Ecological Succession Succession u u Succession is a

Ecological Succession

Succession u u Succession is a series of regular, predictable changes in community structure over time. Activities of organisms change their surroundings and make the environment suitable for other kinds of organisms. – Examples of activities: u u Climate Available seed sources Frequency of disturbance Invasions of organisms

Succession u There are 2 kinds of ecological succession – Primary succession – Secondary succession u The difference between the two is the starting point.

Primary Succession u u Primary succession begins with a total lack of organisms and bare mineral surfaces (for example a lava field) or water. There is no gross productivity.

Secondary Succession u Secondary succession occurs when an existing community is disturbed or destroyed (for example by fire, flood, or human activity) but much of the soil and some of the organisms remain.

Secondary Succession u Gross productivity is low due to initial conditions and low density of producers. u Few organisms = little respiration = low energy lost = high net productivity. – The system is growing and biomass is accumulating.

Secondary Succession – Because the soil and nutrients remain, the process can advance more rapidly than primary succession. – Plants and organisms that survive the disturbance can grow quickly and reestablish themselves. – Nearby undamaged communities can serve as sources of seeds and animals. – The new climax community is likely to resemble the destroyed community.

Succession u There are 2 places where ecological succession takes place. – Terrestrial – Aquatic

Terrestrial Primary Succession u Terrestrial primary succession – A pioneer community is a collection of organisms able to colonize bare rock (e. g. , lichens). Lichens help break down rock and accumulate debris, helping to form a thin soil layer. u The soil layer begins to support small forms of life. u

Terrestrial Primary Succession u Steps to terrestrial primary succession 1. Lichen community replaced by annual plants. 2. Annuals replaced by perennial community. 3. Perennial community replaced by shrubs. 4. Shrubs replaced by shade-intolerant trees. 5. Shade-intolerant trees replaced by shadetolerant trees. 6. Stable, complex, climax community eventually reached.

Terrestrial Primary Succession

Terrestrial Secondary Succession u An example of terrestrial secondary succession in the Pacific Northwest is clear cutting.

Secondary Terrestrial Succession Each step in the process is known as a seral stage, and the sequence of stages is called a sere. Secondary succession on land

Climax Community u A climax community is a relatively stable, long-lasting community that is the result of succession. The kind of climax community that develops is primarily determined by climate and soil type. – Eg. Pacific Northwest old growth forest or a desert

Climax Communities u Climax communities show certain characteristics when compared with successional communities. – Climax communities maintain species diversity for an extended period. – They contain multiple specialized ecological niches. – They maintain high levels of organism interactions. – Climax communities recycle nutrients while maintaining a relatively constant biomass.

Climax Community u The general trend in succession is toward increasing complexity and more efficient use of matter and energy. A coral reef

Climax Community u Increased consumer community means a high gross productivity which is balanced by respiration (loss of energy) so net productivity approaches 0 – The production: respiration (P: R) approaches 1.

Climax Community u If disturbed by continual human activity or natural disasters, ecological communities are not allowed to reach climax communities. – The community remains at an equilibrium at a sub-climax community u Eg. Logging every 75 years.

Diversity and Resiliency u The more diverse the habitat, the more genetic and species diversity, – the more diversity = more resilient to change. – The more resiliency = faster recuperation due to a disturbance.

Aquatic Primary Succession u Aquatic primary succession – Except for oceans, most aquatic systems are considered temporary. – All aquatic systems receive inputs of soil particles and organic matter from surrounding land. – This results in the gradual filling of shallow bodies of water. u Roots and stems below water accumulate more material. u Establishment of wet soil.

Primary Succession Primary succession from a pond to a wet meadow.

Floating Bog

u This graph shows how GPP and respiration differ as ecological succession progress.

Changes During Succession Size of organisms increases—more trees u Energy flow is more complex—more complex food webs u Soil depth, humus, water-holding capacity, mineral content and nutrient cycling all increase u Biodiversity increases because more niches (lifestyle opportunities) appear, and then falls as the climax community is reached u

Equilibria u A steady-state equilibrium is when the recently observed behavior of the system will continue into the future. It refers to a system that is not closed and there is a constant input of reactants and outflow of products. – should be understood as the common property of most open systems in nature. – Example: A plant

Equilibria u A static equilibrium is when the system experiences no change. – It is a condition to which natural systems can be compared. – There are no naturally occurring static equilibrium scenarios in ecosystems.

Disturbances u The relative stability of an equilibrium is the tendency of the system to return to that original equilibrium following disturbance rather than adopting a new one. – Example: ecological succession.