Ecological Succession and Population Dynamics

Ecological Succession

  • Succession occurs following a disturbance in an ecosystem.

Definition and Purpose of Succession

  • Succession regenerates or creates a community after a disturbance.

  • It involves a sequence of biotic changes where:

    • Damaged communities are regenerated.

    • New communities arise in previously uninhabited areas.

Types of Succession

  • There are two main types of succession:

    1. Primary Succession

    2. Secondary Succession

Primary Succession

  • Definition:

    • Primary succession is started by pioneer species, such as lichens and mosses.

    • It occurs in previously uninhabited areas.

  • Example:

    • Primary succession can be observed when bare rock is exposed by a receding glacier.

Stages of Primary Succession

  1. Pioneer Stages

    • Initial colonizers such as lichens appear on bare rock.

  2. Intermediate Stages

    • Development of small annual plants, lichens, and then perennial herbs and grasses.

  3. Climax Community

    • The final stable community, including shade-tolerant trees and shade-intolerant trees.

    • This full process may take hundreds of years.

Secondary Succession

  • Definition:

    • Secondary succession is started by remaining species after a disturbance.

    • It occurs following events such as fires or natural disasters.

Examples of Disturbances Leading to Secondary Succession

  • Examples of disturbances include:

    • Forest Fire

    • Natural Disasters

    • Deforestation

Types of Disturbances Related to Succession

  • Primary Disturbances:

    • Volcano Eruption

    • Glaciers Retreating

  • Secondary Disturbances:

    • Forest Fire

    • Other Natural Disasters

    • Deforestation

Dispersal Patterns

  • Patterns of Population Distribution:

    1. Clumped Distribution

      • Organisms are clustered together in groups.

      • This may reflect a patchy distribution of resources in the environment.

      • This is the most common pattern of population dispersion.

    2. Random Distribution

      • Organisms have an unpredictable distribution.

      • This pattern is typical of species where individuals do not interact strongly.

    3. Uniform Distribution

      • Organisms are evenly spaced over the area they occupy.

      • This is typical of species that compete for scarce environmental resources, such as water in a desert.

Types of Speciation

  • There are two main types of speciation:

    1. Allopatric Speciation

    • Involves geographical isolation leading to species divergence.

    1. Sympatric Speciation

    • Occurs through reproductive isolation even within the same geographic area.