Fundamental Concepts and Principles of Ecology

There are certain basic fundamental ecological principles which describe various aspects of living organisms e.g. evolution and distribution of plants and animals, extinction of species consump­tion and transfer of energy in different components of biological communities, cycling, and recycling of organic and inorganic sub­stances, interactions and inter-relationships among the organisms and between organisms and physical environment, etc.

Organisms and the Environment

Organisms are individual living things. Despite their tremendous diversity, all organisms have the same basic needs: energy and matter. These must be obtained from the environment. Therefore, organisms are not closed systems. They depend on and are influenced by their environment. The environment includes two types of factors: abiotic and biotic.

Biotic vs. Abiotic Components

Biotic Components

• Definition: All living organisms and products derived from living or once-living matter.
• Examples: Living creatures, bones, shells, coral skeletons, feathers, teeth, hair, waste, and fossils.
• Energy Sources: Includes all coal types (peat, lignite, bituminous, anthracite) and petroleum, as they are formed from decayed organic matter.
• Biotic vs. Living: “Living” is a subset of “Biotic.” In ecology, the terms are often used interchangeably for simplicity, though biotic technically includes once-living matter.

Abiotic Components

• Definition: The nonliving physical and chemical factors of an ecosystem.
• Examples: Climate, weather, soil, water, and natural phenomena like lightning.

Habitat

• Habitat is the physical environment in which an organism lives. Each organism has particular requirements for its survival and lives where the environment provides for those needs.
• A habitat‘s features are determined mainly by abiotic factors such as temperature and rainfall. These factors also influence the traits of the organisms that live there.
• For example, the habitat of an elephant would be a forest, and the habitat of a tapeworm is the human gut. Forests, oceans, rivers, etc., are habitats of various organisms.
• Earth has four major habitats: Terrestrial, Freshwater, Estuarine and Ocean.
• The features of the habitat can be represented by its structural components, namely: space, food, water and shelter or cover.

Niche

• One of the most important concepts associated with the ecosystem is the niche.
• A niche refers to the role of a species in its ecosystem. It includes all the ways that the species interacts with the biotic and abiotic factors of the environment.
  • Two important aspects of a species‘ niche are the food it eats and how the food is obtained. Each species eats a different type of food and obtains the food in a different way.
• The functional characteristics of a species in its habitat are referred to as its niche in that common habitat. The habitat of a species is like its address, whereas the niche can be basically thought of as its ecological role or profession.
• The term ‘niche’ means the sum of all the activities and relationships of a species by which it uses the resources in its habitat for its survival and reproduction.
• A niche is unique for a species, while many species share the habitat. Two different species cannot occupy the same niche in the same place for very long. This is known as the competitive exclusion principle.
  • This is because if two species occupy the same niche, they will compete with one another until one is displaced. Once a niche is left vacant, other organisms can fill that position.
• Niche plays an essential role in the conservation of organisms. If we must conserve species in their native habitat, we should know their niche requirements.

Adaptation

• Every organism is suited to live in its particular habitat. An adaptation is thus the structural, physiological or behavioural characteristic of the life of an organism that enables it to survive in a particular environment.
• Examples of basic adaptations that help animals and plants to survive in their respective environments are as follows:
  • The shape of a bird’s beak.
  • The thickness or thinness of fur.
  • Presence of feathers and wings in birds.
  • Evergreen and deciduous nature of trees.
  • Presence and absence of thorns on leaves and stems.
  • Presence of gills and fins in fishes.
• Adaptation may be:
  • Morphological (Structural): Physical features that help organisms survive.
    • E.g., giraffes have long necks that allow them to feed on leaves high up in trees. This trait evolved over generations.
  • Physiological: Internal body processes that enable or enhance survival.
    • E.g., in the absence of an external water source, the kangaroo rat in North American deserts can meet all its water requirements through internal fat oxidation (in which water is a by-product). It can also concentrate its urine, thereby minimising the volume of water required to remove excretory products.
  • Behavioural: Actions or patterns that help organisms survive a stressful habitat.
    • E.g., the Savanna Great Migration in which millions of wildebeest, zebra, and gazelle undertake a year-long, clockwise migration through Tanzania’s Serengeti and Kenya’s Masai Mara, following seasonal rains to access fresh grazing lands.

Examples of Adaptation:

Morphological –

• Many desert plants reduce transpiration by developing thick cuticles on leaf surfaces, producing succulent leaves (thick, fleshy leaves adapted to store water) and sunken stomata (stomata in deep pits).
  • Some species eliminate leaves altogether by reducing them to spines to prevent transpiration, while flattened, green stems perform photosynthesis.
• In some trees, such as sal, red sanders, and silk-cotton trees, dieback is an adaptive response that helps them survive severe stress, especially drought. In this process, a plant or tree undergoes progressive death from the tip toward the base, allowing it to shed shoots while keeping the roots alive.
• Allen’s Rule states that endothermic (warm-blooded) animals, such as polar bears and penguins, in colder climates have shorter limbs and extremities (e.g., ears, flippers, and tails) to minimise heat loss. In contrast, those in warmer climates have longer limbs and extremities.
  • Elephants have enormous ears primarily for thermoregulation—a built-in air conditioning system to release body heat and stay cool in hot climates.
• A hyperthermophile is an organism that thrives in extremely hot environments. For example, archaea (archaebacteria) flourish in hot springs and deep-sea hydrothermal vents because of a specialised protein that helps these organisms form a protective, lipid-linked cellular membrane, which is key to withstanding extremely salty environments (halophiles) and acidic habitats (thermoacidophiles).

Physiological –

• We need to breathe faster when we are in high mountains. After a few days, the body adjusts to the changed conditions. Such small changes in the body over short periods to overcome minor challenges arising from environmental changes is called acclimatisation. The body compensates for low oxygen availability by increasing the respiratory rate and red blood cell/haemoglobin production.
  • Haemoglobin (Hb) is an iron-rich protein in red blood cells that carries oxygen from the lungs to the body’s tissues and returns carbon dioxide to the lungs, powering cells and providing energy.

Behavioural

• Desert lizards lack physiological thermoregulation; therefore, they bask in the sun to warm themselves and retreat to shade to avoid overheating.
• Likewise, some rodents burrow into soil to escape aboveground heat.

Physiological and Behavioural

• Hibernation and aestivation are both physiological and behavioural adaptation mechanisms.
• Hibernation: A drastic slowdown of metabolic processes achieved through a prolonged, deep state of inactivity to survive harsh winters. It is observed in some endotherms in colder climates.
  • E.g., bats, ground squirrels, hedgehogs, chipmunks, and some bear species—that hibernate to endure extreme cold and limited food during winter.
• Aestivation: Unlike hibernation, which prepares animals for cold, aestivation (summer sleep) is a survival strategy for extreme heat or drought. In this state of dormancy, animals reduce their metabolic activity—often by burying themselves in the ground, retreating into cool burrows, or forming protective cocoons.
  • E.g., African lungfish (creates a mucus cocoon to survive drought), snails (seal shell opening with mucous layer), earthworms (coil deep in soil), frogs, toads, some lizards and crocodiles, etc.

Species

• A species is defined as “a group of similar populations of organisms whose members are capable of interbreeding and producing fertile offspring (children)”.
• A tiger, a lion, a lotus and a rose are examples of different species. Every species has its own set of genetic characteristics that make the species unique and different from other species.

Species Formation

Variation

• Changes in genetic makeup (addition, deletion or rearrangement of specific genes) due to mutations, recombinations, changes in climate, geographical barriers, etc., induce variations over a period of time.
  • Recombination is the rearrangement of existing genes during sexual reproduction (fertilisation), or cell division (meiosis), producing new combinations of traits. It doesn’t create new genes but only rearranges already existing alleles. Thus, members of the same species show variation and are not identical. For example, siblings can look different even when they have the same parents.
• The difference in the colour of skin, type of hair, curly or straight, eye colour, and blood type among different ethnic groups represents the variation within the human species.

Phenotypic Plasticity

• It is the ability of a single genotype (the same set of inherited genes) to produce different phenotypes (a population with varying traits) in response to environmental conditions. In simple words, phenotypic plasticity is the environmentally induced variation in an organism’s traits without changes in its genetic makeup.
• Examples include:
  • Sun vs shade leaves: Sun leaves → thicker, smaller; 6hade leaves → thinner, broader.
  • Acclimatisation: High altitude triggers increased RBC production to compensate for low oxygen.
  • Tanning: Skin darkens due to increased melanin production in response to UV exposure.
  • Seasonal fur changes in Arctic fox, snowshoe hare—white fur in winter, brown fur in summer.

Adaptive Radiation

• Adaptive radiation is the diversification of organisms from a common ancestor into multiple new forms or species, driven by new environmental challenges or the availability of new ecological niches.
• Darwin’s finches on the Galápagos Islands – about 13 species evolved from a common ancestor – are a classic example of adaptive radiation. Variations in beak size and shape enabled them to specialise as seed-eaters, insectivores, and other feeders, reducing competition for limited resources.

Speciation

• Speciation is the evolutionary process where a single population splits and diverges into two or more genetically distinct, reproductively isolated species. It occurs when gene flow stops between populations, often due to geographic barriers or ecological niches, allowing genetic differences to accumulate over time.
• Speciation is driven by several mechanisms that create reproductive barriers, stopping populations from interbreeding:
  • Natural Selection: Populations adapt to different environments (ecological niches), leading to unique adaptations that prevent interbreeding.
  • Genetic Drift: Random fluctuations in allele frequencies in small, isolated populations can lead to divergence.
  • Sexual Selection: Variations in mating preferences can drive rapid separation between populations.
• Types of Speciation – Scientists categorise speciation based on the geographic relationship of the diverging populations: 
  • Allopatric Speciation: Occurs when populations are geographically separated by physical barriers (e.g., mountains, oceans).
  • Sympatric Speciation: Occurs within the same geographic area without physical barriers, often driven by, for example, exploiting different resources within the same habitat.
  • Peripatric Speciation: A small, peripheral population becomes isolated and evolves into a new species.
  • Parapatric Speciation: Populations are separated by a shared border but are not fully isolated geographically; they evolve reproductive isolation due to different selective pressures at the boundary.

Allopatric Speciation

• Often, different populations of a species remain isolated due to geographic barriers (geographic isolation) such as mountains, oceans, rivers, etc. After an extended period, isolated subpopulations may diverge substantially (genetic drift) and become reproductively isolated (they no longer interbreed).
• Later, even after the barrier is removed, the subpopulations are unable to interbreed and thus become distinct species (allopatric/geographic speciation).
• Examples include:
  • Red Panda: The Himalayas gave rise to the Himalayan and Chinese red pandas.
  • Salamanders in California: Isolated by the Central Valley, they evolved into distinct populations.
  • Darwin’s Finches: Different islands in the Galápagos with distinct niches have led to the evolution of 13+ new finch species.
  • Masai Giraffe: Separated by the Gregory Rift in Tanzania and Kenya, they show significant genetic divergence, though not yet considered a separate species.

Parapatric Speciation

• Parapatric speciation occurs when populations in adjacent areas are only partially separated or not separated at all.
• Still, limited gene flow, resulting from significant environmental differences, causes them to diverge into separate species.
• For example, baboon species occupy neighbouring habitats (savanna, woodland, highlands) and interbreed only minimally where their ranges meet.

Sympatric Speciation

• In sympatric speciation, new species evolve within the same geographic area, without any physical barrier due to disruptive selection, in which different subgroups specialise in different ecological niches, food sources, or mating preferences, leading to reproductive isolation.
• Familiar examples include cultivated banana, wheat, tobacco and cotton varieties (triploid), which arose through polyploidy, which causes instant reproductive isolation from the parent plants (diploid).
  • Polyploidy is the condition in which an organism has more than two sets of chromosomes (3n, 4n, 6n, etc.), instead of the usual diploid number (2n). Polyploid individuals usually cannot interbreed with the original diploid population, making it one of the fastest sympatric speciation mechanisms.

Hybridisation

• Hybridisation occurs when two different species mate and produce hybrid offspring. In some cases, these hybrids can give rise to new species.
• For example, the mule is a hybrid between a donkey and a horse.

Polyploidy

• It is the heritable condition of possessing more than two complete sets of chromosomes.
• Polyploids are common among plants, as well as among certain groups of fish and amphibians. For instance, some salamanders, frogs, and leeches are polyploids.

Recombination-Speciation

• It can be viewed as the evolution of restrictions on the freedom of genetic recombination: new combinations of alleles can be generated within species, but alleles from different species cannot be brought together.

Mutation

• A mutation is a sudden, permanent change in the DNA sequence (genes/chromosomes) of an organism due to errors in DNA replication, radiation, chemical action, etc.
• Mutations generate new genetic variations (i.e., new genes) in a population, which constitutes the raw material for evolution.

Natural Selection

• Natural selection is the process through which populations of living organisms adapt and change.
• Natural selection is the evolutionary mechanism that selects among variations, i.e. genes that help the organism to survive, reproduce and adapt to its environment.
  • Such genes, with favourable heritable traits, are more likely to be reproduced in a population and passed on to the next generation. For example, longer-necked giraffes survived droughts better and hence reproduced more and became dominant.

Isolation

• Geographical Isolation: The members of a population of a species live in a particular environment and are capable of breeding with members of another population of the same species.
• Ecological Isolation: It is caused by differences in temperature, humidity, pH, etc. in the environment of the two populations.
• Reproductive Isolation: It is caused by interference in interbreeding between members of different populations of a species.

Evolution

• Evolution is the gradual change in the heritable traits of a population across generations, leading to the development of new forms, adaptations, and sometimes new species.
• Mechanisms such as mutation, recombination, natural selection, variation, gene flow, and genetic drift (speciation) drive it.

Genetic Drift

• It describes random fluctuations in the numbers of gene variants in a population. Genetic drift takes place when the occurrence of variant forms of a gene, called alleles, increases and decreases by chance over time. These variations in the presence of alleles are measured as changes in allele frequencies.

Extinction

• The primary reason behind extinctions is environmental change or biological competition. Most extinctions occur when species cannot evolve rapidly enough to adapt to environmental change.
• Currently, the 6th Mass Extinction (Anthropogenic Extinction) is underway.

Population

• The population is defined as a group of freely interbreeding individuals of the same species present in a specific area at a given time.
• For example, when we say that the population of a city is 50,000, we mean that there are 50,000 humans in that city. However, all populations of humans living in any part of the world constitute the species Homo sapiens.

Factors for Population Growth

• The characteristics of any population depends on:
  • Density of the population
  • Natality (birth rate)
  • Mortality (death rate)
  • Dispersal
  • Biotic potential
  • Age distribution.

Density of the Population

• The number of individuals per unit area at a given time is termed population density. For example, you may notice more plant and animal species in the garden.

Natality (Birth Rate)

• The rate at which new individuals are born and added to a population under given environmental conditions is called natality.

Mortality (Death Rate)

• Loss of individuals from a population due to death under given environmental conditions is called mortality. The number of individuals dead in a year is calculated for obtaining the mortality rate or death rate.

Dispersal

• The movement of individuals of a population out of a region on a permanent basis is termed emigration, while immigration refers to the movement of individuals into a new area, where dispersal includes both emigration and immigration of individuals.

Biotic Potential

• Biotic potential refers to the maximum reproductive capacity of an organism under optimum environmental conditions. It is often expressed as a proportional or percentage increase per year. Full expression of the biotic potential of an organism is restricted by the environmental resistance, i.e. any factor that inhibits the increase in the number of the population.

Age Distribution

• Natural populations include individuals of all age groups. It, therefore, becomes necessary for us to consider the age distribution of a population. Age distribution refers to the proportions of individuals of different age groups in a population.
• A rapidly growing population will usually contain a large proportion of individuals in the reproductive age group; a stationary population (where there is no increase or decrease in population) contains an even distribution of all age groups, and a declining population contains a large proportion of old or post-reproductive age of an individuals.

Life History Variation

• Under a particular set of selection pressures, organisms evolve towards the most efficient reproductive strategy. Populations evolve to maximise their reproductive fitness, also called Darwinian fitness, in the habitat in which they live.
• Ecologists suggest that life history traits of organisms have evolved in relation to the constraints imposed by the abiotic and biotic components of the habitat in which they live. Evolution of life history traits in different species is currently an important area of research.

Population Interactions

• The biological community of an area or ecosystem is a complex network of interactions.
• The interaction that occurs among different individuals of the same species is called intraspecific interaction, while the interaction among individuals of different species in a community is termed as interspecific interaction.

Types of Interactions

Positive Interactions

• Commensalism: In this relationship, one of the species benefits while the other is neither harmed nor benefited. Some species obtain the benefit of shelter or transport from another species. For example, sucker fish, remora, often attach to a shark by means of their sucker, which is present on the top side of their head. This helps the remora get protection, a free ride as well as a meal from the leftovers of the shark’s meal.
• Mutualism: This is a close association between two species in which both species benefit. For example, honey bees and flowers are in a mutual relationship, where honey bees benefit through collecting nectar and for the flower, the bees help in pollination. However, some mutualisms are so intimate that the interacting species cannot live without each other. Such close associations are called symbiosis. Example: corals and zooxanthellae are in a mutual relationship.

Neutral Interactions

• Neutralism: Neutralism describes the relationship between two species that interact but do not affect each other. It is to describe interactions where the fitness of one species has absolutely no effect whatsoever on that of the other. Example: interaction between a rainbow trout and a dandelion in a mountain valley or cacti and tarantulas living in the desert.

Negative Interactions

• Amensalism: This is a negative association between two species in which one species harms or restricts the other species without itself being adversely affected or harmed by the other species. Example: Juglone secreted from the roots of black walnut destroys its surrounding plants, and the development of wheat is hindered by Convolvulus arvensis.
• Predation: In this type of interaction, the predator captures, kills and eats an animal of another species called the prey. The predator naturally benefits from this relationship, while the prey is harmed. Example: owls hunting mice, or shrews hunting worms, and insects.
• Parasitism: In this type of interaction, one species is harmed and the other benefits. Parasitism involves a parasite, usually a small-sized organism living in or on another living species called the host, from which the parasite gets its nourishment and often shelter. The parasite benefits, and the host is harmed. The roundworm, tapeworm, malarial parasites, many bacteria, fungi and viruses are common parasites of humans.
• Competition: This is an interaction between two populations in which both species are harmed to some extent. Competition occurs when two populations or species both need a vital resource that is in short supply. Example: Plants compete with each other for light exposure, temperature, humidity, pollinators, soil nutrients and growing space.