Please wait while the transcript is being prepared...
0:00
Hello. I'm Daniel Botkin,
Professor of Biology Emeritus,
University of California, Santa Barbara.
I'm going to talk to you today about a second introduction to ecology,
following from the first,
which you may have already watched.
I'd begin with a curious question,
and its curious answer.
How many species could exist on Earth?
Ecological theory says very few,
but there are many.
This has to do with the competitive exclusion principle.
This is an important concept in ecology.
It states that two species with
exactly the same requirements cannot coexist in exactly the same habitat.
This is expressed most succinctly as complete competitors cannot coexist.
This principle is illustrated in the next slide.
1:00
This principle is illustrated by
the intentional introduction of the American gray squirrel into Great Britain.
It was introduced intentionally because some people thought it was attractive,
exotic, and would be a pleasant addition to the British landscape.
This wasn't just casual,
about a dozen attempts were made.
The first, perhaps as early as 1830.
1:27
By the 1920, American gray squirrel was well-established in Great Britain,
and in the 1940s and '50s,
its numbers expanded greatly,
as you can see in this map.
There are about 2.5 million gray squirrels in Great Britain,
and only about 140,000 red squirrels.
That is the red squirrels only make up six percent
of the population of the American grays in Great Britain.
Pushed to the margins,
as you will see in this map,
the red squirrels are on islands,
remote areas of Scotland,
and other distant areas of this nation,
where the gray population is relatively small.
The problem is that the two species have almost exactly the same habitat requirements.
Thus, the two species seem to confirm the competitive exclusion principle.
As a result, many British people have come to hate the American gray.
An article in the British newspaper, The Guardian,
quotes a Patrick Barkham,
who joined a hunt to kill American grays.
He writes, "The gray are sleek, North American import,
swaggering across parks, raiding bird tables,
all fat hunches and bulbous black eyes.
In contrast, the red squirrel,
although native to Britain, looks exotic;
So dainty and alertly pretty,
with fine tuffs of hair above its ears as extravagant as it's eyebrows."
