Tuesday, February 2, 2010

Patches, Corridors, and Matrixes in Making Greenways

Dr. John threw out his back over the weekend and is playing hurt today. But, it might make him looser and score more than ever during his lecture. Sometimes that happens.

Any landscape can be described as a mosaic of repeating patterns of patches and corridors, and the matrix within which these elements are positioned.

The ratio of elements to each other is important for how the environment is able to sustain organisms. For example, two patches of forest may be able to be separated at some distance and have certain animals use both patches, especially if there is a corridor of forest linking them.

Generalist species tend to be able live near humans and adapt well to us, e.g., deer and cayotes vs. bobcats. Edge generalists can utilize corridors. Others, such as Blue Jays, that need to use forest cover to escape Cooper's Hawk, wouldn't venture out into the corridors. But, "stepping stone" habitat patches can be introduced to help such species. Otherwise, a "unified metapopulation" might become isolated and would tend to inbreed and die. On the other hand, corridors can spread disease, so one needs to know about the species one is connecting through a new corridor or stepping stones.

The patches may not be homogeneous themselves, though. Within patches there is a diversity of flora and areas, or of wet and dry lands.

Functional connectivity - how does the connectivity of elements help a species function, e.g, spread their genes.
(The inverse, "functional isolation" - might also benefit a species in terms protection from disease, etc.)

There is a point at which fragmenting a patch can be suboptimal for a species; that's the point where one has fragmented it's "home range". If that's done, the species may be able to limp along for a while, but it won't take much to kill it off from there.

E. O. Wilson's Theory of Island Biogeography...

The first sentence of a book Dr. John is reading by Humphries is: "Most of the interesting things in life happen at the boundaries"

Raperian zones are transition zones between patches, such as between forest interior and meadow, stream, bayou, etc. They offer:
  • structural complexity (to live)
  • dependable water (to drink)
  • rich soils and biomass for food (to eat)
There are important areas. E.g., 80% of species in upland Arizona depend on raparian corridors.

Often small landowners can collectively have the cummulative effect of gragmented home ranges and hurting ecosystems.

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