2.5 ESS

Topic 2.5: Zonation, Succession, and Change in Ecosystems

Guiding Questions

• How do ecological systems change over time and over space?

2.5.1 Zonation

• Zonation Definition: Zonation refers to the changes in community along an environmental gradient.

  • It is influenced by factors such as:

  • Changes in altitude

  • Changes in latitude

  • Changes in tidal level

  • Changes in soil types

  • Changes in distance from a water source

• Characteristics of Zonation:

  • It represents a spatial change.

  • Differences in the ecological community can be observed when moving from one point (A) to another point (B) across a landscape.

Example of Zonation: Elevation Zones

• High Elevation Zones:

  • Snow/Ice

  • Alpine Tundra

  • Subalpine Coniferous Forest

• Mid Elevation Zone:

  • Temperate Forest

• Low Elevation Zones:

  • Deciduous Forest

Example of Zonation: Latitude Zones

• North-Pole Zones:

  • Polar regions at the North Pole

  • Arctic Tundra

  • Northern Taiga

• Comparison Analogy:

  • Hiking up a mountain is similar to traveling toward the North Pole in terms of experiencing major ecosystems.

  • As elevation increases while hiking, temperature decreases, leading to a change in organisms residing in that zone.

Additional Zonation Types

• Tidal Zonation:

  • Consists of high tide, low tide, subtidal channels, and marshes which provide different habitats for various species.

  • Habitat descriptions include:

  • Mudflats:

    • Rich in invertebrates, important for shorebirds.

  • Low Marsh:

    • Habitat for cordgrass, insects, herons, egrets, and clapper rails.

  • High Marsh:

    • Hosts pickleweed and cordgrass, which supports Savannah Sparrows and Clapper Rails.

2.5.2 Transects to Measure Along a Gradient

• Transect Definition: A transect is a sample path, line, or strip along which the occurrence or distribution of plants and animals is recorded in a study area.

• Importance of Transects:

  • They help measure biotic (living) and abiotic (non-living) factors along environmental gradients to determine variables affecting species distribution.

• Types of Transects:

  1. Line Transect:

     • A string or measuring tape is laid in the direction of the environmental gradient, and species touching the string are recorded.

  2. Belt Transect:

     • A strip of chosen width is sampled by laying two parallel line transects, usually 0.5-1 m apart, between which individuals are sampled.

       • Continuous Transects: All plants and animals along the line are sampled.

       • Interrupted or Systematic Transects: Samples taken at predetermined intervals along the transect.

  • Can combine transects with quadrats.

Kite Graphs

• Kite Graph Definition: A graphical representation where:

  • The length represents the distance from the gradient origin.

  • The width (green areas) represents the number of organisms for each species.

• Analysis Questions:

  • Which species are present along the entire transect?

  • Which species increase with distance from the footpath?

2.5.3 Ecological Succession

• Succession Definition: Succession is the replacement of one community by another in an area over time due to changes in biotic and abiotic variables.

  • Over time, the composition of a community changes or develops.

• Sere: Sets of communities (seral communities) that succeed one another throughout succession at a given location.

Types of Succession

1. Primary Succession:

   • Occurs on newly formed substratum with no soil or pre-existing community.

   • Examples include:

     • Rock formed by volcanic activity.

     • Moraines revealed by retreating glaciers.

     • Sand dunes and waterborne silt.

   • Early Successional Species: e.g., Algae, mosses, and lichens, which secrete acids that allow nutrient absorption and soil formation.

   • Mid-Successional Species: Grasses and wildflowers adapt to exploiting young, nutrient-poor soil.

   • Late-Successional Species: Species depend on biome characteristics such as temperature and rainfall.

2. Secondary Succession:

   • Happens on bare soil after the destruction of an existing biological community, retaining soil.

   • Disturbances leading to secondary succession include:

     • Forest fires

     • Abandonment of agricultural fields

   • Pioneers: Include grasses and wildflowers with light, wind-borne seeds, eventually replaced by better-suited competitors.

   • Pioneer Tree Species: Examples include aspen and cherry trees, rapid growers that start to shade each other, allowing shade-tolerant species to come in.

Differences Between Zonation and Succession

• Zonation: Spatial change observable across landscapes; differences can be observed from point A to point B.

• Succession: Temporal change observable over time as communities develop and replace one another.

2.5.4 Pioneer Species

• Pioneer Communities: The initial communities consisting of fast-growing species that begin to colonize previously uninhabited areas.

  • Characteristics:

    • Small, fast-growing, and fast-reproducing, initially low biodiversity (e.g., lichens).

• Climax Communities: Mature communities at the end of a series of succession stages.

  • High biodiversity with K-strategists able to thrive, dependent on the specific biome characteristics such as vegetation type.

2.5.5 Factors Influencing Succession and Ecosystem Change

• Key Points:

  • Each seral community influences environmental conditions, aiding the replacement of communities through competition until reaching a stable climax.

  • Changes in environmental conditions affect community dynamics over time.

  • Human activity can interfere with succession, potentially resulting in a plagioclimax community.