Plant Succession | Botany Optional for UPSC PDF Download

Introduction

The concept of a community, also known as a biocenose, is central to understanding the intricate dynamics of ecosystems. Communities are aggregations of organisms that come together to form distinct ecological units, characterized by specific flora, fauna, or a combination of both. These units can vary greatly in size, from minute collections of invertebrates and fungi inhabiting a decaying log to vast ecosystems encompassing diverse habitats.
In this article, we delve into the concept and dynamics of community-plant succession, exploring the interactions, stability, and the fascinating process of ecological succession.

The Biotic Community and Ecosystem

The heart of an ecosystem lies in its biotic community, which comprises plants, animals, bacteria, and fungi coexisting within a given environment. These diverse populations interact in intricate ways, making the ecosystem a finely tuned machine. The biotic community, along with its physical habitat, forms what ecologists refer to as an ecosystem.

Types of Communities

Communities can be categorized into two main types: major and minor. Major communities, in conjunction with their habitats, create self-sustaining ecosystems, primarily relying on solar energy as their essential input. In contrast, minor communities, often called societies, are subsidiary aggregations within major communities and are not entirely independent when it comes to energy circulation.
The biotic community can be further divided into specialized groups like plant communities, animal communities, and microbe communities, each playing crucial roles. Plants provide food, shelter, and oxygen to animals, while animals assist in processes like pollination, soil aeration, and dispersal. Microbes are vital in breaking down organic matter, contributing to nutrient cycling.

Interactions Within the Biotic Community

A fundamental aspect of the biotic community is the various interactions among its members. These interactions can be neutral, positive, or negative, shaping the community's dynamics and stability.

1. Scavenging: Scavenging involves feeding on dead organisms. Animals that consume the flesh of deceased animals are known as scavengers, such as vultures, jackals, and hyenas. Even ants play a role in scavenging, contributing to the ecosystem's cleanliness.

2. Commensalism: Commensalism is a relationship where one organism benefits without causing harm to the other. Examples include E. coli in the human intestine and epiphytes perched on other plants solely for space.

3. Mutualism: Mutualism is a mutually beneficial interaction between individuals of different species. It encompasses relationships like fungus and alga in lichen and Rhizobium bacteria aiding nitrogen fixation in legume roots.

4. Protocooperation: Protocooperation is a non-obligatory beneficial relationship that forms when two different organisms associate, as seen in cattle egrets feeding on lice and ticks of cattle.

5. Amensalism: Amensalism occurs when one organism inhibits another with the release of chemicals, with limited benefits. Examples include Penicillium secreting penicillin against staphylococcus and Chlorella vulgaris affecting diatom Nitzschia frustrulum.

6. Competition: Competition arises when organisms vie for the same resources, often leading to population size reduction or adaptation. It can result in competitive exclusion, where one species eliminates another.

7. Mimicry: Mimicry involves resembling other organisms or surroundings for various purposes, such as protection or predation. Examples include stick insects and the viceroy butterfly mimicking the monarch butterfly.

8. Parasitism: Parasitism sees one organism, the parasite, deriving nourishment from another, the host. This interaction can be temporary or permanent, ectoparasitic or endoparasitic, and may even involve hyperparasites.

9. Predation: Predation involves one organism, the predator, capturing and killing another, the prey. Predators are typically carnivores but can also include herbivores that devastate plants and seeds.

10. Negative Human Interactions: Human activities like deforestation, hunting, overgrazing, and introducing invasive species can have negative impacts on the biotic community and disrupt ecosystems.

Biotic/Ecological Succession

Types of Succession

There are two primary types of ecological succession:

• Primary Succession: This occurs on lifeless substrates like rocks or open water, where organisms gradually colonize and change the environment. It includes xerarch succession on land and hydrarch succession in open water.
• Secondary Succession: Secondary succession takes place when an existing community is disturbed, such as through human activity or natural events like fires. It involves the gradual return of vegetation to the area.

Drivers of Succession

Succession happens because species modify the habitat and available resources, often favoring other species. Three dynamic concepts underlie this process: tolerance, facilitation, and inhibition. Tolerant species thrive in harsh, early successional stages, facilitating the growth of less weedy species. Sometimes, changes in the habitat caused by one species can inhibit the growth of others.

Timeframes

Primary succession is a lengthy process, often spanning over a thousand years, while secondary succession occurs more rapidly, taking decades or centuries, depending on the type of ecosystem.

Pioneer, Seral, and Climax Communities

In ecological succession, the pioneer community is the first to establish itself on a barren surface. Seral communities are transitional phases during succession, while the climax community represents the stable, self-perpetuating final stage in harmony with the local climate.

Dominant Species

Dominant species in a community are the most numerous and influential, exerting a significant impact on community dynamics.

Sere

Sere refers to the sequence of developmental stages from pioneer to climax communities, each playing a unique role in shaping the ecosystem.

Conclusion

The concept of the biotic community and ecological succession are fundamental to understanding the complex web of interactions within ecosystems. Communities are dynamic entities where species coexist and depend on each other in various ways. Ecological succession, whether primary or secondary, highlights nature's ability to adapt and evolve over time. Recognizing these intricate relationships is essential for the conservation and management of our natural world.