are famous for attaining motionless pebble-like appearance when they are in danger from predators. This phenomenon is called feigning death or conscious mimicry.

Warning Colouration

Sometimes, concealing form as well as coloration enables the animal species to avoid its natural predator.

Adaptation to Water Scarcity in Animals:

Animals that live in arid regions show two kinds of adaptations such as:

(i)         Reducing loss of water from their bodies, and

(ii)        Ability to tolerate arid conditions.

Adaptations to cold in Animals

Animals like barnacles and molluscs of intertidal zones of cold areas live in sea and cannot undergo hibernation. Also, sessile animals cannot migrate. These animals and some others (e.g. several insects, spiders) have adapted to excessive cold conditions by developing cold hardening. These animals are commonly called freeze tolerant organisms. They possess ice nucleating proteins which induce ice formation in the extra cellular spaces at very low sub zero temperatures.

Echolocation

This behavioural adaptation is depicted by bats. These are flying mammals and are nocturnal. They do not use eyesight for locating food, path or place of rest. Instead, they produce high frequency sounds which work on the principle of sonar. The high frequency sounds after striking various objects produce echoes which are received by the bats to locate their path.

Population Attributes

In nature, we rarely find isolated, single individuals of any species; majority of them live in groups in a well defined geographical area, share or compete for similar resources, potentially interbreed and thus constitute a population. Although the term interbreeding implies sexual reproduction, a group of individuals resulting from even an a- sexual reproduction is also generally considered a population for the purpose of ecological studies.

In earlier chapters you have learnt that although an individual organism is the one that has to cope with a changed environment, it is at the population level that natural selection operates to evolve the desired traits. Population ecology is, therefore, an important area of ecology because it links ecology to population genetics and evolution.

A population has certain attributes that an individual organism does not. An individual may have births and deaths, but a population has birth rates and death rates. In a population these rates refer to per capital births and deaths, respectively. The rates, hence, are expressed is change in numbers (increase or decrease) with respect to members of the population.

Another attribute characteristic of a population is sex ratio. An individual is either a male or a female but a population has a sex ratio (e.g. 60 per cent of the population are females and 40 per cent males).

Ecological significance of flora & fauna in knowing its population attributes for building up population growth models:

Population Growth Models

We have been concerned about unbridled human population growth and problems created by it in our country in particular and throughout the world in general. It is therefore natural for us to be curious if different animal populations in nature behave the same way or show some restraints on growth. Perhaps we can learn a less or two from nature on how to control population growth.

Exponential growth Model:  

Resource (food and space) availability is obviously essential for the unimpeded growth of a population. Ideally, when resources in the habitat are unlimited, each species has the ability to realize fully its innate potential to grow in number, as Darwin observed while developing his theory of natural selection. Then the population grows in an exponential or geometric fashion. This innate potential of a population to grow in size or number is referred to as the ‘intrinsic rate of natural increase’ usually represented by ‘r’. This is indeed a very important parameter chosen for assessing impacts of any biotic or abiotic factor on population growth.

            It must be noted that any specie’s growth exponentially under unlimited resource conditions can reach enormous population densities in a short time. Darwin showed how even a slow growing animal like elephant could reach enormous numbers in the absence of any checks and balances.

Connecting concepts: How big a population can grow, if growing exponentially?

Here is an anecdote popularly narrated to demonstrate dramatically how fast a huge population could build up when growing exponentially.

The king and the minister sat for a cheese game. The king, confident of winning the game, was ready to accept any bet proposed by the minister. The ministry humbly said that if he won, he wanted only some wheat grains, the quantity of which is to be calculated by placing on the chess board on grain in Square 1, then two in Square 2. Then four in Square 3, and eight in Square 4, and so on, doubling each time the previous quantity of wheat on the next square until all the 64 squares were filled. The king accepted the seemingly silly bet and started the game, but unluckily for him, the minister won. The king felt that fulfilling the minister’s bet was so easy. He started with a single grain on the first square and proceeded to fill the other squares following minister’s suggested procedure, but by the time he covered half the chess board, the king realized to his dismay that all the wheat produced in his entire kingdom pooled together would still be inadequate to cover all the 64 squares. Now think of a tiny Paramecium staring with just one individual and through binary fission, doubling in numbers every day, and imagine what a mind-boggling population size it would reach in 64 days. (provided food and space remain unlimited). Does this really happen in nature?

We may find its answer in another population growth model called as:

Logistic growth Model

 This is nature’s universal fact that no population of any species in nature has at its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. Eventually, the ‘fittest’ individual will survive and reproduce. The governments of many countries have also realized this fact and introduced various restrains with a view to limit human population growth. In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. We may call this limit imposed by nature as the nature’s “carrying capacity” (K) for that species in that habitat.

 A population growing in a habitat with limited resources show initially a lag phase, followed by phases of acceleration and deceleration and finally an asymptote, when the population density reaches the carrying capacity.

 Since resources for growth for most animal populations are finite and become limiting sooner or later, the logistic growth model is considered a more realistic one.

Life History Variation

Populations evolve to maximize their reproductive fitness, also called Darwinian fitness (higher r value), in the habitat in which they live. Under a particular set of selection pressures, organisms evolve towards the most efficient reproductive strategy. Some organisms breed only once in their lifetime (Pacific salmon fish, bamboo) while others breed many times during their lifetime (most birds and mammals). Some produce a large number of small-sized offspring (Oysters, pelagic fishes) while others produce a small number of large-sized offspring (birds, mammals). So which is desirable for maximizing fitness? Ecologists suggest that life history traits of organisms have evolved in relation to the constraints imposed by the biotic components of the habitat in which they live. Evolution of life history traits in different species is currently an important area of research being conducted by ecologists.

Interactions among the organisms of the same species: Intra-specific Interactions:

As we know that the organisms of the same species living together in a particular habitat come to form a population. How do they interact with each other form second important topic of ecological studies and hold an ecological significance of flora and fauna in the sense of limiting the population size so that a perpetually constant ecological balance can be maintained in the nature. From these intra-specific interactions we can certainly drive home a lesson about containing the ever burgeoning human population sizes. Although, the members of a species interact in several ways yet, these interactions fall into two main categories broadly viz: Cooperative interactions and Competitive interactions.

Noted that both types of these interactions are more evident in animals than in plants for the obvious reason their being sessile in nature.

Cooperative Interactions

 In cooperative interactions, the members of a species work together to achieve the same end.

 The sheer advantage of these cooperative intraspecific interactions is that it contributes to the survival of the species.

Let’s zero in on each of them in brief to get a fair idea about these interactions:

1.   Mating: Its ecological significance to identify certain species in a particular area:  

      Pairing of male and female individuals for the purpose of reproduction is known as mating. It is also called as copulation or coition. Cooperation for mating is the most fundamental and universal inter-action among the organisms of the same species.

2.   Parental Care: It refers to an activity wherein the eggs or the young ones are being looked after either by one of the parents or by both. Care arises from responsibility or affection for others among the organisms and varies from mild attention to a profound concern. Although, it is not a universal feature as most animals do not show parental care. They thus leave their eggs or young ones hatching from them to be tended by nature. Yet, many animals do exhibit a unique behaviour of care for their eggs and young ones. This behaviour manifests in many forms and modes such as: 

 (a)  Ootheca Formation: Some animals pro-vide food and protection to the eggs and pay no further attention to the offspring. Earthworm and cockroach belong to this category. They lay food-laden eggs in protective egg-eases called as oothecae and deposit the same in a safe place.

(b) Nest Building: Many animals prepare special nests for storing their eggs. They may store food in the nest, guard the eggs, or incubate the eggs.

      Parental care: Care of the Young: It is interesting to note that the care of the young is not only a phenomenon common to animals but, it also occurs in the plants as well. Among animals, it is probably more glaringly exhibited among honey bees than in others. The worker honeybees look after and feed the larvae with great care. The mother scorpion carries the offspring on the back for about a week. The Surinam toads keeps in skin pockets not only the eggs but also the emerging tadpoles that complete metamorphosis there and leave as small, tailless adults. The mother crocodile looks after the eggs as well as the young ones when hatched. The young of some birds, such as pigeon, sparrow, dove, crow and bulbul, are naked and help-less at the time of hatching. They are thus fed and looked after in the nest itself by the parents for a long time. All mammals look after their young ones with great care and affection. This period of care has a great importance for the offsprings as they are taught during this time what the race has learnt through the ages. The female kangaroo protects and nourishes the very helpless young in her abdominal pouch called rnarsupium. The female rabbit, rat, cat and dog keep their naked, blind and helpless offspring in a burrow or under bushes or other objects, and may shift them to a safer place if threatened with danger. Parental care is prolonged in primates and is of course, maximum in humans.

      Insofar as plants are concerned, they nourish the young (embryos) and release them with various devices that protect them and help them to reach suitable sites so as to establish their permanent growth there.

      Noted that the sheer advantage of parental care among organisms is that it greatly increases the chances of survival of the progeny and continuation of the race.

1. Aggregations: Aggregation refers to the habitual occurrence of the individuals of a species in large groups for various purposes. Such aggregations among animals may be temporary, while others may be more or less permanent.

      Although, there many advantages that accrue to animals from such aggregations, yet the most significant is protection against predators and environmental hazards. It has been validly confirmed through many field observations and laboratory experiments that the individuals in an aggregation are more likely to survive than a single individual of the same species placed in the same environment. A herd of deer is less likely to be surprised by a predator than a single deer be-cause of many noses and many pairs of eyes and ears. A pack of wolves is more likely to make a kill than a single wolf.

4.   Altruism (Altruistic Behaviour): Altruism is the behaviour whereby an individual increases the welfare of another individua1 of its species at the expense of its own welfare. The individual which shows altruistic behavior is called altruistic individual or altruist. In altruism, the altruist suffers whereas the other individual is favoured (benefited). Many live examples of altruism are exhibited by the animals in nature and the most important of them are exhibited by the following animals:

 (a) Spotted Deer: When a herd of spotted deer is attacked by a predator, such as tiger or panther, the stag' having the best antlers is surrounded by other members of the herd, to save its life. As such, one or more surrounding defenders may likely be killed by the predators.

(b) Bees: A worker bee defends the hive by stinging the intruder even though it will rip out its inside while leaving the victim as its sting is left behind on the body of the victim. This way, it sacrifices itself life for the sake of defending its hive. The sheer advantage that altruism fetches for the organisms is that it saves the best individual or the colony from death through sacrifice of life by one or more individuals.

5.   Dominance-Subordination Behaviour: Dominance-subordination behaviour is a kind of hierarchical social order seen in a flock or herd in which there is ranking of individuals. Often the females are subordinate to males and the Youngs are subordinate to adults. High, ranking or dominant individuals casually displace the low-ranking or subordinate ones from areas of shelter and sources of food and water, whereas low-ranking individuals withdraw or submit themselves on the approach of high-ranking ones. In these social systems, social dominance is established by a series of threats including aggressive postures or actual fights. Each individual in a social group knows its rank, and all live peace-fully. If a conflict arises, the higher-ranking individual gives a formal threat display, and the lower-ranking one at once assumes a submissive or appeasement posture to avoid injury. Thus, there is no serious bloodshed, and confrontations are averted by ritualized submission. If a new individual joins the group or a member is injured, threats and fights ensue to readjust the status of the members in the social group. A member that remains absent from the group for some time is downgraded. Dominance once established is more or less permanent. However, a member of a lower rank may get a higher rank by defeating the senior ranks.

      In a social group, the highest rank always has a first chance at the available food, mate and resting site, and the lower ranks must wait for their turn. Among animals, such dominance hierarchies have been found in fishes, lizards, mice, rabbits, wild dogs, wolfs, goats, horses, Lions, tigers, monkeys and apes. Dominance hierarchies occur in such gregarious animals in which groups are small and stable so that the members may know one another individually. Its importance lies in the fact that it maintains an order and discipline in social groups which are likely to be disturbed by aggressive members.

1. Leadership Behaviour: Leadership behaviour is a tendency on the part of the members of a group to follow a certain member called the leader. The leader keeps the other members of the group together when they are on the move. The leader determines the feeding and resting rhythms of the members in the herd. Facing the intruder or fleeing from the site is also ordered by the leader. The leadership behaviour is beneficial for the group as well as the individuals, especially in times of emergency. The relationship between the leader and the followers is different from that between the dominant member and the subordinates. The leader does not enjoy special social privileges and there is mutual dependence of the leader and the followers. This Leadership behaviour is common in mammals, but it does exist in birds, lizards, fishes and arthropods.

1. Territorial Behaviour and Home Range: This particularly involves marking off a particular area by an individual or a group of breeding individuals either for the purposes of breeding or defending the same against any trespass typically by members of the same species, except the mates. The area so marked off is called as territory.

      These territories may be set up on a seasonal or a permanent basis. Size of the territory depends upon the food requirements of the breeding pair and their offspring. Territories are found, prior to breeding, usually by males. Boundary of the territory is marked with urine, faeces or through odorous secretions. Animals usually set up a single territory for feeding and breeding.

8.   Animal Societies:  Certain insects, namely, termites, bees, ants and wasps, form well organized and highly integrated societies. In such a society, a large number of individuals of the same species live together in some sort of a nest which may be called as hive or comb in honey bees; termitarium or termite hill in termites and formicarium in ants. The individuals in all such insect societies are morphologically specialized into distinct types so called as castes (polymorphism) for performing different activities or jobs (division of labour). Each individual contributes to the welfare of the entire colony. There is so much specialization and interdependence of individuals in insect societies that they cannot survive outside the colony. Although, the different insect societies have evolved separately and differ in their composition and activities, they have much in common. In all cases, there are three. main castes : queen, males (drones in bees and kings in other social insects) and workers. The first two are reproductive individuals, The workers perform all other duties such as preparation of nest, collection and storing of food, rearing of young ones and protection of the colony from predators.

       The honeybee colony consists of 3 castes of individuals namely, queen, drones and workers. An average-sized colony has some 10,000-16,000 individuals. Of these, only one is queen, 500-1000 are drones, and the rest are all workers.

       In Termites, besides having the 3 castes of individuals as found in honeybees, termites do have soldiers to fight the intruders as well as for fighting a chemical warfare.

      Similarly, in an Ant society besides having soldiers, they also have sexual castes and workers. Ants cultivate fungus gardens and rear ant cows (aphids) for feeding. The aphids excrete a sweet fluid through a pair of honey dew tubes located at their back. The ants eat the honeydew.

9.   Communication: As the term is itself self explanatory, communication means transmission or exchange of information among the members of a species. This communication among animals takes place by means of different kinds of signals and   each animal possess an ability to not only send and receive signals, but also to interpret them meaningfully. As such these signals may be chemical, tactile, visual, auditory or electrical in nature. Let’s discuss the nature of these signals in brief for better understanding:

Chemical Signals

 Animals use two types of chemicals for communication; pheromones and allochemicals.

Pheromones:  Chemicals released by an animal into the environment to evoke a certain behavior in other members of the species are called pheromones. The latter are detected by smell or taste.

Allochemicals:  The chemicals that are released by one species and affect another species are termed allochemicals. Allo means- different. These are of two types called as Allomones and kairomones.

So far as allomones are concerned, they give a sort of adaptive advantage to an  organism which produces them by acting either as repellents or attractants. Repellents provide defence against an attack.

The Kairomones on other hand, give adaptive advantage to an organism which receives them. Some predators find their prey by chemicals given off by the latter, e.g., Scoliodon can smell food from a long distance. Mouse can smell the odour of a cat and hide or run away.

Tactile Signals: These signals are generally used as a mode of communication when the sender of a signal is in close contact with the receiver of the same such that a variety of messages can be communicated between them by varying the frequency, pressure, and duration of contact. Tactile communication is common in courtship and mating behaviour. For example, mutual preening in birds and grooming in primates are modes of this kind of communication.

Visual Signals:  Specific structures indicate sex of the individual, e.g., mane in lion, white rump of antelope, brilliant plumage in peafowl and pheasant. Firefly emits light to attract a mate. Some animals feign death as a protection from enemy. Honeybees perform dance movements to indicate the direction and distance of the food source. A dog expresses a threat by baring its teeth and raising the fur on the back.

 Auditory Signals: This is a mode of communication by means of sound. Many animals make mating calls

10.       Cannibalism:   Cannibalism is an intraspecific interaction in which the larger members     eat up the smaller ones of their own species. An individual that eats is known as a     cannibal, and the one that is being eaten is called a prey. Cannibalism is common in      insects such as cockroaches, ants and termites. It is also noticed in frogs, cobras and scorpions. Female spider eats up the male after mating. Ecologically, cannibalism has its own share of advantage in the sense that it enables a cannibal to obtain proteins similar to             those of its own kind from the prey. Some animals limit their population by cannibalism and thus maintain a natural balance in the nature.

Competitive intraspecific Interactions (Competition)

 Since every individual in this nature needs food, space, protection from enemies and many other similar requirements of life. It thus always comes in contact with other organisms for the said purpose and competes with it. It is not easy to get all these requirements fulfilled as the earth is already crowded with life. There is competition among the organisms for their needs, and it may be quite intense. No habitat is peaceful. The animals occupying it are engaged in killing others so that they themselves may live. Sparrows fighting with one another for shelter and wall lizards chasing each other to catch an insect are common sights in our houses. Yet amid all this death and destruction, there always exists sort of a balance, ecological equilibrium, which permits the maximum individuals to live and leave their progeny. This natural balance is achieved by competition which in nature may manifest itself in two forms called as intraspecific and interspecific. Of the two, the intraspecific competition is always very fierce and severe because, all the members of a species have the same requirements of food and shelter, and they are nearly equal in their structural, functional and behavioural adaptations. This is the reason that the individuals of solitary animals often live spaced apart so that each has a better chance to satisfy its needs. Many birds and mammals establish territories for the same purpose. Intraspecific competition is maximum when the resources are limited. At other times, the animals arc well spread out and can satisfy their needs. If overcrowding occurs, the excess individuals fail to get their requirements and are eliminated.

Competition in Plants: Competition occurs in plants also. Seedlings growing under the parent tree seldom survive because of competition with the parent. Seedlings growing close together compete for space, light, water and minerals. Those growing faster than others succeed in getting their requirements and survive others perish. Seed dispersal is a mechanism for reducing competition in plants by spacing out the seedlings. Roots of some desert plants produce certain chemicals which check the germination of seeds within a certain distance to conserve scarce water and minerals.

Ecological significance of flora and fauna can thus be discerned from this competitive interaction among the organisms either of intraspecific or interspecific nature, as this competition regulates the population size to establish an ecological balance between the available resources and the population of a species.

What is a “Biotic Community”?

We already know that no habitat in this nature contains the individuals of only one species. In fact, a population of a single species cannot survive by itself because there is always an interdependence of one form of life on another at least, for food; any species requires one more species on which it can feed. Even the plants which are autotrophs by nature, cannot survive on their own as they also require the soil microbes to break down the complex organic matter to supply them with the essential minerals and nutrients and then the plants also require a pollinating agent (insects) for pollination. There is thus always an interdependence among the organisms in this nature or in a given habitat such that a kind of living community (biotic community) comes into being. This natural association of the interdependent populations of different species inhabiting a common environment or habitat as a viable, self-contained unit is called a biotic community, or biocoenosis. In short, a biotic community may be considered as a multi-species population.

Population Interactions- Ecological significance:

Population interactions are inherently interspecific in nature because, these interactions essentially arise from the interaction of populations of two different species. They could be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both.  To understand them in a better way, let’s assign a ‘+’ sign for beneficial interaction, ‘-‘sign for detrimental and ‘0’ for neutral interaction and then try to look at all the possible outcomes of interspecific interactions through the table given below:

Table: Population Interactions

Species A	Species B	Name of Interaction
+	+	Mutualism
-	-	Competition
+	-	Predation
+	-	Parasitism
+	0	Commensalism
-	0	Amensalism

From the above table, we can easily understand that           both the species benefit in mutualism and both lose in competition in their interactions with each other. In both parasitism and Predation only one species benefits (parasite and predator, respectively) and the interaction is detrimental to the other species (host and prey, respectively). The interaction where one species is benefitted and the other is neither benefitted nor harmed is called commensalism. In amensalism on the other hand, one species is harmed whereas the other is unaffected. Predation, parasitism and commensalisms share a common characteristic – the interacting species live closely together. Let’s briefly discuss about the very nature of these interactions…

(i)   Predation: What would happen to all the energy fixed by autotrophic organisms if the community has no animals to eat the plants? We can think of predation as nature’s way of transferring to higher trophic levels the energy fixed by plants. When we think of predator and prey, most probably it is the tiger and the deer that readily come to our mind, but a sparrow eating any seed is not less a predator. Although animals eating plants are categorized separately as herbivores, they are, in a broad ecological context, not very different from predators.

      Besides acting as ‘conduits’ for energy transfer across trophic levels, predators ecologically play other important roles as well. They keep prey populations under control. But for predators, prey species could achieve very high population densities and cause ecosystem instability. When certain exotic species are introduced into a geographical area, they become invasive and start spreading fast because the invaded land does not have its natural predators. The prickly pear cactus introduced into Australia in the early 1920s caused havoc by spreading rapidly into millions of hectares of rangeland. Finally, the invasive cactus was brought under control only after a cactus-feeding predator (a moth) from its natural habitat was introduced into the country. Biological control methods adopted in agricultural pest control are based on the ability of the predator to regulate prey population. Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. In the rocky intertidal communities of the American Pacific Coasts the starfish Pisaster is an important predator. In a field experiment, when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year, because of interspecific competition.  

      If a predator is too efficient and overexploits its prey, they the prey might become extinct and following it, the predator will also become extinct for lack of food. This is the reason why predators in nature are ‘prudent’. Prey species have evolved various defenses to lessen the impact of predation. Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator. Some are poisonous and therefore avoided by the predators. The Monarch butterfly is highly distasteful to its predator (bird) because of a special chemical present in its body. Interestingly, the butterfly acquires this chemical during its caterpillar stage by feeding on a poisonous weed.

      For plants, herbivores are the predators. Nearly 25 per cent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants). The problem is particularly severe for plants because, unlike animals, they cannot run away from their predators. Plants therefore have evolved an astonishing variety of morphological and chemicals that make the herbivore sick when they are being eaten by them inhibit feeding or digestion disrupt its reproduction or even kill it. This can be exemplified through an obnoxious weed called as Calotropis, growing in abandoned fields. The plant produces highly poisonous cardiac glycosides and that is why we would never see any cattle or goats browsing on this plant. A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine, caffeine, quinine, strychnine, opium, etc.,) are produced by them actually as defences against grazers and browsers.

(ii)  Competition: When Darwin spoke of the struggle for existence and survival of the fittest in nature, he was convinced that interspecific competition is a potent force in organic evolution. It is generally believed that competition occurs when closely related species compete for the same resources that are limiting, but this is not entirely true. Firstly, totally unrelated species could also compete for the same resources. For instance, in some shallow South American lakes visiting flamingoes and resident fishes compete for their common food, the zooplankton in the lake. Secondly, resources need not be limiting for competition to occur; in interference competition, the feeding efficiency of one species might be reduced due to the interfering and inhibitory presence of the other species, even if resources (food and space) are abundant. Therefore, competition is best defined as a process in which the fitness of one species (measured in terms of its ‘r’ the intrinsic rate of increase) is significantly lower in the presence of another species. It is relatively easy to demonstrate in laboratory experiments, as Gause and other experimental ecologists did, when resources are limited, the competitively superior species will eventually eliminate the other species, but evidence for such competitive exclusion occurring in nature is not always conclusive. Strong and persuasive Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, apparently due to the greater browsing efficiency of the goats. Another evidence for the occurrence of competition in nature comes from what is called competitive release. A species, whose distribution is restricted to a small geographical area because of the presence of a competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed. Connell’s elegant field experiments showed that on the rocky sea coasts of Scotland, the large and competitively superior barnacle Balanus dominates the intertidal area, and excludes the smaller barnacle Chathamalus from that zone. In general, herbivores and plants appear to be more adversely affected by competition than carnivores.

Connecting concepts: What is Gause’s Competitive Exclusion Principle?

Gause’s Competitive Exclusion Principle states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true if resources are limiting, but not otherwise. More recent studies do not support such gross generalizations about competition. While they do not rule out the occurrence of interspecific competition in nature, they point out that species facing competition might evolve mechanisms that promote co-existence rather than exclusion. One such mechanism is resource partitioning. If two species compete for the same resource, they could avoid competition by choosing, for instance, different times for feeding or different foraging patterns. MacArthur showed that five closely related species of warblers living on the same tree was able to avoid competition and co-exist due to behavioural differences in their foraging activities.

(iii) Parasitism: Considering that the parasitic mode of life ensures free lodging and meals, it is not surprising that parasitism has evolved in so many taxonomic groups from plants to higher vertebrates. Many parasites have evolved to be host-specific (they can parasitize only a single species of host) in such a way that both host and the parasite tend to co-evolve; that is, if the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to counteract and neutralize them, in order to be successful with the same host species. In adaptations such as the loss of unnecessary sense organs, presence of adhesive organs or suckers to cling on to the host, loss of digestive system and high reproductive capacity. The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of its primary host. The human liver fluke (a trematode parasite) depends on two intermediate hosts (a snail and a fish) to complete its life cycle. The malarial parasite needs a vector (female Anopheles mosquito) to spread to other hosts. Majority of the parasites harm the host; they may reduce the survival, growth and reproduction of the host and reduce its population density. They might render the host more vulnerable to predation by making it physically weak. Isn’t it correct to say that an ideal parasite should be the one to be able to thrive within the host without harming it?

      Parasites that feed on the external surface of the host organism are called ectoparasites.

      In contrast, endoparasites are those that live inside the host body at different sites (liver, kidney, lungs, red blood cells, etc.). The life cycles of endoparasites are more complex because of their extreme specialisation. Their morphological and anatomical features are greatly simplified while emphasizing their reproductive potential.

      Brood parasitism in birds is a fascinating example of parasitism in which the parasitic bird lays its eggs in the nest of its host and lets the host incubate them. In nature, it is seen live in case of cuckoo laying her eggs in Crow’s nest. During the course of evolution, the eggs of the parasitic bird have evolved to resemble the host’s egg in size and colour to reduce the chances of the host bird detecting the foreign eggs and ejecting them from the nest. This can be easily observed in nature by watching the movements of the cuckoo (koel) and the crow in our neighbourhood park particularly, during the breeding season (spring to summer) and hence, brood parasitism in live action.

(iv) Commensalism: This is an interaction in which one species benefits and the other is neither harmed nor benefited.

(v)  Mutualism: This interaction confers benefits on both the interacting species. Lichens represent an intimate mutualistic relationship between a fungus and photosynthesizing algae or cyanbacteria. Similarly, the mycorrhizae are associations between fungi and the roots of higher plants. The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy-yielding carbohydrates.

Concept of “Key-stone” species in a biotic community & their ecological significance:

Connecting concepts: What are “Keystone & Critical link species”?

Such animal or plant species, living in a particular habitat, whose presence in that very habitat is so important that it influence the survival and existence of many other species in the same habitat, are referred to as key stone species. Say for example, a few animals produce long-lasting changes which alter or maintain their environment. They are called keystone species. These species play crucial role in regulating the relative abundance of other species.

Examples:  Elephants and crocodiles can be quoted as few examples of keystone species in the following sense:

(i)   Elephants damage trees by browsing the lower branches, stripping the bark and uprooting them. This prevents forests from encroaching on the grasslands where grazing beasts and other herbivores flourish.

(ii) Crocodiles by their swimming movements dig and maintain deep pits free of rooted swamp vegetation. Fishes and other aquatic animals survive dry periods by gathering in these pits.

Critical Link species: Since, only a few species can actually function as keystone species. Several other species play an important role in supporting network species by providing food or acting as pollinators of flowers or for that matter, acting as dispersal agents of seeds and fruits or facilitate in the absorption or circulation of nutrients say, microbes in the soil. Such species are called critical link species because; these serve to link different species thereby, forming either a food chain or food web as such in the nature.  For example, Mycorrhizal fungi are critical link species which help the vascular plants in obtaining nutrients from the soil and organic residues. Tropical rain forests are rich in critical link species due to high degree of zoophily and zoochory.

What is ‘Ecotone’ and ‘Edge Effect’?

The adjacent biotic communities do not ways have sharp lines of demarcations between them. There are usually transition zones between any two habitats which comprise or house the species from both the adjacent habitats. This transition zone is what we call the ecotone. An ecotone often has some populations from each adjacent community and some species which are characteristic to itself only. Therefore, the total number of species is often greater in the ecotone (transition zone) than in the adjoining communities. The presence of a greater number and diversity of species in this transition or ecotone region is referred to as “edge effect.”