Sir Arthur Tansley introduced the term “ecosystem” in 1935. Ecosystems represent segments of the natural world where living organisms engage with one another and their surroundings. These systems consist of a biotic community harmoniously connected to its physical environment, facilitating the exchange of energy and the recycling of nutrients.
STRUCTURE OF ECOSYSTEM
- The arrangement of both living (biotic) and non-living (abiotic) elements defines the structure of an ecosystem.
- This encompasses the flow of energy within the environment, as well as the prevailing climatic conditions specific to that particular ecosystem.
FUNCTIONS OF ECOSYSTEM
- Ecological Succession or Ecosystem Development:
- Homeostasis (or Cybernetic) or Feedback Control Mechanisms:
- Energy Flow Through the Food Chain:
- Nutrient Cycling (Biogeochemical Cycles):
Ecological Succession:
- Ecological succession refers to the process through which communities of plant and animal species in a particular area undergo replacement or transformation over time.
- This universal and directional change in vegetation occurs on an ecological time scale and is often prompted by large-scale alterations or destruction, whether natural or human-induced.
The progression of ecological succession involves a series of changes where one community gradually replaces another, ultimately leading to the establishment of a stable, mature, and enduring climax community.
Stages:
Pioneer Community:
- The initial plant community that colonizes an area is termed the pioneer community.
- These species, often hardy microbes, lichens, and mosses, play a crucial role in shaping the habitat conditions.
Successional Stages or Seres:
- The series of transitional communities formed and replaced during succession are referred to as successional stages or seral communities.
- Each stage contributes to the overall process of community evolution.
Climax Community:
- The final stage of succession is the climax community, characterized by stability, maturity, increased complexity, and long-lasting features.
- It represents a state of ecological equilibrium.
Characteristics of Succession:
- Increased Productivity: Succession leads to enhanced productivity as communities evolve and adapt.
- Shift of Nutrients: Nutrient reservoirs experience a shift during succession, contributing to the changing dynamics of the ecosystem.
- Increased Diversity: Over the course of succession, there is a noticeable increase in the diversity of organisms, fostering a richer ecological community.
- Gradual Food Web Complexity: The complexity of food webs gradually intensifies as succession progresses, creating a more intricate network of interactions.
Primary Succession:
- Primary succession unfolds in areas where no previous community has existed.
- Examples include rock outcrops, newly formed deltas, sand dunes, emerging volcanic islands, lava flows, and glacial moraines. In terrestrial primary succession, the process initiates with hardy pioneer species such as microbes, lichens, and mosses.
- These pioneers, through their growth and development over several generations, modify the habitat conditions, paving the way for the establishment of more complex communities.
- The rate of succession can vary, with areas in the middle of large continents experiencing faster succession due to the quicker arrival of seeds from different seral communities.
Secondary Succession:
- Secondary succession is the gradual development of biotic communities that occurs after the total or partial destruction of an existing community.
- This process of ecological renewal is a response to events such as natural disasters like floods, droughts, fires, or storms, as well as human interventions including deforestation, agriculture, and overgrazing.
When a mature or intermediate community is disrupted, the abandoned land undergoes a predictable sequence of changes:
Invasion by Hardy Species:
- Initially, the abandoned area is invaded by hardy species of grasses capable of surviving in bare, sun-baked soil.
- These grasses play a vital role in stabilizing the soil.
Succession of Grasses and Herbaceous Plants:
- As time progresses, the grasses are joined by taller grasses and herbaceous plants.
- These dominant species, along with the presence of mice, rabbits, insects, and seed-eating birds, contribute to the ecological dynamics of the area.
Emergence of Trees:
- Over time, trees begin to appear in the area, with their seeds being dispersed by wind or carried by animals.
- This marks a significant transition as the community evolves.
Development into a Forest Community:
- Through successive stages, the area transforms into a forest community as more trees establish themselves.
- Over the years, the once-abandoned land becomes dominated by a diverse array of trees, completing the process of secondary succession.
Secondary succession exemplifies nature’s resilience and adaptive capacity, showcasing how ecosystems can recover and regenerate after disturbances. The resulting community may differ from the original one, but it attains a stable and functional state over time.
Autotrophic and Heterotrophic Succession:
- Autotrophic succession is characterized by an initial dominance of green plants in greater quantities, while heterotrophic succession involves a larger presence of heterotrophs.
- In autotrophic succession, the primary producers, such as green plants, play a significant role in shaping the ecosystem.
In contrast, heterotrophic succession is marked by the prominence of organisms that rely on organic compounds produced by others, such as decomposers and consumers.
Succession in Plants:
- Xerarch Succession:
- Occurs in dry areas with low moisture content, like on bare rocks. Over time, xerarch succession leads to the conversion of a xerophytic habitat (adapted to dry conditions) into a mesophyte habitat (needing a moderate amount of water).
- Hydrarch Succession:
- Takes place in water bodies such as ponds or lakes. Both hydrarch and xerarch successions lead to mesic conditions—neither too dry (xeric) nor too wet (hydric). Over time, the water body can undergo a transformation into land.
Succession in Water:
- Primary Succession in Water:
- Phytoplankton, the small floating plants, act as pioneers in the initial stages of primary succession in water. Over time, they are replaced by free-floating angiosperms, then rooted hydrophytes, sedges, grasses, and ultimately trees. The climax community in this aquatic succession is often a forest.
- Conversion of Water Body into Land:
- As succession progresses, the water body is gradually transformed into land. This conversion is a significant outcome of ecological processes in aquatic environments.
- Common Climax Community:
- All successions, whether in water or on land, tend to lead to a similar climax community—the mesic community. This community is characterized by moderate moisture conditions and represents a stable and mature state in the succession process.
Homeostasis in Ecosystem:
Homeostasis:
- Homeostasis refers to the maintenance of a stable equilibrium, particularly through physiological processes.
- Organisms strive to keep their internal environment constant despite external environmental variations that may disrupt their homeostasis.
- This balance is often achieved through regulatory mechanisms that ensure a stable internal environment.
Regulation in Homeostasis:
- Some organisms can regulate their internal environment through physiological and sometimes behavioral means, such as migrating to shade for temperature control.
- This regulation aims to maintain constant body temperature, osmotic concentration, and other vital parameters.
- Birds, mammals, and a few lower vertebrates and invertebrates are capable of such regulation, performing activities like thermoregulation and osmoregulation.
The success of mammals, for example, is attributed to their ability to regulate body temperature, allowing them to thrive in diverse environments like Antarctica or the Sahara Desert.
Conformation in Homeostasis:
- Contrastingly, a significant majority of animals and almost all plants cannot maintain a constant internal environment.
- Their body temperature tends to change in response to the ambient temperature. In aquatic animals, the osmotic concentration of body fluids fluctuates with the osmotic concentration of the surrounding water.
- These organisms, both animals and plants, are considered conformers as they adjust to external conditions rather than actively regulating their internal environment.
While regulation and conformation are distinct approaches to homeostasis, both strategies are vital for the survival and adaptation of different species within the dynamic ecosystems they inhabit.
FOOD CHAIN
- The sun, as the ultimate source of energy on Earth, plays a pivotal role in sustaining life.
- It provides the energy needed for plant life, and plants, in turn, harness this energy through photosynthesis to synthesize their food.
- During the process of photosynthesis, light energy is converted into chemical energy, forming the basis for the intricate network known as the food chain.
- This energy is then transferred successively through trophic levels in an ecosystem.
- The journey starts with producers, moves to consumers, and ultimately reaches the apex predators or detritivores.
- In the food chain, dead and decaying matter, as well as organic debris, are essential components.
- Scavengers break down these materials into their basic constituents. Reducers then absorb these constituents, gaining energy in the process.
- Subsequently, the reducers release molecules into the environment, completing a cycle that can be utilized anew by the producers.
- This cyclic flow of energy through different trophic levels not only sustains the life of various organisms but also maintains the balance and functionality of ecosystems.
- The food chain, a fundamental concept in ecology, underscores the interconnectedness of all living organisms within an ecosystem and highlights the continuous recycling of energy.
BIOGEOCHEMICAL CYCLE
- In ecosystems, two fundamental functions are paramount—energy flow and nutrient circulation.
- While energy is lost as heat, nutrients derived from food matter exhibit a unique quality—they can be recycled indefinitely, undergoing a continuous process known as biogeochemical cycling.
- The composition of living organisms, including human bodies, is primarily composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus.
- These elements, both as compounds and individual elements, constitute a significant portion of the mass of all living entities.
- In addition to these primary elements, about 15 to 25 other elements are crucial for the survival and well-being of plants and animals.
- These mineral nutrients are in constant circulation, transitioning from non-living components to living organisms and then returning to the non-living components of the ecosystem.
- This cyclical movement is termed biogeochemical cycling, where “bio” represents living organisms, and “geo” signifies the atmosphere.
- Two prominent nutrient cycles central to the functioning of ecosystems are the carbon nutrient cycle and the nitrogen nutrient cycle.
- However, numerous other nutrient cycles, including various trace mineral nutrient cycles, play essential roles in ecological processes.
- The interconnectedness of these cycles ensures the sustainability and health of ecosystems, highlighting the intricate balance between living organisms and their environment.
FAQs
1. What is an ecosystem, and who introduced the term?
A: Sir Arthur Tansley introduced the term “ecosystem” in 1935. An ecosystem represents segments of the natural world where living organisms interact with each other and their surroundings.
2. How is the structure of an ecosystem defined?
A: The structure of an ecosystem is defined by the arrangement of both living (biotic) and non-living (abiotic) elements. It includes the flow of energy within the environment and the prevailing climatic conditions specific to that ecosystem.A:
3. What are the major functions of ecosystems?
A: The major functions of ecosystems are energy flow and nutrient circulation. Ecosystems facilitate the exchange of energy and the recycling of nutrients, contributing to the overall balance and sustainability of the environment.
4. What is ecological succession, and why is it important?
A: Ecological succession is the process by which communities of plant and animal species undergo replacement or transformation over time. It is important for the adaptation and resilience of ecosystems in response to disturbances.
5. Can you explain the stages of ecological succession?
A: Ecological succession involves stages such as the pioneer community, successional stages or seres, and the climax community. Each stage contributes to the evolution of the ecosystem, leading to stability and maturity.
6. How does secondary succession differ from primary succession?
A: Secondary succession occurs after the partial or complete destruction of an existing community, often due to natural disasters or human interventions. In contrast, primary succession starts in areas where no previous community has existed.
7. What is autotrophic and heterotrophic succession?
A: Autotrophic succession is characterized by an initial dominance of green plants, while heterotrophic succession involves a larger presence of heterotrophs. Both contribute to the shaping of ecosystems.
8. What is the significance of the food chain in ecosystems?
A: The food chain represents the transfer of energy from producers to consumers and, ultimately, to apex predators or detritivores. It plays a crucial role in sustaining life and maintaining the balance within ecosystems.
9. How does homeostasis contribute to ecosystem stability?
A: Homeostasis, the maintenance of a stable internal environment, is achieved through regulatory mechanisms. Some organisms can regulate their internal conditions, while others conform to external changes. Both strategies contribute to ecosystem stability.
10. What is biogeochemical cycling, and why is it important?
A: Biogeochemical cycling involves the continuous recycling of nutrients in ecosystems. Elements like carbon, hydrogen, oxygen, nitrogen, and phosphorus circulate between living and non-living components, ensuring sustainability and the health of ecosystems.
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