Classically, communities have been seen as a part of an ever-changing succession of species with rapidly colonizing weeds eventually giving way to shrubs and trees until a climax, stable community is reached.  An alternate view is that there are a set of alternate communities that can co-exist over a landscape with each remaining stable until they reach a threshold of environmental conditions where they are rapidly displaced.

The diagram depicts a threshold landscape.  Small changes in the environment would be necessary to displace Community 1 beyond its Threshold and 'downhill' to Community 2, but large changes would be needed to return Community 2 beyond its Threshold and 'uphill' to Community 1 or to move it to Community 3.

We are investigating threshold dynamics in shallow-water communities of the southern New England region.