Jun

20

Invasive species

June 20, 2021 |

quote of day of extreme relevance: "A hundred years of faster and bigger transport has kept up and intensified this bombardment of every country by foreign species brought accidentally or on purpose by vessel and by air and also over land from that used to be isolated… the real thing is that we are living in a period of the world's history when the mingling of thousands of kinds of organisms from different parts of the world is setting up terrific dislocations in nature. We are seeing huge changes in the natural population balances of the world." Elton, 1958. The Ecology of Invasion by Animals and Plants. the key to crypto moves.
 
A reader expands:
 
Chair has pointed to N. Shigesada's work on Biological Invasions. The three phases before saturation are covered on p. 27 with many examples from plants, insects and humans for each.
 
A key concept is the Range Distance. Consider a new species, for example the Muskrat unknown in Europe before 1905. In 1905 five muskrats escaped from a farm near Prague; in the next 20 years they spread through all of Germany and Austria-Hungary in a pattern of roughly concentric circles on a map. The range  distance is defined as the square root of the occupied area divided by sqrt(pi). (there are also some other formulas for cases of highly non-concentric spread).
 
How does the Range Distance look like when plotted against time? There are 3 patterns that occur again and again.
 
In the initial establishment phase the range distance shows no increase. After this the Expansion Phase begins.
 
In the simplest and most common case Type 1, it shows linear growth. In the case of the muskrat it is pretty remarkable how close the observations come to a straight line. In the next phase the Saturation Phase the curve levels off and becomes a horizontal straight line.
 
Type 2 called biphasic expansion shows a slow initial linear spread, followed by linear spread at a higher rate. This was seen for the Himalyan thar, the European Starling and European finch, and the Japanese beetle.
 
Type 3 expansion shows a slope constantly increasing over time, resulting in an exponential looking curve. Nevertheless even in this case the Saturation phase follows and the slope decreases to zero. I assume the expansion of cryptocurrencies may be of the Type3 although I have never seen it drawn.
 
There are various explanations for these phases (for example why is there an Establishment Phase with no growth at all) that I will skip over for now. Hope this clarifies a few things. 

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