1067-4136/02/3303- $27.00 © 2002
Russian Journal of Ecology, Vol. 33, No. 3, 2002, pp. 186–193. Translated from Ekologiya, No. 3, 2002, pp. 201–208.
Original Russian Text Copyright © 2002 by Korytin.
The dynamics of an isolated population is a result of
the interaction between two population parameters,
birthrate and mortality rate. Detailed data on changes in
these parameters are necessary for understanding the
mechanisms of ﬂuctuations in population size. Both
increase and decrease in population size may result
from changes in only one parameter in the entire popu-
lation or even in a structural group within the popula-
tion. To date, we cannot unambiguously determine
what actually causes the growth or decline of a popula-
tion: changes in survival, fecundity, or both.
As far as I know, ichthyologists were the ﬁrst to ana-
lyze the animal survival curves as related to age (for
review, see Biverton and Kholt, 1969; Ricker, 1979).
This method of studying population structure has sel-
dom been applied to terrestrial vertebrates with rela-
tively long life spans. For example, Deevey (1947, cited
from Odum, 1975) obtained survival curves for the
Dall’s sheep. Later, this method was used when study-
ing the populations of the New Zealand tahr (Caughley,
1970), the red deer (Lowe, 1969), African ungulates
and proboscidians (Spinage, 1972), and (in a modern-
ized form) the wolf (Smirnov, 1983). This method is
rarely applied to large terrestrial vertebrates, because it
is difﬁcult to determine age in long-lived animals; the
very possibility to estimate it accurately only appeared
after the studies by Smirnov (1959) and Klevezal’ and
The ultimate practical goal of studying the red fox,
as well as any species that is used by man, is to develop
the optimal exploitation strategy. In the case of the spe-
cies that have been exploited for a long period of time
and have not disappeared, the development of this strat-
egy requires data on the spontaneously forming rela-
tionship between the rate of animal removal from the
population and the size of this population.
The rate of removal can be estimated from the gen-
eral mortality rate (according to Ricker, 1979). It is
interesting to determine whether mortality remains
constant or changes depending on the population
growth rate. Theoretically, we may expect several con-
sistent patterns of changes in the removal rate, depend-
ing on changes in population size. Naturally, the num-
bers of animals killed during the entire population cycle
will be different for different patterns.
I attempted to analyze changes in the estimations of
fecundity and mortality (and the inverse value, sur-
vival) in fox populations during the entire population
MATERIALS AND METHODS
The materials of this study were carcasses and skulls
of red foxes (
L.) obtained from trappers
in different years. I used data on a total of 1598 foxes.
During ﬁve trapping seasons (from 1976–1977 to
1980–1981), 839 fox carcasses were collected in the
Sverdlovsk, Kurgan, and Tyumen oblasts (hereinafter,
this whole region is called Transural). To study the pop-
ulation structure and fecundity of foxes from Kirov
oblast, I used the same material that was earlier used in
studies performed in collaboration with Solomin
, 1978; Korytin and Solomin, 1980; etc.).
The population structure was analyzed on the basis of
data on 759 fox carcasses collected during nine trap-
ping seasons (from 1966–1967 to 1974–1975). Herein-
after, this region is called Cisural.
The fecundity of foxes was estimated from the num-
ber of embryos and placental spots. When calculating
the average fecundity, the numbers of the spots and
embryos were matched with respect to the dates of cub
birth. When estimating the ecological fecundity (
I assumed that the sex ratio at birth was 1 : 1.
The age of the animals was determined according to
Smirnov (1959) and Klevezal and Kleinenberg (1967).
Preliminarily, the greatest width of the canal of the fang
Analysis of Survival of the Red Fox (
at the Phases of Population Growth and Decline
N. S. Korytin
Institute of Plant and Animal Ecology, Ural Division, Russian Academy of Sciences, ul. Vos’mogo Marta,
Yekaterinburg, 620144 Russia
Received February 7, 2000
—Changes in the survival parameters of the red fox were analyzed at different phases of the popula-
tion cycle. It was found that the survival rate in all age classes, including newborns, drastically increased at the
phase of population growth. The relationship between the general mortality rate and population size was deter-
mined. A hypothesis concerning the mechanism of these changes in the general mortality rate is suggested.
: survival, fecundity, dynamics, numbers, population, red fox.