POPULATION CYCLES IN SMALL MAMMALS
Authority. Authority remembers its experts or appoints some : they
ought to know. The experts advise a Cure. The Cure can be almost
anything: golden mice, holy water from Mecca, a Government Commission, a culture of bacteria, poison, prayers denunciatory or tactful,
a new god, a trap, a Pied Piper. The Cures have only one thing in
common: with a little patience they always work. They have never been
known entirely to fail. Likewise they have never been known to prevent
the next outbreak. For the cycle of abundance and scarcity has a rhythm
of its own, and the Cures are applied just when the plague of voles is
going to abate through its own loss of momentum.
269
Although outbreaks of voles were known for thousands of years, the
cyclic periodicity of high population levels was not recognized until
the 1920’s. Collett (1895), for example, discussed in detail the natural
history of the Norwegian lemming (Lemmus lemmus), but in concentrating on years of very high density and the “migrations” which accompanied them, he concluded that “prolific years” recurred at
irregular and unpredictable intervals. Hewitt (1921) was one of the
first to quantify the popular idea of cycles in wildlife species in Canada,
and he showed that lynx and red fox populations reached peaks at
regular intervals of nine to ten years while the arctic fox fluctuated
more rapidly with peaks at regular intervals of four years.
In 1923 Charles Elton read Collett’s book and Hewitt’s book and
realized that the “migration years” of the Norwegian lemming might
be a reflection of a regular fluctuation in populations of these small
rodents. Little was known of population changes in animals in the
1920’5, and the prevailing belief was that populations were stable in
size and that all outbreaks of species were due to man’s interference
with nature (Egerton, 1968). Elton recognized that regular fluctuations
in populations of rodents in arctic regions would challenge the simple
“balance of nature” idea, and would open up a field of research on the
causes of periodic fluctuations and their evolutionary consequences
(Elton, 1924).
If periodic fluctuations in small rodents were to be understood,
detailed population data would be needed. But in 1923 there was not a
single census of a rodent population to show the changes from year to
year, nor was there much information on birth and death rates. Elton
organized at Oxford a group of biologists to study fluctuations, and
this group evolved into the Bureau of Animal Population.
Interest and research on rodent populations has increased greatly
since the 1930’s. The importance of voles as pests of farmers and
orchard growers and their role in the spread of diseases stimulated work
in the U.S.S.R. and in the U.S.A., and we now turn to a review of the
modern work on periodic fluctuations.
Authority. Authority remembers its experts or appoints some : they
ought to know. The experts advise a Cure. The Cure can be almost
anything: golden mice, holy water from Mecca, a Government Commission, a culture of bacteria, poison, prayers denunciatory or tactful,
a new god, a trap, a Pied Piper. The Cures have only one thing in
common: with a little patience they always work. They have never been
known entirely to fail. Likewise they have never been known to prevent
the next outbreak. For the cycle of abundance and scarcity has a rhythm
of its own, and the Cures are applied just when the plague of voles is
going to abate through its own loss of momentum.
269
Although outbreaks of voles were known for thousands of years, the
cyclic periodicity of high population levels was not recognized until
the 1920’s. Collett (1895), for example, discussed in detail the natural
history of the Norwegian lemming (Lemmus lemmus), but in concentrating on years of very high density and the “migrations” which accompanied them, he concluded that “prolific years” recurred at
irregular and unpredictable intervals. Hewitt (1921) was one of the
first to quantify the popular idea of cycles in wildlife species in Canada,
and he showed that lynx and red fox populations reached peaks at
regular intervals of nine to ten years while the arctic fox fluctuated
more rapidly with peaks at regular intervals of four years.
In 1923 Charles Elton read Collett’s book and Hewitt’s book and
realized that the “migration years” of the Norwegian lemming might
be a reflection of a regular fluctuation in populations of these small
rodents. Little was known of population changes in animals in the
1920’5, and the prevailing belief was that populations were stable in
size and that all outbreaks of species were due to man’s interference
with nature (Egerton, 1968). Elton recognized that regular fluctuations
in populations of rodents in arctic regions would challenge the simple
“balance of nature” idea, and would open up a field of research on the
causes of periodic fluctuations and their evolutionary consequences
(Elton, 1924).
If periodic fluctuations in small rodents were to be understood,
detailed population data would be needed. But in 1923 there was not a
single census of a rodent population to show the changes from year to
year, nor was there much information on birth and death rates. Elton
organized at Oxford a group of biologists to study fluctuations, and
this group evolved into the Bureau of Animal Population.
Interest and research on rodent populations has increased greatly
since the 1930’s. The importance of voles as pests of farmers and
orchard growers and their role in the spread of diseases stimulated work
in the U.S.S.R. and in the U.S.A., and we now turn to a review of the
modern work on periodic fluctuations.