2. Obj.Assessment StatementNotes 2.6.5 Describe the concept and processes of succession in a named habitat. Page 265-270 Students should study named examples of organisms from a pioneer community, seral stages and climax community. The concept of succession, occurring over time, should be carefully distinguished from the concept of zonation, which refers to a spatial pattern. 2.6.6 Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stages of succession. Page 265-274 In early stages, gross productivity is low due to the initial conditions and low density of producers. The proportion of energy lost through community respiration is relatively low too, so net productivity is high, that is, the system is growing and biomass is accumulating. In later stages, with an increased consumer community, gross productivity may be high in a climax community. However, this is balanced by respiration, so net productivity approaches zero and the production:respiration (P:R) ratio approaches one. 2.6.7Describe factors affecting the nature of climax communities. Page 266-267 Climatic and edaphic factors determine the nature of a climax community. Human factors frequently affect this process through, for example, fire, agriculture, grazing and/or habitat destruction.

3. Ecological Succession Succession is the gradual change in species composition of a given area Change occurs in response to changing environmental conditions Succession can also be describe as a sequence of communities (a sere) with each transitory community as a seral stage. Two types of succession: Primary and Secondary Primary succession – Establishing communities on nearly lifeless ground. Secondary succession – Changing species composition in an area where a biotic community already exists

4. Primary Succession Places where primary succession occurs: bare rock; cooled lava flows; abandoned pavement. Before a biotic community can be established, there must be a soil. Terrestrial pioneer species can attach themselves to bare rock/barren areas and begin the soil formation process Examples: Moss, lichens, certain grasses Pioneer species extract nutrients from precipitation, dust, bare rock.

5. Soil Formation Trap wind blown soil particles and detritus Produce small amounts of organic matter Secrete acids that weather the rock to break it down Once it has begun to break down, physical weathering (freezing) breaks it down even more As patches of soil build up, the pioneer species is replaced by early successional plant species. This process takes hundreds to thousands of years

6. Early Successional Species As soil begins to form, small grasses and ferns begin to grow. Seeds dispersed to the area by wind or birds Early successional species grow quickly and have short generations and life spans. Early successional species continue to break rock by growing roots Their short life span means dead organic material quickly builds on the small layer of soil.

7. Mid-successional Species Early successional species continue to add layers to the soil horizon. When the soil is deep enough (hundreds of years) and can hold enough moisture and nutrients, mid-successional species take root. These would include taller grasses and ferns, and low shrubs. Eventually these are replaced by trees species that need plenty of sunlight (shade intolerant).

8. Late Successional Species As shade intolerant trees grow, shade is produced. This allows for shade tolerant tree species to begin to grow. The shade tolerant trees (late successional species) will outcompete the shade intolerant species and take over. This is the end stage of succession and an equilibrium is reached. A climax community is established. Climax community – A community of organisms that is in equilibrium with natural environmental conditions; the end point of ecological succession. Primary Succession

9. Secondary Succession A disturbance to an already established biotic community allows for the succession process to start again. Examples: an abandoned field; burned forests; heavily polluted streams Secondary succession can proceed much faster because the soil has already been prepared by the previous community Primary and Secondary Succession

10. Communities in Succession The actual climax community found in an ecosystem depends heavily on the climatic factors and soil (edaphic) factors at that location. Leading up to the climax community, it is interesting to note that the presence of the pioneer, early, mid-successional organisms essentially alters the environment (eg. shade, pH, moisture, temperature, chemical composition) sufficiently so that it is no longer suitable for their own offspring to continue That is, the populations change the environment so drastically, both biotically and abiotically that it is now more suitable for other populations and less suitable for itself. This leads to the succession of one sere after another until a climax is reached and the changes in the environment are now not so drastic as to produce any further major changes.

11. Succession and Productivity Ecosystem characteristicTrends in ecological succession Gross productivity (GP)Increasing during early stages of primary succession then little or no increase during final stages of secondary succession Net productivity (NP)Decreasing Respiration (R)Increasing

12. Trends in Succession Ecosystem characteristic Trends in ecological succession Food chainsSimple food chains becoming more complex food webs Relative species abundance Changes rapidly first, changes slower in the later stages. Total biomassIncreasing Humus (non- living organic matter) Increasing Species diversity Low diversity in the early stages, then increasing in the intermediate stages and then stabilizing in the final stages as an equilibrium is approached

13. Trends in Succession Ecosystem characteristicTrends in ecological succession Mineral cycles Becomes more self-contained in later stages Nutrient recycling Increases in later stages

14. Pioneer Communities vs. Climax Communities Pioneer CommunityClimax Community Unfavorable environmentFavorable environment Biomass increases quicklyBiomass is generally stable Energy consumption inefficient Energy consumption efficient Some nutrient lossNutrient cycling and recycling r – strategistsK - strategists Low species diversity, habitat diversity, genetic diversity High species diversity, habitat diversity, genetic diversity