260 TELFORD: MULTIMAMMATE RAT POPULATION BIOLOGY IN TANZANIA

 1982-83: October, November, and December had
 extremely high rainfall.
 1983-84: December and January had exceptionally
 high rainfall.
 1984-85: November had very heavy rain, followed
 by very little in December and January.


 Population Biology ofPraomys natalensis at Morogoro.


 Identity of the population studied.-- Karyotype studies elsewhere in
Africa have shown the presence of two karyotypes in Praomys populations: in
Sierra Leone (Robbins et al. 1983) and Ivory Coast (Bellier 1975), diploid
numbers of 32 and 38 have been have been distinguished as Praomys
(Mastomys) huberti and Praomys (Mastomys) erythroleucus, respectively
(Robbins et al. 1983). In southern Africa, a 32 chromosome form is
considered to be Praomys (Mastomys) natalensis, and a species with 36
chromosomes is thought to represent Praomys (Mastomys) coucha (Green et
al. 1980; Lyons et al. 1977; Gordon 1978;, and Lyons et al. 1980). However,
Hubert et al. (1983), without clearly stating their justification for their action,
have assigned the name natalensis to the 36 chromosome species, apparently
on the basis of a karyotype obtained by Matthey (1954) from a single specimen
sent him from Johannesburg. They thus ignored the opinions based upon far
more extensive studies of the South African populations by Lyons et al. (1977),
Gordon (1978), Green et al. (1980) and Lyons et al. (1980). While P. huberti
evidently does occur in East Africa, at least in Somalia (Capanna et al. 1982),
the status of Praomys (Mastomys) natalensis populations in Kenya, Tanzania,
and Malawi has not been resolved. Accordingly, the position taken here will be
that of Smithers (1983) for the South African populations: the Morogoro
shamba rats should be referred to as Praomys (Mastomys) natalensis sensu
latu.
 A total of 35 multimammate rats from the university campus population
at Morogoro were karyotyped: all showed a diploid number of 32
chromosomes. Scattered samples from other localities had the same diploid
number.

 Reproduction.-- Praomys natalensis is an annual species, reproducing
during the first and only year of its life, with parous females disappearing from
the population before the next breeding season begins (Fig. 9).
 Mark and release studies on the campus population showed that females
do not survive to enter a second breeding season, and very few males live over
one year (Tang Christensen pers. comm.). This is consistent with the estimate