Ecology is the scientific study of how living organisms interact with each other and their non-living environment. The term comes from Greek roots: “oikos” (house/environment) and “logia” (study of).
Ecology overlaps with fields like biology, genetics, and ethology, and it plays a critical role in understanding energy flow and matter cycling in ecosystems. Organisms depend on constant energy and matter flow for survival, without which life ceases to exist.
Ecologists study how biodiversity influences ecosystem functions and how organisms adapt and interact in their surroundings.
Every species has a particular distribution pattern, shaped by ecological and historical factors. For example, Koalas live only in Australia, and White Tigers are native to Indian forests. Similarly, pine trees grow in the Himalayas but not in lowland river basins.
Such distribution is studied through a branch called biogeography, which focuses on the spatial patterns of species. It is divided into two major branches:
This branch explores how species spread from their centers of origin. It considers large-scale evolutionary timeframes and factors like climatic and geological changes that may have forced or supported migration and diversification.
Historical biogeography studies living as well as extinct species across global regions over extended periods.
Ecological biogeography is concerned with how organisms respond to immediate environmental conditions. It focuses on local habitats and shorter time scales.
Organisms interact with both abiotic factors (e.g., temperature, light, soil, water, acidity) and biotic factors (e.g., predators, parasites, competitors, and humans).
Each species has a specific tolerance range that determines where it can survive and reproduce. Organisms differ in their reproductive strategies, behavior, and adaptability, but none exist in isolation.
Ecology examines relationships across various scales—from microbial communities and forests to the biosphere as a whole.
It provides the foundation for understanding ecosystems of all sizes and how species interact with both their physical environment and other organisms.
You are now studying this unit with utmost interest. To complete the entire unit, you may essentially need to sit and concentrate for considerable time. For this, you require some kind of energy. To complete any task or physical work, one must have energy. We get energy by consuming food. If we eat more food than we utilize, the excess energy is stored as body weight. This principle applies not only to humans but also to all living organisms in an ecosystem. The importance of energy in ecosystem functions is discussed in the sections below.
Life is associated with the interactions of many organisms. Living organisms function together with land, soil, water, and the atmosphere, forming a complex relationship that supports life on Earth. According to Tansley (1935), the term ecosystem refers to "the system resulting from the integration of all the living and non-living factors of the environment."
The biosphere is a massive ecosystem where biotic and abiotic components continuously interact, bringing about structural and functional changes. Ecosystems can be classified as:
An ecosystem consists of living and non-living components. The non-living or abiotic part includes land, water, atmosphere, and soil. The living or biotic community involves species interacting within the system.
Biotic components, part of the biosphere, include all living forms categorized into:
Abiotic components are non-living factors essential for life. These include:
Other abiotic factors include:
Energy and matter are crucial components in every ecosystem, influencing how organisms live and interact with their surroundings.
All living organisms on Earth require energy and matter to grow and function. The primary source of energy for nearly all life forms is the Sun. Even in deep ocean waters, algae survive due to solar energy. Plants capture solar energy to grow, which is then transferred through the food chain as animals feed on plants and other animals. This energy sustains both prey and predators, enabling them to build body structures from essential tissues and cells.
Matter includes solids, liquids, gases, and all living and non-living entities that occupy space and possess mass. It consists of atoms such as carbon, nitrogen, and phosphorus, and molecules like water (H2O). Organisms assimilate these substances from the environment to construct their bodies, and later release them back through respiration, excretion, or decomposition.
Organisms continuously use and recycle these substances in a cyclic manner.
Energy and matter constantly move within and between the atmosphere, lithosphere, hydrosphere, and biosphere. Organisms grow using environmental energy and return matter upon death or decay. Fungi and bacteria play a vital role in decomposition, releasing different energy forms back into the environment.
This cycle maintains a dynamic ecosystem system.
Ecosystems operate based on two main processes:
Living organisms require organic compounds such as proteins, carbohydrates, lipids, and nucleic acids, all of which consist of elements like carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
These cycles involve the movement of key elements in biological, geological, and chemical processes. The four main elements in these cycles are:
These processes operate in a circular path between the environment and living organisms, forming the foundation of life-supporting systems.
A set of interacting species function together in a particular environment to ensure the continuation of life. The interaction of individuals within a community occurs through feeding on one another, facilitating the transfer of energy and nutrients from one organism to another along the food chain. The linkage of feeding interactions between individuals is referred to as the food chain.
For example, an eagle consumes snakes, which eat rats, which in turn eat insects to gain energy. More complex linkages between organisms form a food web, with organisms grouped into various trophic levels.
Plants require water and chemical elements for their growth and development. These nutrients are primarily absorbed from the soil. However, the depth of root penetration to absorb these nutrients varies among plant species.
Therefore, it is clear that each species has developed its own unique mechanism for survival.
The niche of an organism refers to its demands on physical and chemical conditions, space, and food supply within its environment. It also explains how a species interacts with and exploits its environment. This is otherwise known as the species’ adaptation to environmental conditions.
Human ecology refers to the scientific study of the dynamic interactions between human beings and their surrounding environments. Unlike other organisms within the Earth’s biosphere, humans exhibit a unique capacity to influence, adapt, and transform their ecosystems.
The study of human ecology reveals that human distribution and population density are subject to ecological principles similar to other species. However, the human footprint is often far-reaching due to our ability to construct, destruct, and innovate, directly impacting both our abundance and distribution across the globe. Therefore, an in-depth understanding of human behavior becomes essential when studying this domain.
Human behavior varies dramatically across different regions and eras. While other species are typically confined to specific habitats, humans continuously evolve and adapt, refusing to exist in isolation from nature. For millions of years, humans have passed down traditional knowledge and survival skills through generations.
In contrast to animals that rely on physical adaptations such as claws, beaks, or teeth for survival, humans have developed a vast array of technological tools to source food and extract natural resources. These tools have played a significant role in reshaping the environment and enhancing quality of life.
The complexity of human behavior arises from the interplay between genetics, cultural practices, and environmental factors. Human ecology draws upon a range of interdisciplinary insights to decode these interactions.
Due to the multidimensional nature of human behavior, studying human ecology requires integrating various academic disciplines. Below is an overview of the fields contributing to our understanding of human-environment interaction:
This multifaceted approach underscores why human ecology is such a complex field of study.
Human progress over the past 2–3 million years has been deeply influenced by numerous technological and cultural breakthroughs. These include:
Historically, humans relied heavily on their natural environment for sustenance, particularly in terms of food production. These environmental interactions played a key role in shaping various forms of societal structures—from early hunter-gatherer communities to today’s urban civilizations.
Hunting and Gathering is the oldest and most widespread form of human technological activity in both time and space. It began with the use of pebble tools found alongside the remains of early hominids in Africa, especially Ethiopia, around 3 million years ago. During the Pleistocene, early humans were confined to Africa until Homo erectus expanded into Eurasia around 1 million years ago.
With the emergence of Neanderthals around 100,000 years ago, humans adapted to cold climates and began hunting with hand-held weapons. Homo sapiens evolved between 100,000 and 50,000 years ago and spread across the globe, including Australia and America.
They developed from Palaeolithic hand axes to more sophisticated tools such as spears, bows, choppers, and knives. Food preparation was basic, often over open fires, and shelters were simple. Eskimos developed kayaks, igloos, and winter clothing to survive harsh conditions.
Hunter-gatherers had keen tracking skills and knowledge of plant and animal behavior. Speech and communication were early human developments. Social systems were simple, with women gathering and men hunting. Their survival relied on contributions from both genders.
Before the agricultural revolution 10,000 years ago, hunter-gatherers lived globally with an estimated population of 5 million, spread sparsely. North America hosted diverse hunter-gatherer cultures into the 19th century.
Horticulture developed about 10,000 years ago in the Middle East and spread gradually. Societies practiced subsistence agriculture using tools like stone axes, wooden sticks, and spades. Pottery and textiles became common, and iron tools emerged in Africa.
Wet tropics with nutrient-leached soils limited population density. Amazonia and New Guinea hosted small, scattered communities. Leadership often fell to a tribal chief, with women playing key roles in gardening and food production.
Humanity transitioned from foraging to farming by domesticating plants and animals. This shift laid the foundation for cultural and civilizational development.
Pastoral societies emerged with a focus on herding domesticated animals. Nomadic herders lived in portable shelters and moved in response to ecological conditions. These societies adapted to grasslands and deserts.
Carts, caravans, and knowledge of animal husbandry were vital. Diets were plant-based, supplemented with animal products. Leather, horn, wool, and animal traction were traded for grain and manufactured goods.
Men herded large livestock, while women handled crafts, food, and small herds. Pastoralism played a major ecological role in pre-civilization human societies.
Humans began using cattle for labor and milk, combining horticulture and pastoralism. Agriculture emerged as a transformative force in human development, increasing population and settlement sizes.
Ploughs, wheels, metallurgy, and weaving were key advancements. Plough use began 5,000 years ago in the Middle East. Ox-drawn carts became widespread, notably in the Indus Basin.
Ploughing and seeding transformed ecosystems, replacing native flora. The North American Prairies became sites for wheat and corn farming. Today, humanity relies mainly on four crops: wheat, rice, maize, and potatoes.
Agriculture enabled urbanization. Men’s labor became central, while environmental factors like climate, soil, and irrigation affected productivity. Irrigation marked an early human environmental intervention.
Urban settlements first arose around 6000 to 5000 years ago in river basins such as Tigris-Euphrates and Nile. By the 17th century, human environmental impact accelerated with science and technology.
Beginning around 1800, the Industrial Revolution led to a shift from agricultural to non-farm occupations in Western Europe and the USA. Mechanical energy sources revolutionized production and transport.
Seaborne trade expanded in the 16th–17th centuries, leading to the global spread of spices, metals, textiles, and sugar. Innovations included steamships, railroads, automobiles, and aircraft.
Fertilizers, pesticides, and genetic engineering boosted agriculture. The 20th century saw population rise from 1.5 to 6 billion. Urbanization surged, bringing infrastructure and medical improvements but also environmental degradation.
Humans have altered Earth’s ecosystems more drastically than any other species, impacting plant and animal life, soil, water, and climate.