Disturbances are Common in Communities

Negative-Natural disasters can lead to injuries and many worse things. such as loss of property, land and lives.

Positive-They could bring people together as they work to help each other recover

How disturbances can have positive and negative effects

 Primary Succession• occurs when a major, massive 

disturbance such as a glacial retreat, volcanic eruptions, etc. destroys all the plants in an area, allowing other species to colonize

•  The initial colonists on a terribly disturbed site vary depending on the nature of it: smooth, bare rocks will attract lichens, gravel will attract perennial herbs, and sand will be covered by grasses.

• These plants increase the amount  of nitrogen in the soil, attracting legumes and other nitrogen fixers, which further develop the nitrogen pools 

Secondary Succession

• Occurs when a disturbance (fire, windstorms, etc.) occurs but does not wipe out all the plants in an area

• Leaves behind a seed-bank or a number of vegetative areas. Short lived, fast growing plants take over first, followed by herbaceous perennials, short-lived trees, and finally slow-growing, long-lived trees.

Comparison between both Primary succession occurs following an opening of a pristine habitat, for example, a lava flow, an area left from retreated glacier, or abandoned strip mine.  In contrast, secondary succession is a response to a disturbance, for example, forest fire, tsunami, flood, or an abandoned field.   Secondary                                                          Primary

How do human activities affect species diversity?• Over-exploitation•  pollution and habitat conversion are the main

threats to species diversity. • They cause a gradual loss of species on local,

regional and global levels. • Additionally, the introduction of species into new

ecosystems destroys natural balance.

Articles

http://www.katrina.noaa.gov/ http://news.bbc.co.uk/2/hi/8455629.stm