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ecolog[w87,jmc]		Ideas about ecology

Andrewartha and Birch, 1954 and 1984
Andrewartha 1961

Andrewartha and Birch have a chapter on human ecology that is mostly
a crib from Ehrlich and neglects to apply the principles developed
in the rest of the book.  For example, they don't ask whether human
population today is density limited.

Ecological propositions:

1. One may have to wait a long time to determine what evolutionary
pressures really exist, because of the important role played by rare
population crunches.

2. Consider the rabbits in Australia as described in Andrewartha and
Birch 1984.  They have population crunches from droughts that wipe
them out except in certain areas where washes concentrate what little
rain there is.  In good times these are relatively bad areas for
rabbits and support very few, but this small population is what
survives the drought.  Since the rest of the population is wiped
out by the droughts, all the evolution that takes place is limited
to this small group.  Suppose, for example, that the only rabbits
living in these areas are those driven out by larger and stronger
rabbits from the more attractive areas.  Then evolution would favor
meek rabbits.

The main point is that examining a population in any but crunch
years may be quite misleading as to the direction of its evolution.