Variation, Competition & Succession of Organisms


A population represents a dynamic assembly of organisms belonging to the same species, coexisting within a defined geographical region over a specific duration. This collection of individuals, whether of plants, animals, or microorganisms, forms a vital ecological unit that undergoes continual changes and interactions.

Variation, on the other hand, encompasses the array of disparities that naturally occur among members of this population. These distinctions can manifest in various aspects, including physical characteristics, genetic makeup, behavior, and even reproductive strategies. They arise from a multitude of factors such as genetic mutations, environmental influences, and selective pressures.

These variations within a population serve as the raw material for evolution, as they can lead to the development of new traits and adaptations over time. Evolutionary processes like natural selection act upon this diversity, favoring traits that confer advantages in a given environment and shaping the population’s genetic composition.

A population comprises organisms of the same species residing within a specific area during a defined timeframe, while variation encompasses the inherent differences among these individuals, driving the evolutionary processes that shape the species over generations. Together, these concepts form the foundation of our understanding of the dynamics and adaptability of life on Earth.

Types of variations

Variability within a species is a fundamental aspect of the biological world, and it can manifest in various ways. Two primary categories of variations are morphological variation and physiological variation, each shedding light on different facets of how living organisms adapt and interact with their environment.

1. Morphological Variation:

Morphological variation refers to the visible and tangible differences in the physical appearance of individuals belonging to the same species. This form of variation typically undergoes gradual changes within a population, demonstrating a continuum from one extreme to another, often referred to as continuous variation. Examples of morphological variation include:

– Size (Height or Weight): Within a population of a species, individuals can exhibit a range of sizes, with some being taller or heavier than others.

– Coloration: The coloration of organisms, whether it’s the fur of mammals, feathers of birds, or scales of reptiles, can vary significantly within a population.

– Fingerprints: Even the unique patterns of fingerprints on human hands display morphological variation, with each individual having distinct ridge patterns.

These observable physical differences contribute to the diversity and adaptability of a species, allowing it to thrive in various environments.

2. Physiological Variation:

Physiological variation, on the other hand, encompasses differences in how individuals of the same species behave or respond to the conditions in their environment. Unlike morphological variation, physiological variation is not readily apparent through physical observation but relates to the internal functioning of an organism’s body. This type of variation often falls into the category of discontinuous variation, where individuals can be grouped into distinct classes without intermediates. Examples of physiological variation include:

– Behavior: Individuals within a species can exhibit varying behaviors, such as being temperamental, accommodating, excited, or calm in response to stimuli and situations. These differences in behavior contribute to the complex social dynamics of species.

– Blood Groups: The blood type of individuals within a population can vary, with individuals belonging to different blood groups like A, B, AB, or O.

– Taste Sensitivity: Some individuals may have the ability to taste certain substances like phenylthiocarbamide, while others cannot detect these tastes, showcasing variations in sensory perception.

Such physiological variations are essential for the survival and reproduction of a species as they enable different members to excel in specific ecological niches or under varying environmental conditions. Together, morphological and physiological variations underscore the remarkable adaptability and diversity found within the biological world.


Variation, the diversity seen within a population, arises from two primary sources, each contributing in its own distinct way:

1. Genetic Differences:

Genetic differences serve as one of the fundamental contributors to the mosaic of diversity within a species. These differences stem from alterations within the genetic code, and they can be inherited through generations. The most notable mechanism for genetic variation is mutation. Mutations can manifest as sudden changes or errors in the DNA sequence, which can subsequently be passed on to offspring through the process of reproduction.

For instance, consider a hypothetical plant species with green fruits. If a mutation occurs within the gene responsible for fruit coloration, it might result in a change that leads to the production of yellow fruits instead of green. Over time, this genetic alteration can become prevalent within the population, creating a new variant with a different fruit color. These genetic variations serve as the raw material for the process of evolution, allowing species to adapt to changing environmental conditions and giving rise to the diversity of life on Earth.

2. Environmental Differences:

Environmental factors encompass a wide range of external influences that can shape an individual’s development and characteristics. These factors encompass everything from the physical environment (such as housing and climate) to socio-economic conditions (including access to food, healthcare, educational facilities, and parental care). Environmental differences can exert a significant impact on an individual’s traits and abilities.

For instance, consider the case of intelligence. While genetics undoubtedly play a role in determining an individual’s intellectual potential, environmental factors also hold substantial sway. An intelligent person placed in an unfavorable environment, lacking access to quality education, adequate nutrition, and supportive caregivers, may find their cognitive abilities stifled. Conversely, an individual with a genetic predisposition toward lower intelligence may excel in a nurturing and intellectually stimulating environment. This stark contrast illustrates how environmental factors can either amplify or diminish the inherent genetic potential within an individual.

The causes of variation in a population are multifaceted. Genetic differences, driven by mutations and inheritance, lay the foundation for diversity within species. Simultaneously, environmental differences play a pivotal role in shaping the expression of genetic traits, underlining the intricate interplay between nature and nurture in the fascinating tapestry of life.


  1. Crime detection: Use of finger prints which can be arch, loop, whorl or compound.
  2. Determination of paternity using blood group
  3. Development of hybrids of desired traits in agriculture
  4. Classification of human race based on skin colour, shape of nose, texture of the hair into Caucasoid (European), Negroid (Black African) Mongoloid (Chinese and Japanese), Australoid (Australian)
  5. Blood transfusion: The blood group of the donor must be compatible with that of the recipient. If not, the donor’s RBC will clump in the recipient’s blood vessels causing serious harm to the recipient. Each blood group is characterized by specific proteins in the blood which are antigens in the RBC and antibodies in the blood plasma. The table below shows antigen-antibody reactions between donor and recipient bloods.






(Antigen a)


(Antigen b)


(Antigen a + b)



 A (Antibody b) + +
B (Antibody a + +
AB (None) + + + +
O (Antibody a + b) +

+    means positive reaction (no clumping)

–    means negative reaction (clumping)

Note: O is a universal donor while AB is a universal recipient



Competition is a pivotal and natural process that plays a fundamental role in shaping ecosystems and driving the evolution of species. It is the dynamic struggle that unfolds within the confines of a habitat, where living organisms vie for limited, indispensable resources crucial for their survival and reproduction. This relentless contest for essential elements within the environment has far-reaching implications for the balance and structure of ecosystems.

In the realm of plants, competition takes root in the battle for precious resources like sunlight, space, nutrients, and water. In an environment where these resources are scarce and highly sought after, plant species engage in an unceasing struggle to access them. For instance, within a densely packed forest, trees reach towering heights to capture sunlight, while their roots extend deep into the soil to extract vital nutrients and water. In this botanical battleground, only the most adept competitors thrive, ensuring the continued existence and propagation of their genetic lineage.

Animals, too, are active participants in the theater of competition. Their battles revolve around the pursuit of food, territory, and mates. The hunt for sustenance is a never-ending quest, where predators and prey engage in a perpetual game of cat and mouse. In the quest for survival, animals are compelled to establish and defend territories, creating a competitive arena where they must assert dominance to secure their place in the ecosystem’s hierarchy. Furthermore, the pursuit of suitable mates instigates intense competition, as individuals strive to exhibit their superior traits and secure the privilege of reproducing and passing on their genes to the next generation.

In the grand tapestry of life, competition serves as the crucible in which the concept of “survival of the fittest” finds its fullest expression. Organisms better equipped to navigate these fierce struggles are more likely to endure and reproduce, passing on their advantageous traits to their offspring. Conversely, those ill-suited to the challenges of competition may face elimination or diminished reproductive success.


Two distinct forms of competition characterize this intricate web of interactions:

1. Intraspecies Competition:

This form of competition unfolds among organisms belonging to the same species. For example, when numerous maize seedlings vie for space, light, nutrients, and water in a confined area, they engage in intraspecies competition. In this scenario, members of the same species vie with one another, sharpening their competitive skills in the process.

2. Interspecies Competition:

Interspecies competition, on the other hand, occurs between organisms of different species. Picture a scenario where both maize and pepper seedlings are vying for the same limited resources within a confined space. Here, the competition extends beyond the boundaries of a single species, as the maize and pepper plants compete for the available resources. Such interspecies competition adds a layer of complexity to the ecological landscape, as different species must adapt to coexist or risk being outcompeted by more specialized counterparts.

In the grand theater of life, competition remains an enduring and indispensable force, sculpting ecosystems, driving evolutionary change, and ultimately shaping the course of life on our planet. It is through this relentless struggle that nature continues to evolve, with the fittest individuals and species emerging triumphant, their genetic legacies interwoven into the intricate tapestry of Earth’s biodiversity.

Relationship between competition and succession

Succession is the change in a population caused by the replacement of the old members with new ones as a result of competition. The newly formed habitat is gradually colonized by different species of plants in a stepwise manner until a relatively stable community is established and later the habitat will be inhabited by animals. As soon as a habitat is established, competition sets in. The early inhabitant modify the habitat by their activities while the later arrivals compete and outgrow the previous inhabitants which gradually loss out.

See also:


Reproductive Behaviours: Courtship Behaviour, Display of Colours & Seasonal Migration

Fruits : Types, Structure, Dispersal of Fruits, Agents of Dispersal of Fruits

The Eyes | Anatomy, Functions, Problems, Solutions, Symptoms or Signs, Care For Eyes

Seeds | Zygotes, Conditions for Seed Germination, Formation & Seeds Germination

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