Ecological Succession: Primary and Secondary Changes in Communities, Summaries of Soil Mechanics and Foundations

Download Ecological Succession: Primary and Secondary Changes in Communities and more Summaries Soil Mechanics and Foundations in PDF only on Docsity!

Lesson Overview

4.3 Succession

Primary and Secondary Succession

How do communities change over time?

Ecosystems change over time, especially after disturbances, as some species die out and new species move in.

Primary Succession

Volcanic explosions can create new land or sterilize existing areas.

Retreating glaciers can have the same effect, leaving only exposed bare rock behind them.

Succession that begins in an area with no remnants of an older community is called primary succession.

Primary Succession

For example, in Mount Saint Helens, Washington, an erupting volcano decimated all nearby living organisms.

Changes in this community will continue for centuries.

Mt. St. Helens immediately after eruption

Primary Succession

The first species to colonize barren areas are called pioneer species.

One ecological pioneer that grows on bare rock is lichen—a mutualistic symbiosis between a fungus and an alga.

Primary Succession

Over time, lichens convert, or fix, atmospheric nitrogen into useful forms for other organisms, break down rock, and add organic material to form soil.

Certain grasses are also pioneer species.

Mt. St. Helens 15-35 years post eruption

Mt. St. Helens 15-35 years post eruption

Mt. St. Helens 35-80 years post eruption

Secondary Succession

Sometimes, existing communities are not completely destroyed by disturbances. In these situations, secondary succession occurs.

Secondary succession proceeds faster than primary succession, in part because soil survives the disturbance. As a result, new and surviving vegetation can regrow rapidly.

Secondary Succession

This series shows secondary succession taking place in abandoned fields of the Carolinas’ Piedmont.

Over the last century, these fields have passed through several stages and matured into oak forests. Changes will continue for years to come.

Why Succession Occurs

Every organism changes the environment it lives in.

One model of succession suggests that as one species alters its environment, other species find it easier to compete for resources and survive.

For example, as lichens add organic matter and form soil, mosses and other plants can colonize and grow.

As organic matter continues to accumulate, other species move in and change the environment further.

Over time, more and more species can find suitable niches and survive.