ecological succession and facilitative replacement

- Question: Are communities capable of changing? - Ecological succession is the change in community structure over time. Disturbances such as fire, flood, glaciation, and human activity are possible causes for ecological succession. - In facilitative replacement, a species improves conditions of the environment for another species. For example, an organism that increases the acidity of soil improves conditions for conifers.

- begins in an area that completely lacks community structure. Primary succession can result from a catastrophic event like glaciation, earthquake, or forest fire. - After a glacier retreats, the exposed rock is completely barren of life. Successional stages on the rock include pioneer organisms, short grasses, and short trees. pioneer organisms—bacteria, fungi, algae, and lichens—are the first to colonize the rock. The biological activity of the organisms, especially the lichen, builds soil on the rock. Hundreds of years later, enough soil is present to permit the growth of short grasses. The growth of short trees, such as willows and alders, represents the third stage of the ecological succession.

- A lichen (not pictured) is a symbiotic association of millions of photosynthetic algae cells enmeshed in fungal hyphae. The fungi absorb water and minerals, and the algae fix carbon through photosynthesis. The lichen attaches itself to a rock via the fungal hyphae. When the lichen dries out, it releases acids that break down the rock to form soil. - The picture on the far left shows the colonization of short grasses. Eventually short trees such as willows develop. The willows increase the nitrogen content of the soil, favoring the growth of alder trees. The graph on the immediate left shows a spike in the number of alder trees (shaded red) when soil conditions are favorable.

In primary succession, why are the initial pioneers overtaken by other species?

- The pioneer community changes the environmental conditions, ultimately making it unfavorable for themselves.

Which of the following is an example of a substrate that will not be subject to primary succession?

- soil inhabited by a community of microorganisms

14.7.1 Community Disturbance: Succession Flashcards by Irina Soloshenko

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14.7.1 Community Disturbance: Succession Flashcards

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