Biology SS 3 Biology (1st, 2nd & 3rd Term)

Organism | Meaning, Population, Succession, Competition, Overcrowding

1. Ecology of Population

An ecological population refers to a group of individuals of the same species that live in the same area and interact with each other. This concept is fundamental to the field of ecology, which is the study of how organisms interact with each other and their environment. A population is defined by its specific geographic location, its members’ ability to interbreed, and its potential to increase in number through reproduction.

2. Succession:

Succession is a process of ecological change in a specific area over time. It describes how the composition of species and the structure of an ecosystem evolve and change as an area transitions from a barren or disturbed state to a more mature and stable state. Succession can be classified into two main types: primary succession, which occurs in areas without any previous biological community, and secondary succession, which happens in areas that have been previously colonized by life but have been disturbed or disrupted.

3. Structural Change in Species Composition, Variety, and Increase in Number:

This phrase describes the changes that occur in an ecosystem as it progresses through succession. Initially, in a barren or disturbed area, there may be only a few species present. As succession occurs, new species arrive, biodiversity increases, and the overall structure of the ecosystem becomes more complex. This is often accompanied by an increase in the population numbers of various species as the ecosystem becomes more stable and provides more resources.

4. Primary Succession in Aquatic Habitat:

Primary succession in an aquatic habitat involves the colonization and establishment of life in a water body that previously lacked any significant biological community. This can happen, for example, in newly formed ponds or lakes created by geological processes such as glacial retreat. Over time, aquatic plants, algae, and animals gradually colonize and establish themselves, leading to a more complex and stable aquatic ecosystem.

This type of succession initiates from barren land, exposed rock surfaces, or unoccupied bodies of water.

The process of primary succession on land can be observed in scenarios like a construction site where a pile of subsoil, rocks, or concrete blocks remains after building. In aquatic environments, primary succession can be witnessed in newly formed artificial ponds.

The pioneers of any succession, referred to as primary colonizers, are typically autotrophic plants. These plants have uncomplicated life requirements and can endure harsh conditions. As the primary succession progresses into its second year, the growth of algae, lichens, and mosses may become more pronounced. Over time, these organisms contribute to soil formation through growth, decay, and decomposition.

Moving into the third year, small herbaceous plants might establish themselves. These plants play a role in transforming the habitat by outcompeting smaller plants, leading to their decline. The dropping of leaves from these plants further contributes to soil enrichment, making it more conducive for other organisms. As years pass, an increasing variety of species join the habitat, while some species dwindle. This succession of species continues until a climax community is achieved. This climax community heralds the presence of larger life forms like shrubs and trees.

5. Meaning and Examples of Secondary Succession:

Secondary succession refers to the ecological process that occurs in an area that has previously supported life but has been disturbed or disrupted by events such as fires, clear-cutting, or abandoned agricultural land. The existing soil and some plant and animal species still remain, allowing for a faster and somewhat different recovery process compared to primary succession. An example would be a forest regrowing after a wildfire.

Secondary succession takes place in areas where soil and vegetation haven’t been completely eradicated. This process unfolds at a faster pace compared to primary succession, owing to the pre-existing presence of soil. Additionally, it transpires when a farmer abandons an old field. The commencement of secondary succession stems from a pre-established community that has experienced disturbances due to human activities and other influencing factors. Incidents such as fire, drought, and floods can trigger secondary succession.

Differences Between Primary And Secondary Succession

1 Starts on a bare surface Starts on already colonized surface
2  It is slower or takes longer time to reach a climax community It is faster or takes a shorter time to reach a climax community
3 Starts with lower organisms Starts with fairly complex organisms

Primary and secondary succession are two ecological processes that describe how ecosystems develop and change over time. They differ in several key ways:

Primary Succession Differences:

1. Bare Surface: Primary succession begins on a bare, lifeless surface with no previous soil or organisms. Examples include recently formed volcanic islands, glacial moraines, or areas devastated by a landslide.

2. Slower Progression: Primary succession is a slow process that can take centuries or even millennia to reach a climax community. This is because it starts with no soil, and pioneer species like lichens and mosses must first establish themselves and break down the rock or substrate to create suitable soil for more complex plants.

3. Lower Organisms: Primary succession starts with very simple, hardy organisms like lichens, mosses, and algae. These pioneer species are adapted to harsh conditions, and they gradually create conditions for more complex plants to colonize the area.

Secondary Succession Differences:

1. Already Colonized Surface: Secondary succession occurs on an area that has been previously colonized by life but has undergone a disturbance that removes most or all of the existing vegetation and soil. Common examples include abandoned agricultural fields, areas affected by wildfires, or land cleared for construction.

2. Faster Progression: Secondary succession is a faster process compared to primary succession. This is because there is already soil and a history of biological activity in the area. Seeds and root systems of plants may still be present, which allows vegetation to reestablish relatively quickly. It can take decades or centuries to reach a climax community, depending on the specific circumstances.

3. Fairly Complex Organisms: Secondary succession starts with fairly complex organisms like grasses, shrubs, and small trees. These are often referred to as early successional species. They are better adapted to compete for resources in an environment where soil and some organic matter are already present.

In summary, the primary difference between primary and secondary succession lies in the starting conditions and the pace of ecological development. Primary succession begins on barren surfaces and progresses slowly with simple organisms, while secondary succession occurs on previously colonized surfaces and progresses more rapidly with relatively complex organisms.

Succession Characteristics

  1. Pioneer organisms are primarily plants, acting as producers.
  2. The population of organisms generally increases each year until a climax state is achieved.
  3. The diversity of species in the ecosystem grows progressively year by year.
  4. Succession follows a systematic and advancing pattern, commencing with microscopic green plants and culminating in mature trees.
  5. Each generation of species contributes to habitat transformation, enhancing soil quality through decay.
  6. Organisms engage in competition, vying for essential resources such as water, CO2, O2, light, and space. Superior competitors outcompete others.
  7. Changes in species composition occur as the fittest organisms thrive and less adapted species diminish.

Succession Outcomes

  1. Structural modifications and community activities bring about alterations in the physical environment.
  2. The initial simple organisms are progressively replaced by more intricate ones in an evolutionary trajectory.
  3. Equilibrium is achieved as a variety of organisms colonize abandoned farmland.
  4. The ultimate result of succession is the establishment of a climax or stable community.

6. Relationship Between Competition and Succession:

Competition plays a significant role in the process of succession. As species colonize an area, they often compete for resources like sunlight, water, and nutrients. Over time, certain species that are better adapted to the available resources become dominant, leading to changes in the composition of the ecosystem. Succession involves a gradual shift from early colonizers, which are usually r-strategists and opportunistic species, to later successional species that are often K-strategists and more specialized.

7. Factors That Cause Overcrowding:

Overcrowding in a population can result from factors such as limited resources (food, water, shelter), high birth rates, low death rates, and reduced emigration. When a population exceeds the carrying capacity of its environment, it can lead to competition for resources and stress on the ecosystem.

8. Ways of Avoiding Overcrowding:

Populations can avoid overcrowding by various means, including controlling birth rates through reproductive strategies, dispersing to new areas through emigration, and adapting behaviours to manage resource utilization. Predation, disease, and other ecological factors also play a role in naturally regulating populations.

9. Effect of Food Shortage: Competition, Reproduction, Emigration Rate:

Food shortage can have several effects on a population. Competition for limited food resources can increase as organisms strive to secure enough sustenance to survive and reproduce. This competition can influence reproductive rates, with some individuals potentially reproducing less if resources are scarce. Additionally, in response to food scarcity, the emigration rate might increase as individuals seek out areas with better resource availability. Overall, food availability can significantly impact population dynamics and ecosystem interactions.

See also:

Sense Organs | Skin, Eyes, Ears, Nose & Tongue

Kidney | Structure, Functions, Diseases, Effects, Remedies & Osmoregulator

Hormones | Animal Hormones & Plant Hormones



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