MEV 011: Unit 08 - Ecological Succession and Climax

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 UNIT 8 – ECOLOGICAL SUCCESSION AND CLIMAX

8.1 Introduction

The natural world is constantly changing. One of the key ecological processes responsible for this change is ecological succession—a gradual and orderly process of change in the species structure and ecosystem functions over time. Succession leads to the development of a stable and mature community known as the climax community. Understanding succession is essential for ecological restoration, conservation, and predicting future environmental conditions.

8.2 Objectives

After studying this unit, you will be able to:

·         Explain the causes and patterns of ecological succession.

·         Describe the types and stages of succession (Hydrosere and Lithosere).

·         Understand the concept of climax community and its models.

·         Understand ecological adaptations of plants and animals in different habitats.

8.3 Causes and Trends of Succession

Succession occurs due to a variety of causes, including:

·         Climatic changes (e.g., rainfall, temperature shifts)

·         Biotic factors (grazing, human interference, invasive species)

·         Catastrophic events (volcanic eruptions, floods, fires)

·         Soil development and nutrient accumulation

Trends observed during succession include:

·         Increase in species diversity

·         Improved nutrient cycling

·         Greater biomass and stability

·         Development from simpler to complex communities

8.4 Different Kinds of Succession

Succession is broadly classified into:

·         Primary Succession: Starts from a barren area with no life (e.g., lava flow, bare rock).

·         Secondary Succession: Occurs in areas where life existed previously but was disturbed (e.g., after forest fire or flood).

·         Autogenic Succession: Driven by the biological activities of organisms within the ecosystem.

·         Allogenic Succession: Caused by external environmental factors (e.g., wind, water, climate).

8.5 General Process of Succession

Succession involves a series of seres or stages. Each stage is characterized by the appearance and dominance of different plant and animal communities.

Stages include:

1.      Nudation – Formation of a bare area.

2.      Invasion – Arrival of pioneer species.

3.      Competition and Reaction – Interaction between species and modification of the environment.

4.      Stabilization – Establishment of climax community.

8.5.1 Hydrosere (Succession in Freshwater)

Hydrosere begins in aquatic ecosystems like lakes or ponds and progresses through the following stages:

1.      Phytoplankton stage

2.      Submerged vegetation stage

3.      Floating vegetation stage

4.      Reed-swamp stage

5.      Sedge-meadow stage

6.      Woodland stage

7.      Climax forest

8.5.2 Lithosere (Xerarch Succession on Bare Rock)

Lithosere starts on bare rock and includes:

1.      Crustose lichen stage

2.      Foliose lichen stage

3.      Moss stage

4.      Herbaceous stage

5.      Shrub stage

6.      Climax forest stage

8.6 Climax Community

The climax community is the final, stable, self-sustaining stage of ecological succession. It maintains dynamic equilibrium with the environment.

8.6.1 Monoclimax Concept

Proposed by Clements, it suggests that each region has one stable climax community determined by climate. All seral stages lead to this final state.

8.6.2 Polyclimax Concept

Proposed by Tansley, it suggests that multiple climax communities can exist in the same area depending on soil, topography, moisture, and disturbances.

8.7 Ecological Adaptations

Adaptation refers to the special structural, physiological, or behavioral characteristics of organisms that enable them to survive and reproduce in specific environments.

8.7.1 Tolerance Ranges

Organisms survive within specific ranges of environmental factors such as temperature, moisture, light, and pH. This is known as the range of tolerance.

8.7.2 The Liebig’s Law of Minimum

States that the scarcest resource (limiting factor) controls the growth and survival of an organism, even if other resources are abundant.

8.7.3 The Law of Tolerance

Shelford's Law of Tolerance states that the presence and success of an organism depend on the extent to which environmental factors fall within the maximum and minimum limits.

8.7.4 Ecological Adaptation in Hydrophytes

Hydrophytes are water-loving plants. Their adaptations include:

·         Thin cuticle or no cuticle

·         Poorly developed xylem

·         Air-filled tissues for buoyancy (aerenchyma)

·         Floating leaves with stomata on upper surface

Examples: Lotus, Water hyacinth

8.7.5 Ecological Adaptation in Mesophytes

Mesophytes live in moderate conditions (not too dry or wet).

·         Well-developed root and shoot systems

·         Moderate cuticle

·         Balanced water absorption and loss

Examples: Mango, Sunflower

8.7.6 Ecological Adaptations in Xerophytes

Xerophytes are drought-resistant plants found in arid regions.

·         Thick cuticle and sunken stomata

·         Reduced leaves or spines

·         Deep root system

·         Water-storing tissues

Examples: Cactus, Acacia

8.7.7 Ecological Adaptations in Halophytes

Halophytes are salt-tolerant plants found in saline soils or coastal areas.

·         Salt glands to excrete excess salts

·         Succulent leaves

·         Specialized roots

Examples: Mangroves (Avicennia)

8.7.8 Ecological Adaptation in Animals

Animals show adaptations to temperature, water availability, and salinity.

·         Desert animals: Water conservation (e.g., kangaroo rat)

·         Aquatic animals: Streamlined body, gills for respiration

·         Arctic animals: Thick fur and fat layers (e.g., polar bear)

·         High-altitude animals: Greater lung capacity, hemoglobin affinity

8.8 Let Us Sum Up

·         Succession is a natural process of change in community structure over time.

·         Hydrosere and lithosere are two examples of primary succession.

·         Climax communities are stable end-stages of succession.

·         Ecological adaptations enable species to survive in specific environments.

·         Plants like hydrophytes, xerophytes, and halophytes have distinct features based on their habitat.

·         Animals adapt structurally and physiologically to survive extreme conditions.

 

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