State briefly what are biomes, ecotones and ecological succession. Give an account of the causes, trends and general process of ecological succession in nature.

Biomes

Biomes are large geographic areas characterized by specific climate conditions, animal populations, and plant life. They are defined by factors like temperature, rainfall, and latitude. Examples include tropical rainforests, deserts, grasslands, and tundra. Each biome supports a unique community of organisms adapted to its specific conditions.

Ecotones

Ecotones are transitional zones between two or more different ecological communities. They exhibit characteristics of both adjacent communities and often have higher species diversity than either. They are zones of tension where species from both communities interact. For example, the area between a forest and a grassland is an ecotone.

Ecological Succession

Causes of Ecological Succession

Ecological succession is initiated by disturbances, both natural and anthropogenic. These disturbances create opportunities for new species to colonize and establish themselves.

• Primary Succession: This occurs in newly formed or exposed habitats devoid of life and soil, such as volcanic rock, glacial till, or sand dunes. The process begins with pioneer species like lichens and mosses that can colonize bare rock and initiate soil formation.
• Secondary Succession: This occurs in areas where a pre-existing community has been disturbed but the soil remains intact, such as abandoned farmland, forests cleared by fire, or areas affected by floods. Secondary succession is generally faster than primary succession because of the presence of soil and seed bank.

General Process of Ecological Succession

Ecological succession follows a predictable pattern, although the specific species involved can vary depending on the environment. The process can be broadly divided into stages:

• Pioneer Stage: Characterized by hardy species (pioneer species) that can tolerate harsh conditions. These species modify the environment, making it more suitable for other species.
• Intermediate Stages (Seres): A series of communities develop, each replacing the previous one. These stages are often named after the dominant vegetation. Examples include:
  • Xerosere: Succession in dry areas, starting with lichens and progressing to shrubs and eventually forests.
  • Hydrosere: Succession in aquatic environments, starting with phytoplankton and progressing to rooted plants, marshes, and eventually forests.
  • Halosere: Succession in saline environments, starting with salt-tolerant plants and progressing to less salt-tolerant species as salinity decreases.
• Climax Stage: The final, stable community that is best adapted to the prevailing environmental conditions. The climax community is relatively stable and self-perpetuating. However, it's important to note that the concept of a static climax community is increasingly challenged, with the understanding that ecosystems are dynamic and subject to ongoing change.

Trends in Ecological Succession

Several trends are observed during ecological succession:

• Increase in Species Diversity: Species richness generally increases during succession, reaching a peak in the climax community.
• Increase in Biomass: The total amount of living organic matter increases over time.
• Increase in Stratification: The development of more complex vertical structure in the community.
• Decrease in Nutrient Cycling Time: Nutrients are cycled more efficiently in later successional stages.
• Increase in Niche Specialization: Species become more specialized in their resource use.

The rate of succession is influenced by factors such as climate, soil type, disturbance regime, and the availability of propagules (seeds, spores, etc.).