The Population dynamics of Rodents at Pongola, Northern Zululand, exposed to Dieldrin coverspraying

Abstract

Four grids, each 3,42 ha (4 morgen) in size, were live trapped from April 1967 through May 1969 in two soil and vegetation types (black turf~ Acacia nigrescens community, and brown reddish soil: Acacia tortilis community) at Pongola, northern Zululand, to determine the effect of dieldrin coverspraying, at a dosage of 87,4 g/hectare (2,64 oz/morgen), on rodents. Low population numbers before and especially at the time of spraying made clear-cut conclusions impossible to reach. Rodent populations (mainly Praomys (Mastomys) natalensis, Saccostomus campestris, and Lemniscomys griselda) were apparently not adversely effected, although L. griselda numbers showed a decline which was not in correspondence with that on the control area. This might be ascribed to dieldrin spraying. Relatively higher numbers of s. campestris and L. griselda were observed during periods of lower P.( M.) ~talensis numbers. Decreases in P.( Me) natalensis populations coincided with times of food scarcity. Praomys (Mastomys) natalensis are thus found in association with other rodents when abundant food is available, but seems to give way when competition due to food scarcity occurs. Reproductive data obtained from the study were too meagre to allow any conclusions concerning the effect of spraying thereon. The method involving the calculation of maximum distance between captures was used to express movement patterns of the species studied. Populat~on structure is express~d in terms of sex ratios, and frequency per mass class for each season. The size of animals was investigated by measuring total length, tail length, and head and body length. Behavioural features of the species captured were also noted.